



NFSv4                                                     D. Noveck, Ed.
Internet-Draft                                                    NetApp
Updates: 8881, 7530 (if approved)                       25 November 2025
Intended status: Standards Track                                        
Expires: 29 May 2026


                    ACLs within the NFSv4 Protocols
                    draft-ietf-nfsv4-acls-update-00

Abstract

   This document is part of the set of documents intended to update the
   description of NFSv4 Minor Version One as part of the rfc5661bis
   respecification effort for NFSv4.1.  It describes the structure and
   function of NFsv4 Access Control Lists within all existing minor
   versions of NFSv4.

   It describes the structure of NFSv4 ACLs and their role in the NFSv4
   security architecture.  While the focus of this document is on the
   role of ACLs in providing a more flexible approach to file access
   authorization than is made available by the POSIX-derived
   authorization-related attributes, the potential provision of other
   security-related functionality is covered as well.

   [Consensus Needed (Item #117a)]: Because of the failure of previous
   specifications to provide a satisfactory approach to either of the
   two ACL models for which support was originally intended, this
   document clarifies the status of draft-POSIX ACLs, with the
   expectation that support for these might be provided via a later
   extension.  In addition, this document will include some small
   protocol extensions to correct protocol defects, as provided for in
   RFC8178.

   [Consensus Needed (Item #117a)]: In this document, the relationship
   among the multiple ACL models for which support was intended has
   changed.  A core set of functionality, shared in large part with that
   derived from a subset of the functionality provided by the now-
   withdrawn draft-POSIX ACLs is presented as the conceptual base of the
   feature set.  Additional sets of features used to provide the
   functionality within the NFSv4 ACL model and the full draft-POSIX ACL
   model are considered as OPTIONAL extensions to that core, with the
   latter not yet present in NFsv4.1.

   [RFC Editor: please remove this parapgraph and the following
   paragraph prior to publishing this document as an RFC].





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   The current version of the document is intended, in large part, to
   result in working group discussion regarding repairing problems with
   previous specifications of ACL-related features and to enable work to
   provide a greater degree of interoperability than has been available
   heretofore.  The drafts provide a framework for addressing these
   issues and obtaining working group consensus regarding changes that
   will be necesasary before publication of RFCTBD10.

   When the resulting document is eventually published as an RFC, it
   will supersede the descriptions of ACL structure and semantics
   appearing in existing minor version specification documents for
   NFSv4.0 and NFSv4.1, thereby updating RFC7530 and RFC8881.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 29 May 2026.

Copyright Notice

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   document authors.  All rights reserved.

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   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow



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   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   5
     1.1.  Relationship to the Overall Security Document . . . . . .   7
     1.2.  Relationship to the V4.1 Respecification Effort . . . . .   8
     1.3.  Protocol Defects That Might Need to be Corrected  . . . .  12
     1.4.  Effect on Various Minor Versions  . . . . . . . . . . . .  13
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .  15
     2.1.  Keyword Definitions . . . . . . . . . . . . . . . . . . .  15
     2.2.  Special Considerations  . . . . . . . . . . . . . . . . .  15
     2.3.  Use of the Term "SHOULD . . . . . . . . . . . . . . . . .  16
   3.  Problems to Address . . . . . . . . . . . . . . . . . . . . .  17
     3.1.  Nature of the Existing Problems . . . . . . . . . . . . .  19
     3.2.  Probable Problem Sources  . . . . . . . . . . . . . . . .  19
     3.3.  Semantic Laxity . . . . . . . . . . . . . . . . . . . . .  21
     3.4.  Problems in the Handling of Draft POSIX ACLs  . . . . . .  23
     3.5.  Challenges We Now Face  . . . . . . . . . . . . . . . . .  24
     3.6.  Work Necessary to Address Interoperability Issues as Part
           of NFSv4.1 Respecification Effort.  . . . . . . . . . . .  26
   4.  ACL-based Authorization-related Attributes  . . . . . . . . .  30
     4.1.  Definition to Support ACL-related attributes  . . . . . .  30
       4.1.1.  Definitions related to ACE mask bits. . . . . . . . .  30
       4.1.2.  Definitions related to Aclchoice. . . . . . . . . . .  31
       4.1.3.  Designation of the Absence of an ACL  . . . . . . . .  31
     4.2.  Table of ACL-related Attributes . . . . . . . . . . . . .  32
     4.3.  Types of ACLs . . . . . . . . . . . . . . . . . . . . . .  33
     4.4.  The Acl Attribute (v4.0)  . . . . . . . . . . . . . . . .  35
     4.5.  The Aclsupport Attribute (v4.0) . . . . . . . . . . . . .  37
     4.6.  The Aclchoice Attribute (v4.1 extension for bis)  . . . .  39
     4.7.  The Dacl Attribute (v4.1) . . . . . . . . . . . . . . . .  48
     4.8.  The Sacl Attribute (v4.1) . . . . . . . . . . . . . . . .  49
   5.  Structure of the ACL-related Features . . . . . . . . . . . .  50
     5.1.  Role of the Core UNIX ACL model . . . . . . . . . . . . .  51
     5.2.  Potential Support for the POSIX ACL Model . . . . . . . .  52
     5.3.  Server Behavioral Restrictions to Apply when Aclchoice is
           not Supported . . . . . . . . . . . . . . . . . . . . . .  54
     5.4.  Feature Extensions With Clear Semantics . . . . . . . . .  55
     5.5.  Features with wide Semantic Ranges  . . . . . . . . . . .  58
     5.6.  Implementation Behavioral Choices . . . . . . . . . . . .  60
     5.7.  ACL Choices in Various Stages of Development  . . . . . .  64



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   6.  Structure and Function of Access Control Lists within
           NFSv4 . . . . . . . . . . . . . . . . . . . . . . . . . .  65
     6.1.  Overview of ACL Semantics Choices . . . . . . . . . . . .  66
     6.2.  ACL Semantics Choices . . . . . . . . . . . . . . . . . .  68
     6.3.  Limited Inference Regarding ACL Semantics . . . . . . . .  69
   7.  Structure of NFSv4 Access Control Entries . . . . . . . . . .  70
     7.1.  ACE Type  . . . . . . . . . . . . . . . . . . . . . . . .  70
       7.1.1.  Existing ACE Types  . . . . . . . . . . . . . . . . .  70
       7.1.2.  ACE Type Support Discovery  . . . . . . . . . . . . .  72
       7.1.3.  ACE Type Extension  . . . . . . . . . . . . . . . . .  73
     7.2.  ACE Access Mask . . . . . . . . . . . . . . . . . . . . .  73
       7.2.1.  Changes in Descriptions of Mask Bits  . . . . . . . .  76
       7.2.2.  Role of Sticky Bit in ACL-based Authorization . . . .  78
       7.2.3.  Handling of OPTIONAL Mask Bits  . . . . . . . . . . .  79
       7.2.4.  Uses of Core Mask Bits  . . . . . . . . . . . . . . .  79
       7.2.5.  Finer-grained Mask Bits Derived from Write  . . . . .  82
       7.2.6.  Finer-grained Mask Bits Derived from Ownership  . . .  86
       7.2.7.  Other Mask Bits . . . . . . . . . . . . . . . . . . .  87
       7.2.8.  Possible Uses of Additional Mask Bits . . . . . . . .  92
       7.2.9.  ACE Mask Bit Extension  . . . . . . . . . . . . . . .  93
       7.2.10. Reporting of Mask Bit Support and Characteristics . .  94
       7.2.11. ACE Mask Support Info . . . . . . . . . . . . . . . .  99
       7.2.12. ACE Mask Support Discovery  . . . . . . . . . . . . . 101
       7.2.13. ACE Mask Bit Support Defaults . . . . . . . . . . . . 103
       7.2.14. ACE Mask Adaptation . . . . . . . . . . . . . . . . . 104
       7.2.15. Handling of Deletion  . . . . . . . . . . . . . . . . 105
       7.2.16. Handling of Deletion (Vestigial)  . . . . . . . . . . 109
     7.3.  ACE flag bits . . . . . . . . . . . . . . . . . . . . . . 111
       7.3.1.  Details Regarding ACE Flag Bits . . . . . . . . . . . 112
       7.3.2.  ACE Flag Support Discovery  . . . . . . . . . . . . . 114
       7.3.3.  ACE Who . . . . . . . . . . . . . . . . . . . . . . . 116
   8.  Special Inheritance Features  . . . . . . . . . . . . . . . . 120
   9.  Processing Access Control Entries . . . . . . . . . . . . . . 123
   10. Combining Authorization Models  . . . . . . . . . . . . . . . 126
     10.1.  Background for Combined Authorization Model  . . . . . . 126
     10.2.  Needed Attribute Coordination  . . . . . . . . . . . . . 128
     10.3.  Computing a Mode Attribute from an ACL (proposed)  . . . 131
     10.4.  Computing a Mode Attribute from an ACL (vestigial) . . . 133
     10.5.  Alternatives in Computing Mode Bits (vestigial)  . . . . 134
     10.6.  Setting Multiple ACL Attributes  . . . . . . . . . . . . 135
     10.7.  Setting Mode and not ACL (overall) . . . . . . . . . . . 135
       10.7.1.  Setting Mode and not ACL (vestigial) . . . . . . . . 135
       10.7.2.  Setting Mode and not ACL (Discussion)  . . . . . . . 136
       10.7.3.  Setting Mode and not ACL (Proposed)  . . . . . . . . 138
       10.7.4.  Setting Mode and not ACL in the Unix ACL Case
               (Proposed)  . . . . . . . . . . . . . . . . . . . . . 144
       10.7.5.  Setting Mode and not ACL in the NFSv4 ACL Case
               (Proposed)  . . . . . . . . . . . . . . . . . . . . . 145



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       10.7.6.  Setting Mode and not ACL in Certain Hybrid ACL Cases
               (Proposed)  . . . . . . . . . . . . . . . . . . . . . 146
     10.8.  Setting ACL and Not Mode . . . . . . . . . . . . . . . . 147
     10.9.  Setting Both ACL and Mode  . . . . . . . . . . . . . . . 147
     10.10. Retrieving the Mode and/or ACL Attributes  . . . . . . . 147
     10.11. Use of Inherited ACL When Creating Objects . . . . . . . 149
     10.12. Combined Authorization Models for NFSv4.2  . . . . . . . 149
   11. Other Uses of Access Control Lists  . . . . . . . . . . . . . 150
   12. Aclchoice Details . . . . . . . . . . . . . . . . . . . . . . 150
     12.1.  Provisions for Aclchoice Modification  . . . . . . . . . 150
     12.2.  Storing of ACLs which are not Enforced . . . . . . . . . 151
     12.3.  Advice/Recommendations Regarding ACL Choices . . . . . . 152
   13. Security Considerations . . . . . . . . . . . . . . . . . . . 155
   14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 156
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . . 156
     15.1.  Normative References . . . . . . . . . . . . . . . . . . 156
     15.2.  Informative References . . . . . . . . . . . . . . . . . 157
   Appendix A.  Issues for which Consensus Needs to be
           Ascertained . . . . . . . . . . . . . . . . . . . . . . . 158
     A.1.  List of Issues  . . . . . . . . . . . . . . . . . . . . . 158
     A.2.  Issue Changes . . . . . . . . . . . . . . . . . . . . . . 172
       A.2.1.  Issue Changes Until Acls-01 . . . . . . . . . . . . . 172
       A.2.2.  Issue Changes In Acls-02  . . . . . . . . . . . . . . 172
       A.2.3.  Issue Changes In Acls-05  . . . . . . . . . . . . . . 172
     A.3.  Issue Priorities  . . . . . . . . . . . . . . . . . . . . 173
   Appendix B.  Prospective Aclchoice Changes  . . . . . . . . . . . 177
     B.1.  Possible Simplifications  . . . . . . . . . . . . . . . . 177
     B.2.  Possible Additions  . . . . . . . . . . . . . . . . . . . 177
   Appendix C.  Future Handling of Draft POSIX ACLs  . . . . . . . . 178
   Appendix D.  Possible Future Extensions . . . . . . . . . . . . . 178
     D.1.  Finer-grained Authorization Support For Extended
           Attributes  . . . . . . . . . . . . . . . . . . . . . . . 179
     D.2.  Client Choice Regarding Mode Display  . . . . . . . . . . 180
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 180
   RFC Editor Notes  . . . . . . . . . . . . . . . . . . . . . . . . 180
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . 181

1.  Introduction

   This document describes the existing ACL-related features of the
   NFsv4 protocol, all of which are accessed through the use of a set of
   OPTIONAL attributes described in Section 4.  These attributes
   provide:

   *  Additional means of specifying file access authorization
      constraints that are more flexible than those provided by the
      authorization model inherited from POSIX, based on the attributes
      mode, owner, and owner_group.



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   *  A number of security-related facilities separate from
      authorization that use ACLs to identify sets of actions that might
      be subject to various forms of monitoring as described in
      Section 11.

   Because of the unsatisfactory state of current specifications of the
   ACL features, the work needed to make the description appropriate as
   part of an updated description of NFSv4.1 is far beyond the level of
   clarification and cleanup that would normally be expected for a
   feature that has been part of the NFSv4 protocols for so many years.
   This includes addressing the following major issues:

   *  The unacceptable level of laxity regarding the specification of
      ACL semantics, as described in Section 3.3.

   *  The unsuccessful attempt to support multiple ACL models, without
      explicitly making the choice OPTIONAL, leaving the issue of
      client-server agreement unaddressed.  For details, see Section 5.

   *  The lack of proper attention to the semantics of draft-POSIX ACLs,
      which led to the unjustified assumption that such support was
      essentially already available, when, in fact, it was not.  For
      details, see Section 3.4.

   Necessary work to address these issues includes the addition of
   protocol extensions to correct existing defects as described in
   Section 1.3.  For more discussion of the reasons that this situation
   exists and insights into the work necessary work to provide a
   satisfactory description, see Section 3.

   [Consensus Needed (Item #104a, #105a)]: One important element of a
   new description of the ACL features is a means by which the client
   can determine which set of features a server has implemented when the
   ACL-related attributes are supported.  For reasons discussed in more
   detail in Section 3, that information has not previously been
   available to NFSv4 clients making it necessary that we provide, for
   NFsv4.1 and later minor versions, a new OPTIONAL attribute, Aclchoice
   to provide this information, as described in Section 4.6.  While we
   normally do not make additions to the XDR within an existing minor
   version, we have taken this step now as it crucial to provide
   interoperability for this important security-related feature, making
   it necessary to address this matter as a correctible protocol defect.
   Addressing such defects is allowed by Section 9 of [RFC8178] to
   enable updates to provide necessary corrections of this sort.







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   [Consensus Needed (Item #104a), Through end of section]: Given the
   scale of the problems we now face, it appears that the following
   additional steps are also necessary to arrive at a satisfactory
   description:

   *  A conceptual restructuring of the existing material to consider a
      small set of UNIX-based features as the conceptual core together
      with the extensions incorporated in the description as OPTIONAL
      extensions to that core.

      That restructuring, which is laid out in detail in Section 5 will
      be the basis for the new the Aclchoice attribute.

   *  [Consensus Needed (Item #117b), Through end of bulleted item]:
      Clarifying the relationship between the NFSv4 ACL model and the
      draft-POSIX ACL model described in [Grünbacher].

      Because previous specifications did not take proper notice of Many
      important semantic difference between the draft-POSIX and NFSv4
      ACL models, it is now necessary to prepare for the possibility,
      alluded to in Appendix C, that future minor versions or extensions
      thereof might provide support Access Control Lists and Access
      Control Elements whose structure is different from those presented
      in this document.

   *  Addressing the unfortunate consequences of the current semantic
      laxity, by reducing the range of behavioral diversity to that
      which is truly necessary.

1.1.  Relationship to the Overall Security Document

   This document is best understood when it is read together with
   RFCTBD20 which also discusses security features provided that are not
   connected with ACLs, and which is a complete description in cases in
   which the OPTIONAL ACL-related attributes are not implemented.

   In many cases, the overall security document will have abbreviated
   descriptions that serve as an introduction to material in this
   document and reference sections within this document.  Similarly,
   there will be occasions where it is necessary for this document to
   reference general features of NFSv4 security documented in RFCTBD20.

   For the most part, these two documents are independent, except for
   the inter-document references discussed above.  However, the
   following exceptions should be noted:

   *  Section 1 of RFCTBD20, in its entirety, applies to both documents,
      even in the absence of explicit inter-document references.



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   *  The terminology defined in Section 4.1 of RFCTBD20 in intended to
      be used in either document, without an explicit inter-document
      reference for each use.

   *  The sections dealing with Security Considerations and IANA
      Considerations appearing in RFCTBD20, i.e., Sections 18 and 19 of
      that document apply to the security-related changes being made in
      the current update as a whole, i.e., to both documents.

   *  Appendix A of RFCTBD20, in describing the security-related changes
      made from previous specifications, includes changes made in both
      this document and the overall security document.

   *  The Appendices devoted to tracking Consensus Items, i.e.,
      Appendix A of this document and Appendix B of
      [I-D.dnoveck-nfsv4-security], need to be considered together, even
      though each appendix applies only to the document in which it
      appears.

      This is because there are related consensus items in the several
      documents whose resolution might affect one another, including
      some that are the descendants of consensus items affecting
      material now in multiple documents.

1.2.  Relationship to the V4.1 Respecification Effort

   This document is a necessary part of the rfc5661bis effort which
   seeks to provide an updated and corrected specification of NFSv4
   Minor Version One.  Since ACLs are part of that minor version, a
   corrected and updated specification of the processing of ACLs would
   be required as part of that effort.

   However, given the wide scope of the ACL model presented in [RFC3530]
   and subsequent specifications and the wide allowances made in those
   documents for non-implementation of various elements of that
   specification, there is necessarily a great deal of uncertainty about
   the necessary scope of a respecification.  Many features might have
   never been implemented by servers or used by clients and could have
   been purely speculative when described.












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   This situation is complicated by the long time between the initial
   inclusion of this package of features and now.  In many cases, there
   might not be a clear understanding of the gaps between the feature
   set in the specification and that commonly implemented.  In addition,
   gaps between the specification and implementation of protocol
   elements which were implemented may not have been understood or were
   forgotten after implementation work in this area ceased.  The
   practices discussed in Section 3.3 and the attitudes that led to
   them, make it likely that this would happen without extensive
   attention being devoted to regularizing this situation.

   [Consensus Needed (Items #104b, #105b, #110a, #114a), Through end of
   section]:

   Since we now consider the extensions to the core UNIX ACL model as
   OPTIONAL features, we have a framework to consider the suitability of
   these extensions to the protocol.  We are now in a different
   situation from that confronting the working group when the original
   approach to ACLs was first arrived at.  At that time, the idea of
   conceiving of these extensions as individually selectable OPTIONAL
   features was not available.

   In any case, the realities that make that view appropriate now
   existed then as well.  The way in which the Working Group chose to
   accommodate the situation have left us with a set of challenging
   issues that have been exacerbated by the passage of time, as
   described in Section 3.5.

   It appears that the specification of ACLs to be done as part of the
   rfc561bis effort cannot include all of the possible features we are
   able to identify since:

   *  Some of these features might not have been implemented due to a
      lack of interest in the feature.

   *  There could have been issues exposed by implementation attempts
      that might have excluded them as candidates for implementation.

   *  Many of the issues that made these difficult-to-implement in some
      environments (e.g. UNIX) might have been more refractory than
      expected.

   *  Even where none of the above issues exist, it might not be able to
      research the relevant issues in a reasonable time.







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   Since it appears impossible to resolve all the questions left
   unanswered since ACLs were included in the protocol, it appears
   necessary to focus on the most important subsets in the near term
   while allowing further development to proceed in later minor
   versions.  The two important feature subsets are:

   *  The feature set of the core UNIX ACL model, which is the subset
      that that servers are essentially required to implement and which
      clients have been capable of using so far.

      Because of the way previous specifications chose to deal with
      expected server behavioral diversity (see Section 3.3), there is
      considerable work involved in identifying probable sources of
      diversity and making the choices allowed into OPTIONAL features
      that the client is to be made aware of.

   *  [Consensus Needed (Item #117c), Through end of bulleted item]: The
      subset of extensions to the core UNIX ACL model intended to allow
      support of NFsv4 ACLs by servers and server-side file systems
      originally implemented to provide the functionality to support the
      draft-POSIX ACL model.

      For reasons discussed in more detail in Section 3.4, this subset
      had been mostly ignored.  As a result, clarifying the relationship
      between draft-POSIX ACLs and NFsv4 ACLs is an essential part of
      our work, although providing full support for POSIX ACL semantics
      on either the client or server is unlikely to be doable as part of
      the respecification effort, for reasons made clear in in
      Section 5.2.  Possible ways of addressing issues outside the
      respecification effort are discussed in Appendix C.

   Work involving extensions to support the remainder of the extensions
   within the NFSv4 ACL model will necessarily have a lower priority.
   Nevertheless, the effort done to identify the extensions will make it
   possible for clients to use these extensions.  Work will be necessary
   in later minor versions to decide which of these extensions make
   sense, to remove those that don't, and to make sure clients and
   server can use these extensions interoperably.

   The likely work to be completed as part of the NFSv4.1
   respecification is discussed below:

   *  The work to provide interoperability needs to focus on the core
      ACL features, each of which is part of the UNIX ACL subset.  This
      will include the interaction of clients depending on this
      functionality to interoperably interact with servers that support
      any of the extensions within the more inclusive NFSv4 ACL model.




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      The inclusion of two different means of computing modes from ACLs
      is a flaw that is desirable to remove, but that is probably not
      possible to eliminate now given the likely existence of servers
      implementing these two approaches.  The possibility of making this
      a client choice will be deferred to a later minor version as
      discussed in Appendix D.2

      Unless other issues arise, the current draft is expected to
      provide this level of interoperability, for those not depending on
      any of the extensions.

   *  Consensus Needed (Item #117c)]: For clients depending on the NFSv4
      extensions necessary to support the draft-POSIX ACL model, we will
      need to provide clarification of the semantic differences between
      NFSv4 ACLs and draft-POSIX ACLs.  The result of this clarification
      is to eliminate unrealistic expectations regarding the ability of
      mappings between these two models to provide adequate support.
      For discussion of the basic elements of that support, man of which
      will not be available in NFsv4.1, see Section 5.2.

   *  For clients depending on some of the other NFSv4 extensions, the
      situation is different in that we will try to provide
      interoperability, but we have to prepared for the possibility that
      it will not be possible to provide it in time for the completion
      of the rfc5661bis effort.

      We will give priority to features used by clients for which server
      implementations exist.  While we hope to find no noteworthy
      behavioral variants, giving us a specification supporting
      interoperability, that is not guaranteed but we do have the
      option, as described in Section 12.1 of allowing multiple variants
      for now and working toward a common approach in later drafts or in
      subsequent minor versions.

   *  There will probably be features for which there is no prospect of
      either client use or server implementations.  Although this raises
      the possibility of eventually deleting such never-implemented
      proposed features, this will not happen before the end of the
      respecification effort.

      Such feature deletions would only be possible in a new minor
      version that allows features to be designated mandatory-to-not-
      implement, as described in Section 12.1.








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1.3.  Protocol Defects That Might Need to be Corrected

   Although normally, protocol respecifications in bis documents do not
   modify the protocol and focus instead on clarifications, there are
   provisions within [RFC8178] to provide needed OPTIONAL extensions as
   a means of correcting protocol defects.

   Determining what issues are sufficiently important to justify taking
   that step is best left to the judgment of the working group.  In this
   draft, I have limited its use to defects that sufficiently compromise
   the usefulness of the either of two ACL model as to make that model
   essentially unusable.  The following possibilities were considered:

   *  The lack of any way to determine which of the extensions to the
      core UNIX ACL model is supported by a particular server.  This
      includes the majority of ACE mask bits, the ACE flags, all of
      which are effectively OPTIONAL, and various allowed behavioral
      differences with significant semantic consequences.

      This issue has been addressed by the creation of the OPTIONAL
      attribute Aclchoice

   *  The different handling of partial satisfaction of ALLOW ACEs by
      draft-POSIX ACLs and non-POSIX ACLs appeared to require a means
      for clients to make visible their different requirements in this
      regard.

      The option of defining a new ACE4_NPS_ACE flag to allow the client
      to request the proper handling of this situation was seriously
      considered.  However, as this issue turned out to be only a small
      part of the different approaches of the two ACL model in resolving
      authorization questions, the choice was made to defer resolving
      this issue in NFsv4.1 and address it later as described in
      Appendix C.

   *  The handling of ACL inheritance by means of default ACLs was not
      supported despite the intention to consider valid servers
      supporting the draft-POSIX ACL model.  From the viewpoint of the
      Supersession Narrative referred to in Section 3.4, the included
      ACEs could be dealt with as inherit-only ACEs applying to all
      object types but that made the necessary adaptation by draft-POSIX
      ACL clients unduly difficult.









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      This issue could have been addressed by defining the
      ACE4_DEFAULT_ACE flag to allow the client to specify that an
      inherit-only ACE applying to both file and subdirectories would be
      treated as part of a default ACL, not normally modified when ACLs
      were set on an object.  To complement this, flags were to be added
      to the aclflag4 word in the sacl and dacl attributes to allow
      control of which acl(s) were to be modified.

      Eventually, it was decided to defer this item as well and address
      it later by using a separate attribute for default ACLs as
      described in Appendix C.

   *  [Consensus Needed (Item #117d), Through end of bulleted item]:
      Because the existing definition of the OWNER@, GROUP@, and
      EVERYONE made it impossible to translate reverse-slope modes to
      ACLs unless DENY ACEs (not part of draft-POSIX ACLs) were
      supported, it was considered whether it was necessary to define
      the special users GROUPNOTOWNER@ and OTHERS@ and to provide
      Aclchoice support to indicate the presence of handling of these
      special who values.

      Eventually, it was decided not to do this and instead to warn
      implementors of the unfortunate consequences of non-support
      despite its formal status as OPTIONAL.  This is despite the
      previous use of "SHOULD" which was not taken seriously because of
      its clear contradiction of the intention to allow use of servers
      supporting draft-POSIX ACLs which have no DENY ACEs.  See
      Section 3.4 for more details.

   As a result, the only protocol extension provided was the addition of
   the Aclchoice attribute.  See Section 4.6 for further discussion of
   this attribute, its motivation, and the reason that its absence
   needed to be treated as a defect.

1.4.  Effect on Various Minor Versions

   Because of the profound underspecfication of ACL feature and the
   associated misuse of RFC2119-defined keywords, it is necessary that
   this document, when publised as an RFC, supersede the existing
   specification of ACLs for all NFSv4 minor versions ([RFC7530]
   [RFC8881]).

   However, because of the rules relating to minor versions changes
   introduced in [RFC8178] and associated practical considerations
   regarding minor versions not under active development, the following
   differences should be noted:





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   *  In the case of minor version zero, despite the supesession noted
      above, there is no change to the protocol described or to the XDR
      described by [RFC7531].

      The changes in this document provide a more complete description
      with more clarity regarding the parts of ACL feature whose
      implementation is OPTIONAL.  As a result, there is no new
      functionality introduced or compatibility issues expected.

      While there is a conceptual change that allows new forms of ACLs
      to be defined, this change cannot be realized in minor version
      zero, since additional attributes to use them cannot be added.

   *  In the case of minor version one, the description of ACLs in this
      document supersedes that in [RFC8881].  In addition, it will
      provide the ACL description for minor version one that applies
      once the successor of [I-D.ietf-nfsv4-rfc5661bis] is published as
      an RFC.  That document will explicity refer to the ACL description
      being published here.

      The changes in this document, while provding a more clear
      description of the OPTIONAL nature of many elements of the ACL
      feature, also corrects a number of protocol defects.  The
      correction of protocl defects is explicitly allowed in revised
      specifications of existig minor versions, as described in
      Section 9 of [RFC8178].  The limited XDR changes associated with
      such corrections will be included in the RFC to be derived from
      [I-D.dnoveck-nfsv4-rfc5662bis]

      Section 1.3 disscuses such potential defects, including a number
      of potential changes to allow for semantics compatible to drafft
      POSIX ACLs to be incorprated in NFsv4.1.  While such changes could
      be considered correctible defects, it was decided to defer support
      for draft-POSIX ACLs to a later minor version, thus leaving the
      only defect being corrected here as the lack of a way for the
      client to determine what OPTIONAL protocol elements were
      implemented by the server, addressed by defining the Aclchoice
      attribute.

      Bcause the Aclchoice attribute is OPTIONAL, its inclusion cannot
      result in compatibility issues.

   *  In the case of later minor versions, the ACL description is
      inherited from minor version one and the modification descrbed
      above will apply to those minor version as well.






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      Because these minor versions are allowed to define new attributes,
      the conceptual change in this document, allowing the definition on
      new forms of ACLs could be taken advantage of in minor version
      two, by adding a protocol extension, as provided for by [RFC8178].

2.  Requirements Language

2.1.  Keyword Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as specified in BCP 14 [RFC2119]
   [RFC8174] when, and only when, they appear in all capitals, as shown
   here.

2.2.  Special Considerations

   Because this document needs to revise previous treatments of its
   subject, it will need to cite previous treatments of issues that now
   need to be dealt with in a different way.  This will take the form of
   quotations from documents whose treatment of the subject is being
   obsoleted, most often direct but sometimes indirect as well.

   Paragraphs headed "[Previous Treatment] or otherwise annotated as
   having that status, as described in Section 1 of
   [I-D.dnoveck-nfsv4-security], can be considered quotations in this
   context.

   Such treatments in quotations will involve use of these BCP14-defined
   terms in two noteworthy ways:

   *  The term may have been used inappropriately (i.e not in accord
      with [RFC2119]), as has been the case for the "RECOMMENDED"
      attributes, which are in fact OPTIONAL.

      In such cases, the surrounding text will make clear that the
      quoted text does not have a normative effect.

   *  The term may have been used in accord with [RFC2119], although the
      resulting normative statement is now felt to be inappropriate.

      In such cases, the surrounding text will need to make clear that
      the text quoted is no longer to be considered normative, often by
      providing new text that conflicts with the quoted, previously
      normative, text.






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2.3.  Use of the Term "SHOULD

   [Consensus Needed (Item #4a), Through end of Section]:

   The use of the BCP14-defined term "SHOULD" merits particular
   attention because of its mistaken use common in earlier discussions
   of matters addressed in this document and because of its central role
   in defining interoperability for client and server implementations.
   In particular, we will use the BCP14-defined term "SHOULD" in order
   to designate recommended implementation characteristics without
   retrospectively defining existing implementations as non-compliant.

   In previous treatments of ACLs this term was used extensively in
   contexts in which it was not made clear what might be valid reasons
   to bypass the implied recommendation, as required by [RFC2119].

   *  In some cases, specific uses of the term were described as
      "intentional", with the apparent implication that the reason for
      the use of this term was to allow implementations to ignore the
      recommended action simply because it was felt to be inconvenient.
      The effect was that such uses of "SHOULD" were interpreted as
      "MAY" with the added expectation that implementations bypassing
      the recommendation should be expected.

      This left uncertain the question of how an "unintentional" use
      should be interpreted but it made quite clear that this term was
      not being used in accordance with BCP14.

   *  The majority of uses of this term, presumably unintentional ones,
      do not seem to be in accord with [RFC2119] either in that it is
      not made clear what might be valid reasons to bypass the
      recommendation.  The only conclusion that can be reached at this
      point is that the author felt that there might be valid reasons to
      bypass the recommendation but was unsure if any existed.  However,
      it appears likely that, in most cases the threshold for
      considering a reason valid in this context were quite low, most
      likely because it was often assumed that the possible existence of
      existing software components (e.g. file systems designed without
      regard to NFSv4's needs) which made it difficult to conform to the
      recommendation would constitute a valid reason to bypass the
      recommendation, the effect on feature interoperability
      notwithstanding.

   As might be expected, this pattern and other cases of excessive
   deference to server implementation choices created a difficult
   interoperability situation, which it is now the job of the working
   group to correct.  As part of doing so, we will, as was done in the
   companion security document RFCTBD20, when using "SHOULD" without



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   reference to specific valid reasons to bypass the recommendation, the
   understanding is that, in this context, reliance on an earlier
   specification which allowed behavior now recommended against is a
   valid reason to continue to behave in that manner even if the
   allowance was previously communicated through the mistaken use of
   RFC2119-defined keywords,

   Also, with regard to such residual uses of "SHOULD", it needs to be
   understood that:

   *  With regard to new server implementations, there are no further
      valid reasons to bypass the recommendation unless those are
      explicitly mentioned.

   *  That when reporting implementation characteristics (e.g. by use of
      the Aclchoice attribute) the right to bypass a recommendation is
      not to be accepted does not allow an implementer to report the
      recommendation as being adhered to.

   *  That clients are under no obligation to accept such variances from
      these recommendations and MAY, as the implementors judge prudent,
      decide to not use the ACL feature or to restrict its use to avoid
      reliance on particular troublesome instance of recommendations
      being bypassed.

3.  Problems to Address

   [Consensus Needed (Item #104c, #105c), Through end of section]:

   Because of the problems described in Section 3.1 the state of the
   description of ACLs in current minor version specification documents
   [RFC7530] [RFC8881] makes it impossible to use these as a basis for
   the current specification without the kind of major revisions
   discussed below.

   In order to better understand how this troubling situation came
   about, see Section 3.2 which outlines the mistakes that led to out
   current predicament.  Other sections will discuss our options to undo
   the damage without imposing unacceptable compatibility issues on
   implementations that were allowed, intentionally or not, by this
   older approach.

   As described in Section 3.5, the state of the ACL-related features is
   such that the work necessary to provide a specification as part of
   the rfc5661bis effort far exceeds what might reasonably be expected
   for a feature that has been part of a Proposed Standard for two
   decades.




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   The work that has been done and that still needs to be done to arrive
   at a satisfactory specification for the acl-related features can only
   be understood if we address the fundamental problem that was
   mishandled early in the development of NFSv4 and understand how that
   led to the current unsatisfactory situation.

   This problem arose, as described in Section 3.2, arose when the
   working group had to deal with two very different approaches to the
   ACL issue and was unable to either choose one or arrive at a
   compromise.  Early acl work for the rfc5661bis effort focused on
   clarifying the situation and allowing clients to determine which of
   two ACL models had been implemented.

   As we started to look at the implementations that diverged from the
   UNIX ACL model, it appeared unlikely that we would find many (or even
   any) implementing the NFSV4 ACL model presented in the current
   specifications as canonical.  The result of the basic approach to
   accommodate multiple ACL models had resulted in situation in which
   implementation of UNIX ACLs and various hybrids of the two models
   predominated, with the model presented as canonical in existing
   specification rarely (or never) implemented.

   Later it was realized that the approach that was used to avoid
   explicitly choosing an acl model had resulted in the creation of a
   much more refractory situation as described in Section 3.5.  In an
   attempt to bring order to the situation the work described in
   Section 5 was undertaken.  As a result, the less ambitious approach
   was considered as the core and the various extensions to that model
   were considered optional extensions.  That required several further
   steps of which only the first few are accomplished in the current
   document with the remaining work doable as part of the rfc5661bis
   effort.

   *  Reorganize the presentation of the ACL-related features, along the
      lines suggested Section 5.  As part of this process, the
      extensions to the UNIX ACL model to create the full NFSv4 ACL
      model will be identified as OPTIONAL features whose presence is
      made known to the client as Aclchoice flag bits.

   *  Find any allowed behavioral variants, whether these are explicitly
      called out as allowed in the existing specifications or present in
      existing implementations so that they need to be accommodated.
      Most such variants will be identified as OPTIONAL features whose
      presence is made known to the client as Aclchoice flag bits.
      However, some are too complicated to do that and will be
      represented as Aclchoice data items.





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   *  To the degree possible, eliminate or simplify such behavioral
      variants.  That will be difficult in many cases because of the
      existence of server manifesting different behaviors, making it
      difficult to get to agreement on a common approach.

      One possible path toward convergence is the association of certain
      Aclchoice flag bits with various sort of advice/ recommendations,
      as is done in Section 12.3.

3.1.  Nature of the Existing Problems

   [Consensus Needed (Item 104d), Through end of section]:

   Acl handling within the NFSv4 protocols is in an unsatisfactory
   state, characterized by a troubling level of underspecification that:

   *  Leaves potential implementers unsure about what is needed to
      implement the feature.

   *  Provides no reasonable way for the client to determine what part
      of the existing feature specifications a server implements.

   *  Puts interoperability essentially beyond reach.

3.2.  Probable Problem Sources

   [Consensus Needed (Item #104d), Through end of section]:

   Existing difficulties appear to have arisen from a misguided attempt
   to accommodate two very different approaches to the issue of
   providing ACL support within NFSv4, each one with its own strengths
   and weaknesses:

   *  An approach based on a subset of ACL work being done for local
      UNIX file systems.  This was consistent with the pattern used in
      earlier versions of NFS in which the focus the effort was on
      making file system functions previously accessible locally
      available over a network.













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      [Consensus Needed (Items #105d, #117e), Through end of bulleted
      list]: In this document, we refer to this approach as the core
      UNIX ACL model.  Although this approach was derived from the now-
      withdrawn POSIX draft ACLs there are some elements of the latter
      that are considered distinct and turned out not to be
      representable within the NFsv4 ACL model.  These include the
      approach to computing Mode based on an ACL, the handling of
      partial satisfaction of authorization requests using ALLOW ACEs,
      and the method of supporting ACL inheritance (described as
      "default ACLs" in the POSIX drafts).

      While this approach would have provided a relatively simple path
      toward implementation on both the client and server sides, it was
      eventually not chosen.

      Unfortunately, it was never made clear what specific gaps caused
      that result and it still remains unclear to what degree the
      extensions made available by a more ambitious approach could be
      used by UNIX clients, even if they could be successfully
      implemented on the server side.

   *  A more ambitious approach not so strongly tied to the UNIX
      ecosystem.  This eventually turned out to be one based on Windows
      ACLs.

      Although many elements of this more ambitious approach have been
      implemented, it is not clear that the more ambitious approach,
      which we refer to as the NFSv4 ACL model was ever implemented by
      any server.

   The more ambitious approach to providing ACL support was added to
   [RFC3010] as a five-page section that outlined an approach based on
   Windows ACLs.  That section was not really a feature specification
   did not appear to be attempting to fill that role.  Instead, like
   other ambitious proposals in that RFC, it was a statement of ambition
   and its approval as a proposed standard did not involve a commitment
   by implementers to implement that proposal.

   When [RFC3530] was published, the ACL section followed the same basic
   approach.  At the same time, there were clear indications that
   implementations based on the proposal in [RFC3010] might not be
   possible in many environments.  Despite this justified concern, a
   shift to a more UNIX-oriented approach was not made.  Instead, the
   more ambitious approach continued to be presented as canonical while
   the specification was revised in an attempt to allow ACLs based on
   the withdrawn POSIX draft ACLs to be implemented within the XDR
   established for the original, more ambitious approach.




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   As things turned out, that attempt failed, since the subset of the
   NFSv4 ACL model that was treated as required ignored some aspects of
   the draft-POSIX ACL model.

   As a result, the fundamental differences between these two approaches
   were obscured.  Instead of providing explicitly for two distinct
   approaches, the core UNIX and NFSv4 approaches to ACLs were presented
   as variant implementations of the same underlying approach, simply
   because they were expressed using the same XDR.  Semantic differences
   were dealt with only when absolutely necessary and the wider semantic
   range of the NFSv4 model led to an incorrect approach in which the
   core UNIX and draft-POSIX ACL model were considered as obstacles to
   be overcome as part of a supersession narrative.

   In order to accommodate these multiple ACL models, the specifications
   were drafted with a troubling level of semantic laxity, as described
   in "PROB-lax"/>.  As a result, clients had no way to determine what
   approach a server had implemented.  As a result, most clients could
   only depend on the features of the least ambitious model while these
   needing features of the more ambitious models could only use them if
   they approached the issue with no prospect of interoperability and
   chose particular server implementations based on the features which
   each supported and adapted each client to each server used.  As a
   result,

   *  Clients that needed the functionality of draft-POSIX ACLs had to
      deal with mapping between two sets of ACE masks, without
      documentation of the process, uncertainty about the partial ALLOW
      satisfaction required by this model and with no direct support for
      the default ACL semantic.

      They had to deal with the core UNIX ACL subset which was not a
      good fit for their needs.

   *  Clients that needed functionality provided by the NFSv4 extensions
      had no API for users to use to request those services.  In
      addition, it was impossible for clients to determine whether the
      particular extension was supported.

3.3.  Semantic Laxity

   [Consensus Needed (Item #104e), Through end of section]:

   As we consider the extraordinary semantic laxity regarding ACLs in
   current specifications, it appears that a number of factors were
   involved in arriving at the approach we see reflected in [RFC7530]
   and [RFC8881].




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   *  A lack of concern about and experience with defining semantics.

      For NFSv3, this was not an issue since all necessary semantics was
      inherited from POSIX semantics with regard to file access,
      originally defined to support local operation.

      Unfortunately, the working group's members with this background
      were unable to shift their approach to adapt to a very different
      environment, in which semantic extensions to POSIX, such as named
      attributes and ACLs required a different approach.

   *  A lack of concern with authorization issues combined with a
      tendency to treat these as inherently-server specific.

   *  A lack of familiarity with the needs of standards-based
      specifications together the expectation, derived from the history
      of NFS, that there would be coordinated dominant client and server
      implementations that would resolve semantic issues at the
      implementation level.

   These resulted in a situation in which important behavioral
   specifications, important to provide interoperability, were left
   unresolved by writing the specs in various ways that, appear, in
   retrospect, to be ill-advised:

   *  The use of SHOULD without any attention to a clear
      characterization of the supposed "valid reasons" to bypass the
      recommendation.

      The common use of this keyword in connection with actions to be
      taken in implementing ACLs might or might not have affected actual
      implementations as there was often no reason to bypass the
      recommendation.  Nevertheless, it created a substantial
      uncertainty about many elements of the specification since it
      allowed the possibility of variant implementations to develop with
      clients forced to adapt.

   *  The designation of certain choices by uses of SHOULD explicitly
      identified as "intentional".

      Essentially, these uses of SHOULD, had the same effect as if MAY
      had been used but the fact that MAY was not used obscured the
      reality that the degree of freedom thereby granted to the server
      had negative consequences for interoperability.

   *  In many cases, the specification simply cited distinct possible
      server behavior, implying that it was the job of the client to
      adapt to the server behavior.



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   The unfortunate consequences of this approach and the means by which
   it needs to be addressed are discussed in Section 3.5.

3.4.  Problems in the Handling of Draft POSIX ACLs

   [Consensus Needed (Item #117f), Entire section]:

   In previous specifications, it was assumed that, because the draft-
   POSIX ACL model provided a coarser-grained approach to authorization,
   support for this model could be provided by servers supporting the
   NFSv4 ACL model.  Essentially, the draft-POSIX model was considered
   to be as a submodel.  In this document, we refer to this unjustifed
   assumpton as the "Supersession Narrative" since it was driven by the
   idea the NFSv4 finer-grained NFSv4 ACL model could supersede the
   draft-POSIX model.

   In addition, it was asssumed that servers built to support draft-
   POSIX ACLs could serve in this role while providing support for a
   subset of NFSv4 ACLs.  It was assumed that, for a clearly defined
   subset of NFSv4 ACLs, a simple translation to the NFSv4 format could
   provide for effective implementation of something sufficiently close
   to the draft-POSIX ACL model to be useful.  The assumption that it
   was possible to use such servers to support NFSv4 ACLs ignored many
   of the fundamental differences between the two ACL models.  Analysis
   of the differences between the semantics of the NFSv4 ACL model and
   the draft-POSIX ACL model established that this was unachievable for
   the reasons discussed below.

   *  The handling of inheritance within the NFSv4 ACL model, was not
      usable in the draft-POSIX ACL context, because the draft-POSIX ACL
      concept of default ACLs had no correlate within the NFSv4 ACL
      model.

   *  The one case in which a specific semantic difference was
      mentioned, with the presumed draft-POSIX ACL semantics explicitly
      made essentially OPTIONAL (although confusingly described by an
      "intentional SHOULD") did not accomplish the intended purpose
      because it did not accurately reflect draft-POSIX ACL semantics.

   *  The role of the acl mask within the draft-POSIX ACL approach was
      essentially ignored.

      This made it extremely difficult to extend the NFSv4 ACL model to
      incorporate draft-POSIX ACLs because important information needed
      to support it was excluded from the already-defined ACE/ACL
      structures.





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   *  Most important was the two different approaches to authorization
      checking.  For draft-POSIX ACLs a single ACE is selected based on
      the requesting principal, while in the NFsv4 ACL model any number
      of applicable ACEs can allow or deny the requested operation.
      This restricts the set of translatable ACLs but is even more
      troublesome in that it makes the translation dependent on group
      membership.  This requires the translator to have extensive
      knowledge in order to be able to determine when two named groups
      or a name user and named groups might intersect and means that a
      translation can be rendered invalid post facto in response to
      group membership changes.

   Given the above, the assumption that servers built to support draft-
   POSIX ACLs could support a submodel of the NFSv4 ACL model appears to
   be grossly mistaken.  It appears that the neglect of the details of
   the defined semantics noted previously caused the semantic
   requirements of draft-POSIX ACLs to be essentially ignored.

   In addition, The corresponding assumption regarding client support
   neglected much of the semantics of draft-POSIX ACLs.  As a result,
   only a subset of the possible ACLs within the draft-POSIX ACL model
   were expressible within NFSv4 ACL model.

   Given the pervasive lack of attention to semantic details, it seems
   to have been assumed that the draft-POSIX ACL model could be handled
   in the framework of the Supersession Narrative discussed above,
   leaving others with the job of providing true support for draft-POSIX
   ACLs.

3.5.  Challenges We Now Face

   [Consensus Needed (Items #104f, #105e), Through end of section]:

   The way in which the features incorporated in the original NFSv4 ACLs
   model were selected and specified raises difficult-to-resolve issues
   as we try to provide now what should have been provided at an earlier
   stage.

   Often, when the specification is at variance with existing
   implementation, we can create a specification that matches the
   existing implementation.  This was the approach taken when the
   internationalization specified in [RFC3530] was replaced by that in
   [RFC7530].








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   In that case, we were able to make that switch because the existing
   specification had essentially been ignored by implementers and their
   uniform choice, which provided widespread interoperability, was based
   on previous NFSv3 practice and was consistent with the needs of UNIX
   users, clients, and servers and could be adapted carefully to meet
   some of the needs that motivated the approach in [RFC3530].

   In this case we have a far more difficult situation to deal with,
   because of the following factors:

   *  Implementation was not uniform in that there were two basic
      implementation patterns to fill, with the non-POSIX pattern
      presenting implementers many choices about the feature set to
      support.

   *  Much more time has elapsed making it harder to access information
      about implementations.

   *  Even within the POSIX-oriented set of implementations, there were
      a significant set of behavioral choices allowed, whether
      explicitly or by a lax approach to the specification of expected
      behaviors.

   As a result, the following needs be done for each of the constituent
   features:

   *  Assess the suitability of the extension for inclusion in NFSv4
      based on user needs, server implementability, and issues
      concerning the consistency of the extension with the rest of the
      NFSv4 protocol.

      In connection with this, the existence of implementations is a
      clear indications of need/usefulness, but their non-existence
      cannot be considered dispositive.

   *  Find server implementations of the feature

      We will wind up with certain cases in which the number of servers
      implementing the feature is low or zero.

      It might take considerable time to find them and ascertain details
      of their implementation, especially since this might depend on the
      local file system used.

   *  Specify details of the required behavior.






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      In the ideal case, we will find an interoperable client-server
      pair but even in that case, we will need to find out if other such
      pairs exist, which might take considerable time.

      If multiple such pairs exist it is possible, although unlikely,
      that agreement on a single approach can be achieved.  A more
      likely result in that case is that one or more behavioral variants
      will be allowed and there will be a way for the server to provide
      the client information about its behavioral choices as described
      in Section 4.6

   It is unlikely that it we will be able to complete all of the above
   for all of the extensions to the core UNIX ACL model described in
   Section 5.1 in a reasonable time, as part of the NFSv4.1
   respecification effort.  As a result, we will focus on a more limited
   of goals described in Section 3.6.

3.6.  Work Necessary to Address Interoperability Issues as Part of
      NFSv4.1 Respecification Effort.

   The ideal state for a feature group such as ACL support is one in
   which the set of allowable server behavioral variants is limited as
   follows:

   *  Allowed behavioral variation should be used primary to allow the
      presence or absence of specific OPTIONAL features not needed by
      all clients but usable by some client subset.

      These can be supplemented by allowing multiple behaviors if the
      reasons to allow multiple behaviors outweigh the difficulty, for
      clients and users, of dealing with servers that manifest different
      behaviors.

   *  There is a good way for the client to determine the server's
      behavioral choices and adapt to them, to provide to users a common
      result independent of particular server choices.

      In many cases, the client, if provided with appropriate
      information about server behavior, can provide the same interface
      to its users, irrespective of server choices.

   While it would have been possible to design ACL support to meet the
   above, the problem was not then recognized, leaving us to try to
   correct it after the fact.  In this case, the difficulty of doing so
   has been compounded by the development of a server support with a
   wide range of behavioral variation although we are still unclear
   about the variation that actually exists.




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   A critical part of addressing this issue is definition of the
   Aclchoice attribute described in Section 4.6 Aclchoice provides a
   means of specifying the server's choices when there are allowable
   behavioral variants including elements of the protocol for which
   support is essentially OPTIONAL and other behavioral variants that
   exist.  Because of the ways ACLs were described previously (See
   Section 3.3), we can never be sure of knowing all of these, but items
   have been included as described below and the set of allowed variants
   is subject to later extension.

   *  We have included all cases in which feature-like elements are
      essentially made OPTIONAL in previous specifications.  This is
      done even though those specifications did not specify this choice
      in those terms or recognize the full implications of their
      optional nature.

      These cases include the fact that each ACE type is OPTIONAL
      (choices reported by the Aclsupport attribute), the fact that
      almost all ACE mask bits are OPTIONAL (See details below), and the
      optional nature of each of the items of ACE flag support.  In the
      latter two cases, the only ways that the client can determine
      which features are supported is through use of the Aclchoice
      attribute.

   *  We have not included many cases in which the servers is implicitly
      allowed to manifest different behaviors via the otherwise
      unexplained use of the keyword "SHOULD".  Given the lack of
      explanation and the pervasive misuse of RFC2119-defined terms in
      these specification, it is hard to conclude that there was any
      specific reason to allow these recommendations to be bypassed and
      it is likely that no implementations actually did so.  If we find
      cases in which servers did bypass the recommended action, they can
      be added by an extension of the Aclchoice attribute.

      There is one case in which a possible behavioral variant is
      introduced by what is referred to as an "intentional 'SHOULD'".
      Because it is hard to conclude, given the context, that anything
      different than "MAY" was intended, this choice, as to how to
      compute a mode value from an ACL, was added as a valid behavioral
      variant within Aclchoice.

      There is one case which an unexplained SHOULD is used but the
      recommended action (i.e supporting DENY ACEs) has been treated as
      OPTIONAL nevertheless.  This partly because of the specification's
      need, mentioned in a number of places, to support servers
      implementing draft POSIX ACLs which have no DENY facility, but it
      also reflects other elements in which such support is presented as
      OPTIONAL including the definition of the Aclsupport attribute.



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   *  In some cases connected with modifying an ACL to reflect the
      potential change to the low-order bit of the mode attribute, we
      have created allowable behavioral variants to reflect the fact
      that the existing specification are self-contradictory about what
      does and does not need to be done many potentially existing ACEs.
      See Section 10.7 for details.

   *  There are a number of cases in which certain behavioral variants
      necessary to provide explicit support for draft POSIX ACLs are
      explicitly disallowed.  This is despite the desire, mentioned in
      other places to allow use of such servers.

      As allowed by Section 9 of [RFC8178], we have provided additional
      flexibility to accept such server behavior and to allow its use to

   The other critical element in addressing these issues in the context
   of the NFSv4.1 respecification effort involves the reorganization of
   the specification into a required core and several sets of extensions
   as described in Section 5.  As mentioned above, each of these sets
   will have its own requirements in the context of the respecification
   effort as described below.  This gives us the option of providing
   further steps later in areas that are not a current priority,
   allowing us move towards the sort of implementation we should have
   started with.

   *  For the core functionality described in Section 5.1, our goal as
      part of this respecification is simply to recognize and document
      the fact that this is a set core functionality that needs to be
      present whenever ACLs are used to provide authorization instead of
      using the mode attribute.

      This is in contrast to the current approach which treats the full
      NFSv4 ACL model as canonical, but essentially treats almost any
      variation from the specified behavior as something that clients
      have to accept but do not need to be informed about.

      Within this document, the three ACE mask bits corresponding to the
      POSIX read, write and execute privilege bits are always expected
      to be supported.  While the same expectation is made by the
      existing specification, that is never clearly stated and it is
      possible to read the statement allowing the server to choose mask
      bit granularity on its own as allowing something even more coarse-
      grained.  This is despite the fact that the lack of an API
      correlate of any such implementation would make it essentially
      unusable.






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   *  The definition and support of ACE mask bits beyond the three
      corresponding to the three POSIX privilege bits are an important
      part of the extensions needed by the NFSv4 ACL model.  See
      Section 7.2.3 for details.  Previously, many important aspects of
      the handling of these bits was left to the server's discretion or
      assumed to follow naturally from the position of each bit in a an
      assumed granularity hierarchy that was not documented and is not
      viable as a full framework for the existing mask bits.

   [Consensus Needed (Item #117g), Through end of bulleted list]: While
   it would be helpful to address the following items as part of the
   respecification effort by making the draft-POSIX ACL model a submodel
   of the NFSv4 ACL model, it has proved impossible to do so, because of
   the large set of semantic differences between the two models
   described in Section 3.4.  For discussion of ways to address draft-
   POSIX ACL semantics in later minor versions, see Appendix C.

   *  The different handling of ACL inheritance in the draft POSIX and
      NFSv4 ACL models.  The NFSv4 approach is more general but the
      POSIX approach is simpler to use and understand.

   *  The very different approaches to authorization determination in
      which POSIX checks only a single ACE based on the principal while
      NFSv4 scans the entire ACL for potential principal matches.

   *  The very different approaches taken to the interaction of mode and
      ACLs including the use of the ACL mask.

   Given this framework the degree of satisfaction of our basic goals to
   be expected as part of the respecification varies with the area, as
   described below:

   *  The definition of the core UNIX ACL model presented in this
      document is adequate as it stands and will be part of the
      respecification effort.

      The corresponding work to allow clients using this model to
      interact correctly with servers implementing the NFSv4 ACL model
      in whole or in part is also adequate as it stands and will be part
      of the respecification effort.

   *  Support for the draft-POSIX ACL model is not possible as part of
      the respecification effort and will need to be deferred to an
      NFsv4.2 extension.

   *  Considerable effort has been done to provide better support for
      servers that implement some or all of the extensions within the
      NFSv4 ACL model and for clients that need these extensions.



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      Considerable advances have already been made by recognizing these
      as OPTIONAL extensions and allowing the client, using Aclchoice,
      to determine the extension that are supported.

      To reach an a truly interoperable state, we would need either a
      full definition of expected semantics, as we have in the case of
      draft-POSIX ACLs, or a complete understanding of the allowable
      behavioral variants.  Since the latter was not provided as part of
      the design of the feature as would normally be expected, these
      decisions would have be done after-the-fact based on the details
      of all existing server implementations, That step is likely to be
      delayed and is not expected be done as part of the NFsv4.1
      respecification effort.

4.  ACL-based Authorization-related Attributes

   [Author Aside: (Items #14a, #15a... ), Applies to entire top-level
   section]: The treatment of the various ACL-based attributes in the
   included subsections replaces the corresponding sections in earlier
   documents, in which the attribute descriptions were not consolidated
   in one place and were disbursed among a number of top-level sections.
   Where it has been necessary to make significant changes, the
   annotations for those changes, including author asides and proposed
   text, appear here while vestigial text that is now superseded has not
   been brought forward.

   The per-object attributes Acl, Dacl, and Sacl all contain an ACL
   object as described in Sections 6 and 7 and their subsections.

4.1.  Definition to Support ACL-related attributes

   The definitions of the acemask4 and some other data structures
   related to the Aclchoice attribute appear in included subsections.
   These need to be done earlier than others for a number of reasons:

   *  They are used directly in the definition of ACL-related attributes
      as well as within the definition of the ACE structure in
      Section 7.

   *  They need to be referenced as part various data elements that need
      to incorporated into the Aclchoice attribute, defined in
      Section 4.6.

4.1.1.  Definitions related to ACE mask bits.

   typedef uint32_t        acemask4;





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   The definition of the individual bits within mask words of type
   acemask4 appears in Section 7.2

4.1.2.  Definitions related to Aclchoice.

   typedef uint32_t        ombr4word;

   struct nfs4acds {
               uint32_t    acd_offset;
               uint32_t    acd_length;
   };
   typedef struct nfs4acds nfs4acdi;

   struct nfs4acas {
               bitmap4     aca_bits;
               nfs4acdi    acs_ditems<>;
               opaque      aca_dpool<>;
   };

   Words of type omnr4word are used to describe the particular usage of
   ace mask bits whose semantics is not currently determinable.  The
   definition of the individual bit fields appears in Section 7.2.10.

   An nfs4aclc structure is used to represent a particular value of the
   per-fs scope read-only aclchoices attribute.  This structure is
   designed to be extensible with the definition in this document
   capable of being extended in subsequent minor versions in the same
   way that the set of attributes is extended using the method explained
   [RFC8178].  It consists of the following elements:

   *  A bitmap containing flags with each indicating the presence or
      absence o a particular feature extending the functionality
      available using UNIX ACLs.

   *  An array of nfs4acdi elements, with each element designating a
      particular set of data providing additional information about the
      details of a particular feature.

4.1.3.  Designation of the Absence of an ACL

   [Consensus Needed (Item #118a), Through end of section]:

   ACL-related attributes are represented as or contain an array of
   ACEs.  While it is possible to treat zero-length arrays of ACEs
   within this framework and consider them as ACLs, these are treated
   differently for the following reasons:





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   *  There needs to be some way to indicate the absence of an ACL,
      rather than a particular ACL value, when interrogating or setting
      such attributes as acl, dacl, and sacl.

      Intuitively, a zero-length ACE array could server this purpose.

   *  There is no good reason to interpret such an empty array as an
      ACL, since the natural result, an ACL denying all access, would
      not serve useful purpose.

      Given the relationship between mode and acl-related attributes,
      such universal denial would most easily be expressed using a mode
      whose nine low-order bits were all zero.

      Such an interpretation would make it hard to delete an existing
      dacl, while retaining the access specified by the mode attribute.

4.2.  Table of ACL-related Attributes

   The following table summarizes all the ACL-related attributes,
   including:

   *  Attributes to support ACL-based authentication: Acl, Dacl.

   *  Attributes to provide other security-related services: Sacl.

   *  Attributes to provide information regarding the level of ACL
      support provided: Aclchoices, Aclsupport.

      +============+====+==========+===========+=====+=============+
      | Name       | Id | Ver      | Data Type | Acc | Defined in: |
      +============+====+==========+===========+=====+=============+
      | Acl        | 12 | 4.0      | nfsace4<> | R W | Section 4.4 |
      +------------+----+----------+-----------+-----+-------------+
      | Aclchoice  | 87 | 4.1(bis) | nfsaclc4  | R   | Section 4.6 |
      +------------+----+----------+-----------+-----+-------------+
      | Aclsupport | 13 | 4.0      | uint32_t  | R   | Section 4.5 |
      +------------+----+----------+-----------+-----+-------------+
      | Dacl       | 58 | 4.1      | nfsacl41  | R W | Section 4.7 |
      +------------+----+----------+-----------+-----+-------------+
      | Sacl       | 59 | 4.1      | nfsacl41  | R W | Section 4.8 |
      +------------+----+----------+-----------+-----+-------------+

                                 Table 1







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4.3.  Types of ACLs

   The ACL allows authorization schemes outside those conforming to the
   POSIX approach to be specified and applied to file objects.  This
   provides additional flexibility in a number of ways:

   1.  There may be multiple users or sets of users assigned different
       privileges to address cases in which the appropriate privilege
       assignments do not conform to the POSIX model in that they are
       different for users in the same group or different for two groups
       outside the owning group.

       ACLs support this additional flexibility by allowing an array of
       Access Control Entries, each of which specifies handling for a
       user or user group.

   2.  For particular users or sets of users, the set of operations to
       be allowed might not be expressible using the three bits provided
       by POSIX as supplemented by special privileges for operations
       reserved to file owner.

   NFSv4 ACLs, as described in Section 6, address both issues by
   defining, within the Access Control Entry, a large set of distinct
   privilege bits, modeled on those provided by Windows ACLs.

   ACLs based on a the core subset of NFSv4 ACLs (i.e., the parts which
   are not OPTIONAL whenever ACL-related attributes are supported make a
   more limited change to the POSIX authorization model and are
   represented by the same sorts of structures as NFSv4 ACLs, although
   there are restrictions imposed by the UNIX ACL model.  These ACLs are
   based on a subset of the draft-POSIX ACL model.

   Although these two models (i.e., NFsv4 ACLs and draft-POSIX ACLs)
   have some common goals and are presented in a common XDR framework,
   they are substantially different, for reasons listed below.  Previous
   specifications have assumed that server implementations of the draft-
   POSIX ACLs could serve to support NFsv4 ACLs and ignored the issues
   that the semantic differences would pose for clients attempting to
   support the draft-POSIX model.

   *  The draft-POSIX ACLs address only the first of the motivations for
      extension, while the NFSv4 ACL model is intended to address both
      of them, by defining a large range of bits in the ACE mask, rather
      than the three POSIX bits.

   *  NFSv4 ACLs, by supporting DENY entries allow specific privileges
      to be allowed for most members of a group and be denied to some
      particular users.



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   *  NFSv4 ACLs provide additional security-related facilities in
      addition to authorization control, through the use of AUDIT and
      alarm ACEs.

   *  These models implement very different approach to authorization in
      that the NFSv4 ACL model is based on the sequential scanning of
      all ACEs to verify authorization for all requested actions, while
      the draft-POSIX ACL model scans a limited subset of these and
      requires that all authorization for each requested action be
      determinable based on a single ACE.

   *  Both have very different approaches to managing the interaction of
      the mode attribute and ACL-related attributes.  In particular,
      draft-POSIX ACLs use the middle three of the nine bits controlling
      authorization to establish an ACL mask applying to all ACEs except
      those controlling access to the owning user and to everyone.

   *  They have very different approaches to the management of ACL
      inheritance.

   {Author Aside (Item #61a)]: In order to justify an eventual shift of
   the Acl and Dacl attributes back to be truly OPTIONAL, it is
   necessary to define for each file system, the type of ACL semantics
   provided, using information such as that provided by the Aclchoice
   attribute.  In so doing, we will have to make provision for various
   hybrids if such implementations actually exist, while not necessarily
   seeking to preserve the ability to generate other such potential
   hybrids, in all cases.

   [Consensus Needed, Including List (Item #61a)]: The determination of
   the type of ACL semantics proceeds as follows:

   *  If the aclsupport attribute indicates that either AUDIT or ALARM
      ACEs are supported, then it can be assumed that, in general, NFSv4
      ACL semantics are provided, although some OPTIONAL ACE mask might
      not supported.

   *  If the Aclsupport attribute is not supported, then if the Sacl
      attribute is supported then it also can be assumed, as above, that
      NFSv4 ACL semantics are provided.

   *  Otherwise, If the Aclsupport attribute is not supported then the
      presence of support for DENY ACEs determines whether support for
      NFSv4 ACL semantics is provided.  However, it is required that
      clients determine whether support for DENY ACEs is provided by
      attempting to set ACLs containing such ACEs





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   *  In the case in which neither the Aclsupport attribute nor the SACL
      attribute is supported, then it is not possible to determine of
      support for NFSv4 ACL semantics, as opposed to core UNIX ACL
      semantic is provided.

      As a consequence, server implementations providing support for
      NFsv4 extensions need to support the Aclsupport attribute.  This
      is because, if they do not, the client could legitimately assume
      that support for the NFSv4 ACL model is not present.

4.4.  The Acl Attribute (v4.0)

   This per-object attribute consists of an array of Access Control
   Entries which apply to operations performed on the current object,
   controlling authorization and monitoring of attempted operations.

   [Consensus Needed (Item #118b)]: When this attribute is interrogated,
   it either returns an array of all ACEs in effect for this object
   including those related to authorization and to the monitoring of
   attempted operations.  When there are no such ACEs, a zero-length
   array is returned, indicating that there is no ACL (and thus no SACL
   or DACL) associated with the object.

   [Consensus Needed (Item #118b)]: When this attribute is set the
   values of the SACL and DACL attributes are also affected.  When it is
   set to a zero-length array, indicating the deletion an ACL, both the
   SACL and DACL attributes will subsequently return an indication that
   there is no such ACL.  If the ACL value being set only contains ALLOW
   and DENY ACEs, the SACL attribute will subsequently return an
   indication that there is no such ACL.  Similarly, if the ACL value
   being set only contains AUDIT and ALARM ACEs, the DACL attribute will
   subsequently return an indication that there is no such ACL.

   This attribute, consists only of an ACE array and does not support
   automatic inheritance or default ACEs.  Although some inheritance
   features might be supported, some of the inheritance features of the
   draft-POSIX ACL model are not accessible using this attribute.

   The acl attribute is OPTIONAL and there is no requirement that a
   server support it.  However, when the dacl attribute is supported, it
   is a good idea to provide support for the acl attribute as well, in
   order to accommodate clients that have not been modified to use the
   dacl attribute.








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   [Consensus needed, Including List (Item #65a)]: While the original
   intention was to define a usable OPTIONAL attribute based on the
   NFSv4 ACLs defined previous specifications, it is now more
   appropriate to designate this under-specified attribute as
   experimental although still formally OPTIONAL, until the items below
   have been addressed.

   *  The intention to support, as values of this attribute two
      different ACL approaches, each with its own semantics.  These
      include both the NFSv4 ACLs based on the Windows ACL model and a
      subset based on the more restricted semantics provided by the
      withdrawn POSIX ACL document with a straightforward mapping of
      those into the format of NFSv4 ACLs.

      The association of two such different semantic models without
      giving the client a way to determine which semantic model is in
      effect makes interoperability essentially impossible to provide.

   *  The potential interoperability problems are vastly expanded by the
      specific method by which these two models are supported.

      Instead of allowing servers to choose between these two
      approaches, e.g. by using the term "MAY", most statements
      regarding ACL semantics use the term "SHOULD", described in the
      text as "intentional", apparently assuming that the result is
      essentially equivalent to the use of "MAY".  Even apart from the
      misuse of the terms defined in [RFC2119], this has the effect of
      replacing a single choice by allowing a large number of
      uncoordinated choices, exponentially raising the number of
      possibly valid semantic models that clients and users have to
      accommodate.

   *  It is not clear how far this pick-and-choose approach extends.  In
      the case of the ace mask bits which are finer-grained than the
      three bits in the mode and in POSIX ACLs, there is no explicit
      text indicating how the coarser-grained approach would be
      supported by a server built to support POSIX ACLs, leaving the
      actual requirements uncertain.

   *  Although some efforts have been made to limit the damage caused by
      this specification uncertainty by urging clients to determine
      authorization decisions using ACCESS rather than by examining the
      ACL itself, this only addresses half of the problem and the
      question of what ACL to set to effect a particular authorization
      regime remains unaddressed, limiting the usefulness of the ACL-
      related features.





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      Although significant efforts have been made to widen the
      information returned by ACCESS beyond the three-bit POSIX model,
      there are still cases in which it is insufficiently fine-grained.
      For example, adding a new file and a new sub-directory which have
      different ACE mask bits are both represented by a single bit in
      ACCESS.

   [Author Aside]: Although it has generally been assumed that changes
   to sacl and dacl attributes are to be visible in the acl and vice
   versa, NFSv4.1 specification do not appear to document this fact.

   [Consensus Item, Including List (Item #16a)]: For NFSv4.1 servers
   that support Both the acl attribute and one or more of the sacl and
   dacl attributes, changes to the ACE's need to be immediately
   reflected in the other supported attributes:

   *  The result of reading the dacl attribute MUST consist of a set of
      ACEs that are exactly the same as the ACEs ALLOW and DENY ACEs
      within the acl attribute, in the same order.

   *  The result of reading the sacl attribute MUST consist of a set of
      ACEs that are exactly the same as the AUDIT and ALARM ACEs within
      the acl attribute, in the same order.

   *  The result of reading the acl attribute MUST consist of a set of
      ACEs that are exactly the same as the union of ACEs within the
      sacl and dacl attributes.  Two ACEs that both appear in one of the
      sacl or dacl attributes will appear in the same order in the acl
      attribute.

4.5.  The Aclsupport Attribute (v4.0)

   A server need not support all of the ACE types described in
   Section 6.1.  This attribute indicates which ACE types are supported
   for the current file system by any of the acl, sacl, or dacl
   attributes.

   [Consensus Needed (Item #61b)]: Although this attribute is OPTIONAL,
   there are important reasons, in certain cases, to provide support, as
   described in Section 4.3.

   The bitmask constants used to represent the abovementioned
   definitions within the aclsupport attribute are as follows:

         const ACL4_SUPPORT_ALLOW_ACL    = 0x00000001;
         const ACL4_SUPPORT_DENY_ACL     = 0x00000002;
         const ACL4_SUPPORT_AUDIT_ACL    = 0x00000004;
         const ACL4_SUPPORT_ALARM_ACL    = 0x00000008;



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   [Author Aside (Item #14b)]: Even though support aclsupport is
   OPTIONAL, there has been no mention of the possibility of it not
   being supported.

   [Consensus Needed (Item #14b)]: If this attribute is not supported
   for a server or filesystem, the client is entitled to assume that, if
   the acl attribute is supported, support for ALLOW ACEs is present.
   Thus, if such a server supports the sacl attribute, clients are not
   likely to use it if aclsupport is not supported by the server.

   [Previous Treatment (Item #110a)]: Servers that support either the
   ALLOW or DENY ACE type SHOULD support both ALLOW and DENY ACE types.

   [Author Aside, Including List: (Item #110a)]: The use of "SHOULD" in
   the preceding is unhelpful for the following reasons:

   *  While it is unclear what the intention is, it is certainly is not
      in accord with RFC2119 since there is no indication of potential
      harm or what might be valid reasons to do otherwise.

   *  While it might be one of "intentional" SHOULDs, that would make
      the paragraph meaningless since such SHOULDs are essentially equal
      to MAYs.

   *  The most likely source of divergence, the fact that UNIX ACLs do
      not support DENY ACEs, is not mentioned at all.

   [Consensus Needed (Item #110a)]: Servers that support the DENY ACE
   type MUST support the ALLOW ACE type as well.

   [Consensus Needed, Including bulleted list (Item #110a)]: Clients
   should not attempt to set an ACE unless the server claims support for
   that ACE type.  The server MUST reject requests with
   NFS4ERR_ATTRNOTSUPP if any of the following apply:

   *  If the server receives a request to set an ACE type that is not
      allowed as part of the acl attribute being set.

   *  If the server receives a request to set an ACE, it cannot store.

   Support for any of the ACL attributes is OPTIONAL.  However, certain
   restrictions apply regarding the interaction of support for these
   attributes, A server that supports either of the newer ACL attributes
   (dacl or sacl) MUST support use of the new ACL attributes to access
   all of the ACE types that it supports.  In other words, if such a
   server supports ALLOW or DENY ACEs and the sacl attribute, then it
   MUST support the dacl attribute and any ALLOW or DENY ACE types
   supported by the acl attribute MUST be supported in the dacl



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   attribute as well.  Similarly, if it supports AUDIT or ALARM ACEs and
   the dacl attribute, then it MUST support the sacl attribute any AUDIT
   or ALARM ACE types supported by the acl attribute MUST be supported
   in the dacl attribute as well.

4.6.  The Aclchoice Attribute (v4.1 extension for bis)

   [Consensus Needed (Item #105f), Through end of section]:

   The Aclchoice attribute provides information regarding the server's
   provision of various OPTIONAL elements or valid behavioral choices in
   implementing NFSv4 ACLs and using them for authorization or other
   security-related functions.

   This has been necessary by the approach taken in previous
   specification, in which numerous extensions of the core UNIX ACL
   model are mentioned as possibilities but there is no attention at all
   to the problems that this creates for clients without a way to
   determine whether any particular extension is supported.  Without
   such facilities, the ability to determine whether the necessary
   extensions are supported is severely compromised.  We consider that
   inability as a protocol defect justifying the extension of the
   protocol via the addition of a new OPTIONAL attribute.

   While it might be supposed that this attribute could be rendered
   unnecessary since the server would be expected to reject requests for
   unsupported services, the definition of ACLs in previous
   specifications make that impossible for the following reasons:

   *  In many cases, existing specifications are written, so that such
      rejection is not required and sometimes it is suggested that it is
      undesirable.  For example, [RFC8881] contains the following.

         It is tempting to accomplish this by rejecting any ACL that
         falls outside the small set that can be represented accurately.
         However, such an approach can render ACLs unusable without
         special client-side knowledge of the server's mapping, which
         defeats the purpose of having a common NFSv4 ACL protocol.
         Therefore, servers should accept every ACL that they can
         without compromising security.

         So it may be useful for a server to accept an ACL even if not
         all of its modules are able to support it.

         For example, suppose a client tries to set an ACE with
         ACE4_FILE_INHERIT_ACE set but not ACE4_DIRECTORY_INHERIT_ACE.
         If the server does not support any form of ACL inheritance, the
         server should reject the request with NFS4ERR_ATTRNOTSUPP.  If



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         the server supports a single "inherit ACE" flag that applies to
         both files and directories, the server may reject the request
         (i.e., requiring the client to set both the file and directory
         inheritance flags).  The server may also accept the request and
         silently turn on the ACE4_DIRECTORY_INHERIT_ACE flag.

      As a result of this and similar statements in the existing
      specifications, it is impossible to rely on rejection in the cases
      we concerned with.

   *  Much of the existing vagueness about the handling of ACE mask bits
      is exacerbated by the false assumption that all such mask bits can
      be treated as part of granularity hierarchy mappable to the
      coarse-grained approach of three permissions derived from POSIX.

   *  A further source of difficulty arises from the possibility,
      alluded to in previous specifications that a server might accept
      ACLs it is not prepared to enforce, in the expectation that
      another that is capable of enforcing the ACL might later do so.

      As a result, ACLs could be accepted with this expectation, with no
      way of determine whether they are enforced where first created or
      any other server to which they might be copied.

   While it is now easy to see that the choices above were ill-advised,
   it is impossible to change them now without created compatibility
   issues not acceptable in the bis context.  As a result, our only
   realistic option is to define a protocol extension to correct this
   defect as provided for by Section 9 of [RFC8178].






















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   const FATTR4_ACLCHOICE     = 87; -

   enum acc4bitnums {
               ACC4BN_NEINGM   = 0,
               ACC4BN_SEPFWX   = 1,
               ACC4BN_SEPAFD   = 2,
               ACC4BN_SEPDE    = 3,
               ACC4BN_RNASDI   = 4,
               ACC4BN_NAD      = 5,
               ACC4BN_NADMOD   = 6,
               ACC4BN_MBCA     = 7,
               ACC4BN_SMJUST3  = 8,
               ACC4BN_SMOLD    = 9,
               ACC4BN_SMFULL   = 10,
               ACC4BN_3MASKB   = 11,
               ACC4BN_AUTHWHO  = 12,
               ACC4BN_IN1BIT   = 13,
               ACC4BN_INHFULL  = 14,
               ACC4BN_INHAUTO  = 15,
               ACC4BN_RVINV    = 16,
               ACC4BN_OTHWHO   = 17,
               ACC4BN_SVTX     = 18,
               ACC4BN_SVTXOLD  = 19
   };

   enum acc4dinums {
               ACC4IN_OWNMB    = 0,
               ACC4IN_ODDMB    = 1,
               ACC4IN_STOREUA  = 2,
               ACC4IN_TSUPP    = 3
   };

   The tables below provide information about the individual
   implementations that are communicated in the Aclchoice attribute.
   One table is used for specific bits for cases in which the choice is
   specified with the associate bit map.  The other is used when the
   choice is combined with some additional info in a subsidiary data
   item.  In both cases, the table identifies the choice class while is
   selected from the following list:

   Mbcs:  Mask bit with clear semantics

   Mbus:  Mask bit with uncertain semantics

   Obv:  Original behavioral variant

   Lbv:  Later behavioral variant




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   These tables and the sections they point to will contain restrictions
   making certain sets of flags or data items invalid.  When such
   restrictions are violated, the client is free to ignore the Aclchoice
   attribute and treat it as unsupported.

    +============+=======+=========+==================================+
    | Id         | Class | Section | Description                      |
    +============+=======+=========+==================================+
    | BN_NEINGM  | Obv   | S 5.6   | Whether ALLOW ACEs for named     |
    |            |       |         | entities contribute to the group |
    |            |       |         | mode bits.                       |
    +------------+-------+---------+----------------------------------+
    | BN_SEPWX   | Mbcs  | S 5.4   | Whether to separately authorize  |
    |            |       |         | extension of a file and          |
    |            |       |         | rewriting of existing bytes.     |
    +------------+-------+---------+----------------------------------+
    | BN_SEPAFD  | Mbcs  | S 5.4   | Whether to separately authorize  |
    |            |       |         | adding of subdirectories and     |
    |            |       |         | additional of other sort of      |
    |            |       |         | directory entries.               |
    +------------+-------+---------+----------------------------------+
    | BN_SEPDE   | Mbcs  | S 5.4   | Whether to separately authorize  |
    |            |       |         | deletion of directory entries    |
    |            |       |         | and other modifications of       |
    |            |       |         | directories.                     |
    +------------+-------+---------+----------------------------------+
    | BN_RNASDI  | Lbv   | S 5.6   | Whether Rename within a          |
    |            |       |         | directory are to require         |
    |            |       |         | specific permissions to add and  |
    |            |       |         | delete entries within the        |
    |            |       |         | encompassing directory.          |
    +------------+-------+---------+----------------------------------+
    | BN_NAD     | Mbus  | S 5.4   | Whether to separately authorize  |
    |            |       |         | access to and modification of    |
    |            |       |         | named attribute directories      |
    +------------+-------+---------+----------------------------------+
    | BN_NADMOD  | Lbv   | S 5.6   | Whether to use the mask bits     |
    |            |       |         | associated with named attributes |
    |            |       |         | to control operations within     |
    |            |       |         | those directories, in addition   |
    |            |       |         | to the use of OPENATTR.          |
    +------------+-------+---------+----------------------------------+
    | BN_MBCA    | Obv   | S 5.6   | Whether the server is allowed to |
    |            |       |         | convert sets of mask bits or     |
    |            |       |         | other flags it cannot enforce or |
    |            |       |         | undertake to store and retain    |
    |            |       |         | unmodified to mask bits it does  |
    |            |       |         | support, rather than returning   |



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    |            |       |         | an error.                        |
    +------------+-------+---------+----------------------------------+
    | BN_SMJUST3 | Obv   | S 5.6   | Whether the server when          |
    |            |       |         | processing a change to the mode, |
    |            |       |         | sets the acl to represent the    |
    |            |       |         | handling specified by those mode |
    |            |       |         | bits, making no effort to        |
    |            |       |         | preserve other aspects of the    |
    |            |       |         | ACL                              |
    |            |       |         |                                  |
    |            |       |         | Although this appears to be an   |
    |            |       |         | alternative to BN_SMOLD and      |
    |            |       |         | BN_SMFULL, there are situation   |
    |            |       |         | in which multiple of these can   |
    |            |       |         | be true simultaneously           |
    +------------+-------+---------+----------------------------------+
    | BN_SMOLD   | Obv   | S 5.6   | Whether the server when          |
    |            |       |         | processing a change to the mode, |
    |            |       |         | sets the acl to represent the    |
    |            |       |         | handling specified by those mode |
    |            |       |         | bits, while making the efforts   |
    |            |       |         | to preserve other aspects of the |
    |            |       |         | ACL as recommended by the        |
    |            |       |         | existing specifications.         |
    |            |       |         |                                  |
    |            |       |         | Although this appears to be an   |
    |            |       |         | alternative to BN_SMJUST3 and    |
    |            |       |         | BN_SMFULL, there are situation   |
    |            |       |         | in which multiple of these can   |
    |            |       |         | be true simultaneously           |
    +------------+-------+---------+----------------------------------+
    | BN_SMFULL  | Obv   | S 5.6   | Whether the server when          |
    |            |       |         | processing a change to the mode, |
    |            |       |         | sets the acl to represent the    |
    |            |       |         | handling specified those mode    |
    |            |       |         | bits, while making the efforts   |
    |            |       |         | to preserve other aspects of the |
    |            |       |         | ACL as recommended by            |
    |            |       |         | Section 10.7.3                   |
    |            |       |         |                                  |
    |            |       |         | Although this appears to be an   |
    |            |       |         | alternative to BN_SMJUST3 and    |
    |            |       |         | BN_SMOLD, there are situations   |
    |            |       |         | in which multiple of these can   |
    |            |       |         | be true simultaneously.          |
    +------------+-------+---------+----------------------------------+
    | BN_3MASKB  | Mbus  | S 5.4   | Indicates the server only        |
    |            |       |         | supports the three ACE mask bits |



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    |            |       |         | derived directly from the POSIX  |
    |            |       |         | privilege bits.                  |
    +------------+-------+---------+----------------------------------+
    | BN_AUTHWHO | Obv   | S 5.6   | [Consensus Needed (Item #50a),   |
    |            |       |         | Entire entry]:                   |
    |            |       |         |                                  |
    |            |       |         | Indicates whether the server     |
    |            |       |         | treats ACEs with the special who |
    |            |       |         | values related to authentication |
    |            |       |         | defined in Section 7.3.3 as      |
    |            |       |         | valid.                           |
    |            |       |         |                                  |
    |            |       |         | Although existing specifications |
    |            |       |         | treat this as a feature, the     |
    |            |       |         | uncertainty associated semantics |
    |            |       |         | makes it inappropriate to treat  |
    |            |       |         | it that way so we will treat the |
    |            |       |         | acceptance of ACEs containing    |
    |            |       |         | such values of the "who" field   |
    |            |       |         | as behavioral variants.          |
    +------------+-------+---------+----------------------------------+
    | BN_INNO    | Obv   | S 5.6   | Indicates there is no support    |
    |            |       |         | for ACL inheritance.             |
    +------------+-------+---------+----------------------------------+
    | BN_IN1BIT  | Obv   | S 5.4   | Indicates there is some support  |
    |            |       |         | for ACL inheritance but no       |
    |            |       |         | support for separate inheritance |
    |            |       |         | bits for file and directories    |
    +------------+-------+---------+----------------------------------+
    | BN_INHFULL | Mbcs  | S 5.4   | Indicates there is full support  |
    |            |       |         | for ACL inheritance but not      |
    |            |       |         | necessarily for automatic        |
    |            |       |         | inheritance.                     |
    +------------+-------+---------+----------------------------------+
    | BN_INHAUTO | Mbcs  | S 5.4   | Indicates that there is support  |
    |            |       |         | for automatic ACL inheritance.   |
    +------------+-------+---------+----------------------------------+
    | BN_RVINV   | Lbv   | S 5.6   | Indicates that the server will,  |
    |            |       |         | in some cases, when presented    |
    |            |       |         | with incorrect or unsupported,   |
    |            |       |         | ACLs modify them to be valid/    |
    |            |       |         | acceptable rather than rejecting |
    |            |       |         | them.                            |
    +------------+-------+---------+----------------------------------+
    | BN_OTHWHO  | Obv   | S 5.6   | [Consensus Needed (Item #50a),   |
    |            |       |         | Entire entry]:                   |
    |            |       |         |                                  |
    |            |       |         | Indicates whether the server     |



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    |            |       |         | treats ACEs with the special who |
    |            |       |         | values not related to either     |
    |            |       |         | authentication or support for    |
    |            |       |         | draft-POSIX ACL semantics that   |
    |            |       |         | are defined in Section 7.3.3 as  |
    |            |       |         | valid.                           |
    |            |       |         |                                  |
    |            |       |         | Although existing specifications |
    |            |       |         | treat this as a feature, the     |
    |            |       |         | absence of any specification of  |
    |            |       |         | associated semantics makes it    |
    |            |       |         | inappropriate to treat it that   |
    |            |       |         | way so we will treat the         |
    |            |       |         | acceptance of ACEs containing    |
    |            |       |         | such values of the "who" field   |
    |            |       |         | as behavioral variants.          |
    +------------+-------+---------+----------------------------------+
    | BN_SVTX    | Lbv   | S 5.6   | [Consensus Needed (Item #12a),   |
    |            |       |         | Entire entry]:                   |
    |            |       |         |                                  |
    |            |       |         | Indicates that the server, in    |
    |            |       |         | authorizing file deletion and    |
    |            |       |         | RENAME operations, takes special |
    |            |       |         | account of the setting of        |
    |            |       |         | MODE4_SVTX in the mode attribute |
    |            |       |         | of the encompassing directory.   |
    |            |       |         |                                  |
    |            |       |         | This bit, like BN_SVTXOLD,       |
    |            |       |         | applies to POSIX-based as well   |
    |            |       |         | as to ACL-based authorization.   |
    |            |       |         | This is necessary since two have |
    |            |       |         | to work together, irrespective   |
    |            |       |         | of whether various entities      |
    |            |       |         | involved have ACLs.              |
    |            |       |         |                                  |
    |            |       |         | When this bit is set, ACL-based  |
    |            |       |         | authorization semantics reflects |
    |            |       |         | the treatment set out in         |
    |            |       |         | Section 7.2.15.  This bit should |
    |            |       |         | not be set together with         |
    |            |       |         | BN_SVTXOLD.                      |
    |            |       |         |                                  |
    |            |       |         | When authorization of deletes    |
    |            |       |         | and RENAMEs depends on the set   |
    |            |       |         | of MODE_SVTX and ACLs are not    |
    |            |       |         | supported, in is desirable that  |
    |            |       |         | Aclchoice be supported           |
    |            |       |         | nevertheless, with this bit set  |



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    |            |       |         | to indicate the use of           |
    |            |       |         | MODE4_SVTX in authorization.     |
    +------------+-------+---------+----------------------------------+
    | BN_SVTXOLD | Lbv   | S 5.6   | [Consensus Needed (Item #12a),   |
    |            |       |         | Entire entry]:                   |
    |            |       |         |                                  |
    |            |       |         | Indicates that the server, in    |
    |            |       |         | authorizing file deletion and    |
    |            |       |         | RENAME operations, takes special |
    |            |       |         | account of the setting of        |
    |            |       |         | MODE4_SVTX in the mode attribute |
    |            |       |         | of the encompassing directory.   |
    |            |       |         |                                  |
    |            |       |         | This bit, like BN_SVTX, applies  |
    |            |       |         | to POSIX-based as well as to     |
    |            |       |         | ACL-based authorization.  This   |
    |            |       |         | is necessary since two have to   |
    |            |       |         | work together, irrespective of   |
    |            |       |         | whether various entities         |
    |            |       |         | involved have ACLs.              |
    |            |       |         |                                  |
    |            |       |         | When this bit is set, ACL-based  |
    |            |       |         | authorization semantics reflects |
    |            |       |         | the treatment set out in         |
    |            |       |         | Section 7.2.15.  This bit should |
    |            |       |         | not be set together with         |
    |            |       |         | BN_SVTX.                         |
    +------------+-------+---------+----------------------------------+

                        Table 2: Aclchoice flag bits

   +============+=====+=====+======+=============+=====================+
   | Id         |Class|Ov.  |Det.  | Data        | Description         |
   |            |     |Sect.|Sect. |             |                     |
   +============+=====+=====+======+=============+=====================+
   | IN_OWNMB   |Fwsr |S 5.5|S     | acemask4    | Provides            |
   |            |     |     |7.2.10|             | information         |
   |            |     |     |      |             | relating to the     |
   |            |     |     |      |             | support of ACE      |
   |            |     |     |      |             | mask bits whose     |
   |            |     |     |      |             | scope can only be   |
   |            |     |     |      |             | accounted for as a  |
   |            |     |     |      |             | finer-granularity   |
   |            |     |     |      |             | variant of file     |
   |            |     |     |      |             | ownership           |
   +------------+-----+-----+------+-------------+---------------------+
   | IN_ODDMB   |Fwsr |S 5.5|S     | ombr4word<> | Provides            |
   |            |     |     |7.2.10|             | information         |



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   |            |     |     |      |             | relating to the     |
   |            |     |     |      |             | support of ACE      |
   |            |     |     |      |             | mask bits defined   |
   |            |     |     |      |             | within              |
   |            |     |     |      |             | Section 7.2.7,      |
   |            |     |     |      |             | whose scope cannot  |
   |            |     |     |      |             | accounted for as a  |
   |            |     |     |      |             | finer-granularity   |
   |            |     |     |      |             | variant of one of   |
   |            |     |     |      |             | the three POSIX     |
   |            |     |     |      |             | privilege bits or   |
   |            |     |     |      |             | file ownership      |
   |            |     |     |      |             |                     |
   |            |     |     |      |             | Also used to        |
   |            |     |     |      |             | provide             |
   |            |     |     |      |             | information about   |
   |            |     |     |      |             | mask bits defined   |
   |            |     |     |      |             | in Sections 7.2.5   |
   |            |     |     |      |             | and 7.2.6, when     |
   |            |     |     |      |             | the treatment of    |
   |            |     |     |      |             | that mask bit does  |
   |            |     |     |      |             | not fully accord    |
   |            |     |     |      |             | with the            |
   |            |     |     |      |             | requirement of the  |
   |            |     |     |      |             | defining section.   |
   +------------+-----+-----+------+-------------+---------------------+
   | IN_STOREUE |Fwsr |S 5.5|S 12.2| acc4storeua | Provides            |
   |            |     |     |      |             | information         |
   |            |     |     |      |             | relating to the     |
   |            |     |     |      |             | support of ACE      |
   |            |     |     |      |             | mask bits, ACE      |
   |            |     |     |      |             | type, and special   |
   |            |     |     |      |             | who values which    |
   |            |     |     |      |             | are not enforced    |
   |            |     |     |      |             | by current NFSv4    |
   |            |     |     |      |             | server              |
   |            |     |     |      |             | implementation but  |
   |            |     |     |      |             | are stored and      |
   |            |     |     |      |             | retrieved so that   |
   |            |     |     |      |             | ACLs with these     |
   |            |     |     |      |             | feature can be      |
   |            |     |     |      |             | preserved for use   |
   |            |     |     |      |             | by other NFsv4      |
   |            |     |     |      |             | servers, other      |
   |            |     |     |      |             | remote file access  |
   |            |     |     |      |             | protocol, or for    |
   |            |     |     |      |             | local file access.  |
   +------------+-----+-----+------+-------------+---------------------+



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   | IN_TSUPP   |Fwsr |S 5.5|S     | uint32_     | Provides            |
   |            |     |     |7.1.2 |             | information         |
   |            |     |     |      |             | relating to the     |
   |            |     |     |      |             | support of ACE      |
   |            |     |     |      |             | types, including    |
   |            |     |     |      |             | newer ones not      |
   |            |     |     |      |             | included in the     |
   |            |     |     |      |             | Aclsupport          |
   |            |     |     |      |             | attribute.          |
   +------------+-----+-----+------+-------------+---------------------+

                                  Table 3

4.7.  The Dacl Attribute (v4.1)

   The dacl attribute was added in NFSv4.1 in order to divide ACLs so
   that the authorization-related entries (i.e.  ALLOW and DENY entries
   were no longer combined in the same attribute as AUDIT and ALARM
   entries.

   [Consensus Needed (Item #118c)]: When this attribute is interrogated,
   it returns an array of ACEs of types ALLOW and DENY, in an order
   consistent with the ordering of those ACEs in the Acl attribute.
   When there are no such ACEs, it return a zero-length ACE array,
   indicating the absence of a DACL associated with the current file
   object.

   [Consensus Needed (Item #118c)]: When this attribute is set to a
   value represent by a zero-length ACE array, all ALLOW and DENY ACEs
   are removed from the Acl attribute.  If there were no AUDIT and ALARM
   ACEs, the Acl attribute will subsequently return a zero-length ACE
   array indicating the absence of an ACL for the current file object.

   [Consensus Needed (Item #118c)]: When this attribute is any other
   value, any existing ALLOW and DENY ACEs are removed from the Acl
   attribute and the ones specified are added.  Subsequently the Acl and
   Dacl attributes will not return a zero-length array because there
   will be an ACL an a DACL associated with the current file object.

   {Consensus needed, Thru rest of Section (Item #65b)]: While the
   original intention was to define a usable OPTIONAL attribute based on
   the NFSv4 ACLs defined previous specifications, it is now more
   appropriate to designate this under-specified attribute as
   experimental although still formally OPTIONAL until the issues
   discussed in Section 4.4 are addressed






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   Although the issues applying to the acl attribute apply equally to
   the dacl attribute, given the description in earlier specifications,
   it might be easier to resolve them in the case of the dacl attribute
   for the following reasons:

   *  Implementations of POSIX ACLs might not have been updated to
      support the sacl attribute, since doing so would add no value.

   *  Even if such POSIX-ACL-oriented implementations of the sacl
      attribute did exist, it might be easier to get agreement on
      regularizing the sacl attribute since, if acl were left as it is,
      the POSIX ACL support would still be available.

4.8.  The Sacl Attribute (v4.1)

   The sacl attribute is like the acl attribute, but sacl allows only
   AUDIT and ALARM ACEs.  The sacl attribute supports automatic
   inheritance and default ACEs (see Section 8).

   [Consensus Needed (Item #118d)]: When this attribute is interrogated,
   it returns an array of ACEs of types ALLOW and DENY, in an order
   consistent with the ordering of those ACEs in the Acl attribute.
   When there are no such ACEs, it return a zero-length ACE array,
   indicating the absence of a DACL associate with the current file
   object.

   [Consensus Needed (Item #118d)]: When this attribute is set to a
   value represent by a zero-length ACE array, all AUDIT and ALARM ACEs
   are removed from the Acl attribute.  If there were no ALLOW or DENY
   and ACEs, the Acl attribute will subsequently return a zero-length
   ACE array indicating the absence of an ACL for the current file
   object.

   [Consensus Needed (Item #118d)]: When this attribute is any other
   value, any existing AUDIT and ALARM ACEs are removed from the Acl
   attribute and the ones specified are added.  Subsequently the Acl and
   sacl attributes will not return a zero-length array because there
   will be an ACL an a SACL associated withe current file object.

   {Consensus needed, Thru rest of Section (Item #65c)]: While the
   original intention was to define a usable OPTIONAL attribute based on
   the NFSv4 ACLs defined in previous specifications, it is now more
   appropriate to designate this under-specified attribute as
   experimental although still formally OPTIONAL until the issues
   discussed in Section 4.4 are addressed






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   The Sacl attribute was added in NFSv4.1 in order to divide ACLs so
   that the non-authorization-related entries (i.e.  AUDIT and ALARM
   entries) would no longer be combined in the same attribute with the
   ALLOW and DENY entries.

   [Author Aside, Including List (Items #61c, #105g, #110b)]: Although
   the existing discussion of ACE structure results in the same sort of
   lack of clarity affecting the Acl and Dacl attributes, it us more
   likely that these will resolved in the case of the Sacl attribute as
   compared to the Acl or Dacl attributes, even though the problems with
   the existing text are essentially the same.

   *  There are no AUDIT or ALARM entries, in POSIX ACLs, so there would
      be no need accommodate existing implementations of these that
      embody a more POSIX-oriented semantic model.

      As a result, it is likely to be easier to get WG approval for
      changes that clearly state that the ACE mask bits are to followed
      strictly for the these types of ACEs.

   *  Since such entries have no role in compute a corresponding mode
      attribute, the effect of this issue for the sacl attribute is not
      problematic.

5.  Structure of the ACL-related Features

   [Consensus Needed (Items #104g, #105h), Through end of section]:

   Until now, the set of OPTIONAL features, had been limited to the set
   of ACL-related attributes: acl, aclsupport, sacl, and dacl.  Many of
   these had a vast semantic range which resulted from the existence of
   two different ACL models and the way in which previous specifications
   attempted to accommodate those two models and the range of behaviors
   provided by existing file systems.

   In this specification, we will take a different approach in which,
   where multiple approaches are to be allowed to server
   implementations, we explicitly designate them as OPTIONAL and make
   them visible to the client using the Aclsupport and Aclchoice
   attributes.

   These choices had a number of sources and were previously dealt with
   in a number of ways:








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   *  An important set of choices arose from the expansion of the set of
      distinct actions that could be subject to authorization control
      using ACLs.  The options ranged from no expansion relative to
      three privilege bits inherited from POSIX to the major expansion
      of the set of ACE mask bits in [RFC3530].

      Each of these additions is best thought of as distinct feature.
      Most of them, for which the basic semantics can be inferred, based
      on existing specifications, are discussed in Section 5.4.

      In the existing specifications, most of these mask bits, the ones
      described in Section 7.2.5, are dealt with by simply making
      reference to the possibility of mask bits having different action
      granularities.

   *  A number of cases in which multiple behaviors are allowed will be
      addressed by defining the choice as a feature even without any
      clear benefit to either approach.  These are discussed in
      Section 5.6.

      These include cases in which multiple behaviors were allowed to
      accommodate existing server behavior and also some cases in which
      the utility of the approach was doubtful, and a different approach
      was specified.

      Because of the development of many distinct server implementations
      with a specification that took the semantically lax approach
      discussed above, there will inevitably more such cases as work on
      ACLs proceeds.  Since it is agreement on a uniform approach to
      such issues is unlikely at this point, the Aclchoice attribute
      will need to extended to accommodate them as described in
      Section 12.1


5.1.  Role of the Core UNIX ACL model

   [Consensus Needed (Items #64a, #105i), Through end of section]

   Although the working group did not adopt the ACLs in the withdrawn
   POSIX draft, the continued existence of implementations of them and
   variants sharing important features with them in UNIX contexts has
   created protocol difficulties that need to be resolved.  In many
   cases, such ACLs and their associated semantics are the basis for ACL
   support in UNIX client-side APIs and in UNIX file systems supported
   by NFSv4.

   In the context of this document, the Core UNIX ACL model is defined
   as any approach which shares all of the following features:



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   *  Supports only the ACE mask bits that are direct replacements for
      the three POSIX privilege bits.

      When the Aclchoice attribute is supported, this characteristic is
      reported to the server using the flag bit ACC4BN_3MASKB.

   *  Supports only ALLOW ACEs.

   *  [Consensus Needed (Item #117h)]: Has no support for ACL
      inheritance.  For a discussion of how this affects support for
      handling of POSIX ACLs, see Section 5.2.

   The following characteristics of draft-POSIX ACLs are not included in
   this definition but are treated as allowable behavioral variants
   within the UNIX ACL model:

   *  The inclusion of mask bits derived from ALLOW ACEs for named users
      and groups in the group mode bits.

      When the Aclchoice attribute is supported, this characteristic is
      reported to the server using the flag bit ACC4BN_NEINGM.

   *  The non-support for partial satisfaction of ALLOW ACEs, so that
      each authorization request can only be supported by a single ALLOW
      ACE.

      When the Aclchoice attribute is supported, this characteristic is
      reported to the server using the flag bit ACC4BN_AANPS.

   [Consensus Needed (Item #117h)]: Although the semantic range of core
   UNIX ACLs is a subset of that for NFSv4 ACLs, expecting clients to
   perform the mapping between NFSv4 ACLs and draft-POSIX ACL on their
   own has not worked well.  Those issues are addressed for NFv4.1 as
   described in Section 5.2 while possible approaches to correct this
   situation are discusssed in Appendix C.

5.2.  Potential Support for the POSIX ACL Model

   [Consensus Needed (Item #117i), Though end of section]:

   A helpful summary of the draft-POSIX ACL model can be found in
   [Grünbacher].  Although this document deals only with the Linux
   implementation, the guidance it provides regarding required semantics
   is expected to be helpful to other potential implementations as well.







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   Although considerable efforts were made to accommodate POSIX ACL
   implementations with in the existing NFSv4 ACL model, those efforts
   left support for POSIX ACLs in an unfortunate state for the following
   reasons:

   *  Many important parts of the POSIX ACL model, such as inheritance
      were not REQUIRED and no attention was paid to the differences
      between those functions in the two different ACL models that were
      to be supported.

   *  While efforts were made to accommodate semantic differences
      between those models, the effect was limited since many
      differences were simply ignored due to a lack of interest in
      semantic description.  In addition, behavioral differences that
      were recognized were addressed in a way that gave the client no
      ability to select its preferred variant or even determine the
      choice made by the server.

   The development of the Aclchoice attribute served to address some of
   these issues, but did not provide full support, as discussed below.

   *  The uncertainty about the mapping between ACL and modes (and
      between core UNIX ACLs an server NFSv4 ACLs has been addressed by
      making this server choice one that the client can find out about,
      where Aclchoice is supported.

      Fully addressing this variability would most likely require a
      significant degree of attribute incompatibility making it only
      possible in NFSv4.2 or later.

   *  The differences in the processing of ALLOW ACEs has been addressed
      by making either of the approaches an allowable server behavioral
      variant as was done in the mode computation case discussed above.
      As part of that change, the server choice was made one that the
      client can find out about, where Aclchoice is supported.

      The fact that this had not been done previously was treated as an
      easily remedied oversight, given the clear intention to allow
      servers supporting POSIX ACLs to be used, without, as previous
      specifications put it, "invalidating" them.

   As a result, it became necessary to accommodate support for draft-
   POSIX ACLs as a separate ACL model.  The details of that model are
   best deferred to an extension of a later minor version as discussed
   in Appendix C.  What is necessary in this document is to
   appropriately prepare for future specification of multiple ACL models
   by doing the following things:




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   *  Distinguishing between ACLs in general and the specifics of NFSv4
      ACLs, that, for some time, are expected to be the only ACL
      structures that exist.  Since it is difficult to name NFSv4 ACL
      structure as anything other than "ACL", we retain that naming but
      refer to the general concept as "Access Control List".  In
      addition, the term "Authorization Control List" will refer to any
      ort of Access Control List that is only capable of controlling
      authorization, such as the Dacl attribute.

   *  Distinguishing between ACEs in general and the specifics of NFSv4
      ACEs, that, for some time, are expected to be the only ACE
      structures that exist.  Since it is difficult to name NFSv4 ACE
      structures as anything other than "ACE", we retain that naming but
      refer to the general concept as "Access Control Element".

   *  Making it clear that the material in Section 10 applies only to
      ACLs and that the handling of co-ordination of the mode with other
      sorts of Access Control Lists is the jobs of the extensions
      defining those new models.

5.3.  Server Behavioral Restrictions to Apply when Aclchoice is not
      Supported

   [Author Aside (Item #116a)]: This section explores possible
   additional behavioral restrictions to avoid situations in which the
   lax approach to the specification of server semantics could
   unacceptably interfere with client operation.  Given the difficulty
   of supporting NFSv4 extensions without the use of Aclchoice, we are
   focusing for now on NFSv4-oriented clients, although the working
   group might consider what could be done for other clients in later
   drafts.

   [Consensus Needed (Item #116a), Through end of section]:

   Because of the uncertainty about the proper handling of the ACE mask
   bits defined in Section 7.2.7, the recommendations below SHOULD be
   adhered to by servers that do not support the Aclchoice attribute in
   order to allow clients to convert UNIX ACLs to NFSv4 ACLs as
   described in Section 7.2.14.  In the context of the above
   recommendations, the only valid reason to bypass them is reliance on
   previous specifications that do not make clear the importance of
   adhering to these constraints.  Further, those implementing such
   servers need to be aware that they are compromising the utility of
   the implementation for UNIX-oriented clients and that other clients
   might not be able to with their semantics either.






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   When transforming an ALLOW ACE using only the three ACE mask bit that
   correspond to POSIX privilege bits, the corresponding bit mask SHOULD
   be constructed as follows:

   *  When ACE4_READ_NAMED_ATTRIBUTES is not excluded (i.e., when named
      attributes are supported) it is to be set if the mask bit
      corresponding to the read privilege bit (i.e., ACE4_READ_DATA or
      ACE4_LIST_DIRECTORY) is set.

      The bit can also be set in other circumstances, such as when the
      ACE4_EXECUTE MASK bit is set.

   *  ACE4_READ_ATTRIBUTES is always to be set.

   *  ACE4_READ_NAMED_ACL is always to be set.

   *  [Consensus Needed (Item #62a), Through end of bulleted item]:
      ACE4_DELETE is always to be set.

      This applies to authorization in the case in which the "sticky"
      bit for the directory is set as well as the case in which it is
      not set.

   *  ACE4_WRITE_RETENTION and ACE4_WRITE_RETENTION_HOLD are not to set
      unless the mask bit corresponding to the write privilege bit
      (i.e., ACE4_WRITE_DATA or ACE4_ADD_FILE) is set.

      Servers MAY condition these settings on other conditions (e.g.,
      only setting the bit for ACEs for the owner of a file).

   The above recommendations do not apply when Aclchoice is supported
   because the information provided allows the mapping described in
   Section 7.2.14 to be performed as needed by the semantics provided by
   the server.

   [Author Aside (Item #116a)]: The possibility of extending these
   restrictions to case in Aclchoice is supported needs to be
   considered, as does the possibility of follow-on restrictions
   regarding the details of the mapping between modes and ACLs.  Much
   will depend on the range of existing server behaviors.  This might
   enable further simplification of the ACC4IN_ODDMB data item.

5.4.  Feature Extensions With Clear Semantics

   [Consensus Needed (Items #104h, #105j), Through end of section]:






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   The following extensions of UNIX ACL model are now considered
   OPTIONAL feature whose support, on each given file system, can be
   determined using the Aclsupport and Aclchoice attributes.  These
   include some for which the core semantics is clear but there are
   potential behavioral differences, that resolved based on the
   existence of other features described in Section 5.6.

   *  The provision of separate authorization control for extending a
      file and for overwriting existing bytes is represented by the flag
      bit ACC4BN_SEPFWX of the Aclchoice attribute.

      When this feature is available and different authorization apply
      to a file authorization decision cannot be made at OPEN time but
      are reflected in the results returned to ACCESS and enforced on
      each Write.

   *  The provision of separate authorization control for adding a new
      entry to a directory and making sorts of modification for the
      directory is represented by the flag bit ACC4BN_SEPAE of the
      Aclchoice attribute.

      The detailed semantics of this feature are affected by the feature
      represented by the ACC4BN_RNASDI flag bit, discussed in
      Section 5.6.  Note that when this bit is not set, renaming of
      objects within the directory would be affected by restrictions on
      adding new entries.

   *  The provision of separate authorization control for adding a sub-
      directories to a directory and for adding other sorts of entries
      to a directory represented by the flag bit ACC4BN_SEPAFD of the
      Aclchoice attribute.

      This feature bit is only meaningful if feature represented by the
      ACC4BN_SEPAE flag bit is also in effect.

      The detailed semantics of this feature are affected by the feature
      represented by the ACC4BN_RNASDI flag bit, discussed in
      Section 5.6.  Note that when this bit is not set, the ability to
      rename a subdirectory and a file within a directory would be
      controlled by different ACE mask bits and that renaming of objects
      within the directory would be affected by restrictions on adding
      new entries.

   *  The provision of separate authorization control for deleting a new
      entry to a directory and making other sorts of modification to the
      directory is represented by the flag bit ACC4BN_SEPDE of the
      Aclchoice attribute.




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      The detailed semantics of this feature are affected by the feature
      represented by the ACC4BN_RNASDI flag bit, discussed in
      Section 5.6.  Note that when this bit is not set, renaming of
      objects within the directory would be affected by restrictions on
      deleting existing entries.

   *  The provision of separate authorization control for operations
      involving a file object's named attribute directory is represented
      by flag bit ACC4BN_NAD of the Aclchoice attribute.

      The detailed semantics of this feature are affected by the feature
      represented by the ACC4BN_NADMOD flag bit, discussed in
      Section 5.6.  Note that when this bit is not set the creation of a
      new name attribute directory would be controlled by a separate ACE
      mask bit but this same bit would not control the authorization of
      otherwise modifying the named attribute directory.

   *  The server's support for a limited set of mask bit derived from
      the three POSIX privilege bits is represented by flag bit
      ACC4BN_3MASKB of the Aclchoice attribute.

      This bit cannot be validly combined with any of the bits
      ACC4BN_SEPFWX, ACC4BN_SEPAE, ACC4BN_SEPDFD, ACC4BN_SEPDE, or with
      any use of the data items ACC4IN_OWNMB or ACC4IN_ODDMB.

   *  The server's support for DENY ACEs is indicated by the bit
      ACL4_SUPPORT_DENY_ACL in the Aclsupport attribute or by the bit
      with numeric value two in the word associated with data item
      ACC4IN_TSUPP.

   *  The server's support for AUDIT ACEs is indicated by the bit
      ACL4_SUPPORT_AUDIT_ACL in the Aclsupport attribute or by the bit
      with numeric value four in the word associated with data item
      ACC4IN_TSUPP.

   *  The server's support for ALARM ACEs is indicated by the bit
      ACL4_SUPPORT_ALARM_ACL in the Aclsupport attribute or by the bit
      with numeric value eight in the word associated with data item
      ACC4IN_TSUPP.

   *  The server's support for newly defines ACE types is indicated a
      bit the word associated with data item ACC4IN_TSUPP.  The selected
      bit is one left-shifted by the value of the ACE type.

   *  The server support's support for a limited form of ACL inheritance
      is indicated by the flag bit ACC4BN_IN1BIT.  In this form of
      inheritance there is no provision for separate control of
      inheritance for subdirectories and for non-directory objects.



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      Because this level of inheritance support is needed for
      implementation of the draft-POSIX ACL model, clients needing that
      support requires a file system with either ACC4BN_IN1BIT or
      ACC4BN_INHFULL set.

      When this form of inheritance is supported, ACEs in
      ACE4_FILE_INHERIT_ACE and ACE4_DIRECTORY_INHERIT_ACE are set to
      different values are generally rejected.  However, when
      ACC4BN_RVINV is set the server is allowed to convert the ACE to
      one in which the two values are the same.

      This bit is incompatible with ACC4BN_INNO and ACC4BN_INHFULL.

   *  The server support's support for full ACL inheritance is indicated
      by the flag bit ACC4BN_INHFULL.  In this form of inheritance there
      IS separate control of inheritance for subdirectories and for non-
      directory objects.

      This bit is incompatible with ACC4BN_INNO and ACC4BN_IN1BIT.

   *  The server's support for automatic ACL inheritance is indicated by
      the flag bit ACC4BN_INHAUTO.

      This bit in incompatible with ACC4BN_INNNO.

   *  The server's support for ACL inheritance using the concept of
      default ACLs is indicated by the flag bit ACC4BN_INHDEF.

      This approach to ACL inheritance is needed for the support of the
      draft-POSIX ACLs model, but can be used by others as well.

      This bit in incompatible with ACC4BN_INNNO.

5.5.  Features with wide Semantic Ranges

   [Consensus Needed (Item #105k), Through end of section]:

   There are a number of features in which the wide latitude given to
   server implementers creates a set of uncertainties that cannot be
   reduced to a small set of individual binary choices.  These cases are
   dealt within the Aclchoice attribute by defining a data item to
   provide the necessary data, as listed below:









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   *  The Aclchoice data item with index ACC4IN_TSUPP is used to provide
      information the ACE types that a server accepts and enforces.
      Unlike the Aclsupport attribute it is not limited to the current
      set of known ACE types, but is designed so that new types, added
      via the protocol extension mechanism have ready-made means to
      indicate whether support is present.

   *  The Aclchoice data item with index ACC4IN_ODDMB is used to provide
      information about the nature of the support for ACE mask bits
      which are neither REQUIRED nor a finer-grained corelate of another
      REQUIRED mask bit.

      There are many aspects of the support for these mask bits that are
      not clearly discussed in the existing specifications.  That is
      most likely because it was incorrectly assumed that all the mask
      bits did fit in this model, making detailed explanation necessary.

      As a result, it remains unclear, for each of these bits, how
      authorization for the corresponding operation is to be determined,
      when ACLs are generated based on the setting of mode.  Similarly,
      their contribution, if any, to modes computed from existing ACLs
      needs to be clarified.

      See Section 7.2.10 for details about how such information is made
      available to the client, when the server supports any of these ACE
      mask bits.

   *  The Aclchoice data item with index ACC4IN_STOREUA is used to
      provide information about cases in which a server accepts, store,
      and returns ACLs that it is not prepared to enforce.

      This includes cases in which the client specifies different
      handling for two mask bits that the server is not prepared to
      distinguish, an also cases in which there are other features of
      the NFSv4 ACL model that the server is not prepared to support
      (e.g. DENY ACEs, ACL inheritance).

      While the possibility of servers accepting ACLs that they are not
      prepared to enforce is mentioned in a number of places in the
      existing specifications, there is no normative text regarding this
      practice.  In this document, we treat it as an OPTIONAL feature
      with details of the set of ACLs supported in this way described
      using the structures defined in Section 12.2.








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      Within the existing specifications, the possibility of accepting
      ACLs that cannot be enforced has the unfortunate consequence that
      clients needing particular ACL functionality might set ACLs using
      that functionality and have them accepted with no way of finding
      that the required functionality is not available.

      When the Aclchoice attribute is supported, there is a way to find
      out the ACE types for which support is available.  Nevertheless,
      it is still helpful to be notified when unsupported ACLs are set.
      When the ACC4IN_STOREUA is not present, clients can often be
      assured of such notification.  See Section 12.2 for details.

   The handling of the ACE mask bit ACE4_SYNCHRONIZE could arguably
   dealt with as part of either of the above data items, since it does
   not fit in the varying-granularity model and, by its nature, it
   cannot be enforced within NFsv4 semantics.  Within the context of
   this specification, this mask bit's handling is addressed in the
   ACC4IN_ODDMB data item.

   It is possible that the above data items might be eventually replaced
   by a small set of feature bits, as described in Section 12.1.  For
   that to be possible, the working group would need information about
   servers that supported this feature and decide if a small set of bits
   could adequately represent the needed semantic range.  That could be
   done for either of the above data items as part of the rfc5661bis
   effort, as described in Section 5.7.

5.6.  Implementation Behavioral Choices

   [Consensus Needed (Items #12b, #105l), Through end of section]:

   There are a number of cases in which for various reasons, multiple
   behaviors are allowed in implementing some function.  Since it is
   necessary that clients be aware of these differences, they are being
   treated as features within the Aclchoice attribute, even though they
   might not be considered features in other contexts.

   Such behavioral choices can arise as a result of an explicit decision
   to allow multiple server behaviors, or because the lack of a clear
   semantic description allowed multiple approaches to develop.  In the
   latter case, we may currently be unaware of these different
   approaches, so that it is expected, as described in Section 12.1 to
   extend Aclchoice as these different behaviors are discovered.

   One additional source of such possible behavioral differences results
   from cases in which existing specifications describe the function of
   various ACE mask bits in a way that does not seem to make sense and
   other approaches have had to be added to allow useful authorization



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   control.  In such cases, the newer approach is presented as a
   distinguishable feature, at least until such time as a consensus can
   be arrived at to standardize on a single approach.

   The following behavioral differences are treated as features within
   the Aclchoice attribute:

   *  The Aclchoice flag bit BN_NEINGM specifies the behavior
      implemented by the server in computing a mode based on an existing
      ACL.  Because two methods are explicitly allowed in existing
      specifications, we represent this choice as a feature despite the
      lack of a clear benefit to either approach.

      When this flags is set, ALLOW ACEs for named entities contribute
      to the privilege bits used for member of the owning group.

      The inclusion of this choice within the Aclchoice does not imply
      that each of these choices is equally desirable.  It is hard to
      determine whether the existing specifications contains a clear
      recommendation regarding this choice.  In any case, this is a
      matter that would need to be addressed in Section 12.3.

   *  The Aclchoice flag bit ACC4BN_RNASDI specifies that the
      authorization of within-directory renames is to be controlled by
      permission to write the specified directory and does not requires,
      when these operations are authorized separately, specific
      permission to delete directory entries and to add directory
      entries of the type of object being renamed

      This difference was not recognized in the existing specifications
      and the existing text in those documents suggests a different
      approach.  Nevertheless, we take a different approach in this
      document while allowing the older approach because of the
      unfortunate consequences of the earlier approach for clients and
      server that do support a finer-grained approach to the
      authorization of directory-modifications.  See Section 12.3 where
      this issue is addressed as part of Consensus Item #9, for
      specifics.

   *  The Aclchoice flag bit ACC4BN_NADMOD specifies that authorization
      of operations accessing or modifying named attribute directories
      is to be controlled as described in this document.

      This approach is significantly different from the approach taken
      in the existing specification, which essentially ignored the issue
      of authorization of operations on named attribute directories and
      only described authorization for the OPENATTR operation.




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      As there is no known implementation of the earlier approach, it is
      uncertain whether allowances need to be made for such
      implementations.  In any case, the lack of authorization semantics
      for named attribute directories means that the treatment of this
      issue in the existing specifications cannot remain as it is.  The
      precise nature of the advice/recommendations to be provided
      remains unclear but it will be addressed in Section 12.3 was part
      of Consensus Item #111.

   *  The Aclchoice flag bit ACC4BN_MBCA specifies that when faced with
      a request to store an ACL that it does not support and is not
      prepared to enforce the server will sometimes modify it to a
      different one that it can support, without notice to the client.

      This behavior is considered an allowable behavior variant because
      existing specifications allowed it.  Nevertheless, because of the
      general uncertainty it creates and its unfortunate effect on
      interoperability, its use is discouraged as provided for in
      Section 12.3.

   *  The Aclchoice flag bit ACC4BN_SMJUST3 specifies that, when the
      server is processing a change to the mode, it sets the acl to
      represent the handling specified by those mode bits, making no
      effort to preserve other aspects of the ACL

      Although this appears to be an alternative to BN_SMOLD and
      BN_SMFULL, described below, there are situations in which multiple
      of these can be true simultaneously

      For example, in the case of ACLs that fit within the UNIX ACL
      model, there are no inheritable ACEs and no ACEs specifying mask
      bits not controlled by the mode, substituting an ACL consisting of
      three entries derived from the mode would satisfy BN_SMOLD and
      BN_SMFULL as well

   *  The Aclchoice flag bit ACC4BN_SMOLD specifies that, when the
      server when processing a change to the mode, it sets the acl to
      represent the handling specified by those mode bits, while making
      the efforts to preserve other aspects of the ACL recommended by
      the existing specifications.

      This recommendation provide for the retention of inherit-only
      ACEs, but allows effect outside the scope of the mode change in
      that the elimination of inheritable ACEs affects inheritance as
      well as authorization for actions involving the current object.






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      Although this appears to be an alternative to BN_SMJUST3 and
      BN_SMFULL, there are situations in which ACL inheritance is not
      supported so that multiple of these can be true simultaneously.

   *  The Aclchoice flag bit ACC4BN_SMFULL specifies that, when the
      server when processing a change to the mode, it sets the acl to
      represent the handling of authorization specified by the mode bit,
      and avoid any other changes to the authorization of actions
      involving the current object or the authorization for any
      subordinate objects that result from ACL inheritance.

      Unlike the cases of BN_SMJUST3 and BN_SMOLD, the server's action
      is specified in terms of a goal to be to be reached rather than a
      procedure to be applied.  The necessary procedure depends on such
      matters as support for DENY ACEs and the existence of ACL
      inheritance and is discussed in Section 10.7.3.

   *  The Aclchoice flag bit ACC4BN_AUTHWHO indicate that the server
      provides support for special who values relating o the existence
      of requester authentication/identification.

   *  The Aclchoice flag bit ACC4BN_RVINV specifies that the server
      will, at times, deal with invalid ACLs/ACEs that are normally
      rejected by accepting them after modifying them to be valid, as
      provided for by previous specifications.

   *  The Aclchoice flag bit ACC4BN_INNO specifies that there is no
      support for ACL inheritance.

      This bit is incompatible with ACC4BN_IN1BIT, ACC4BN_INHFULL, and
      ACC4BN_INHAUTO.

   *  The Aclchoice flag bit ACC4BN_OTHWHO indicates that the server
      provides for support for a miscellaneous set of special who values
      of uncertain semantics.

   *  The Aclchoice flag bit ACC4BN_SVTX indicates that the server's
      authorization of deletion and RENAME is modified based on the
      directory's setting of MODE4_SVTX, as described in Section 7.2.15.

      In the case in which the objects do not have ACLs, possible
      because of non-support, the handling is as described in
      Section 5.3.1 of [I-D.dnoveck-nfsv4-security].

   *  The Aclchoice flag bit ACC4BN_SVTXOLD indicates that the server's
      authorization of deletion and RENAME is modified based on the
      directory's setting of MODE4_SVTX, as described in
      Section 6.2.1.3.2 [RFC8881].  Although this approach is outdated



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      and SHOULD NOT be used, previous implementations might have
      adopted it and continue to use it, bypassing the current
      recommendation to the contrary.

      In the case in which the objects do not have ACLs, possible
      because of non-support, the handling is as described in
      Section 5.3.1 of [I-D.dnoveck-nfsv4-security].

5.7.  ACL Choices in Various Stages of Development


   The Aclchoice attribute is designed to be modified over time but the
   propriety of any particular modification depends on the state of
   development of the feature.  In doing so, we will need to distinguish
   between extensions and other modifications whose use is more limited.

   During development of this specification, until its eventual
   publication as an RFC, the following stages need to be distinguished:

   *  The initial specification in this document.

      The main goal is to fully cover the valid semantic range provided
      by previous specifications where it reasonable to assume that
      alternate approaches exist.  Because of the lax approach taken to
      the specification of semantics, there could be cases where
      alternatives are allowed but there is no reason to suppose that
      the multiple approaches have been adopted.

   *  As further drafts of this specification are developed there will
      be the opportunity to provide needed changes.

      These will includes the creation of new bits for newly discovered
      variants and the deletion of bits for variants that were
      previously allowed but found not to exist.

      In addition, cases in which detailed behavior must be specified in
      a complicated data item could be simplified if a less general
      approach satisfies the needs of existing implementations.

   *  Subsequent to Working group last call, the state of the attribute
      will be permanently assigned to NFSv4.1 and further change will be
      limited as specified in [RFC8178].

   After the completion of the rfc5661bis effort, handling will depend
   primarily on the minor version, as described below:






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   *  In NFSv4.0, this attribute will not be available.  As a result,
      clients that need the extensions of the UNIX ACL provided by
      servers that do support will be unable to use them since there is
      no good way to determine if they are supported.  In addition, as
      described in Section 7.2.14 certain servers whose semantics is
      allowed by existing specification will not be usable because the
      semantics associated with certain ACE mask bits might be such that
      the client cannot map UNIX ACLs to those maintained by the server.

   *  Similar issues apply to NFSv.1 implementations that were developed
      before rfc56661bis was published.  While it is desirable to update
      them to provide Aclchoice attribute, this might not be possible in
      all cases.

   *  Many implementations of NFSv4.1 will have support for the
      Aclchoice attribute.  As a result, the problems that exist for
      implementations that do not support it will be ameliorated and
      interoperable operation will be available for clients that do not
      need any of the extensions to the UNIX ACL model.

   *  In NFSv4.2, it will be possible make additions to Aclchoice
      attribute as extensions to deal with behavioral variants
      discovered after thc5661bis was published.

   *  In a later minor version we will be able to further restrict
      allowable behavior if the Working Group can reach a consensus.
      One example would be to make standard the ACE mask bits where the
      varying-granularity model is workable and expand it cover all mask
      bits or eliminate mask bits that don't fit.  As a result many
      existing elements of the Aclchoice attribute could be made
      mandatory-to-not-implement and what was left could be limited to
      the distinct extensions made to the UNIX ACL model to arrive at
      the NFSv4 ACL model plus a few behavioral variants that the
      working group decides to accommodate.

6.  Structure and Function of Access Control Lists within NFSv4

   Subsections within this section and Section 7 describe the structures
   using to implement a specific sort of security-related semantics.
   All such semantic currently defined within current NFSv4 minor
   version fit within this model or a submodel within it.  This does not
   exclude the possibility that addition of similar structures might be
   defined in later minor versions in order to support other semantic
   models (see Appendix C.

   NFSv4 Access Control Lists consisting of one or more Nfsv4 Access
   Control Elements.  Issues related to the limiting case of an empty
   list of Nfsv4 Access Control Elements are discussed in Section 4.1.3.



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   While originally designed to support a more flexible authorization
   model, these lists have multiple uses within NFSv4, with the use of
   each element depending on its type, as defined in Section 7.1.

   *  Access Control Lists may be used to provide a more flexible
      authorization model as described in Section 8.4 of
      [I-D.dnoveck-nfsv4-security].  In the NFSv4 ACL model, this
      involves use of Access Control Entries of the ALLOW and DENY
      types.

   *  ACLs may also be used to provide the security-related services
      described in Section 11.  In the NFsv4 ACL model, t his involves
      use of Access Control Entries of the AUDIT and ALARM types.

   [Consensus Needed (Items #61d, #105m, #110c)]: Subsections of this
   section and of Section 7 define the structure of and semantics of
   NFSv4 ACLs, whether they are used to represent the UNIX ACLs defined
   in Section 5.1 or ACLs supporting various extensions thereof
   supported by the server, which may include any of the extensions
   defined in this document.

   Some Matters that relate only to extensions provided to support NFSv4
   ACLs are discussed in 11 and summarized in Section 8.4 of
   [I-D.dnoveck-nfsv4-security].  The definition of the NFSv4.1-specific
   attribute Sacl used only in connections with these functions is
   provided in Section 4.8.

6.1.  Overview of ACL Semantics Choices

   [Consensus Needed (Items #105n, #110d), Through end of section]:

   For reasons discussed in Section 3, there is an extremely wide range
   of ACL-related semantics that servers are allowed to support.  While
   it would be desirable to narrow this range, there are sufficient
   practical problems in doing so that we need to focus on helping
   clients deal appropriately with this wide range of semantic
   variability.  The following means are available:

   *  Where supported by the server, the Aclchoice attribute, described
      in Section 4.6, can provide extensive information about the ACL
      semantics provided by the server.

      [Consensus Needed (Item #14c)]: The set of supported ACE types is
      also needed.  Normally, this is provided by the Aclsupport
      attribute.  However, when it is not supported, the default
      discussed in Section 4.5 is available.





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      For a discussion of how the client can best use this information,
      see Section 6.2.

   *  Where the Aclchoice is not supported, information is more limited.
      This includes the case of use with Minor Version Zero, in which
      this attribute is not defined.

      For a discussion of how the client can best use the available
      information, see Section 6.3.

   The classes of semantic variability listed below are of potential
   importance to clients.  In some cases, the client's need for
   information is related to the client's own semantic expectations with
   an important distinction being that between client's expecting
   support for the UNIX ACL model and those that require certain
   features provided by the extensions to that model that servers MAY
   provide.  In the list below, we refer to the former as "UNIX-
   oriented" clients.

   *  The set of ACE mask bits supported and how actions are mapped to
      them.

      Although clients might need this information, UNIX-oriented
      clients can interacts with servers since support for the mask bits
      needed by these clients is REQUIRED.  See Section 7.2.14 for
      details.

   *  The presence of authorization-related extensions to the UNIX ACL
      model such as ACL inheritance and support for DENY ACEs.

      This information is of no interest to UNIX-oriented clients.

   *  Support for the security-related services described in Section 11.

      This information is of no interest to UNIX-oriented clients.

   *  The presence of semantics associated with the withdrawn POSIX
      draft ACLs that we do not treat as part of the UNIX ACL model.
      These include the way in which a mode is computed from an ACL when
      an ACL is set (see Section 10.3) and the POSIX-draft-specified
      handling of the partial satisfaction of ALLOW ACEs in which
      multiple ACEs can collectively allow an operations even if none of
      them does so completely.

      Although this information might be of interest to clients when it
      is available, clients will need to allow for a range of sever
      behaviors in cases in which Aclchoice is not supported




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   *  Allowable behavioral variability in the handling of existing ACLs
      when the mode is set.

      This information is only available to the client when Aclchoice is
      supported.

6.2.  ACL Semantics Choices

   [Consensus Needed (Items #14d, #61e, #105o, #110d), Through end of
   section]:

   There is a wide range of potential ACL semantics that servers can
   provide.  When the Aclchoice attribute is supported, the client can
   determine the semantics provided by the server as described below.

   *  The set of supported ACE mask bits can be determined as described
      in Section 7.2.12.  Also described there is how other elements of
      the ACE mask support information can be derived from the contents
      of the Aclchoice attribute.

   *  Supported ACE types can be determined using the Aclsupport
      attribute or the appropriate default value described in
      Section 4.5.

   *  The level support for ACL inheritance, including the automatic
      inheritance features, can be determined as described in
      Section 7.3.2.

   *  The way in which the mode corresponding is to be computed based on
      the objects ACL is that described in Section 10.3.  Note that the
      effect of that procedure for a given file system depends on the
      ACE mask support information for that file system.

   *  The way in which existing ACLs are modified when the mode
      attribute is set is described Section 10.7.3.  Note that the
      effect of that procedure for a given file system depends on the
      ACE mask support information for that file system.

   *  The way is which an ACL being set UNIX-oriented client (which only
      support three ACE mask bits) can be mapped to an appropriate ACL
      for the current server is discussed in Section 7.2.14 Note that
      the effect of that procedure for a given file system depends on
      the ACE mask support information for that file system..








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6.3.  Limited Inference Regarding ACL Semantics

   In cases in which the Aclchoice attribute is not supported, including
   use of the minor version for which it is not defined (i.e. NFSv4.0)
   there are very limited ways to determine the extensions supported.
   As a result clients that need to use the extensions to the UNIX ACL
   are generally unable to determine whether that extension is
   supported.

   It is only possible for clients to use these extensions, if they do
   so without providing for interoperability, by only using servers that
   are known, from experience that support the required extensions, in
   addition to those supporting the Aclchoice attribute where the set of
   extensions available can be found as described in Section 6.2.

   Although it is possible to test for the presence such extensions,
   this is generally not helpful because of inherent complexity of
   making such determinations when crossing into new file systems and
   because of the freedom given to servers to avoid returning errors for
   situations in which extensions are used bur not supported.

   As will be seen in the following list, paralleling the one in
   Section 6.2, clients that need to use features beyond those provided
   by UNIX ACLs are generally limited to use servers supporting
   Aclchoice or to using the features in a non-Interoperable way as
   discussed above.

   *  The set of supported ACE mask bits in addition to those which are
      REQUIRED cannot be determined.  This is not a problem for UNIX-
      oriented clients, but those that need to use extensions to that
      set are basically unable to take advantage of the extensions.

   *  Supported ACE types can be determined using the Aclsupport
      attribute or the appropriate default value described in
      Section 4.5.

   *  There is no way to determine the level of support for ACL
      inheritance, including the automatic inheritance features.  The is
      particular troubling since draft-POSIX ACLs require some acl
      inheritance,

   *  The way in which the mode corresponding is to be computed based on
      the objects ACL is that described in Section 10.3.  Because that
      computation depends on information provided by the Aclchoice
      attribute, the client winds up having to accept the server's
      preferences in this matter.





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   *  The way in which existing ACLs are modified when the mode
      attribute is set is described Section 10.7.3.  As in the case of
      computing a mode from an ACL, that computation depends on
      information provided by the Aclchoice attribute.  As a result, the
      client winds up having to accept the server's preferences in this
      matter.

   *  The way is which an ACL being set UNIX-oriented client (which only
      support three ACE mask bits) can be mapped to an appropriate ACL
      for the current server is discussed in Section 7.2.14.  Certain
      assumptions have to be made about the server's handling of certain
      ACE mask bits.  However, as long as recommendations in Section 5.3
      are adhered to UNIX-oriented clients can function properly.

7.  Structure of NFSv4 Access Control Entries

   The attributes acl, sacl (v4.1 only) and dacl (v4.1 only) each
   contain an array of Access Control Entries (ACEs) that are associated
   with the file system object.  The client can set and get these
   attributes while the server is responsible for using the ACL-related
   attributes to perform access control.  The client can use the OPEN or
   ACCESS operations to check access without modifying or explicitly
   reading data or metadata.

   NFSv4 extensions have the option of defining new structures that
   serve as Access Control Entries for other ACL models.

   The NFSv4 ACE structure is defined as follows:

   typedef uint32_t        acetype4;

   typedef uint32_t        aceflag4;

   struct nfsace4 {
           acetype4        type;
           aceflag4        flag;
           acemask4        access_mask;
           utf8str_mixed   who;
   };

7.1.  ACE Type

7.1.1.  Existing ACE Types

   The constants used for the type field (acetype4) and as shifts used
   in determining ACE type support are as follows:





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   const ACE4_ACCESS_ALLOWED_ACE_TYPE      = 0x00000000;
   const ACE4_ACCESS_DENIED_ACE_TYPE       = 0x00000001;
   const ACE4_SYSTEM_AUDIT_ACE_TYPE        = 0x00000002;
   const ACE4_SYSTEM_ALARM_ACE_TYPE        = 0x00000003;

   All four are permitted in the Acl attribute.  For NFSv4.1 and beyond,
   only the ALLOWED and DENIED types are used in the Dacl attribute, and
   only the AUDIT and ALARM types are used in the Sacl attribute.

   +==============================+==============+=====================+
   | Value                        | Abbreviation | Description         |
   +==============================+==============+=====================+
   | ACE4_ACCESS_ALLOWED_ACE_TYPE | ALLOW        | Explicitly grants   |
   |                              |              | the ability to      |
   |                              |              | perform the set of  |
   |                              |              | actions specified   |
   |                              |              | in acemask4 to the  |
   |                              |              | file or directory.  |
   |                              |              |                     |
   |                              |              | When all such       |
   |                              |              | actions to be done  |
   |                              |              | by a given          |
   |                              |              | operation are       |
   |                              |              | explicitly          |
   |                              |              | allowed, the        |
   |                              |              | operation is        |
   |                              |              | authorized and      |
   |                              |              | scanning of the     |
   |                              |              | ACL to determine    |
   |                              |              | authorization       |
   |                              |              | stops.              |
   +------------------------------+--------------+---------------------+
   | ACE4_ACCESS_DENIED_ACE_TYPE  | DENY         | Explicitly denies   |
   |                              |              | the ability to      |
   |                              |              | perform the set of  |
   |                              |              | actions specified   |
   |                              |              | in acemask4 to the  |
   |                              |              | file or directory.  |
   |                              |              |                     |
   |                              |              | When any of the     |
   |                              |              | actions to be done  |
   |                              |              | by a given          |
   |                              |              | operation are       |
   |                              |              | explicitly denied,  |
   |                              |              | the operation is    |
   |                              |              | unauthorized and    |
   |                              |              | scanning of the     |
   |                              |              | ACL to determine    |



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   |                              |              | authorization       |
   |                              |              | stops.              |
   +------------------------------+--------------+---------------------+
   | ACE4_SYSTEM_AUDIT_ACE_TYPE   | AUDIT        | Logs (in a system-  |
   |                              |              | dependent way) any  |
   |                              |              | attempt to          |
   |                              |              | perform, for the    |
   |                              |              | file or directory,  |
   |                              |              | any of the actions  |
   |                              |              | specified in        |
   |                              |              | acemask4.           |
   +------------------------------+--------------+---------------------+
   | ACE4_SYSTEM_ALARM_ACE_TYPE   | ALARM        | Generates (in a     |
   |                              |              | system-dependent    |
   |                              |              | way) an alarm upon  |
   |                              |              | any attempt to      |
   |                              |              | perform, for the    |
   |                              |              | file or directory,  |
   |                              |              | any of the actions  |
   |                              |              | specified in        |
   |                              |              | acemask4.           |
   +------------------------------+--------------+---------------------+

                                  Table 4

   The "Abbreviation" column denotes how the types will be referred to
   throughout the rest of this document.

7.1.2.  ACE Type Support Discovery

   [Consensus needed (Item #105p), through end of section]:

   Discovery of the ACE types that it is appropriate to use can occur in
   two ways:

   *  By use of the OPTIONAL attribute Aclsupport, the set of supported
      ACE types can be determined.

      This set is limited to ACE types defined in Section 7.1.1 and
      cannot be easily extended.

   *  By use of the OPTIONAL attribute Aclchoice, the set of supported
      ACE types can be determined using the data item ACC4IN_TSUPP, when
      that item is present.

      This set can include ACE types defined by protocol extensions as
      described in Section 7.1.3 as well as those defined in
      Section 7.1.1.



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   When neither of these attribute values are available, the client has
   no way of determining the ACE types supported and when attempting the
   use of ACE types other than ALLOW needs to be prepared for a failure
   due to non-support.  Similarly, when the Aclfeature attribute is not
   supported, clients attempting to use ACE types other than those
   defined in Section 7.1.1, need to be prepared for failure to be
   returned due to non-support.

7.1.3.  ACE Type Extension

   [Consensus needed (Item #105q), through end of section]:

   Standards-track documents which define NFSv4 protocol extensions, as
   provided for in [RFC8178], can extend the set of ACE types.  The
   definition of a new extension type needs to provide the following
   information:

   *  An ACE type name, generally of the form ACE4_???_????_ACE_TYPE
      which is to be used to define ACEs of the specified type, when
      appearing in the type fields of the ACE.

   *  A numeric value between four and nine that has not been previously
      used as an ACE type value.

      While it is theoretically possible to delete a previously defined
      ACE type as part of a new minor version, the practical
      difficulties that result from these being stored within existing
      file systems require that such numeric values not be reused.

   *  An abbreviation to be used when referring to that ACE type.

   *  A description of the effect of the ACEs of the specified type
      within ACL.  This needs to include, for ACE types that can appear
      within existing ACL-based attributes, how the presence of the ACE
      affects existing scans of ACL-based attributes such as an
      authorization scan or a notification scan in response to action
      successfully or unsuccessfully attempted.

   *  Description of the set of attributes in which the ACE type can
      appear which can include Acl, Dacl, Sacl, and new attributes added
      in the same or previous extensions.

7.2.  ACE Access Mask

   The following bitmask constants can be used within the access mask
   field of the ACE.





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   const ACE4_READ_DATA            = 0x00000001;
   const ACE4_LIST_DIRECTORY       = 0x00000001;
   const ACE4_WRITE_DATA           = 0x00000002;
   const ACE4_ADD_FILE             = 0x00000002;
   const ACE4_APPEND_DATA          = 0x00000004;
   const ACE4_ADD_SUBDIRECTORY     = 0x00000004;
   const ACE4_READ_NAMED_ATTRS     = 0x00000008;
   const ACE4_WRITE_NAMED_ATTRS    = 0x00000010;
   const ACE4_EXECUTE              = 0x00000020;
   const ACE4_DELETE_CHILD         = 0x00000040;
   const ACE4_READ_ATTRIBUTES      = 0x00000080;
   const ACE4_WRITE_ATTRIBUTES     = 0x00000100;
   const ACE4_WRITE_RETENTION      = 0x00000200;
   const ACE4_WRITE_RETENTION_HOLD = 0x00000400;

   const ACE4_DELETE               = 0x00010000;
   const ACE4_READ_ACL             = 0x00020000;
   const ACE4_WRITE_ACL            = 0x00040000;
   const ACE4_WRITE_OWNER          = 0x00080000;
   const ACE4_SYNCHRONIZE          = 0x00100000;

   Note that some masks have coincident values, or are treated
   differently when used with different types of objects.  For example,
   ACE4_READ_DATA and ACE4_LIST_DIRECTORY designate the same mask bit
   which is treated differently depending on whether the object is a
   directory or other type of object.  Note that,

   *  The mask value names ACE4_ADD_FILE, ACE4_ADD_SUBDIRECTORY, and
      ACE4_DELETE_CHILD are intended to be used with directory objects
      that are not named attribute directories and are not supported
      when used with objects of other types.

   *  The mask value name ACE4_APPEND_DATA is intended to be used with
      non-directory objects.

   *  The mask values used for ACE4_READ_DATA and ACE4_LIST_DIRECTORY
      designate the same mask which treated differently depending on
      whether the object is a directory which is not a named attribute
      directory, or other type of object.

      The mask values for ACE4_WRITE_DATA and ACE4_ADD_FILE behave
      similarly.  as do the mask values for ACE4_APPEND_DATA and
      ACE4_ADD_SUBDIRECTORY.  In each case, the same mask bit has two
      different names and controls two different sets of actions,
      depending on whether the underlying object is a directory which is
      not a named attribute directory or another type of object.





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   *  The mask bit designated by ACE4_EXECUTE controls two different
      sets of action depending on whether the underlying object is a
      directory which is not a named attribute directory or another type
      of object.


   [Consensus Needed (Items #102a, #103a), through end of list]: These
   mask bit are explained in more detail in the sections mentioned below
   based on their relationship to the three POSIX-derived permission
   bits: Read, Write, and Execute.  As described in Section 7.2.3, it is
   no longer assumed that different sets of supported can be adequately
   explained as a different server choice as to mask bit "granularity".
   Changes include material in multiple subsections of Section 7.2.

   *  Mask bits whose set of authorized actions corresponds to a single
      POSIX-derived permission bit are explained in Section 7.2.4.

      These mask bits are always to be supported although the set of
      authorized actions is expected to be smaller when other mask bits
      covering a smaller set of actions are supported.

   *  Mask bits whose set of authorized actions is a subset of those
      normally controlled by a single POSIX-derived permission bit are
      explained in Section 7.2.5.  These only include mask bits
      controlled by the write privilege bit.

      These mask bits are not always supported, but depend on ACL
      extensions supported by the server.  For detailed guidance
      regarding how the client can determine which mask bits are
      supported, see Sections 6.2 and 6.3.

   *  Mask bits whose set of authorized actions is a subset of those
      normally allowed to the owner of a file are explained in
      Section 7.2.6.

      These mask bits are not always supported, but depend on ACL
      extensions supported by the server.  For detailed guidance
      regarding how the client can determine which mask bits are
      supported, see Sections 6.2 and 6.3.

   *  Other mask bits are explained in Section 7.2.7.  These include
      mask bits which do not fit in the varying-granularity approach
      since they cannot be considered finer-grained variants of either a
      single POSIX privilege bit or of ownership of the file.  Also
      included are bits where the relationship to POSIX privileges is
      uncertain and might depend on the behavior of particular
      implementations.




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      This section includes some mask bits for which we have found
      existing implementations and some for which no implementations
      have yet been found.  These mask bits are not always supported,
      but clients need to be prepared for support actually present
      depending on the set of ACL extensions supported.

      [Author aside (Item #111a)]: The following paragraph has to be
      considered tentative for now, at least until some implementation
      of this bit is found or it is determined that none exist.

      In at least one case, that of ACE4_READ_NAMED_ATTRIBUTES, we
      include a mask bit for which no implementation has yet been found.
      Although, the specific details differ from those in existing
      specifications, change has been necessary to appropriately co-
      ordinate handling of actions controlled by this bit, with the
      corresponding handling when POSIX authorization is in effect or
      when UNIX ACLs are supported.

   [Consensus Needed (Item #5a) The descriptions in the section below
   are relevant to both authorization and for recognizing operations
   whose success or failure are to be recorded when ACL are used for the
   non-authorization functions described in Section 11.  With regard to
   ACCESS whose returned bits are affected, it is not necessarily the
   case that the occurrence of ACCESS in these lists implies that such
   operations are recordable events.

   [Consensus Needed (Item #4c)]: While it s recommended that The sets
   of actions to be authorized or otherwise noted in connection with
   these mask bits be those cited in the sections below, it is possible
   that existing implementations might behave differently, based on
   their reliance on earlier specifications and a common understanding
   within the working group that it was the job of the specification to
   conform to the implementation, rather than the other way around.  See
   Section 7.2.12 for information about how the client is to be made
   aware of such discordant implementations.

7.2.1.  Changes in Descriptions of Mask Bits

   [Author Aside, Through end of section]: The material in this section
   identifies changes it has been necessary to make in the description
   of the ACE mask bits.  It is likely that it will be removed before
   the successor document is published as an RFC

   The following items should be noted as cases in which a change
   related to the description of ACE mask bits.  In some cases, there
   will be corresponding annotations near the actual text change, but
   this is not always the case.  Nevertheless, there will need to be
   consensus regarding the following changes:



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   *  [Author Aside (Item #3a)]: Because the following sections have
      been moved to be part of a general description of ACEs, not
      limited to authorization, the descriptions no longer refer to
      permissions but rather to actions.  This could be considered a
      purely editorial change, but, to allow for possible disagreement
      on the matter, it will be considered, here and in Appendix A, as
      consensus item #3.

   *  [Author Aside (Item #4d)]: In a large number of places, SHOULD is
      used inappropriately, since there appear to be no valid reasons to
      allow a server to ignore what might well be a requirement.  Such
      changes are not always noted individually below.  However, they
      will be considered, here and in Appendix A, as part of consensus
      item #4.

   *  [Author Aside (Item #5)}: In a significant number of cases the
      ACCESS operation had not been listed as an operation affected by
      the mask bit where logic suggests it needs to be.  These
      individual additions are not noted individually below, although
      there is, in each affected section, an annotation indicating that
      section requires consensus on this point.  In all cases, they will
      be considered, here, in the affected sections and in Appendix A,
      as part of consensus item #5.

      When ACCESS is included as an affected operation, the description
      identifies the returned bits that are to affected.

      When ACCESS is listed as affected, this is only with regard to
      authorization.  Non-authorization uses are discussed elsewhere, as
      part of this consensus item.

   *  [Author Aside, Including entire bulleted item]: In a number of
      cases, there are additional changes which go beyond editorial or
      arguably do so.  These will be marked as their own consensus items
      usually with an accompanying author aside but without necessarily
      citing the previous treatment.  These include the following:

      [Author Aside (Item #7a)]: Revisions were necessary to clarify the
      relationship between READ_DATA and EXECUTE.

      [Author Aside (Item #8a)]: Revisions were necessary to clarify the
      relationship between WRITE_DATA and APPEND_DATA.  These are part
      of consensus item #8.

      [Author Aside (Item #9a)]: Clarification of the handling of RENAME
      by ADD_FILE, ADD_SUBDIRECTORY.





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   *  Revisions in handling of the masks WRITE_RETENTION and
      WRITE_RETENTION_HOLD.  These are parts of consensus items #10.

7.2.2.  Role of Sticky Bit in ACL-based Authorization

   [Author Aside (Item #62b)]: Because of the need to address sticky-bit
   issue as part of the ACE mask descriptions, it is appropriate to
   introduce the subject here.

   [Author Aside (Item #62b)]: Despite the fact that NFSv4 ACLs and mode
   bits are separate means of authorization, it has been necessary, even
   if only for the purpose of providing compatibility with earlier
   implementations, to introduce the issue here, since reference to this
   mode bit are necessary to resolve issues regard directory entry
   deletion, as is done in Section 7.2.15.

   [Consensus Item, Including List (Item #62b): The full description of
   the role of the sticky-bit appears in Section 5.3.2 of
   [I-D.dnoveck-nfsv4-security].  In evaluating and understanding the
   relationship between the handling of this bit when NFSv4 ACLs are
   used and when they are not, the following points need to be kept in
   mind:

   *  This is troublesome in that it combines data normally assigned to
      two different authorization models and breaks the overall
      architectural arrangement in which the mask bits represent the
      mode bits but provide a finer granularity of control.

   *  It might have been possible to conform to the existing
      architectural model if a new mask bit were created to represent
      the directory sticky bit.  It is probably too late to do so now,
      even though it would be allowed, from the protocol point of view,
      as an NFSv4.2 extension.

   *  The new treatment in Section 7.2.15 is more restrictive than the
      previous one appearing in Section 7.2.16.  This raises potential
      compatibility issues since the new treatment, while designed to
      address the same issues was designed to match existing Unix
      handling of this bit.

   *  This handling initially addresses REMOVE and does not address
      directory sticky bit semantics with regard to RENAME.  Whether it
      will do so is still uncertain.








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   *  The handling of this mode bit was not documented in previous
      specifications.  However, there is a preliminary attempt to do so
      in Section 5.3.1 of [I-D.dnoveck-nfsv4-security].  The reason for
      doing so, is that, given the Unix orientation of the mode
      attribute, it is likely that servers currently implement this,
      even though there is no NFSv4 documentation of this semantics

      This treatment needs to be checked for compatibility issues and
      also to establish a model that we might adapt to the case of NFSv4
      ACLs.

   *  In the long term, it would make more sense to allow the client
      rather than the server to have the primary role in determining the
      semantics for things like this.  That does not seem possible right
      now but it is worth considering.

7.2.3.  Handling of OPTIONAL Mask Bits


7.2.4.  Uses of Core Mask Bits

   [Consensus Needed (Items #4e, #5a, #7b, #8b, #106a, #107a, #108a,
   #109a), Throughout section]

   ACE4_READ_DATA (for non-directory objects)

      Operation(s) affected:
         READ

         [Consensus Needed (Item #101a)]: READLINK

         OPEN (for read or read-write)

         ACCESS (ACCESS4_READ)

      Discussion:
         The action of reading the data of the file, or, in some cases,
         providing necessary preparation to do so.

         [Previous Treatment (Items #4e, #7b)]: Servers SHOULD allow a
         user the ability to read the data of the file when only the
         ACE4_EXECUTE access mask bit is allowed.

         [Author Aside (Item #7b)]: The treatment needs to be clarified
         to make it appropriate to all ACE types.






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         [Consensus Needed (Items #4e, #7b)]: When used to handle READ
         or OPEN operations, the handling MUST be identical whether this
         bit, ACE4_EXECUTE, or both are present, as the server has no
         way of determining whether a file is being read for execution
         are not.  The only occasion for different handling is in
         construction of a corresponding mode or in responding to the
         ACCESS operation.

   ACE4_LIST_DIRECTORY (for ordinary directories)

      Operation(s) affected:
         READDIR

         ACCESS (ACCESS_READ)

      Discussion:
         The action of enumerating the contents of a directory, as
         opposed to searching for a particular name.

   ACE4_ADD_FILE(for ordinary directories)

      Operation(s) affected:
         CREATE

         -  Will require ACE4_ADD_SUBDIRECTORY to add a directory , when
            this is supported.

         LINK

         OPEN (which creates file in the directory)

         ACCESS (ACCESS4_EXTEND)

         REMOVE (may require ACE4_DELETE_CHIILD, when this is supported

         RENAME (on the target directory)

      Discussion:
         Operations which modify a directory

         Many of these operations may controlled at a finer granularity,
         when the appropriate mask bits are supported.

   ACE4_WRITE_DATA (for all non-directory object types)

      Operation(s) affected (only when ACE4_WRITE_NAMED-ATTRIBUTES is
      not supported):
         OPENATTR (when createdir is true)



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      Discussion:
         [Consensus Needed (Item #111b)]: Through rest of this entry

         This action is normally controlled by
         ACE4_WRITE_NAMED_ATTRIBUTES, but needs to be controlled by
         ACE4_WRITE_DATA when the former is not supported (e.g. when
         UNIX ACLs are provided by the server).

   ACE4_EXECUTE (for non-directory objects)

      Operation(s) affected:
         READ

         OPEN (for read or read-write)

         ACCESS (ACCESS4_EXECUTE)

      Discussion:
         The action of reading a file in order to execute it.

         Servers MUST allow a user the ability to read the data of the
         file when only the ACE4_EXECUTE access mask bit is allowed.
         This is because there is no way to execute a file without
         reading the contents.  Though a server may treat ACE4_EXECUTE
         and ACE4_READ_DATA bits identically when deciding to permit a
         READ or OPEN operation, it MUST still allow the two bits to be
         set independently in NFSv4 ACLs, and distinguish between them
         when replying to ACCESS operations.  In particular, servers
         MUST NOT silently turn on one of the two bits when the other is
         set, as that would make it impossible for the client to
         correctly enforce the distinction between read and execute
         permissions.

         As an example, following a SETATTR of the following NFSv4 ACL:

            nfsuser:ACE4_EXECUTE:ALLOW

         A subsequent GETATTR of acl attribute for that file will
         return:

            nfsuser:ACE4_EXECUTE:ALLOW

         and MUST NOT return:

            nfsuser:ACE4_EXECUTE/ACE4_READ_DATA:ALLOW

   ACE4_EXECUTE (for directories which are not named attribute
   directories)



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      Operation(s) affected:
         LOOKUP

         ACCESS(ACCESS4_LOOKUP)

         REMOVE

         RENAME

      Discussion:
         The action of traversing directory by searching for a
         particular named item.

7.2.5.  Finer-grained Mask Bits Derived from Write

   [Consensus Needed (Item #103b), Through the end of the following
   list]: The mask bits presented in this section all control some
   subset of the actions controlled by the write permission bit when
   POSIX authorization is in effect.  These mask bits, when fully
   supported, provide for finer-grained control of authorization
   decisions.  The corresponding ACE mask bit, ACE4_WRITE_DATA, still
   control actions for which no corresponding mask bit defined in this
   section provides for finer-grained control.

   Although object deletion is controlled by ACE4_DELETE for all types
   of objects, the situation is different for directories and for non-
   directory objects:

   *  For non-directory objects, once file deletions are excluded, all
      actions can be divided into those controlled by ACE4_WRITE_DATA
      and those controlled by ACE4_APPEND_DATA.

      While separate control of these two bits is not available on
      severs implementing UNIX ACLs, it appears that there will also be
      servers more oriented to the NFSv4 ACL model, that do not
      distinguish these either.  As a result, clients that need control
      of these to be distinct need to use the facilities described in
      Section 7.2.12 to ensure that such support is available before
      relying on different treatment for these two action subsets.

   *  For directories, many actions are subject to finer-grained control
      when the mask bit defined in this section are implemented.  These
      include ACE4_ADD_SUBDIRECTORY and ACE4_DELETE_CHILD.

      [Author Aside (Item #9b)]: The handling of RENAME in
      distinguishing cross-directory and within-directory RENAME options
      has to be considered tentative.  However, even though this is
      different from previous treatments of the issue, it needs to be



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      carefully considered by the working group.  This is primarily
      because there seems to be no clear motivation for the previous
      treatment and because it seems unlikely that restrictions on
      adding or deleting objects would necessitate corresponding
      restrictions on renaming them, in case in which the directory was
      not read-only.

      [Consensus Needed (Item #9b)]: Even when all the above bits are
      fully supported, the action of renaming a file or directory is
      controlled by ACE4_ADD_FILE for the enclosing directory since this
      mask bit is the corelate of the write privilege bit for a
      directory.

   [Consensus Needed (Items #4f, #5a, #7b, #8b, #101a, #106a, #107a,
   #108a, #109a), Throughout rest of section]

   ACE4_ADD_FILE (For directories)

      Operation(s) affected:
         CREATE

         LINK

         OPEN (when creating a new file)

         RENAME (in the cross-directory case)

      Discussion:
         The action of adding a new file in a directory.  The CREATE
         operation is affected when nfs_ftype4 is NF4LNK, NF4BLK,
         NF4CHR, NF4SOCK, or NF4FIFO.  (NF4DIR is not included because
         it is covered by ACE4_ADD_SUBDIRECTORY.)  OPEN is affected when
         used to create a regular file.  LINK is always affected and
         RENAME is affected when a file/directory is moved between
         directories, with ACE4_ADD_SUBDIRECTORY covering the case when
         a directory is renamed between directories.

   ACE4_APPEND_DATA (For non-directory objects)

      Operation(s) affected:
         WRITE

         ACCESS

         OPEN

         SETATTR of size




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      Discussion:
         [Author Aside]: Also needs to be revised to deal with issues
         related to the interaction of WRITE_DATA and APPEND_DATA.

         The action of modifying a file's data, but only starting at
         EOF.  This allows for the specification of append-only files,
         by allowing ACE4_APPEND_DATA and denying ACE4_WRITE_DATA to the
         same user or group.

         [Consensus Needed (Item #8c)]: As there is no way for the
         server to decide, in processing an OPEN or ACCESS request,
         whether subsequent WRITEs will extend the file or not, the
         server will treat masks containing only WRITE_DATA, only
         APPEND_DATA or both, identically.

         [Consensus Needed (Item #8c)]: If the server is processing a
         WRITE request and the area to be written extends beyond the
         existing EOF of the file then the state of APPEND_DATA mask bit
         is consulted to determine whether the operation is permitted or
         whether alarm or audit activities are to be performed.  If a
         file has an NFSv4 ACL allowing only APPEND_DATA (and not
         WRITE_DATA) and a WRITE request is made at an offset below EOF,
         the server MUST return NFS4ERR_ACCESS.

         [Consensus Needed (Item #8c)]: If the server is processing a
         WRITE request and the area to be written does not extend beyond
         the existing EOF of the file then the state of APPEND_DATA mask
         bit does not need to be consulted to determine whether the
         operation is permitted or whether alarm or audit activities are
         to be performed.  In this case, only the WRITE_DATA mask bit
         needs to be checked to determine whether the WRITE is
         authorized.

   ACE4_ADD_SUBDIRECTORY (For directories)

      Operation(s) affected:
         CREATE

         RENAME (in the cross-directory case)

      Discussion:
         [Author Aside]: The RENAME cases need to be limited to the
         renaming of directories, rather than saying, "The RENAME
         operation is always affected."







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         [Consensus Needed (Item #9b)]: The action of creating a
         subdirectory in a directory.  The CREATE operation is affected
         when nfs_ftype4 is NF4DIR.  The RENAME operation is always
         affected when directories are renamed and the target directory
         NFSv4 ACL contains the mask bit ACE4_ADD_SUBDIRECTORY.

         When this bit is not supported, the actions normally controlled
         by it are controlled by ACE4_ADD_FILE.

         When the Aclchoice attribute is supported, support for the
         attribute is reported using the bit ACC4BN_SEPAFD.

   ACE4_DELETE_CHILD (For Directories)

      Operation(s) affected:
         REMOVE

         RENAME (in the cross-directory case)

      Discussion:
         The action of deleting a file or directory within a directory.

         See Section 7.2.15 for information on now ACE4_DELETE and
         ACE4_DELETE_CHILD are to interact.

         When this bit is not supported, the actions normally controlled
         by it are controlled by ACE4_ADD_FILE.

         When the Aclchoice attribute is supported, support for the
         attribute is reported using the bit ACC4BN_SETDE.

   ACE4_WRITE_NAMED_ATTRS

      Operation(s) affected, for all object types:
         OPENATTR (when createdir is true)

      Operation(s) affected, for the associated named attribute
      directory:
         CREATE

         LINK

         OPEN (which creates file in the directory)

         ACCESS (ACCESS4_EXTEND)

         REMOVE




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         RENAME

      Discussion:
         The action of writing the named attributes of a file or of
         creating a named attribute directory.  OPENATTR is affected
         when it is used to create a named attribute directory.  This is
         when createdir is TRUE.

         [Author Aside (Item #111c)]: Despite the original intention for
         this bit, it appears that the original scheme incorrectly
         allowed all sorts of changes to named attributes as long as the
         named attribute directory already existed.  For this reason,
         the current version changes that scheme even though no
         implementation supporting this mask bit has yet been found.  To
         deal with the possibility implementation exists that follows
         the original scheme, it has it needs to be understood that the
         new scheme is RECOMMENDED and that earlier implementations are
         allowed to rely on the earlier scheme.  When Aclchoice is
         supported, the ACC4BN_NADMOD bit indicate whether the new
         scheme is supported and the recommendation to use appears in
         Section 12.3.

         The ability to check whether or not a named attribute directory
         exists depends on the ability to look it up; therefore, users
         also need the ACE4_READ_NAMED_ATTRS permission in order to
         create a named attribute directory.

         [Author Aside (Item #111c)]: Actually, they need that
         permission to create a named attribute.

         When this bit is not supported, the actions normally controlled
         by it are controlled by ACE4_ADD_FILE.

         When the Aclchoice attribute is supported, support for this
         mask bit is reported using the bit ACC4BN_SEPWNA.

7.2.6.  Finer-grained Mask Bits Derived from Ownership

   The mask bits discussed in this section all authorize actions, that,
   in the absence of support for that bit are resolved based on the
   ownership of the file object.










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   When the Aclchoice attribute is supported, the support for each of
   these bits is normally indicated using the data item ACC4IN_OWNMB.
   However, because the existing specifications do no require this
   behavior, it is possible that server may not use that model.  In such
   cases, and when support is different for the directory and non-
   directory cases, support is reported using the data item
   ACC4IN_ODDMB.

   ACE4_WRITE_ATTRIBUTES (for all object types)

      Operation(s) affected:
         SETATTR of time_access_set, time_backup, time_create,
         time_modify_set, mimetype, hidden, system.

      Discussion:
         The action of changing the times associated with a file or
         directory to an arbitrary value.  Also controls changing the
         mimetype, hidden, and system attributes.

      Implementation Information:
         A user having ACE4_WRITE_DATA or ACE4_WRITE_ATTRIBUTES will be
         allowed to set the times associated with a file to the current
         server time.

   ACE4_WRITE_ACL (for all object types)

      Operation(s) affected:
         SETATTR of acl and mode

      Discussion:
         The action of modifying the acl or mode attributes.

   ACE4_WRITE_OWNER (for all object types)

      Operation(s) affected:
         SETATTR of owner and owner_group

      Discussion:
         The action of modifying the owner or owner_group attributes.
         On UNIX systems, this done by executing chown() and chgrp().

7.2.7.  Other Mask Bits

   The mask bits discussed in this section all authorize actions, that,
   in the absence of support for that bit mask bit, are not resolved by
   one of the three POSIX-derived permission bits.





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   It is important to note this fact because previous treatments of the
   bit mask have strongly suggested that each bit is either identical to
   a POSIX permission bit or controls a subset of one, as part of a
   system of controlling actions at a finer level of granularity.  This
   seems to exclude cases like the mask bits defined in this section and
   in Section 7.2.8.

   Where these bits are not supported, the authorization decision will
   be arrived at, in one of the ways listed below, with the specifics
   presented below as part of the discussion of that particular bit.

   *  The authorization can be controlled by file ownership.

   *  The authorization can be controlled by some boolean combination of
      multiple permission bits or the mask bits that correspond to those
      permission bits.

   *  The authorization can be controlled by some boolean combination
      file ownership and permission bits

   [Consensus Needed (Item #102b)]: The authorization information
   presented here is based on the only known implementation of each of
   the specified bits.  Facilities need to be provided to allow the
   specifics to be derived as part of mask support discovery.

   ACE4_READ_NAMED_ATTRS (for all object types)

      Operation(s) affected:
         OPENATTR

         OPEN when the current fh is a named attribute directory(for
         read or read-write)

         ACCESS when the current fh is a named attribute directory
         (ACCESS4_READ, ACCESS4_LOOKUP)

         READDIR when the current fh is a named attribute directory

         LOOKUP when the current fh is a named attribute directory

      Discussion:
         The action of reading the named attribute directory of a file
         or of looking up a named attribute directory.








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         [Author Aside (Item #111d)]: It appears that this bit is
         identical to the or of the read and execute privilege bits for
         the named attribute directory.  Unfortunately, there is no way
         to set the Mode attribute (or any attribute) of the named
         attribute directory.

         [Consensus needed (Item #111d): When this mask bit is not
         supported, the actions normally controlled by it are controlled
         by the or of the two mask bits ACE4_EXECUTE and
         ACE4_LIST_DIRECTORY.

         [Previous treatment (Item 111d)}: OPENATTR is affected when it
         is not used to create a named attribute directory.  This is
         when 1) createdir is TRUE, but a named attribute directory
         already exists, or 2) createdir is FALSE.

         [Author Aside (Item #111d)]: The implication in the above
         paragraph, the OPENATTR is not affected when it is used to
         create a named directory is troublesome, since, regardless of
         the clients intentions, lookup access in the named directory
         should probably be necessary to look up things within it.

   ACE4_SYNCHRONIZE

      Operation(s) affected:
         NONE

      Discussion:
         Permission to use the file object as a synchronization
         primitive for interprocess communication.  This permission is
         not enforced or interpreted by the NFSv4.1 server on behalf of
         the client.

         Typically, the ACE4_SYNCHRONIZE permission is only meaningful
         on local file systems, i.e., file systems not accessed via
         NFSv4.1.  The reason that the permission bit exists is that
         some operating environments, such as Windows, use
         ACE4_SYNCHRONIZE.













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         For example, if a client copies a file that has
         ACE4_SYNCHRONIZE set from a local file system to an NFSv4.1
         server, and then later copies the file from the NFSv4.1 server
         to a local file system, it is likely that if ACE4_SYNCHRONIZE
         was set in the original file, the client will want it set in
         the second copy.  The first copy will not have the permission
         set unless the NFSv4.1 server has the means to set the
         ACE4_SYNCHRONIZE bit.  The second copy will not have the
         permission set unless the NFSv4.1 server has the means to
         retrieve the ACE4_SYNCHRONIZE bit.

      Implementation Information:
         In the only known implementation of this mask bit, its
         effective setting, for ACEs for OWNER@, GROUP@, and EVERYONE@,
         is derived by oring the three POSIX-derived privilege bits for
         that who value.

   ACE4_DELETE (For all types of objects)

      Operation(s) affected:
         REMOVE

      Discussion:
         The action of deleting the associated file or directory.

         See Section 7.2.15 for information on how ACE4_DELETE and
         ACE4_DELETE_CHILD are to interact.

         [Consensus Needed (Item #62c)]: This approach is in support of
         the handling of deletion when the directory's "sticky" bit is
         off.

   ACE4_READ_ACL (For all types of objects)

      Operation(s) affected:
         GETATTR (of sacl, dacl)

      Discussion:
         The action of interrogating the ACL of the associated file or
         directory.

   ACE4_READ_ATTRIBUTES (for all object types)

      Operation(s) affected:
         GETATTR of file system object attributes

         VERIFY




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         NVERIFY

         READDIR

      Discussion:
         The action of reading basic attributes (non-ACLs) of a file.
         On a UNIX system, such basic attributes can be thought of as
         the stat-level attributes.  Allowing this access mask bit would
         mean that the entity can execute "ls -l" and stat.

         [Author Aside (Items #11a, #112a)]: It is not clear that
         existing clients are prepared to deal with denial of
         authorization for such operations.  As a result, if this mask
         bit is retained, there need to be a way for clients to know, in
         advance that such behavior is possible before proceeding to use
         the file system.

         If a READDIR operation requests attributes, this mask needs to
         be allowed for the READDIR to succeed.

         [Author Aside (Items #11a, #112a)]: The suggestion above needs
         to be looked at closely.  Even if it is justifiable to prevent
         access to attribute values, failing the entire READDIR seems
         unduly harsh.  Returning an empty attribute set would be
         preferable as there seems no justification for making it
         impossible to get attributes for other files in the directory
         simply because a single one is so constrained.

   ACE4_WRITE_RETENTION (for all object types)

      Operation(s) affected:
         SETATTR of retention_set, retentevt_set.

      Discussion:
         The action of modifying the durations for event and non-event-
         based retention.  Also includes enabling event and non-event-
         based retention.

         [Previous Treatment]: A server MAY behave such that setting
         ACE4_WRITE_ATTRIBUTES allows ACE4_WRITE_RETENTION.

         [Author Aside]: The use of "MAY" here ignores the potential for
         harm which unexpected modification of the associated attributes
         might cause for security/compliance.

         [Consensus Needed (Items #10a, #11a)]: If this mask bit is not
         supported, the specified action would be controlled by
         ACE4_WRITE_ATTRIBUTES .



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   ACE4_WRITE_RETENTION_HOLD (for all object types)

      Operation(s) affected:
         SETATTR of retention_hold.

      Discussion:
         The action of modifying the administration retention holds.

         [Author Aside]: It seems that if multiple bits are to be
         defined for this and ACE4_WRITE_RETENTION, there would be a
         need to further restrict authorization for the modification of
         administrative retention holds.

         [Previous Treatment]: A server MAY map ACE4_WRITE_ATTRIBUTES to
         ACE_WRITE_RETENTION_HOLD.

         [Author Aside]: The use of "MAY" here ignores the potential for
         harm which unexpected modification of the associated attributes
         might cause for security/compliance.

         [Consensus Needed (Items #10a, #11a)]: If this mask bit is not
         supported, the specified action would be controlled by
         ACE4_WRITE_ATTRIBUTES .

7.2.8.  Possible Uses of Additional Mask Bits

   The mask bits discusssed in this section all have definitions in
   existing specifications, but, so far, no substantive support for them
   has been found.  As a result, any discussion of these is tentative
   and the working group will need to adjust appropriately when
   implementations are found or it is concluded that no such
   implementations exist.

   Information about implementations of these mask bits are not yet
   available for various reasons:

   *  In the case of ACE4_READ_ATTRIBUTES, it is because the
      implementation investigated, while it does accept this bit in ACLs
      and returns it as set or not appropriately it never uses this bit
      to control authorization decisions

      [Author Aside (Item #112a)]: It does not seem likely that client-
      side software would be prepared to deal effectively with a file
      which could be looked up but whose attributes cannot be obtained.
      As a result, it appears unlikely that more substantive
      implementations will exist.





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   *  In the cases of ACE4_WRITE_RETENTION and ACE4_WRITE_RETENTION, it
      is because the implementation investigated does not contain
      support for the specific OPTIONAL attributes affected.

      [Author Aside (Items #10a, #11a)]: It does not appear that the
      descriptions of the mask bits appearing below were fully thought
      out before being incorporated as part of Proposed Standards.  For
      specific cases, asides below will provide more detail.  In any
      case, the working group will need to think about replacements
      while avoiding compatibility issues for any existing
      implementations.  Any replacement would need to:

      1.  If separate bits for these are to be maintained and the server
          is allowed to refer to a coarser-grained bit when the finer-
          rained bit is supported, the client needs a way to determine,
          in advance, whether this will happen.

      2.  There needs to be some recognition of the fact that a
          retention hold, by its nature needs to be protected from
          arbitrary disablement as is likely to happen if the privileges
          to modify these or to change authorization for their change,
          is identical to privileges to establish them.

7.2.9.  ACE Mask Bit Extension

   Standards-track documents which define NFSv4 protocol extensions, as
   provided for in [RFC8178], can extend the set of ACE mask bits.  The
   definition of a new mask bit needs to provide the following
   information:

   *  The set of actions affected by the new mask bit.

   *  The name of the new mask bit together with a previously unused
      mask bit value.

   *  Information about the way that support (or not) for the new mask
      bit is to be determined.

   *  Information about how the actions affected by this bit are dealt
      with when this new bit is not fully supported.

      This includes situations in which this mask bit has to have the
      same state some other mask bit, i.e. it is a finer-grained variant
      of that other bit.







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      In addition case in which the new bit is not a finer-grained
      variant of an existing bit need to be addressed by specifying a
      boolean combination of existing mask bits or of conditions such as
      being the owner of the file or within the owning group of the
      file.

7.2.10.  Reporting of Mask Bit Support and Characteristics

   For the reasons summarized in the list below, it was necessary to
   provide a means of reporting information about the sets of bit masks
   supported, how actions controlled normally controlled by these bits
   are dealt with when these bits are not supported and how bits these
   relate to the efforts server make to coordinate the values of mode
   and acl-related attributes.  Those means involve various aspects of
   the Aclchoice attribute that are explained later.

   *  While existing specifications assume that all mask bits are finer-
      grained variants of the mask bits defined in Section 7.2.4, once
      one looks at all of the defined mask bits, it is clear that this
      cannot be the case.

      Even if that were the case, there is no way that the necessary
      mapping could be deduced based on the existing specifications.

   *  It appears that a considerable set of mask bits are finer-grained
      variants of file ownership.

      While the mask bits listed in Section 7.2.6 appear likely to be
      dealt with in this way, the lack of any explicit statement to this
      effect means that servers might be encountered for which it is not
      true.

   *  While it appears likely that the mask bits defined in
      Section 7.2.5 are treated as finer-grained variants od the write
      privilege, the specifications do not require this.  This make it
      necessary that the client is aware of situations in which it is
      not the case.

      In addition, it is not made clear how the state of these mask bits
      are dealt with in computing mode.

   *  There is a large set of mask bits defined in Section 7.2.7 for
      which it is not clear exactly how the actions controlled are to be
      determined when the mask bits is not supported or where it is
      supported but is not referenced by an ACL.






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   *  For most mask bits, existing specifications provide no way to
      determine whether the actions controlled are to be allowed or
      denied when ACEs are constructed from mode bits (e.g. when the
      mode is changed).  Although reasonable guesses can be made for
      mask bits defined in Sections 7.2.5 and 7.2.6, for those defined
      in Section 7.2.7 considerable variability is allowed and is most
      likely necessary.

   The reporting described below might turn out to be more general than
   is necessary.  However, we have strived to make it as general as
   possible because existing specifications have not put any limits on
   the handling of most mask bits.  Any case in which the result is not
   usable for appropriately mapping a client's ACLs to those of the
   server will be dealt with in Section 12.3.  Because existing
   specifications allowed a large range of potential behaviors in
   handling of mask bits, most indications of the need to avoid certain
   approaches are addressed by using what we term a "residual SHOULD"
   where it is made clear that only valid reason to bypass the
   recommendation is an implementor's reliance on a previous valid
   specification with the consequences of any such bypass on client
   functioning being made clear.

   Reporting is necessary for all defined mask bits except those for
   which the action to be controlled can never occur.  While the case of
   ACE4_SYNCHRONIZE is not included among these, the following cases
   exclusions are sometimes necessary:

   *  ACE4_READ_NAMED_ATTRIBUTES and ACE4_WRITE_NAMED_ATTRIBUTES are to
      be excluded on file systems in which named attributes are not
      supported/

   *  ACE4_WRITE_RETENTION and ACE4_WRITE_RETENTION_HOLD are to be
      excluded on file systems in which the retention attributes are not
      supported.

   Reporting of mask bit characteristics depends initially on the
   subsection in which the mask bit is defined.  In most cases, this
   takes care of the issue, but, for each of the groups listed below, it
   is possible that a later default method will be needed.

   *  For mask bits defined in Section 7.2.4, no reporting is necessary,
      since support for these mask bits is REQUIRED

      Even though these are the only mask bits UNIX-oriented clients
      deal with, such clients need to be able to interact with servers
      that do support other mask bits, as described in Section 7.2.14.





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   *  For mask bits defined in Section 7.2.5, support normally is
      indicated by setting the bits ACC4BN_SEPFWX, ACC4BN_SEPAFD,
      ACC4BN_SEPDE, and ACC4BN_SEPWNA in the Aclchoice attribute

      When the mask bit in question is referred to in computing the mode
      corresponding to an ACL or is not derived from the value of write
      privilege bit, when a mode is set, this mask bit is reported using
      the default method, whether the mask bit is supported or not.

   *  For mask bits defined in Section 7.2.6, support normally is
      indicated by setting the mask bit within the acemask4 associated
      with data item ACC4IN_OWNMB in the Aclchoice attribute.

      When the mask bit in question is referred to in computing the mode
      corresponding to an ACL or is not derived from the mode in any
      other way but by setting the bit in the ACE for OWNER@ this mask
      bit is reported using the default method, whether the mask bit is
      supported or not.

   *  For mask bits defined in Section 7.2.7, the default method is
      always used, whether the mask bit is supported or not.

   When the default method is to be used for a given mask bit, either
   one or two sets of ombr4words are created and added to the data item.
   One can be used if the handling of the mask bit is the same for
   directory and non-directory objects, with use of two being available
   where there is any difference.  Normally, each set consists of only a
   single word is necessary but two can be used to possible conflicting
   uses

   typedef uint32 ombr4word;

   /*
    * Fields in an ombr4word
    8/
   const OMBR4_BNUM_SHIFT  =   0;
   const OMBR4_BNUM_MASK   =   0x1f;
   const OMBR4_OTYP_SHIFT  =   5;
   const OMBR4_OTYP_MASK   =   0X60;
   const OMBR4_SUPP_SHIFT  =   7;
   const OMBR4_SUPP_MASK   =   0X80;
   const OMBR4_MCC_SHIFT   =   8;
   const OMBR4_MCC_MASK    =   0x300;
   const OMBR4_UAM_SHIFT   =   10;
   const OMBR4_UAM_MASK    =   0x3800
   const OMBR4_MSM_SHIFT   =   16;
   const OMBR4_MSM_MASK    =   0xfff00000;




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   /*
    * Values within the otype field
    */
   const OMBR4OT_DIR       =   1;
   const OMBR4OT_NDIR      =   2;
   const OMBR4OT_BOTH      =   3;

   /*
    * Values within the mode-computation-control field
    */
   const OMBR4MCC_NONE     =   0;
   const OMBR4MCC_READ     =   1;
   const OMBR4MCC_WRITE    =   2;
   const OMBR4MCC_EXEC     =   3;

   /*
    * Values within the UNIX-ACL-map field
    */
   const OMBR4UAM_NEVER    =   0;
   const OMBR4UAM_READ     =   1;
   const OMBR4UAM_WRITE    =   2;
   const OMBR4UAM_EXEC     =   3;
   const OMBR4UAM_ALWAYS   =   4;
   const OMBR4UAM_OWNER    =   8;

   /*
    * Values of shifts used in forming the mode-set mask field.
    */
   const OMBR4MSH_RBIT     =   1;
   const OMBR4MSH_WBIT     =   2;
   const OMBR4MSH_XBIT     =   4;
   const OMBR4MSH_OWN      =   8;

   /*
     * Values of the mode-set mask field to reflect dependence on a
     * single one of the indices used in accessing the sixteen-bit
     * integer as a four-dimensional boolean array.
     */
   const OMBR4MSH_RBIT     =   0xaaaa;
   const OMBR4MSH_WBIT     =   0xcccc;
   const OMBR4MSH_XBIT     =   0xf0f0;
   const OMBR4MSH_OWN      =   0xff00;

   Whether one or two words is used, the various fields defined above
   are filled in as described below:






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   1:  The BNUM field gets the bit number of the mask bit being
       described in the form of the number of bit to left-shift the
       value one to get the value of the mask bit

   2:  The OTYP field is set to either OMBR4OT_BOTH, if a single word is
       being filled in applying to all objects, or to OMBR4OT_DIR or
       OMBR4OT_NDIR for each word depending on the objects being
       described.

   3:  The SUPP field is filled in with a one or zero depending on
       whether the mask bit is supported as defined below.

       In this context we define a mask bit as "supported" only if the
       actions controlled can be allowed or disallowed, independently of
       the handing of other actions.

   4:  Fill in the MCC field based the kind of effect the allowance of a
       particular mask has in computing a mode based on ACL:

       The value OMBR4MCC_NONE indicate that the setting of the bit has
       no effect on the mode being computed.

       The value OMBR4MCC_READ indicates that when the action is
       allowed, the associated read privilege bit s is turned on.  on.

       The value OMBR4MCC_WRITE indicates that when the action is
       allowed, the associated write privilege bit is turned on.  on.

       The value OMBR4MCC_EXEC indicates that when the action is
       allowed, the associated exec privilege bit is turned on.  on.

   5:  Fill in the UAM field to indicate the appropriate setting to
       indicate how the bit is to be dealt with in translating a UNIX
       ACL:

       The value OMBR4UAM_ALWAYS indicates that the bit's actions are
       always to be allowed in the resulting ACL.

       The value OMBR4UAM_NEVER indicates that the bit's actions are
       never to be allowed in the resulting ACL.

       The value OMBR4UAM_READ indicates that the bit's actions are to
       be allowed in the resulting ACL if read privilege bit is set.

       The value OMBR4UAM_WRITE indicates that the bit's actions are to
       be allowed in the resulting ACL if the write privilege bit is
       set.




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       The value OMBR4UAM_OWN is ored into the value to indicates that
       the bit's actions are to be allowed in the resulting ACL iff the
       user is the owner of the file.

   6:  Fill in the MSM field to indicate the appropriate handling of
       this mask bit when setting the mode attribute.  The value is a
       sixteen-bit value to indicate whether the action is to be allowed
       based on the setting of the three privilege bits and whether the
       entry being generate is for the owner of the file.

       Each of the bits within this field describes whether action
       specified is to be allowed.  The bit offset for each combination
       of privilege bits and file ownership is determined by summing the
       following values:

       *  OMBR4MSH_RBIT if the read privilege bit is set.

       *  OMBR4MSH_WBIT if the write privilege bit is set.

       *  OMBR4MSH_XBIT if the execute privilege bit is set.

       *  OMBR4MSH_OWN if the ACE being built is for the owner of file.

7.2.11.  ACE Mask Support Info

   This section describes the ACE mask support information that is
   needed to needed to fully specify the needs of client and server for
   information relevant to the handling of ACE mask bits

   (1):  The set of supported ACE mask bits for the filesystem, in the
         form of an acemask4.  There needs to be one such mask for
         directories and one for non-directory objects.

         Initially both mask words are set to the set of ACE mask bits
         defined in Section 7.2.4.  The mask words are the same even
         though different sets of names are used for different object
         types.

   (2):  The information necessary to support the computation of modes
         based on ACLs, as described in Section 10.3.

         This set of information, the set of mode-computation control
         bits, consists of three ACE masks for each of the read, write,
         and execute privilege bits.  There needs to be one such set for
         directories and one for non- directory objects.






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         Initially both sets of mask bits ae filled in with values that
         reflect the mapping between privilege bits and the
         corresponding ACE mask bit so that:

         *  The bit mask for read contains the mask bits for
            ACE4_READ_DATA/ACE4_LIST_DIRECTORY.

         *  The bit mask for write contains the mask bits for
            ACE4_WRITE_DATA/ACE4_ADD_FILE.

         *  The bit mask for execute contains the mask bits for
            ACE4_EXECUTE.

   (3):  The information necessary to support the generations of ACEs
         corresponding to modes, as described in Section 10.7.3.

         This set of information, the set of mode-set mask support bits,
         consists consist of thirty-two unsigned 16-bit integers, one
         for each potential ACE mask bit.  As with the other sorts of
         information that needs to be determined, there needs to be one
         such set for directories and one for non- directory objects.

         Once the appropriate integer is selected, it is used
         essentially as a linearized four-dimensional boolean array,
         with the four indices consisting of the read, write and execute
         privilege bits and whether the current ACE is for the owner of
         the file, as with the MSM field of an ombr4word described in
         Section 7.2.10.

         Initially each of these consist of 32 16-bit zero words.  They
         are then updated to reflect the proper handling of mask bits
         defined in Section 7.2.4 as follows.

         *  The word at position ACE4_READ_DATA/ACE4_LIST_DIRECTORY
            receives the value OMBR4MSH_RBIT.

         *  The word at position ACE4_WRITE_DATA/ACE4_ADD_FILE receives
            the value OMBR4MSH_WBIT.

         *  The word at position ACE4_EXECUTE receives the value
            OMBR4MSH_XBIT.

   (4):  The information necessary to support the conversion of UNIX-
         oriented ACE mask words (i.e., those that only consist of three
         valid ACE mask bis) to those appropriate to a particular file
         system which might support a larger set of mask bits.





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         This set of information, the set of UNIX-ACL-expansion mask
         consists of two sets of three ACE masks for each the read,
         write, and execute privilege bits.  One is used for the file
         owner the other for users other than OWNER@.  As with the case
         of mode-computation control bits, there needs to be one such
         set for directories and one for non- directory objects.

   For clients, the information, where needed, is obtained as follows:

   *  When the Aclchoice attribute is supported, the information
      described above can be derived from the contents of that attribute
      as described in Section 7.2.12.

   *  When the Aclchoice attribute is not supported, the information
      described is replaced by various defaults described in
      Section 7.2.13.  These defaults may be inaccurate in a number of
      respects but they are designed so that UNIX ACLs can be translate
      into those appropriate for servers who support finer-grained
      authorization.  To allow that to happen, servers need to follow
      the recommendations in Section 5.3.  While servers who do not
      follow these recommendations will often be, formally speaking,
      spec-compliant, it needs to be understood that such servers may
      behave in unexpected manners when interacting with clients who
      have no way to find out where exactly the problem lies.

7.2.12.  ACE Mask Support Discovery

   This section describes how to determine the ACE mask support
   information once it is initialized as described in Section 7.2.11.
   On the client, the information is updated using the contents of the
   Aclchoice attribute as described below.  On the server, the values
   presented in the Aclchoice attribute will match the ACE mask support
   used here.  The intention is that the client and server have the same
   ACE mask support information and are aware of each other's handling
   of the related processes.

   Of the ACE mask bits defined above and those added later by
   extensions as described in Section 7.2.9, support for most is
   OPTIONAL.  The only exceptions are for those discussed in
   Section 7.2.4, which need to be supported whenever ACL-related
   attributes are supported.  The ACE mask support information when
   initialized as described in Section 7.2.11 reflects support only for
   those mask bits.

   Information regarding most of the supported mask bits defined in
   Section 7.2.5 is based on determining the sets of mask bits to add to
   for both directory and non-directory objects, as described below
   using the Aclchoice flag bits:



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   *  When the flag bit ACC4BN_SEPFWX is set, ACE4_APPEND_DATA is added
      to the mask bits for non-directory objects.

   *  When the flag bit ACC4BN_SEPDE is set, ACE4_DELETE_CHILD is added
      to the mask bits for directories.

   *  When the flag bit ACC4BN_SEPAFD is set, ACE4_ADD_SUBDIRECTORY is
      added to the mask bits for directories.

   *  When the flag bit ACC4BN_NAD is set, ACE4_WRITE_NAMED_ATTRIBUTES
      is added to both masks.

   Once these masks have been determined, each bit set in one of the
   masks causes the following changes in the ACE mask support
   information:

   *  The mask bit is added to the corresponding mask of supported ACE
      bits.

   *  Within the entry within the set of mode-computation control bits
      devoted to the write privilege, the bit is added to the set of
      corresponding ACE mask bits.

   *  Similar changes are made to the sets of UNIX-ACL-expansion bits.
      The same changes are made to masks for owners and for non-owner.

   *  The set of mode-set mask support bits for the mask bit in question
      receives the value OMBR4MSH_WBIT.

   At the point, the bits set in the mask associated with Aclchoice data
   item ACC4IN_OWNMB are applied to data for both directory and non-
   directory objects.  The following changes are made for each set bit.

   *  The bit is added to the set of supported ACE mask bits.

   *  No changes are made to the set of mode-computation control bits or
      the set of UNIX-ACL-expansion bits.

   *  The entry for the mask bit in set of mode-set mask support bits
      receives the value OMBR4MSH_OBIT.

   After processing the mask bits whose role in the ACL semantics are
   clear, the ombr4words in Aclchoice data item ACC4IN_ODDMB are applied
   to deal, with mask bits defined in Section 7.2.7 and those defined in
   Sections 7.2.5 and 7.2.6 whose semantic is any way atypical.
   Successive ombr4words are obtained from that item and applied to the
   data for directories, non-directory-objects or both as specified in
   the OTYP field.  For each such words, the following changes are made:



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   *  If the SUPP field is non-zero the set(s) of supported mask bits
      are updated to add the current mask bit.

   *  Mode computation bits are update to reflect the value of the MCM
      field. if that field is not OMBR4MCC_NONE, then the current mask
      bit is added to the specific mask denoted by that field current
      mask bit

   *  UNIX-ACL map control bits are updated as specified by the UAM
      field.  Normally the sets for both owner and non-owner entries are
      specified but if OMBR4UAM_OWNER is set, only the owner entries are
      modified.  Form this point the handling depends on the UAM field
      with this it removed.

      If the value is OMBR4UAM_READ, the current mask is ored into the
      mask(s) associated with the read privilege.

      If the value is OMBR4UAM_WRITE, the current mask is ored into the
      mask(s) associated with the write privilege.

      If the value is OMBR4UAM_EXEC, the current mask is ored into the
      mask(s) associated with the execute privilege.

      If the value is OMBR4UAM_ALWAYS, the current mask is ored into the
      masks for all of the privileges.

   *  The value of the MSM field is transferred to the mode-set-mask
      control bit for the specified mask bit

7.2.13.  ACE Mask Bit Support Defaults

   When the Aclchoice attribute is not supported, default ACE mask
   support information is initialized based on the set of write-
   associated mask bits.

   The set of write-associated mask bits starts with a set based on
   object type:

   *  For directories, it includes ACE4_ADD_FILE,
      ACE4_ADD_SUBDIRECTORY,and ACE4_DELETE_CHILD

   *  For non-directory objects, it includes ACE4_WRITE_DATA and
      ACE_APPEND_DATA.

   Then ACE4_WRITE_NAMED_ATTRIBUTES is added to both sets if named
   attributes are supported.  Then the ACE mask support information is
   generated as described below.




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   *  The set of supported mask bits are limited to those that are
      REQUIRED: ACE4_READ_DATA/ACE4_LIST_DIRECTORY, ACE4_WRITE_DATA/
      ACE4_ADD_FILE, and ACE4_EXECUTE.

      This default might be inaccurate but clients have no way to
      determine what extensions are implemented by the server

   *  Within the entry within the set of mode-computation control bits
      devoted to the write privilege, each write-associated bit is added
      to the set of corresponding ACE mask bits.

   *  Similar changes are made to the sets of UNIX-ACL-expansion bits.
      The same changes are made to masks for owners and for non-owner.

   *  The set of mode-set mask support bits for each mask bit within the
      write-associated mask bits receives the value OMBR4MSH_WBIT.

7.2.14.  ACE Mask Adaptation

   When, as is often the case, clients are limited to the use of the
   three REQUIRED ACE mask bit they need to be able to appropriately
   adapt the ACL they use in interacting with the server to reflect a
   larger set of ACE mask bits that the server is using.  This can occur
   when Aclchoice is supported, in which case the UNIX-ACL mapping
   information is derived as described in Section 7.2.12 or when it is
   not supported in which case that information is generated as
   described in Section 7.2.13.

   The ACEs are processed in turn regardless of their ACE types.  For
   each ACE, a new mask needs to be arrived at based on the following
   information:

   *  Whether ACE4_READ_DATA/ACE4_LIST_DIRECTORY is set in the original
      ACE mask.

   *  Whether ACE4_WRITE_DATA/ACE4_ADD_FILE is set in the original ACE
      mask.

   *  Whether ACE4_EXECUTE is set in the original ACE mask.

   *  Whether the ACE specifies OWNER@ s the who value

   Based on the who value, either the owner or non-owner bits are
   selected.

   Then, the appropriate set of masks are ored together with the masks
   selected based on the original ACE mask controlling which masks are
   selected.  The resulting mask become the ACE mask for the new ACE.



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7.2.15.  Handling of Deletion

   [Author Aside, Through end of bulleted list]: This section contains a
   proposal for the revision of the ACL-based authorization handling of
   requests to delete directory entries or to do RENANE operations.  A
   completely new description is necessary because earlier descriptions
   were not appropriately coordinated with the non-ACL authorization of
   these action, do not clearly address the potential no-support of
   ACE4_DELETE, and have other flaws noted later in this section.  The
   handling described in Section 6.2.1.3.2 of [RFC8881] arose as
   follows:

   *  Previous specifications (e.g., [RFC8881]) do not reference the
      role MODE4_SVTX authorizing deletion and RENAME at all in the non-
      ACL case.  As a result the issue of coordinating ACL-based and
      non-ACL authorization was never addressed.

   *  Although previous specifications defined an ACE4_DELETE bit, it
      was never made clear what having such a bit was intended to
      accomplish.  This gap was particularly important given that,
      unlike many ACE mask bit outside of core three, there is no way
      that this bit can be a finer-grained variant of some of the
      privilege bit, since normally (in the non-sticky-bit case), there
      is no additional file-based permission required for deletion.

   *  When [RFC8881] and its predecessors were written, the result wound
      up undercutting the most likely use of ACE4_DELETE, to allow a
      file to be made undeletable.  In addition it allowed the function
      of ACE4_DELETE_CHILD to be undercut without any apparent good
      reason.

      In any case, this would need to be redone to align the ACL-based
      treatment with the authorization described in Section 5.3.1 of the
      new security document ([I-D.dnoveck-nfsv4-security]).  This is
      apart from the need to correct the issues mentioned above.

   [Author Aside]: All unannotated material within this section is to be
   considered part of consensus item #12c.  The associated previous
   treatment is to be found in Section 7.2.16

   This section describes the handling requests of that involve deletion
   of a directory entry or the disappearance of directory entry as a
   result of RENAME.

   It supersedes the previous treatment of these issues that appears in
   Section 6.2.1.3.2 of [RFC8881] and some predecessor specifications.
   Because a number of flaws that will be elaborated on later in this
   section.  that previous description SHOULD NOT be implemented.  In



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   this context the reliance on previous Proposed Standards is
   considered a valid reason to bypass the above recommendation as long
   as the implemented is aware that:

   *  That treatment makes it impossible to use denial of ACE4_DELETE to
      deny users permission to delete a file.  This is of particular
      concern since it is hard to find any other motivation to define an
      ACE4_DELETE ACE mask bit.

   *  The use of MODE4_SVTX to indicate an additional requirement for
      authorization (using the phrase "may also require") may result in
      client and user confusion since it is different from what, as far
      as can be determined from the non-ACL handling of the sticky bit
      on directories.

   *  The allowance of deletion if (only !!) the ACE4_DELETE succeeds
      undercuts the normal assurance about directory write privileges
      and might constitute a security problem.

      This is of particular concern given the lack of a clear statement
      that such allowance needs to be explicit.  Given the lack of
      clarity, it is possible that when this bit is not used or
      supported, the function of the write privilege bit for the
      directory will be totally undercut.

   *  The lack of any discussion of AUDIT and ALRAM ACEs makes it likely
      that if this approach is adopted by servers supporting those ACE
      types, clients are very unlikely to see expected results,
      especially when MODE4_SVTX is set.

   It needs to be noted that when the server chooses to do this it needs
   to signal this choice using the ACC4BN_SVTXOLD bit when the Aclchoice
   attributed is supported

   *  The creation of a new directory entry , as happens in RENAME is
      not covered and is described elsewhere in this document.  That is,
      the directory updates require the privileges for directory
      modification described elsewhere and there is no reason to check
      ACE4_DELETE since no file is deleted.  However, the deletion of
      files and directories as result of RENAMEs (i.e., in the rename-
      over case) is covered.

   *  The deletion of the file's data due to other operations is dealt
      with separately since these actions, including a truncation to
      length zero, requires only ACE4_WRITE_DATA on the target file






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   *  In cases in which a file or directory is deleted, permission
      checks on the directory need to be supplemented by checks of
      ACE4_DELETE on the entity to be deleted.

   *  The server MAY, when MODE4 SVTX is set on the directory allow
      authorization of the modification to depends on the requester
      being the owner of the target file or the directory, rather than
      on write authorization or the appropriate finer-grained ACE-mask
      bit, when that mask bit is supported.

   *  The confused state of previous specifications makes it necessary
      that we have extensive information about existing implementations
      before we close on Consensus Item #12.

   Special authorization of such operations need to be specified here
   because of two special circumstances that mean that the authorization
   cannot be done as described for other operations or for which
   checking needs to be done for a specific permissions on either a file
   or a directory:

   *  In cases in which a file or directory is deleted, permission
      checks on the directory need to be supplemented by checks of
      ACE4_DELETE on the entity to be deleted.

   *  The server MAY, when MODE4 SVTX is set on the directory allow
      authorization of the modification to depends on the requester
      being the owner of the target file or the directory, rather than
      on write authorization or the appropriate finer-grained ACE mask
      bit, when that mask bit is supported.

   With regard to the check made on the entity to be deleted:

   *  If the entity does not have an ACL, the check is unnecessary and
      is deemed to have succeeded.

   *  If the file system being operated upon does not support the
      ACE4_DELETE mask bit, no check is done and success is assumed.

   *  If the file system being operated upon does support the
      ACE4_DELETE mask bit, and that bit is not explicitly allowed or
      denied, the default is chosen by the server.

      In the case in which the default is to allow the operation that
      default needs to be reported when the Aclchoice attribute is
      supported.

   With regard to the permission check made on the directory being
   modified:



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   *  The normal permission check for directory modification is done if
      the MODE4_SVTX bit for the directory is not set.

   *  The appropriate mask bit to be checked depends on the operation
      being performed.

      In the case of a delete, ACE4_DELETE_CHILD is checked.

      In the case of a cross-directory RENAME, ACE4_DELETE_CHILD is
      checked on the source directory and either ACE4_ADD_FILE or
      ACE4_ADD_SUBDIRECTORY (depending on the type of the object being
      renamed) is check on the destination directory.

      In the case of a within-directory RENAME, the server MAY treat
      this as a removal followed by insertion as in the cross-directory
      case or as only a modification to the directory, requiring
      ACE4_ADD_FILE only.  In the former case, the server's choice to
      take this approach is to be reported by setting the ACC4BN_RNASDI
      bit when the Aclchoice attribute is supported.

      In all of the above cases, if the selected mask bit is not
      supported, ACE4_ADD_FILE is checked instead.

   *  If the directory does not have an ACL, the write privilege for the
      directory is checked instead.

   *  If the MODE4_SVTX bit for the directory is set, the server MAY
      replace the normally appropriate directory check by a check as to
      whether the requester is the owner of the directory or of the
      target file.

      The potential is generate limited to the source directory in the
      RENAME case.  The only case in which it applies to the destination
      directory concerns check or deletion in the rename-over case.

      When the server chooses to do this, that choice is reported by
      setting the ACC4BN_SVTX bit when the Aclchoice attribute is
      supported.

   With regard to handling of AUDIT/ALARM when these operations are
   done:

   *  When multiple checks are made, the order is up to the server.

      As a result, when one of the checks fails, the user has no
      guarantee that other checks typically done later are done, so that
      audit and alarm events for these later potential checks might not
      be recognized.



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   *  When the operation succeeds, the user can assume that all check
      are done, so that audit and alarm events for all of the checked
      privileges will be recognized.

   *  When multiple checks are done and some succeed but others fail,
      the audit and alarm events associated with the failed checks will
      be reported as failures, For the successful checks, audit and
      alarm events are recognized as well but it is up to the server
      whether to report them as successes (because the check succeeded)
      or failed attempts (because the operation was not done.

   *  In case in which a directory check is superseded by an ownership
      checks (i.e., because of the presence of MODE4_SVTX), recognition
      of audit and alarm events proceeds as it would have in the absence
      of MODE4_SVTX.

7.2.16.  Handling of Deletion (Vestigial)

   [Author Aside]: This section contains the former content of
   Section 7.2.15.  All unannotated paragraphs within it are to be
   considered the Previous Treatment associated with consensus item
   #12d.

   [Author Aside, Including List]: Listed below are some of the reasons
   that I have tried to replace the existing treatment rather than
   address the specific issues mentioned here and in later asides.

   *  The fact that there is no clear message about what servers are to
      do and about what behavior clients might rely on.  This derives in
      turn from the use of "SHOULD" in contexts in which it is clearly
      not appropriate, combined with non-normative reports of what some
      systems do, and the statement that the approach suggested is a way
      of providing semantics rather unhelpfully describe as "something
      like traditional UNIX-like semantics".

   *  The complexity of the approach without any indication that there
      is a need for such complexity makes me doubtful that anything of
      this sort was actually implemented, especially since the text is
      so wishy-washy about the need for server implementation.  The
      probability that it would be implemented so widely that clients
      might depend on it is even more remote.

   *  The fact that how audit and alarm issues are to be dealt with is
      not addressed at all.

   *  The fact that this treatment makes the most obvious potential use
      of ACE4_DELETE, to deny a user the ability to delete a file,
      essentially unusable.



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   *  The fact that the previous treatment creates a huge security hole,
      by allowing deletion of directory entries in case in which the
      user requesting deletion does not have ownership or any sort of
      write permission on the directory being modified.

   Two access mask bits govern the ability to delete a directory entry:
   ACE4_DELETE on the object itself (the "target") and ACE4_DELETE_CHILD
   on the containing directory (the "parent").

   Many systems also take the "sticky bit" (MODE4_SVTX) on a directory
   to allow unlink only to a user that owns either the target or the
   parent; on some such systems the decision also depends on whether the
   target is writable.

   [Author aside]: Beyond the fact that this observation is a non-
   normative report of server behavior, it is worth noting that the
   motivation for this, to allow users to delete their own files within
   a shared directory, is vitiated by the following paragraph.

   Servers SHOULD allow unlink if either ACE4_DELETE is permitted on the
   target, or ACE4_DELETE_CHILD is permitted on the parent.  (Note that
   this is true even if the parent or target explicitly denies one of
   these permissions.)

   [Author aside]: I don't understand what possible justification might
   allow a directory to be modified when the request is not the owner
   and has no write permission for the directory being *modified*.  In
   any case no justification is offered.  Similarly, this allows
   deletion on a file even when the owner has denied a user the right to
   delete it.  It is hard to figure out why.

   If the ACLs in question neither explicitly ALLOW nor DENY either of
   the above, and if MODE4_SVTX is not set on the parent, then the
   server SHOULD allow the removal if and only if ACE4_ADD_FILE is
   permitted.

   [Author Aside]: Unclear what SHOULD means here and the use of
   ACE4_ADD_FILE is clearly wrong (should be ACE4_DELETE_CHILD).

   In the case where MODE4_SVTX is set, the server may also require the
   remover to own either the parent or the target, or may require the
   target to be writable.

   [Author Aside]: "may also require" differs from how this is
   documented for UNIX in general, where the ownership replaces the test
   for write privilege on the directory.





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   This allows servers to support something close to traditional UNIX-
   like semantics, with ACE4_ADD_FILE taking the place of the write bit.

   [Author Aside]: Given that ACLs might or might not be present,
   "something close" (whatever that means) is not enough, since the ACL
   and non-ACL cases need to work together seamlessly, so as to provide
   something implementable and understandable.

7.3.  ACE flag bits

   The bitmask constants used for the flag field are as follows:

   const ACE4_FILE_INHERIT_ACE             = 0x00000001;
   const ACE4_DIRECTORY_INHERIT_ACE        = 0x00000002;
   const ACE4_NO_PROPAGATE_INHERIT_ACE     = 0x00000004;
   const ACE4_INHERIT_ONLY_ACE             = 0x00000008;
   const ACE4_SUCCESSFUL_ACCESS_ACE_FLAG   = 0x00000010;
   const ACE4_FAILED_ACCESS_ACE_FLAG       = 0x00000020;
   const ACE4_IDENTIFIER_GROUP             = 0x00000040;
   const ACE4_INHERITED_ACE                = 0x00000080;

   [Author Aside]: Although there are multiple distinct issues that
   might need to be changed, in the interest of simplifying the review,
   all such issues within this section will be considered part of
   Consensus Item #13a with a single revised treatment addressing all
   the issues noted.

   [Previous Treatment]: A server need not support any of these flags.

   [Author Aside]: It is hard to understand why such broad license is
   granted to the server, leaving the client to deal, without an
   explicit non-support indication, with 256 possible combinations of
   supported and unsupported flags.  If there were specific issues with
   some flags that makes it reasonable for a server not to support them,
   then these need to be specifically noted.  Some additional problems
   with the existing treatment are that many of the flags in this list
   are not, by their nature, capable of support by the server (e.g.,
   ACE4_INHERITED_ACE) and that some cannot reasonably be made OPTIONAL
   in general (e.g. ACE4_IDENTIFIER_GROUP for all ACEs and both
   ACE4_SUCCESSFUL_ACCESS_ACE_FLAG and ACE4_FAILED_ACCESS_ACE_FLAG for
   AUDIT and ALARM ACES).  Also troubling is the lack of any statement
   regarding the use of unassigned bits and the consequent effect on
   protocol extensibility.

   [Previous Treatment]: If the server supports flags that are similar
   to, but not exactly the same as, these flags, the implementation may
   define a mapping between the protocol-defined flags and the
   implementation-defined flags.



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   [Author Aside]: The above regarding, the possibility of defining a
   mapping between the protocol-defined flags and hypothetical
   implementation-defined flags might store the bits it supports, while
   valid, is out-of-scope and need to be deleted.

   [Previous Treatment]: For example, suppose a client tries to set an
   ACE with ACE4_FILE_INHERIT_ACE set but not
   ACE4_DIRECTORY_INHERIT_ACE.  If the server does not support any form
   of ACL inheritance, the server should reject the request with
   NFS4ERR_ATTRNOTSUPP.  If the server supports a single "inherit ACE"
   flag that applies to both files and directories, the server may
   reject the request (i.e., requiring the client to set both the file
   and directory inheritance flags).  The server may also accept the
   request and silently turn on the ACE4_DIRECTORY_INHERIT_ACE flag.

   [Author Aside]: What is the possible justification for accepting a
   request asking you do something and then, without notice to the
   client, do something else.  I believe there is none.

   Consensus Needed (Item #13a)]: Server support for many of the flags
   defined above is OPTIONAL, although there are constraints in some
   cases so that certain combination of support and non-support are not
   allowed, as described in Section 7.3.1

   Consensus Needed (Item #13a)]: When a server which does not support
   all the flags bits receives a request to set an NFSv4 ACL containing
   an ACE with an unsupported flag bit set the server MUST reject the
   request with NFS4ERR_ATTRNOTSUPP.

   Consensus Needed (Item #13a)]: The case of servers which do not
   provide support for particular flag combinations is to be treated
   similarly.  If a server supports a single "inherit ACE" flag that
   applies to both files and directories, receives a request set an
   NFSv4 ACL with ACE ACE4_FILE_INHERIT_ACE set but
   ACE4_DIRECTORY_INHERIT_ACE not set, it MUST reject the request with
   NFS4ERR_ATTRNOTSUPP.

7.3.1.  Details Regarding ACE Flag Bits

   ACE4_FILE_INHERIT_ACE
      Any non-directory file in any sub-directory will get this ACE
      inherited.

      Support for this flag bit is OPTIONAL.

   ACE4_DIRECTORY_INHERIT_ACE
      Can be placed on a directory and indicates that this ACE is to be
      added to each new sub-directory created.



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      Support for this flag bit is OPTIONAL.

      If this flag is set in an ACE in an NFSv4 ACL attribute to be set
      on a non-directory file system object, the operation attempting to
      set the ACL SHOULD fail with NFS4ERR_ATTRNOTSUPP.

      [Author Aside (Items #13b, #4g)]: Since I am unable to guess what
      might by "valid reasons" to bypass the recommendation in the
      paragraph, keeping this as a residual "SHOULD" for now.  This
      could change if it is determined that the recommendation was never
      bypassed in existing server implementations, or if a specific
      valid reason to bypass the recommendation is found.

   ACE4_NO_PROPAGATE_INHERIT_ACE
      Can be placed on a directory.  This flag tells the server that
      inheritance of this ACE is to stop at newly created child
      directories.

      While Support for this flag bit is formally OPTIONAL, it has no
      use if ACE4_DIRECTORY_INHERIT_ACE is not supported and is REQUIRED
      if it is.

   ACE4_INHERIT_ONLY_ACE
      Can be placed on a directory but does not apply to the directory;
      ALLOW and DENY ACEs with this bit set do not affect access to the
      directory, and AUDIT and ALARM ACEs with this bit set do not
      trigger log or alarm events.  Such ACEs only take effect once they
      are applied (with this bit cleared) to newly created files and
      directories as specified by the ACE4_FILE_INHERIT_ACE and
      ACE4_DIRECTORY_INHERIT_ACE flags.

      If this flag is present on an ACE, but neither
      ACE4_DIRECTORY_INHERIT_ACE nor ACE4_FILE_INHERIT_ACE is present,
      then an operation attempting to set such an attribute SHOULD fail
      with NFS4ERR_ATTRNOTSUPP.

   ACE4_SUCCESSFUL_ACCESS_ACE_FLAG and ACE4_FAILED_ACCESS_ACE_FLAG
      The ACE4_SUCCESSFUL_ACCESS_ACE_FLAG (SUCCESS) and
      ACE4_FAILED_ACCESS_ACE_FLAG (FAILED) flag bits may be set only on
      ACE4_SYSTEM_AUDIT_ACE_TYPE (AUDIT) and ACE4_SYSTEM_ALARM_ACE_TYPE
      (ALARM) ACE types.  If during the processing of the file's NFSv4
      ACL, the server encounters an AUDIT or ALARM ACE that matches the
      principal attempting the OPEN, the server notes that fact, and the
      presence, if any, of the SUCCESS and FAILED flags encountered in
      the AUDIT or ALARM ACE.  Once the server completes the ACL
      processing, it then notes if the operation succeeded or failed.
      If the operation succeeded, and if the SUCCESS flag was set for a
      matching AUDIT or ALARM ACE, then the appropriate AUDIT or ALARM



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      event occurs.  If the operation failed, and if the FAILED flag was
      set for the matching AUDIT or ALARM ACE, then the appropriate
      AUDIT or ALARM event occurs.  Either or both of the SUCCESS or
      FAILED can be set, but if neither is set, the AUDIT or ALARM ACE
      is not useful.

      The previously described processing applies to ACCESS operations
      even when they return NFS4_OK.  For the purposes of AUDIT and
      ALARM, we consider an ACCESS operation to be a "failure" if it
      fails to return a bit that was requested and supported.

   ACE4_IDENTIFIER_GROUP
      Indicates that the "who" refers to a GROUP as defined under UNIX
      or a GROUP ACCOUNT as defined under Windows.  Clients and servers
      MUST ignore the ACE4_IDENTIFIER_GROUP flag on ACEs with a who
      value equal to one of the special identifiers outlined in
      Section 7.3.3.

      Support for this flag bit is REQUIRED.

   ACE4_INHERITED_ACE
      Indicates that this ACE is inherited from a parent directory.  A
      server that supports automatic inheritance will place this flag on
      any ACEs inherited from the parent directory when creating a new
      object.  Client applications will use this to perform automatic
      inheritance.  Clients and servers MUST clear this bit in the acl
      attribute; it may only be used in the dacl and sacl attributes.

7.3.2.  ACE Flag Support Discovery

   [Consensus Needed (Items #13c, #105r), Entire Section]:

   The ability to determine what ACE flags are supported depends on
   information reported by the Aclchoice attribute.

   Because support for all of these flags is OPTIONAL, clients
   interacting with servers on which the Aclsupport attribute is not
   supported have no access to extensions, such as those involving ACL
   inheritance, that require ACE flag support.  This problem is
   exacerbated because there is no way to test for support by using lags
   and depending on the existence of an error return to resolve the
   question.

   When the Aclchoice attribute is supported, support for ACE flags can
   be determined as described below:






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   *  When the flag bit ACC4BN_INHFULL is set, it can be assumed that
      support for the ACE flags ACE4_FILE_INHERIT_ACE,
      ACE4_DIRECTORY_INHERIT_ACE, ACE4_INHERIT_ONLY_ACE, AND
      ACE4_NO_PROPAGATE_INHERIT_ACE is present.

   *  When the flag bit ACC4BN_IN1BIT is set, it can be assumed that
      support for the ACE flags ACE4_FILE_INHERIT_ACE,
      ACE4_DIRECTORY_INHERIT_ACE, ACE4_INHERIT_ONLY_ACE, AND
      ACE4_NO_PROPAGATE_INHERIT_ACE although there is no support for
      dealing separately with inheritance in newly created
      subdirectories and other objects.

      In this case the server does not support ACEs in which the flags
      ACE4_FILE_INHERIT_ACE and ACE4_DIRECTORY_INHERIT_ACE have
      different settings.  While such combinations are normally
      rejected, the server is allowed to modify the ACEs to make these
      settings the same if ACC4BN_RVINV is set.  In addition, such ACEs
      can be accepted but not enforced based on the settings of the data
      item ACC4IN_STOREUA.

7.3.2.1.  ACE Flag Extension

   [Consensus Needed (Item #13d), Entire Section]:

   Although, in general, previously unused bits within flags words such
   as the flag field within an ACE can easily be added in extensions,
   the way that the flag field within is defined creates unusual
   difficulties, since we cannot be sure that undefined bits in these
   words are always zero.  As a consequence, the definition of
   additional flags must satisfy one the following constraints:

   *  Use of the extension needs to be conditioned on support for the
      Aclfeature attribute and the server setting the flag
      AF4FLAG_UNDEF0 in the af4flags word returned.

   *  Definition of the extension has to occur in a future minor version
      that requires that unused bits in an ACE flag word always be sent
      not set.

   Assuming the flag can be defined as discussed above are
   satisfactorily dealt with, definitions of new flags needs the
   following items to be specified:

   *  An XDR definition of the value of the flag assigning an used flag
      value to a symbol typically beginning with "ACE4_".

   *  A definition of what the flag indicates.




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   *  Discussion of the pattern of use of the flag, including whether it
      is set by the client and used by the server, the reverse, or both.

   *  For flags set by the client and interpreted by the server,
      specification of a means by which the client can determine whether
      the flag is supported.

      This can take the form of a new bit with that purpose within the
      af4flags word, the support for or value returned by an OPTIONAL
      attribute, or other means that the client can easily determine
      whether support is present.

7.3.3.  ACE Who

   The "who" field of an ACE is an identifier that specifies the
   principal or principals to whom the ACE applies.  It may refer to a
   user or a group, with the flag bit ACE4_IDENTIFIER_GROUP specifying
   which of the two is referred to.

   There are several special identifiers that need to be understood
   universally, rather than in the context of a particular DNS domain.

   [Author Aside, including list]: The above paragraph is OK, but the
   following issues regarding these special identifiers need to be
   addressed:

   *  Lack of clarity about the question of which of these special
      identifiers have to be supported and for which support is
      OPTIONAL.

   *  Lack of clarity about which special identifiers can be understood
      by NFSv4.

   *  Confusion of "authentication" and "identification".

   [Previous treatment (Item #50b)]: Some of these identifiers cannot be
   understood when an NFS client accesses the server, but have meaning
   when a local process accesses the file.  The ability to display and
   modify these permissions is permitted over NFS, even if none of the
   access methods on the server understands the identifiers.

   [Consensus Needed (Item #50b)]: Server support for the special
   identifiers "OWNER", "GROUP", and "EVERYONE" is REQUIRED.  For others
   support is OPTIONAL with information regarding support discovery
   appearing in Section 7.3.3.1






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   [Consensus Needed (Item #50b)]: Some of these identifiers, such as
   "NETWORK", "DIALUP", "INTERACTIVE", "BATCH", and "SERVICE" cannot be
   reliably understood when an NFS client accesses the server, but might
   have meaning when a local process accesses the file or when protocols
   other than NFSv4 are used As a result, when ACEs containing these who
   values are encountered, a server that supports these values when
   NFSv4 request are processed is free to make its own judgment as to
   whether any particular request will be treated as matching.

   [Consensus Needed (Item #50b)]: The ability to display and modify
   these OPTIONAL permissions is provided for by NFSv4, even though they
   are not, in most cases, useful when processing NFSv4 requests,

   +===============+===================================================+
   | Who           | Description                                       |
   +===============+===================================================+
   | OWNER         | The owner of the file.                            |
   +---------------+---------------------------------------------------+
   | GROUP         | The group associated with the file.               |
   |               |                                                   |
   |               | Note that the mode bits for the group do not      |
   |               | apply to the owner of the file while the owner    |
   |               | of the file is a member of GROUP@                 |
   +---------------+---------------------------------------------------+
   | EVERYONE      | [Previous treatment (Item #50b)]: The world,      |
   |               | including the owner and owning group.             |
   |               |                                                   |
   |               | [Consensus Needed (Item #50b)]: All requesters,   |
   |               | including the owner, members of the owning        |
   |               | group, and requests for which no user             |
   |               | information is available.                         |
   +---------------+---------------------------------------------------+
   | INTERACTIVE   | Accessed from an interactive terminal.            |
   +---------------+---------------------------------------------------+
   | NETWORK       | Accessed via the network.                         |
   +---------------+---------------------------------------------------+
   | DIALUP        | Accessed as a dialup user to the server.          |
   +---------------+---------------------------------------------------+
   | BATCH         | Accessed from a batch job.                        |
   +---------------+---------------------------------------------------+
   | ANONYMOUS     | [Author Aside]: Although AUTH_NONE requests, are  |
   |               | included here it is not clear whether AUTH_SYS    |
   |               | requests, particularly those issued without       |
   |               | client peer authentication should be included.    |
   |               | Although I feel that they are not truly           |
   |               | authenticated, it is hard to be sure of the       |
   |               | intention given the way term "authenticated" has  |
   |               | been used in earlier specifications.  Also hard   |



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   |               | to resolve is the status of "nobody@domain"       |
   |               | which is intended to be anonymous but may well    |
   |               | be authenticated, as some other user.             |
   |               |                                                   |
   |               | [Author Aside]: For now, am doing the best I      |
   |               | can, given that no implementations of these have  |
   |               | been found.  When they are, will need to          |
   |               | consider revision.  If none are found, could      |
   |               | consider deleting these.  In any case, think we   |
   |               | will wind up treating these as opposites, unless  |
   |               | forced to do otherwise by existing                |
   |               | implementations.                                  |
   |               |                                                   |
   |               | [Consensus Needed (Item #50b)]: Accessed without  |
   |               | any authentication of the user principal (e.g.,   |
   |               | via AUTH_NONE).  Also can include user defined    |
   |               | as anonymous such as those which result from      |
   |               | root-squashing, regardless of the quality of      |
   |               | authentication                                    |
   +---------------+---------------------------------------------------+
   | AUTHENTICATED | [Author Aside]: As for the previous case, am      |
   |               | doing the best I can given that no                |
   |               | implementation of these have been found.          |
   |               |                                                   |
   |               | [Consensus Needed (Item #50b)]: Any               |
   |               | authenticated user except those to be treated as  |
   |               | anonymous (opposite of ANONYMOUS).                |
   +---------------+---------------------------------------------------+
   | SERVICE       | Accessed from a system service.                   |
   +---------------+---------------------------------------------------+

                                  Table 5

   To avoid conflict, these special identifiers are distinguished by an
   appended "@" and will appear in the form "xxxx@" (with no domain name
   after the "@"), for example, ANONYMOUS@.

   {Previous treatment (Item #51a)]: The ACE4_IDENTIFIER_GROUP flag MUST
   be ignored on entries with these special identifiers.  When encoding
   entries with these special identifiers, the ACE4_IDENTIFIER_GROUP
   flag SHOULD be set to zero.

   [Author Aside]: I don't understand what might be valid reasons to
   ignore this or how a server would respond in the case the that it was
   ignored.






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   [Consensus Needed (Item #51a)]: The ACE4_IDENTIFIER_GROUP flag MUST
   be ignored on entries with these special identifiers.  When encoding
   entries with these special identifiers, the ACE4_IDENTIFIER_GROUP
   flag should be set to zero.

   It is important to note that "EVERYONE@" is not equivalent to the
   UNIX "other" entity.  This is the case because, by definition, UNIX
   "other" does not include the owner or owning group of a file.
   "EVERYONE@" means literally everyone, including the owner or owning
   group.

7.3.3.1.  ACE Who Value Support Discovery

   [Consensus Needed (Item #50c, #105s, #117j), For entire section]:

   [Author Aside (Item #50c), to the end of the bulleted list]: Given
   that we have not yet encountered any implementations of these special
   OPTIONAL values.  When we complete our analysis of existing
   implementations, we might update this in various ways:

   *  If it is the case that one or more of these special who values is
      never accepted, the group will need to consider whether it make
      sense to delete it now.

      While there is no time gap that, by itself, would justify
      unimplemented feature, the working group could reasonably conclude
      that the absence of implementation for multiple decades could
      consider that there is no real need for he feature.

   *  If an entire class of special who values (e.g. auth-related or
      miscellaneous) were never implemented, it would be possible
      streamline this section to delete it together with the flag bits
      in af4flags supporting its discovery

   The support for special who values is indicated by the following
   flags when Aclchoice is supported, but when that attribute is not
   supported there is no way for the client to determine whether support
   is present.

   *  The flag bit ACC4BN_AUTHWHO indicates the presence of support for
      the special who values INTERACTIVE@, NETWORK@, BATCH@, DIALUP@,
      and SERVICE@.

   *  The flag bit ACC4BN_OTHWHO indicates the presence of support for
      the special who values ANONYMOUS@ and AUTHENTICATED@.

   *  The flag bit ACC4BN_DPWHO indicates the presence of support for
      the special who values GROUPNOTOWNER@ and OTHERS@.



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7.3.3.2.  ACE Who Value Extension

   [Consensus Needed (Item #50d), for entire section]:

   Because use of unknown who values is defined as returning
   NFS4ERR_BADOWNER, standard track documents defining extensions to
   extensible minor versions can define new special who values.
   Definitions of such new values need to include the following:

   *  The string(s) to serve with each together with an appended "@" as
      the new special who value.  The specification should be in term of
      the Unicode characters.  If it is desired that case-insensitive or
      normalization-form-insensitive string matching is desired, then
      multiple strings should be specified rather than specifying the
      type of code- insensitivity desired.

   *  A description of how it is to be determined whether a given NFSv4
      request matches the new special who value.  In this context,
      "never", indicating such ACEs are to be ignored, is acceptable.

      How these affect handling of non-NFSv4 requests can be treated as
      out of scope.

   *  A description of how support for this new value is to be
      ascertained.  This can take the form of the specification of the
      new value as auth-related, miscellaneous, or the identification of
      a new bit within af4whoinf values that indicates whether support
      is present.

8.  Special Inheritance Features

   The acl attribute consists only of an array of ACEs, but the sacl
   (Section 4.8) and dacl (Section 4.7) attributes also include an
   additional flag field.

   struct nfsacl41 {
           aclflag4        na41_flag;
           nfsace4         na41_aces<>;
   };

   The flag field applies to the entire sacl or dacl; the following flag
   values are defined:

   const ACL4_AUTO_INHERIT         = 0x00000001;
   const ACL4_PROTECTED            = 0x00000002;
   const ACL4_DEFAULTED            = 0x00000004;





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   All bits not defined above are to be cleared.  The ACE4_INHERITED_ACE
   flag can be set in the ACEs of the sacl or dacl (whereas it always
   needs to be cleared in the acl).  These bits provide support for the
   two inheritance-related features listed below.  See Section 7.3.2 for
   information about how support for each feature can be ascertained.

   *  ACL4_AUTO_INHERIT, ACL4_PROTECTED, and ACL4_DEFAULTED are used to
      support automatic inheritance, allowing the changes to the ACLs
      for objects higher in directory hierarchy to be selectively
      propagated to objects which have inherited ACLs from ACLs for
      directories above them in the namespace.

      These flags are stored together with the ACEs making up the ACL
      and are returned when the sacl or dacl attribute is interrogated

   These flags have the following meanings:

   *  The flag ACL4_AUTO_INHERIT indicates that the set of ACEs is
      subject to later modification to reflect the propagation of ACL
      changes to lower levels of the directory hierarchy.

   *  The flag ACL4_PROTECTED indicates that the set of ACES is not to
      subject to later modification to reflect the propagation of ACL
      changes to lower levels of the directory hierarchy.

   *  The flag ACL4_DEFAULTED indicates that the set of ACEs is derived
      from ACL inheritance and does not include ACEs specified by the
      creator of the object.  As a result, the propagation of ACL
      changes to lower levels of the directory hierarchy does not need
      to concern itself with the effects of such creator-selected ACEs.

   The elements used allow a server to support automatic inheritance are
   explained in more detail below.

   Inheritable ACEs are normally inherited by child objects only at the
   time that the child objects are created; later modifications to
   inheritable ACEs do not result in modifications to inherited ACEs on
   descendants.

   However, the dacl and sacl attributes provide the ability to have an
   ACL inheritance mechanism that allows a client application to
   propagate changes to inheritable ACEs to an entire directory
   hierarchy.

   A server that supports this feature performs inheritance at object
   creation time in the normal way, and sets the ACE4_INHERITED_ACE flag
   on any inherited ACEs as they are added to the new object.




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   A client application such as an ACL editor can then propagate changes
   to inheritable ACEs on a directory by recursively traversing that
   directory's descendants and modifying each NFSv4 ACL encountered to
   remove any ACEs with the ACE4_INHERITED_ACE flag and to replace them
   by the new inheritable ACEs (also with the ACE4_INHERITED_ACE flag
   set).  It uses the existing ACE inheritance flags in the obvious way
   to decide which ACEs to propagate.  (Note that it may encounter
   further inheritable ACEs when descending the directory hierarchy and
   that those will also need to be taken into account when propagating
   inheritable ACEs to further descendants.)

   The reach of this propagation may be limited in two ways:

   *  Automatic inheritance is not performed from any directory ACL that
      has the ACL4_AUTO_INHERIT flag cleared.

   *  Automatic inheritance stops wherever an ACL with the
      ACL4_PROTECTED flag is set, preventing modification of that ACL
      and also (if the ACL is set on a directory) of the ACL on any of
      the object's descendants.

   This propagation is performed independently for the sacl and the dacl
   attributes; thus, the ACL4_AUTO_INHERIT and ACL4_PROTECTED flags may
   be independently set for the sacl and the dacl, and propagation of
   one type of acl may continue down a hierarchy even where propagation
   of the other acl has stopped.

   New objects are to be created with a dacl and a sacl that both have
   the ACL4_PROTECTED flag cleared and the ACL4_AUTO_INHERIT flag set to
   the same value as that on, respectively, the sacl or dacl of the
   parent object.

   Both the dacl and sacl attributes are OPTIONAL.  However, if a server
   supports one of these, it MUST support the other if it supports any
   of the ACE types are assigned to that attribute.

   A server that supports both the acl attribute and one or both of the
   new dacl or sacl attributes MUST do so in such a way as to keep all
   three attributes consistent with each other.  Thus, the ACEs reported
   in the acl attribute will be the union of the ACEs reported in the
   dacl and sacl attributes, except that the ACE4_INHERITED_ACE flag
   will be cleared from the ACEs in the acl.  And of course a client
   that queries only the acl will be unable to determine the values of
   the sacl or dacl flag fields.

   When a client performs a SETATTR for the acl attribute, the server
   sets the ACL4_PROTECTED flag to true on both the sacl and the dacl.
   By using the acl attribute, as opposed to the dacl or sacl



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   attributes, the client signals that it might not understand automatic
   inheritance, and thus cannot be trusted to set an ACL for which
   automatic inheritance would make sense.

   When a client application queries an NFSv4 ACL, modifies it, and sets
   it again, it needs to leave any ACEs marked with ACE4_INHERITED_ACE
   unchanged, in their original order, at the end of the NFSv4 ACL.  If
   the application is unable to do this, it needs to set the
   ACL4_PROTECTED flag.  This behavior is not enforced by servers, but
   violations of this rule may lead to unexpected results when
   applications perform automatic inheritance.

   When the low-order bits of mode attribute are subject to
   modification, the server will, if possible, set the mode in such a
   way that leaves inherited ACEs unchanged, in their original order, at
   the end of the ACL.  If it is unable to do so, it sets the
   ACL4_PROTECTED flag on the file's dacl.

   Finally, in the case where the request that creates a new file or
   directory does not also set permissions for that file or directory,
   and there are also no ACEs to inherit from the parent's directory,
   then the server's choice of ACL for the new object is implementation-
   dependent.  In this case, the server is to set the ACL4_DEFAULTED
   flag on the ACL it chooses for the new object.  An application
   performing automatic inheritance takes the ACL4_DEFAULTED flag as a
   sign that the ACL is to be completely replaced by one generated using
   the automatic inheritance rules.

9.  Processing Access Control Entries

   To determine if a request succeeds, the server processes each nfsace4
   entry of type ALLOW or DENY in turn as ordered in the array.  Only
   ACEs that have a "who" that matches the requester are considered.  An
   ACE is considered to match a given requester if at least one of the
   following is true:

   *  The "who' designates a specific user which is the user making the
      request.

   *  The "who" specifies "OWNER@" and the user making the request is
      the owner of the file.

   *  The "who" designates a specific group and the user making the
      request is a member of that group.

   *  The "who" specifies "GROUP@" and the user making the request is a
      member of the group owning the file.




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   *  The "who" specifies "EVERYONE@".

   *  The "who" specifies "INTERACTIVE@", "NETWORK@", "DIALUP@",
      "BATCH@", or "SERVICE@" and the requester, in the judgment of the
      server, feels that designation appropriately describes the
      requester.

   *  The "who" specifies "ANONYMOUS@" or "AUTHENTICATED@" and the
      requestor's authentication status matches the who, using the
      definitions in Section 7.3.3

   Each ACE is processed until all of the bits of the requester's access
   have been ALLOWED.  Under most circumstances, once a bit (see below)
   has been ALLOWED by an ACCESS_ALLOWED_ACE, it is no longer considered
   in the processing of later ACEs.  However if the server chooses not
   to allow partial satisfaction of ALLOW ACEs (see below), this does
   not happen and the operation can only be allowed of a single ACE
   allows all required actions.  If an ACCESS_DENIED_ACE is encountered
   where the requester's access still has unALLOWED bits in common with
   the "access_mask" of the ACE, the request is denied.  When the ACL is
   fully processed, if there are bits in the requester's mask that have
   not been ALLOWED or DENIED, access is denied.

   Unlike the ALLOW and DENY ACE types, the ALARM and AUDIT ACE types do
   not affect a requester's access, and instead are for triggering
   events as a result of a requester's access attempt.  AUDIT and ALARM
   ACEs are processed only after processing ALLOW and DENY ACEs if any
   exist.  This is necessary since the handling of AUDIT and ALARM ACEs
   are affected by whether the access attempt is successful.






















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   [Previous Treatment]: The NFSv4.1 ACL model is quite rich.  Some
   server platforms may provide access-control functionality that goes
   beyond the UNIX-style mode attribute, but that is not as rich as the
   NFS ACL model.  So that users can take advantage of this more limited
   functionality, the server may support the acl attributes by mapping
   between its ACL model and the NFSv4.1 ACL model.  Servers must ensure
   that the ACL they actually store or enforce is at least as strict as
   the NFSv4 ACL that was set.  It is tempting to accomplish this by
   rejecting any ACL that falls outside the small set that can be
   represented accurately.  However, such an approach can render ACLs
   unusable without special client-side knowledge of the server's
   mapping, which defeats the purpose of having a common NFSv4 ACL
   protocol.  Therefore, servers should accept every ACL that they can
   without compromising security.  To help accomplish this, servers may
   make a special exception, in the case of unsupported permission bits,
   to the rule that bits not ALLOWED or DENIED by an ACL must be denied.
   For example, a UNIX-style server might choose to silently allow read
   attribute permissions even though an ACL does not explicitly allow
   those permissions.  (An ACL that explicitly denies permission to read
   attributes should still be rejected.)

   [Author Aside]: While the NFSv4.1 provides features that many might
   not need or use, it is the one that the working group adopted by the
   working group, and I have to assume that alternatives, such as the
   withdrawn POSIX ACL proposal were considered but not adopted.  The
   phrase "unsupported permission bits" with no definition of the bit
   whose support might be dispensed with, implies that the server is
   free to support whatever subset of these bits it chooses.  As a
   result, clients would not be able to rely on a functioning server
   implementation of this OPTIONAL attribute.  If there are specific
   compatibility issues that make it necessary to allow non-support of
   specific mask bits, then these need to be limited and the client
   needs guidance about determining the set of unsupported mask bits.

   [Previous Treatment]: The situation is complicated by the fact that a
   server may have multiple modules that enforce ACLs.  For example, the
   enforcement for NFSv4.1 access may be different from, but not weaker
   than, the enforcement for local access, and both may be different
   from the enforcement for access through other protocols such as SMB
   (Server Message Block).  So it may be useful for a server to accept
   an ACL even if not all of its modules are able to support it.

   [Author Aside]: The following paragraph does not provide helpful
   guidance and takes no account of the need of the client to be able to
   rely on the server implementing protocol-specifying semantics and
   giving notice in those cases in which it is unable to so





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   [Previous Treatment]: The guiding principle with regard to NFSv4
   access is that the server must not accept ACLs that appear to make
   access to the file more restrictive than it really is.

10.  Combining Authorization Models

10.1.  Background for Combined Authorization Model

   Both [RFC7530] and [RFC8881] contain material relating to the need,
   when both mode and ACL attributes are supported, to make sure that
   the values are appropriately coordinated.  Despite the fact that
   these discussions are different, they are compatible and differ in
   only a small number of areas relating to the existence absence of the
   set-mode-masked attribute.

   Such co-ordination is necessary is necessary since it is expected
   that servers providing both sets of attributes will encounter users
   who have no or very limited knowledge of one and need to work
   effectively when other users changes that attribute.  As a result,
   these attributes cannot each be applied independently since that
   would create an untenable situation in which some users who have the
   right to control file access would find themselves unable to do so.

   This section and included subsections discuss issues related to the
   use of the NFSv4 ACL model.  Similar issues, as they apply to the use
   of Access Control Lists defined as part of later extensions are to be
   dealt with by the documents defining those extensions.

   [Author Aside]: From this point on, all paragraphs in this section,
   not other annotated are to be considered part of Consensus Item #63a.
   The description in this section of changes to be made reflects the
   author's proposal to address this issue and related issues.  It might
   have to be adjusted based on working group decisions.

   As a result, in this document, we will have a single treatment of
   this issue, in Sections 10.2 through 10.11.  In addition, an
   NFSv4.2-based extension related to attribute co-ordination will be
   described in Section 10.12.

   The current NFSv4.0 and NFSv4.1 descriptions of this co-ordination
   share an unfortunate characteristic in that they are both written to
   give server implementations a broad latitude in implementation
   choices while neglecting entirely the need for clients and users to
   have a reliable description of what servers are to do in this area.







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   As a result, one of the goals of this new combined treatment will be
   to limit the uncertainty that the previous approach created for
   clients, while still taking proper account of the possibility of
   compatibility issues that a more tightly drawn specification might
   give rise to.

   The various ways in which these kinds of issues have been dealt with
   are listed below together with a description of the needed changes
   proposed to address each issue.

   *  In some cases, the term "MAY" is used in contexts where it is
      inappropriate, since the allowed variation has the potential to
      cause harm in that it leaves the client unsure exactly what
      security-related action will be performed by the server.

      The new treatment will limit use of MAY to cases in which it is
      truly necessary, in order to give clients proper notice of cases
      in which server behavior cannot be determined and limit the work
      necessary to deal with a large array of possible behaviors.

   *  There are also cases in which no RFC2119-defined keywords are used
      but it is stated that certain server implementations do a
      particular thing, leaving the impression that that action is to be
      allowed, just as if "MAY" had been used.

      If the flexibility is necessary, MAY will be used.  In other
      cases, SHOULD will be used with the understanding that maintaining
      compatibility with clients that have adapted to a particular
      approach to this issue is a valid reason to bypass the
      recommendation.  However, in no case will it be implied, as it is
      in the current specifications, that the server MAY do whatever it
      chooses, with the client having no option but to adapt to that
      choice.

   *  There was a case, in Section 10.2, in which the term "SHOULD" was
      explicitly used intentionally, without it being made clear what
      the valid reasons to ignore the guidance might be, although there
      was a reference to servers built to support the now-withdrawn
      draft definition of POSIX ACLs, which are part of what is referred
      to in this document as "UNIX ACLs", as described in Section 4.1 of
      [I-D.dnoveck-nfsv4-security].  A discussion of the issues for
      support of for these ACLs appears in Section 5.1.

      [Author Aside]: Despite the statement, now cited in Section 10.2,
      that this was to accommodate implementations "POSIX" ACLs, it now
      appears that this was not complete.  I've been given to understand
      that this was the result of two groups disagreeing on the
      appropriate mapping from ACLs, and specifying both, using the



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      "intentional" "SHOULD" essentially as a MAY, with the text now in
      Section 10.2 discouraging such use as potentially confusing, not
      intended to be taken seriously.  Since the above information might
      not be appropriate in a standards-track RFC, we intend to retain
      this as an Author Aside which the working group might consider as
      it discusses how to navigate our way out of this situation.

      The new approach will use the term "RECOMMENDED" without use of
      the confusing term "intentional".  The valid reasons to bypass the
      recommendation will be clearly explained as will be the
      consequences of choosing to do other than what is recommended.

   *  There are many case in which the terms "SHOULD" and "SHOULD NOT"
      are used without any clear indication why they were used.  In this
      situation it is possible that the "SHOULD" was essentially treated
      as a "MAY" but also possible that servers chose to follow the
      recommendation.

      In order to deal with the many uses of these terms in Section 10
      and included subsections, which have no clear motivation, it is to
      be assumed that the valid reasons to act contrary to the
      recommendation given are the difficulty of changing
      implementations based on previous analogous guidance, which may
      have given the impression that the server was free to ignore the
      guidance for any reason the implementer chose.  This allows the
      possibility of more individualized treatment of these instances
      once compatibility issues have been adequately discussed.

      [Author Aside]: In each subsection in which the interpretation of
      these terms in the previous paragraph applies there will be an
      explicit reference to Consensus Item #63, to draw attention to
      this change, even in the absence of modified text.

10.2.  Needed Attribute Coordination

   On servers that support acl or dacl attributes, together with the
   mode attribute, the server needs to keep the two attributes
   consistent with one another.  The value of the mode attribute (with
   the exception of the high-order bits reserved for client use as
   described in Section 5.3.1 of [I-D.dnoveck-nfsv4-security], are
   modified as necessary to be consistent with the ACLs set by the by
   client.  When the ACL-related attributes are supported, they control
   authorization so that the role is more limited since authorization
   uses the ACL rather than the mode to make decisions.  As a result
   clients that need to change authorization for file have most control
   when they directly affect the ACL which supports a more flexible
   authorization model.  As a result, users and clients that deal with
   the mode value do so for the following reasons:



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   *  They do so to view or modify the three high-order bits of the mode
      that are not devoted to controlling authorization.

   *  They do it to affect authorization for the object in which case
      the ACL needs to be modified to be consonant with it.

      The previous specifications have allowed considerable behavioral
      variation on what does and does not need to be modified.  In
      addition, the existence of mask bits whose relationship to the
      three privilege bits is unclear causes considerable uncertainty.
      As a result, the server handling of this will be different for
      different servers.

   *  They do it to provide a rough, but not deceptive, description of
      the file's authorization status for display.

      Since opinions differ as to what an appropriate summary might be
      and because previous specifications have allowed considerable
      behavioral variation, the server handling of this will be
      different for different servers

   See Sections 10.7 through 10.9 for detailed discussion of these
   matters.

   [Previous Treatment (Item #63b)]: When a mode attribute is set on an
   object, the ACL attributes may need to be modified in order to not
   conflict with the new mode.  In such cases, it is desirable that the
   ACL keep as much information as possible.  This includes information
   about inheritance, AUDIT and ALARM ACEs, and permissions granted and
   denied that do not conflict with the new mode.

   [Author Aside]: one the things that this formulation leaves
   uncertain, is whether, if the ACL specifies permission for a named
   user group or group, it "conflicts" with the mode.  Ordinarily, one
   might think it does not, unless the specified user is the owner of
   the file or a member of the owning group, or the specified group is
   the owning group.  However, while some parts of the existing
   treatment seem to agree with this, other parts, while unclear, seem
   to suggest otherwise, while the treatment in Section 10.7.1 is
   directly in conflict.

   [Previous Treatment (Item #26a)]: The server that supports both mode
   and ACL must take care to synchronize the MODE4_*USR, MODE4_*GRP, and
   MODE4_*OTH bits with the ACEs that have respective who fields of
   "OWNER@", "GROUP@", and "EVERYONE@".

   [Author Aside]: This sentence ignores named owners and group, giving
   the impressions that there is no need to change them.



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   [Previous Treatment (Item #26a)]: This way, the client can see if
   semantically equivalent access permissions exist whether the client
   asks for the owner, owner_group, and mode attributes or for just the
   ACL.

   [Author Aside, Including List:] The above sentence, while hard to
   interpret for a number a reasons, is worth looking at in detail
   because it might suggest an approach different from the one in the
   previous sentence from the initial paragraph for The Previous
   Treatment of Item #26a.

   *  The introductory phrase "this way" adds confusion because it
      suggests that there are other valid ways of doing this, while not
      giving any hint about what these might be.

   *  It is hard to understand the intention of "client can see if
      semantically equivalent access permissions" especially as the
      client is told elsewhere that he is not to interpret the ACL
      himself.

   *  If this sentence is to have any effect at all it, it would be to
      suggest that the result be the same "whether the client asks for
      the owner, owner_group, and mode attributes or for just the ACL."

      If these are to be semantically equivalent it would be necessary
      to delete ACEs for named users, which requires a different
      approach from the first sentence of the original paragraph.

   {Consensus Needed, Including List (Items #26a, #28a)]: A server that
   supports both mode and ACL attributes needs to take care to
   synchronize the MODE4_*USR, MODE4_*GRP, and MODE4_*OTH bits with the
   ACEs that the have respective who fields of "OWNER@", "GROUP@", and
   "EVERYONE@".  This requires:

   *  When the mode is changed, in most cases, the ACL attributes will
      need to be modified as described in Section 10.7.3.

   *  When the ACL is changed, the corresponding mode is determined and
      used to set the nine low-order bits of the mode attribute.

      This is relatively straightforward in the case of forward-slope
      modes, but the case of reverse-slope modes needs to be addressed
      as well.  It is RECOMMENDED that the procedure presented in
      Section 10.3 be used or another one that provides the same
      results.






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   {Consensus Needed (Item #26a)]: How other ACEs are dealt with when
   setting mode is described in Section 10.7.3.  This includes ACEs with
   other who values, all AUDIT and ALARM ACEs, and all ACES that affect
   ACL inheritance.

   [Previous Treatment (Item #27a)]: In this section, much depends on
   the method in specified Section 10.4.  Many requirements refer to
   this section.  It needs to be noted that the methods have behaviors
   specified with "SHOULD" and that alternate approaches are discussed
   in Section 10.5.  This is intentional, to avoid invalidating existing
   implementations that compute the mode according to the withdrawn
   POSIX ACL draft (1003.1e draft 17), rather than by actual permissions
   on owner, group, and other.

   [Consensus (Item #27a)]: In performing the coordination discussed in
   this section, the method used to compute the mode from the ACL has an
   important role.  In this regard, the method described Section 10.3 is
   to be used.  This method allows considerable variation including that
   motivated by a decision allow computation using the method mandated
   by withdrawn POSIX ACL draft (1003.1e draft 17).  Since this means
   that a client, having no way of determining the method the server
   uses may face interoperability difficulties in moving between servers
   which approach this matter differently, these problems need to be
   accepted unless and until the working group revises the protocol to
   require more uniform treatment.  In any case, the Aclchoices
   attribute allows the client to determine which approach is used by
   the current server.  A more complete discussion of handling of the
   UNIX ACLs in general is to be found in Section 5.1.

10.3.  Computing a Mode Attribute from an ACL (proposed)

   [Consensus Needed (Items #27b, #28b, #61f, #105t, #110f), Through end
   of section]:

   The following method (or another one providing exactly the same
   results) SHOULD be used to calculate the MODE4_R*, MODE4_W*, and
   MODE4_X* bits of a mode attribute.  In this case, the only valid
   reason to bypass the recommendation is implementor reliance on
   previous specifications which left this to implementor choice or
   ignored the cases of the owner having less access than the owning
   group or the owning group having less access than others.  Further,
   in implementing or the maintaining an implementation previously
   believed to be valid, the implementor needs to be aware that this
   will result in invalid values in some uncommon cases.







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   First, for each of the sets of mode bits (i.e., user, group other,
   process the ACL in order, with the result in each case with a
   specific evaluation procedure depending on the specific set of mode
   bits being determined.  The result will be two acemask4 words which
   are referred to below as "Allowed" and "Denied".

   For each set there will be one or more special identifiers considered
   in a positive sense so that ALLOW and DENY ACE's are considered in
   arriving at the mode bit.  In addition, for some sets of bits, there
   will be one or more special identifiers to be considered only in a
   negative sense, so that only DENY ACE's are considered in arriving at
   the mode it.

   The users to be considered are as follows:

   *  For the owner bits, "OWNER@", @GROUP, and "EVERYONE@" are to be
      considered, all in a positive sense.

   *  For the group bits, "GROUP@" and "EVERYONE@" are to be considered,
      both in a positive sense, while "OWNER@" is to be considered in a
      negative sense.

      In some cases, ALLOW ACEs specifying named users and groups are
      considered, in a positive sense.  Fundamentally the decision
      whether to do so or not is up to the server, although it needs to
      always make the same choice for all object in a given file system.

   *  For the bits for others, "EVERYONE@" is to be considered in a
      positive sense, while "OWNER@" and "GROUP@" are to be considered
      in a negative sense.

   Regarding the phrases "considered in a ...sense", the following
   actions are indicated:

   *  When the ACE to be considered in a positive sense is an ALLOW ACE,
      the associated mask m is used in AddToAllowed(m), as described
      below.  When it is a DENY ACE, the associated mask m is used in
      AddToDenied(m), as described below.

   *  When the ACE to be considered in a negative sense is an ALLOW ACE,
      the associated mask ignored When it is a DENY ACE, the associated
      mask m is used in AddToDenied(m), as described below.









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   void AddToAllowed(acemask4 m)
   {
       acemask4 ov = Denied & m;

       m &= ~ov;
       Allowed |= m;
   };

   void AddToDenied(acemask4 m)
   {
      acemask4 ov = Allowed & m;
      acemask4 nov = m & ~ov;

      Allowed &= ~ov;
      Denied |= nov;
   };

   acemask4 GetAllowed(void)
   {
      return Allowed & ~Denied;
   }

   Once these ACL masks are constructed, the mode bits for, user, group,
   and others can each be obtained as described below:

   *  The mask to use to determine the privilege bits is obtained using
      GetAllowed().

   *  For each of the mode-computation masks, the associated privilege
      bit is set if all of the mask bits in the associated mask are
      allowed.

10.4.  Computing a Mode Attribute from an ACL (vestigial)

   [Previous Treatment (Item #27c)]: The following method can be used to
   calculate the MODE4_R*, MODE4_W*, and MODE4_X* bits of a mode
   attribute, based upon an ACL.

   [Author Aside]: "can be used" says essentially "do whatever you
   choose" and would make Section 10 essentially pointless.  Would
   prefer "is to be used" or "MUST", with "SHOULD" available if valid
   reasons to do otherwise can be found.









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   [Author Aside, Including List]: The algorithm specified below, now
   considered the Previous Treatment associated with Item #24a, has an
   important flaw in does not deal with the (admittedly uncommon) case
   in which the owner_group has less access than the owner or others
   have less access than the owner-group.  In essence, this algorithm
   ignores the following facts:

   *  That GROUP@ includes the owning user while group bits in the mode
      do not affect the owning user.

   *  That EVERYONE includes the owning group while other bits in the
      mode do not affect users within the owning group.

   [Previous Treatment (Item #28b)]: First, for each of the special
   identifiers OWNER@, GROUP@, and EVERYONE@, evaluate the ACL in order,
   considering only ALLOW and DENY ACEs for the identifier EVERYONE@ and
   for the identifier under consideration.  The result of the evaluation
   will be an NFSv4 ACL mask showing exactly which bits are permitted to
   that identifier.

   [Previous Treatment (Item #28b)]: Then translate the calculated mask
   for OWNER@, GROUP@, and EVERYONE@ into mode bits for, respectively,
   the user, group, and other, as follows:

10.5.  Alternatives in Computing Mode Bits (vestigial)

   [Author Aside]: All unannotated paragraphs within this section are to
   be considered the Previous Treatment corresponding to Consensus Item
   #27d.

   Some server implementations also add bits permitted to named users
   and groups to the group bits (MODE4_RGRP, MODE4_WGRP, and
   MODE4_XGRP).

   Implementations are discouraged from doing this, because it has been
   found to cause confusion for users who see members of a file's group
   denied access that the mode bits appear to allow.  (The presence of
   DENY ACEs may also lead to such behavior, but DENY ACEs are expected
   to be more rarely used.)

   [Author Aside]: The text does not seem to really discourage this
   practice and makes no reference to the need to standardize behavior
   so the clients know what to expect or any other reason for providing
   standardization of server behavior.







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   The same user confusion seen when fetching the mode also results if
   setting the mode does not effectively control permissions for the
   owner, group, and other users; this motivates some of the
   requirements that follow.

   [Author Aside]: The part before the semicolon appears to be relevant
   to Consensus Item #23 but does not point us to a clear conclusion.
   The statement certainly suggests that the nine low-order bits of the
   mode select one of 512 corresponding ACLs is a desirable but the
   absence significant details or a more direct statement to that effect
   suggest that this is a server implementer choice.

   [Author Aside]: The part after the semicolon is hard to interpret in
   that it is not clear what "this" refers to or which requirements are
   referred to by "some of the requirements that follow".  The author
   would appreciate hearing from anyone who has insight about what might
   have been intended here.

10.6.  Setting Multiple ACL Attributes

   In the case where a server supports the sacl or dacl attribute, in
   addition to the acl attribute, the server MUST fail a request to set
   the acl attribute simultaneously with a dacl or sacl attribute.  The
   error to be given is NFS4ERR_ATTRNOTSUPP.

10.7.  Setting Mode and not ACL (overall)

10.7.1.  Setting Mode and not ACL (vestigial)

   [Author Aside]: All unannotated paragraphs are to be considered the
   Previous treatment of Consensus Item #30a.

   When any of the nine low-order mode bits are subject to change,
   either because the mode attribute was set or because the
   mode_set_masked attribute was set and the mask included one or more
   bits from the nine low-order mode bits, and no ACL attribute is
   explicitly set, the acl and dacl attributes must be modified in
   accordance with the updated value of those bits.  This must happen
   even if the value of the low-order bits is the same after the mode is
   set as before.

   Note that any AUDIT or ALARM ACEs (hence any ACEs in the sacl
   attribute) are unaffected by changes to the mode.








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   In cases in which the permissions bits are subject to change, the acl
   and dacl attributes MUST be modified such that the mode computed via
   the method in Section 10.4 yields the low-order nine bits (MODE4_R*,
   MODE4_W*, MODE4_X*) of the mode attribute as modified by the
   attribute change.  The ACL attributes SHOULD also be modified such
   that:

   1.  If MODE4_RGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_READ_DATA.

   2.  If MODE4_WGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_WRITE_DATA or ACE4_APPEND_DATA.

   3.  If MODE4_XGRP is not set, entities explicitly listed in the ACL
       other than OWNER@ and EVERYONE@ SHOULD NOT be granted
       ACE4_EXECUTE.

   Access mask bits other than those listed above, appearing in ALLOW
   ACEs, MAY also be disabled.

   Note that ACEs with the flag ACE4_INHERIT_ONLY_ACE set do not affect
   the permissions of the ACL itself, nor do ACEs of the type AUDIT and
   ALARM.  As such, it is desirable to leave these ACEs unmodified when
   modifying the ACL attributes.

   Also note that the requirement may be met by discarding the acl and
   dacl, in favor of an ACL that represents the mode and only the mode.
   This is permitted, but it is preferable for a server to preserve as
   much of the ACL as possible without violating the above requirements.
   Discarding the ACL makes it effectively impossible for a file created
   with a mode attribute to inherit an ACL (see Section 10.11).

10.7.2.  Setting Mode and not ACL (Discussion)

   [Author Aside]: All unannotated paragraphs are to be considered
   Author Asides relating to Consensus Item #30b.

   Existing documents are unclear about the changes to be made to an
   existing ACL when the nine low-order bits of the mode attribute are
   subject to modification using SETATTR.

   A new treatment needs to apply to all minor versions.  It will be
   necessary to specify that, for all minor versions, setting of the
   mode attribute, subjects the low-order nine bits to modification.





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   One important source of this lack of clarity is the following
   paragraph from Section 10.7.1, which we refer to later as the
   trivial-implementation-remark".

      Also note that the requirement may be met by discarding the acl
      and dacl, in favor of an ACL that represents the mode and only the
      mode.  This is permitted, but it is preferable for a server to
      preserve as much of the ACL as possible without violating the
      above requirements.  Discarding the ACL makes it effectively
      impossible for a file created with a mode attribute to inherit an
      ACL (see Section 10.11).

   The only "requirement" which might be met by the procedure mentioned
   above is the text quoted below.

      In cases in which the permissions bits are subject to change, the
      acl and dacl attributes MUST be modified such that the mode
      computed via the method in Section 10.4 yields the low-order nine
      bits (MODE4_R*, MODE4_W*, MODE4_X*) of the mode attribute as
      modified by the attribute change.

   While it is true that this requirement could be met by the specified
   treatment, this fact does not, in itself, affect the numerous
   recommendations that appear between the above requirement and the
   trivial-implementation-remark.

   It may well be that there are implementations that have treated the
   trivial-implementation-remark as essentially allowing them to
   essentially ignore all of those recommendations, resulting in a
   situation in which were treated as if it were a trivial-
   implementation-ok indication.  How that issue will be dealt with in a
   replacement for Section 10.7.1 will be affected by the working
   group's examination of compatibility issues.

   The following specific issues need to be addressed:

   *  Handling of inheritance.

      Beyond the possible issues that arise from the trivial-
      implementation-ok interpretation, the treatment in Section 10.7.1,
      by pointing specifically to existing INHERIT_ONLY ACEs obscures
      the corresponding need to convert ACE's that specify both
      inheritance and access permissions to be converted to INHERIT_ONLY
      ACEs.

   *  Reverse-slope modes





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      The effect of ignoring this case is often so pervasive that the
      algorithms offered cannot be patched to avoid the issue but need
      to be rethought.

   *  Named users and groups.

      The particular handling of these in computing mode, could
      conceivably affect other aspects of mode handling as well.

      We will need to consider the behavior of clients and servers to
      get a better handle on these issues.

   *  The exact bounds of what within the ACL is covered by the low-
      order bits of the mode.

      A particular concern is the handling of ACE mask bits that are
      neither derived directly from a POSIX permission bit nor control a
      subset of the actions controlled by a POSIX permission bit.  It is
      often assumed in previous specification that no such bits exist
      but, since that is not the case, the issue needs to be addressed
      somehow.

      We have wound up accommodating a large set of bits, but might need
      to revisit this issue if and when we decide to standardize the
      handling of mask bits that are not finer-grained version of one of
      the three POSIX permission bits.

   It appears that for many of the issues, there are many possible
   readings of the existing specs, leading to the possibility of
   multiple inconsistent server behaviors.  Furthermore, there are cases
   in which none of the possible behaviors described in existing
   specifications meets the needs.

   As a result of these issues, the existing specifications do not
   provide a reliable basis for client-side implementations of the ACL
   feature which a Proposed Standard is normally expected to provide.

10.7.3.  Setting Mode and not ACL (Proposed)

   [Author Aside]: This proposed section is part of Consensus Item #30c
   and all unannotated paragraphs within it are to be considered part of
   that Item.  Since the proposed text includes support for reverse-
   slope modes, treats all minor versions together and assumes decisions
   about handling of ACEs for named users and groups, the relevance of
   consensus items #26b, #28, and #29 needs to be noted.






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   [Author Aside]: As with all such Consensus Items, it is expected that
   the eventual text in a published RFC might be substantially different
   based on working group discussion of client and server needs and
   possible compatibility issues.  In this particular case, that
   divergence can be expected to be larger, because the author was
   forced to guess about compatibility issues and because earlier
   material, on which it is based left such a wide range of matters to
   the discretion of server implementers.  It is the author's intention
   that, as the working group discusses matters, sufficient attention is
   placed on the need for client-side implementations to have reliable
   information about expected server-side actions.

   [Author Aside, through end of bulleted list]: In this and subsequent
   sections I have tried to come up with overall recommendations that
   are as consistent with the previous treatment as I can come up with,
   as I have done in other areas.  In this particular case, I have had
   more difficulty than in others since this is the existing text
   treatment is so unclear, making it hard to determine what hard-to-
   accommodate aspects are intentional.  In particular, as the working
   group discusses this area and accommodate actual implementation, the
   following difficult issues will need to be focused on:

   *  The retention or not of ACEs using special who values.  Some of
      the previous text suggests these are to be retained but I have
      specified they can be retained only if it is certain that they
      will have no effect on authorization.

      Allowing these to be retained and used would partially erode the
      control of file authorization by the mode attribute, resulting in
      a confusing situation.

   *  The statement in existing specification about avoiding conflicts
      with the mode derived from the acl is not all that clear about
      which method is intended.  In addition, it is not clear how
      seriously to take this since the purpose of supporting ACLs is
      precisely to express authorization patterns that are different
      from those expressible by all potential mode values and thus
      inconsistent with all of them.

      [Author Aside (Item #105u)]: I have allowed multiple modes of
      computation while providing facilities within Aclchoice for the
      client to be informed of server choices in this regard.

   *  The handling of many of the ACE mask bits is not addressed, or is
      addressed in flawed way because of mistaken that new mask bits
      only change the granularity of the set of action controlled and
      nothing else.




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      We have tried to accommodate mask bits derivable from sets of mask
      bits or from file ownership.  While the result seems to make
      sense, it might not do so once we look at detailed implementation
      characteristics and try to standardize the mappings between mask
      bits and permission bits.

   This section describes how ACLs are to be updated in response to
   actual or potential changes in the mode attribute, when the
   attributes needed by both of the file access authorization models are
   supported.  It supersedes the discussions of the subject in [RFC7530]
   and [RFC8881], each of which appeared in Section 6.4.1.1 of the
   corresponding document.

   Despite this supersession, it needs to be understood that previous
   implementations addressed the issues using relying often on now-
   superseded statements about the requirements to be satisfied and how
   these requirements might be met.  In light of the existence of these
   implementations, in defining what would normally be requirements, we
   use the term "SHOULD" with the understanding that reliance on
   material in these earlier specifications is a valid reason to bypass
   the new recommendation.

   It is necessary to approach the matter differently than in the past
   because:

   *  Organizational changes are necessary to address all minor versions
      together.

   *  Those previous discussions are often internally inconsistent
      leaving it unclear what specification-mandated actions are to be
      performed.

   *  In many cases, servers were granted an extraordinary degree of
      freedom to choose the action to take, either explicitly or via an
      apparently unmotivated use of "SHOULD", leaving it unclear what
      might be considered "valid" reasons to bypass the recommendation.

   *  There appears to have been no concern for the problems that
      clients and applications might encounter dealing ACLs in such an
      uncertain environment.

   *  Cases involving reverse-slope modes were not adequately addressed.

   *  The security-related effects of SVTX were not addressed.

   While that earlier approach might have been considered workable at
   the time, it made it difficult to devise client-side ACL
   implementations that incorporated the extensions within NFSv4 ACLs,



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   even if there had been any interest in doing so.  In order to enable
   this situation to eventually be rectified, we will define the
   preferred implementation here, but in order to provide temporary
   compatibility with existing implementations based on reasonable
   interpretations of [RFC7530] [RFC8881].  To enable such compatibility
   the term "SHOULD" will be used, with the understanding that valid
   reasons to bypass the recommendation, are limited to implementers'
   previous reliance on these earlier specifications and the difficulty
   of changing them now.

   When the recommendation is bypassed in this way, it is necessary to
   understand, that, until the divergence is rectified, or the client is
   given a way to determine the detail of the server's non-standard
   behavior, client-side implementations may find it difficult to
   implement a client-side implementation that correctly interoperates
   with existing servers that based their implementations on various
   pieces of the existing text, now superseded.

   The fundamental recommendation that needs to be addressed is that
   when mode bits involved in determining file access authorization are
   subject to modification, the server MUST, when ACL-related attributes
   have been set, modify the associated ACEs so as not to conflict with
   the new value of the mode attribute.

   The occasions to which this recommendation applies, vary with the
   attribute being set and the type of object being dealt with:

   *  For all minor versions, any change to the mode attribute, triggers
      this recommendation

   *  When the set_mode_masked attribute is being set on an object which
      is not a directory, whether this recommendation is triggered
      depends on whether any of the nine low-order bits of the mode is
      included in the mask.

   *  When the set_mode_masked attribute is being set on a directory,
      whether this recommendation is triggered depends on whether any of
      the nine low-order bits of the mode or the SVTX bit is included in
      the mask of bit whose values are to be set.

   [Consensus Needed (Item #105u)]: In order to accommodate servers who
   based their implementation on the trivial-implementation-remark,
   servers can bypass the recommendation but need to set the flag
   ACC4BN_SMJUST3 when the Aclchoice attribute is supported.







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   When the recommendation is to be followed, ACLs need to be updated to
   be consistent with the new mode attribute.  When the server does so,
   it needs to set the flag ACC4BN_SMFULL when the Aclchoice attribute
   is supported.  The necessary action depends on specific of the ACEs
   involved.

   *  In the case of AUDIT and ALARM ACEs, which are used outside of
      file access authorization, no change needs to be made.

   *  For ALLOW and DENY ACEs, which are marked as inherit-only, no
      change needs to be made since such ACEs have no effect on file
      access authorization for the current file.

   *  For ALLOW and DENY ACEs, which are marked as providing ACE
      inheritance without being marked as inherit-only, the effect of
      these ACEs on inheritance needs to be retained while their direct
      effect on file access authorization needs to be disabled.

      This can be effected by modifying the ACE to be inherit-only or
      ensuring that such ACEs are never reached when scanning an ACL for
      file access authorization.  For example, a DENY ACE for EVERYONE@
      early in the ACL would have this effect

      Because previous specifications did not mention this case, it is
      possible that implementations exist that do not follow the
      trivial-implementation-remark but still do not specifically
      address this case.  Such servers need to set the flag ACC4BN_SMOLD
      when the Aclchoice attribute is supported.

   *  The handling of remaining ACEs with a who-value of OWNER@, GROUP@,
      or EVERYONE@ needs to be adapted to the new mode.

      This could take the form of rewriting them in place or of
      generating new ACEs at the start of the ACL.

   *  The effect on file authorization of remaining ACEs whose who-value
      is a named user needs to be avoided.

      This can be accomplished by rewriting the ACL, eliminating such
      ACEs or by or ensuring that such ACEs are never reached when
      scanning an ACL for file access authorization.  For example, a
      DENY ACE for EVERYONE@ early in the ACL would have this effect.

   *  The effect on file authorization of ACEs whose who-value is one of
      the other special values defined in Section 7.3.3 are to be left
      unmodified.





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      This can be accomplished by rewriting the ACL, eliminating such
      ACEs or by or ensuring that such ACEs are never reached when
      scanning an ACL for file access authorization.  For example, a
      DENY ACE for EVERYONE@ early in the ACL would have this effect.

   How these needs are best effected depends on the ACL model
   implemented.  Of particular importance is the existence of DENY ACEs
   which allow one to force scanning for file access to be stopped at
   some point while retaining later ACEs to be retained without any
   possibility that they will affect file access authorization.  We
   discuss three classes of ACL implementations as discussed below.

   *  For implementation of NFSv4 ACLs and hybrids that contain support
      for DENY ACEs, implementation suggestions appearing in
      Section 10.7.5 are provided.

   *  For implementation of UNIX ACLs, implementation suggestions
      appearing in Section 10.7.4 are provided.

   *  For implementation of various hybrid ACLs that do not provide
      support for DENY ACEs, implementation suggestions appearing in
      Section 10.7.6 are provided.

   All of the abovementioned suggestions share common logic regarding
   the formation of ACE masks used and how the mode bits are mapped to
   ACE masks designating allowed actions.

   The mask of allowed actions for each of OWNER@, GROUP@, and EVERYONE@
   is derived as described below using mode-set mask support
   information, as described below.  For each of the above, the
   following is done:

   *  The three privilege bits are extracted for owner, group, and
      others.

   *  That set of three bits is combined with a fourth which one in the
      case of OWNER@ and zero in the other case.

   *  Those four fits are used to arrive at a shift to get to the
      appropriate bit in the of mode-set masks.

   *  All of the mode set mask words are scanned to find those with that
      specific bit on.  For entries in which it is on the associated ACE
      mask bit is added to the mask being accumulated.

   *  The resulting mask designate the allowed actions for the specific
      who being interrogated.




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10.7.4.  Setting Mode and not ACL in the Unix ACL Case (Proposed)

   [Author Aside]: This proposed section is part of Consensus Item #30d
   and all unannotated paragraphs within it are to be considered part of
   that Item.  Since the proposed text includes support for reverse-
   slope modes, treats all minor versions together and assumes decisions
   about handling of ACEs for named users and groups, the relevance of
   consensus items #26c, #28, and #29 needs to be noted.

   When UNIX ACLs are implemented, the absence of support for DENY ACEs
   forces the ACL to be rewritten in its entirety, rather than have a
   mode-related section prepended to a mostly unchanged ACL.  In
   addition, the absence of support for DENY ACEs requires special
   attention to the possible presence of reverse slope mode because
   OWNER@ is a subset of GROUP@ and both OWNER@ and GROUP@ are subsets
   of EVERYONE@.

   It should be noted however, that the complexity of the rewriting
   process is reduced because of features not part of the UNIX ACL
   model:

   *  The absence of support for ACEs other than ALLOW means only a
      single ACE type needs to be dealt with.

   *  The absence of ACE inheritance means that ACEs marked to be
      inherited or inherit-only, do not exist.

   *  The absence of support for ACEs with OPTIONAL special who value
      allow these cases to be ignored as well.

   The replacement ACL begins with three ALLOW ACEs for the who values
   OWNER@, GROUP@, and EVERYONE@.  The order in which these are placed
   in the resultant ACL needs to be adjusted based on the mode value
   avoid problems with reverse-slope modes.  Such problems can arise
   when a who value processed later contains permission bits not present
   in previous one so that the later who value, covering a superset of
   the principals of the earlier one, receives permissions that should
   not, for example, be granted to the owning user according to the
   POSIX definition of privileges for the owning group

   In order to address this issue the three entries need to be sorted in
   order of descending privilege, using the inclusion relationship for
   the privilege bits of each one.








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   It is possible that two entries will have privilege sets not
   orderable by inclusion, i.e., neither is a subset of the other.
   Given the absence of DENY ACEs, the resulting permissions cannot be
   representing by an ACL, so that the ACL needs to be deleted in this
   case.

   These preliminary ACEs are followed by a series of ACEs derived from
   the existing ACL with entries copied over or not as described below:

   *  ACEs with who value of OWNER@, GROUP@, or EVERYONE@ are not copied
      over.

   *  ACEs with other who values are copied to the ACL, unmodified.

10.7.5.  Setting Mode and not ACL in the NFSv4 ACL Case (Proposed)

   [Author Aside]: This proposed section is part of Consensus Item #30e
   and all unannotated paragraphs within it are to be considered part of
   that Item.  Since the proposed text includes support for reverse-
   slope modes, treats all minor versions together and assumes decisions
   about handling of ACEs for named users and groups, the relevance of
   consensus items #26d, #28, and #29 needs to be noted.

   This covers in addition to NFSv4 ACLs per se, all cases in which
   support for DENY ACEs is present.  The availability of support for
   DENY ACEs affects the generation of a new ACL as follows:

   *  Reverse slope modes do not force a re-ordering of the initial
      ACEs.  To avoid this, each initial ALLOW ACE is paired with a
      corresponding DENY ACE

   *  Detailed analysis of the existing ACEs is not necessary since the
      new ACL will prevent those from ever being referenced in
      connection with file access authorization.  This allows the
      existing ACL to be appended to the three initial ACE pairs.

   The replacement ACL begins with three pairs of ACEs for the who
   values OWNER@, GROUP@, and EVERYONE@.  Each pair consists of an ALLOW
   ACE for that who value followed by a corresponding DENY ACE with the
   same who value.  The ACE mask for the ALLOW ACE is derived from the
   corresponding permission bits as described above.  The mask for the
   DENY ACE is the set of mode-related mask bits with the allows mask
   bits turned off.

   These preliminary ACEs are followed by copies of the ACEs within the
   existing ACL.  It is possible, although not necessary, to eliminate,
   as part of this copy, all ALLOW and DENY ACEs with who values of
   OWNER@, GROUP@, and EVERYONE@.



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10.7.6.  Setting Mode and not ACL in Certain Hybrid ACL Cases (Proposed)

   [Author Aside]: This proposed section is part of Consensus Item #30f
   and all unannotated paragraphs within it are to be considered part of
   that Item.  Since the proposed text includes support for reverse-
   slope modes, treats all minor versions together and assumes decisions
   about handling of ACEs for named users and groups, the relevance of
   consensus items #26e, #28, and #29 needs to be noted.

   This section covers ACL implementations that do not have support for
   DENY ACEs.  In such cases, the absence of support for DENY ACEs
   forces the ACL to be rewritten in its entirety, rather than have a
   mode-related section prepended to a mostly unchanged ACL.  In
   addition, the absence of support for DENY ACEs requires special
   attention to the possible presence of reverse slope modes because
   OWNER@ is a subset of GROUP@ and both OWNER@ and GROUP@ are subsets
   of EVERYONE@.

   The replacement ACL begins with three ALLOW ACEs for the who values
   OWNER@, GROUP@, and EVERYONE@.  The order in which these are placed
   in the resultant ACL needs to be adjusted based on the mode value
   avoid problems with reverse-slope modes.  Such problems can arise
   when a who value processed later contains permission bits not present
   in previous one so that the later who value, covering a superset of
   the principals of the earlier one, receives permissions that should
   not, for example, be granted to the owning user according to the
   POSIX definition of privileges for the owning group

   One way to address this issue is to use ACEs with who values of
   OWNERNOTGROUP@ and OTHERS@ rather than OWNER@ and EVERYONE@, if
   appropriate support is available.

   In order to address this issue in other case, the three entries need
   to be sorted in order of descending privilege, as described in
   Section 10.7.4.  As in that case the existence of sets of privilege
   bits not comparable according to inclusion might force the ACL to be
   deleted, rather than being replaced by an ACL equivalent to the mode,
   which in this case cannot exist.

   These preliminary ACEs are followed by a series of ACEs derived from
   the existing ACL with entries copied over or not as described below:

   *  AUDIT and ALARMS ACEs are copied over.

   *  ALLOW and DENY ACEs that are marked inherit-only are copied over.






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   *  ALLOW and DENY ACEs that are marked as inheritable without being
      inherit-only are copied over in a modified form.  They need to be
      marked as inherit only.

   *  Other ALLOW and DENY ACEs are not copied over.  This applies
      irrespective of the who value, although the reasons for doing this
      are different for different sorts of who values.

      ACEs with who values of OWNER@, GROUP@, and EVERYONE@ are to be
      eliminated because they are dealt with in the prepended ACEs.

      ACEs with a who value denoting a specific user or group are to be
      eliminated because their presence is incompatible with the POSIX
      file access authorization model.

      ACEs with a special who value (auth-related or miscellaneous) are
      to be eliminated in order to assume that the file access
      authorization after setting the mode reflects the mode alone.

10.8.  Setting ACL and Not Mode

   [Author Aside]: The handling of SHOULD in this section is considered
   as part of Consensus Item #63d.

   When setting the acl or dacl and not setting the mode or
   mode_set_masked attributes, the permission bits of the mode need to
   be derived from the ACL.  In this case, the ACL attribute SHOULD be
   set as given.  The nine low-order bits of the mode attribute
   (MODE4_R*, MODE4_W*, MODE4_X*) MUST be modified to match the result
   of the method in Section 10.3.  The three high-order bits of the mode
   (MODE4_SUID, MODE4_SGID, MODE4_SVTX) SHOULD remain unchanged.

10.9.  Setting Both ACL and Mode

   When setting both the mode (includes use of either the mode attribute
   or the mode_set_masked attribute) and the acl or dacl attributes in
   the same operation, the attributes MUST be applied in the following
   order: mode (or mode_set_masked), then ACL.  The mode-related
   attribute is set as given, then the ACL attribute is set as given,
   possibly changing the final mode, as described above in Section 10.8.

10.10.  Retrieving the Mode and/or ACL Attributes

   [Author Aside]: The handling of SHOULD in this section is considered
   as part of Consensus Item #63e.






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   If a server supports any ACL attributes, it may use the ACL
   attributes on the parent directory to compute an initial ACL
   attribute for a newly created object.  This will be referred to as
   the inherited ACL within this section.  The act of adding one or more
   ACEs to the inherited ACL that are based upon ACEs in the parent
   directory's ACL will be referred to as inheriting an ACE within this
   section.

   Implementors need to base the behavior of CREATE and OPEN depending
   on the presence or absence of the mode and ACL attributes by
   following the directions below:

   1.  If just the mode is given in the call:

       In this case, inheritance SHOULD take place, but the mode MUST be
       applied to the inherited ACL as described in Section 10.7,
       thereby modifying the ACL.

   2.  If just the ACL is given in the call:

       In this case, inheritance SHOULD NOT take place, and the ACL as
       defined in the CREATE or OPEN will be set without modification,
       and the mode modified as in Section 10.8.

   3.  If both mode and ACL are given in the call:

       In this case, inheritance SHOULD NOT take place, and both
       attributes will be set as described in Section 10.9.

   4.  If neither mode nor ACL is given in the call:

       In the case where an object is being created without any initial
       attributes at all, e.g., an OPEN operation with an opentype4 of
       OPEN4_CREATE and a createmode4 of EXCLUSIVE4, inheritance SHOULD
       NOT take place (note that EXCLUSIVE4_1 is a better choice of
       createmode4, since it does permit initial attributes).  Instead,
       the server SHOULD set permissions to deny all access to the newly
       created object.  It is expected that the appropriate client will
       set the desired attributes in a subsequent SETATTR operation, and
       the server SHOULD allow that operation to succeed, regardless of
       what permissions the object is created with.  For example, an
       empty ACL denies all permissions, but the server need to allow
       the owner's SETATTR to succeed even though WRITE_ACL is
       implicitly denied.

       In other cases, inheritance SHOULD take place, and no
       modifications to the ACL will happen.  The mode attribute MUST be
       as computed in Section 10.3, with the MODE4_SUID, MODE4_SGID, and



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       MODE4_SVTX bits clear.  If no inheritable ACEs exist on the
       parent directory, the rules for creating acl, dacl, or sacl
       attributes are implementation defined.  If either the dacl or
       sacl attribute is supported, then the ACL4_DEFAULTED flag SHOULD
       be set on the newly created attributes.

10.11.  Use of Inherited ACL When Creating Objects

   [Author Aside]: The handling of SHOULD in this section is considered
   as part of Consensus Item #63f.

   If the object being created is not a directory, the inherited ACL
   SHOULD NOT inherit ACEs from the parent directory ACL unless the
   ACE4_FILE_INHERIT_ACE flag is set.

   If the object being created is a directory, the inherited ACL is to
   inherit all inheritable ACEs from the parent directory, that is,
   those that have the ACE4_FILE_INHERIT_ACE or
   ACE4_DIRECTORY_INHERIT_ACE flag set.  If the inheritable ACE has
   ACE4_FILE_INHERIT_ACE set but ACE4_DIRECTORY_INHERIT_ACE is clear,
   the inherited ACE on the newly created directory MUST have the
   ACE4_INHERIT_ONLY_ACE flag set to prevent the directory from being
   affected by ACEs meant for non-directories.

   When a new directory is created, the server MAY split any inherited
   ACE that is both inheritable and effective (in other words, that has
   neither ACE4_INHERIT_ONLY_ACE nor ACE4_NO_PROPAGATE_INHERIT_ACE set),
   into two ACEs, one with no inheritance flags and one with
   ACE4_INHERIT_ONLY_ACE set.  (In the case of a dacl or sacl attribute,
   both of those ACEs SHOULD also have the ACE4_INHERITED_ACE flag set.)
   This makes it simpler to modify the effective permissions on the
   directory without modifying the ACE that is to be inherited to the
   new directory's children.

10.12.  Combined Authorization Models for NFSv4.2

   The NFSv4 server implementation requirements described in the
   subsections above apply to NFSv4.2 as well and NFSv4.2 clients can
   assume that the server follows them.

   NFSv4.2 contains an OPTIONAL extension, defined in [RFC8257], which
   is intended to reduce the interference of modes, restricted by the
   umask mechanism, with the acl inheritance mechanism.  The extension
   allows the client to specify the umask separately from the mask
   attribute.






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11.  Other Uses of Access Control Lists

   Whether the Acl or Sacl attributes are used, AUDIT and ALARM ACEs
   provide security-related facilities separate from the file access
   authorization provided by ALLOW and DENY ACEs

   *  AUDIT ACEs provide a means to audit attempts to access a specified
      file by specified sets of principals.

   *  ALARM ACEs provide a means to draw special attention to attempts
      to access specified files by specified sets of principals.

12.  Aclchoice Details

   The structure of Aclchoice attribute is extendible for many of the
   same reasons that the set of NFSv4 attributes is extendible and
   shares many of the same mechanisms including use of an easily
   extended bitmap and a nominally opaque array overlain with a
   disparate set of individual items.  However, these are not exactly
   the same and the following important differences should be noted:

   *  The bitmap4 aca_bits is optimized to represent binary choices and
      has no role in defining the use of the nominally opaque area
      within aca_dpool.

   *  The array acs_ditems does define the individual data items that
      overlay pieces of aca_dpool.

      Because of this structure each individual data item can be located
      without knowing the length of all preceding ones, as is the case
      with fattr4.

12.1.  Provisions for Aclchoice Modification

   The structure of the Aclchoice attribute makes it quite easy to add
   or delete existing flag and data item.  However, to ensure
   interoperability, there are a number of policies set out below,
   derived from [RFC8178], that restrict how necessary changes can be
   done.

   *  New items, whether flags or data item can be done whenever new
      attributes or similar item can be added.  Since all such items are
      OPTIONAL, defaults need to be specified to cover the case in which
      the items in question are not present

      This serves a way to address newly discovered behavioral variants.





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      In addition to allowing this in extensible minor versions, we will
      also allow them during the development of this document.  New
      items will be allowed in successive drafts both before and after
      working group adoption.  However, once the document approaches
      Working Group last call, these will need to cease.

   *  Deletions, as such, will not be allowed.  However, as with
      OPTIONAL attributes, there will be the opportunity to make
      existing flags and data items mandatory-to-not-implement in new
      minor versions, such as, for example NFSv4.3.

   It is desirable ability to allow complicated data items by a set of
   binary choices, when that can be done.  In this case the addition of
   the new flags bits can proceed quickly but the data item to be
   superseded will remain in the protocol until it can be made
   mandatory-to-not-implement in a later minor version.

12.2.  Storing of ACLs which are not Enforced

   The potential ability of servers to accept and store ACEs that they
   are not prepared to enforce requires the server that supports the
   Aclchoice attribute to either:

   *  Set acd_length to zero in acsditems[ACC4IN_STOREUA] to indicate
      that this functionality is never provided.

   *  Set acsditems[ACC4IN_STOREUA] to refer to an acc4storeua (as
      described below) within acs_dpool to describe the non-enforced
      ACEs that they accept.

      Acceptance of ACE4_SYNCHRONIZE is not considered a use of this
      facility, since that is true of that bit in all cases.

   struct acc4storeua {
       uint32_t    asua_types;
       uint32_t    asua_flags;
       ace4mask    asua_mask:
   };

   This structure is to be filled in as described below:

   *  asua_types contain a mask of ACE type that are accepted but not
      enforced.  Each type is represented by a one left-shifted by the
      numeric value of the type.

   *  asua_flags contains a mask of ACE flags accepted but and returned
      on fetched ACLs but not enforced.




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      When both ACE4_FILE_INHERIT_ACE and ACE4_DIRECTORY_INHERIT_ACE are
      set, the is no opportunity to determine potential inheritance so
      specifying any of ACC4BN_IN1BIT, ACC4BN_INHFULL, or ACC4BN_INHAUTO
      as part of the Aclchoice attribute is invalid.

      When one of either ACE4_FILE_INHERIT_ACE or
      ACE4_DIRECTORY_INHERIT_ACE is set inheritance is limited to being
      decided by the bit not included if ACC4BN_IN1BIT is set.  In
      addition specifying either of ACC4BN_INHFULL, or ACC4BN_INHAUTO as
      part of the Aclchoice attribute is invalid

   *  asua_mask contains a set of mask bits that the server is prepared
      to accept and return on fetched ACLs, but have no role in
      authorization and are not considered for the AUDIT and ALARM
      functions.

12.3.  Advice/Recommendations Regarding ACL Choices

   [Consensus Needed (Items #12e, #105v, #117k), For entire section]:

   The Aclchoice allows the clients to be informed about behavioral
   choices the server is allowed to make.  The fact that the server is
   allowed to make these choices and report them does not necessarily
   imply that these choices are valid.  They may be allowed solely
   because they always have been allowed since previous specifications
   chose to be quite lax in these matters.  Also, to correct situations
   in which previous specifications gave servers undue latitude in
   making such choices, some behavior previously not felt to be
   noteworthy is recommended against using "SHOULD" or "SHOULD NOT" with
   the understanding that the valid reasons to bypass the recommendation
   are limited to the reliance on earlier specifications.

   In the table below, we summarize the existing items defined within
   the Aclchoice attribute, including both flags and data items,
   providing summary advice/recommendations regarding their use together
   with some expectations/speculations regarding future development.
   The advice is summarized using the codes listed below.

   Vox  Valid OPTIONAL extension.

      An extension to the core that was allowed to be present or not
      according to previous specifications, without clearly stating
      that.  The absence of the extension was treated as an excusable
      implementation flaw.

   Upx  Valid OPTIONAL extension useful for the support of draft-POSIX
      ACLs.




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      An extension to the core that was allowed to be present or not
      according to previous specifications, without clearly stating
      that.  Although the absence of the extension was treated as an
      excusable implementation flaw, it is useful for supporting draft-
      POSIX ACLs.

   Npx  Valid OPTIONAL extension necessary for the support of draft-
      POSIX ACLs.

      An extension to the core that was allowed to be present or not
      according to previous specifications, without clearly stating
      that.  Although he absence of the extension was treated as an
      excusable implementation flaw, it is necessary for supporting
      draft-POSIX ACLs.

   Vax  Valid absence of an OPTIONAL extension

      A choice to support core functionality without any of a set of
      extensions that were allowed to be present or not according to
      previous specifications.  Only the core functionality is provided
      despite the absence of a clear statement that this was REQUIRED.

   Lux  Valid OPTIONAL extension with limited uses

      Mentioned in passing as acceptable in previous specifications.
      Despite the fact that it should avoided because of its unfortunate
      side-effects, it has some valid use cases.

   Vbc  Valid Behavioral Choice

      An extension to the core that was allowed to be present or not
      according to previous specifications.

   Nbc  Needed Behavioral Choice.

      Whether allowed by previous specifications or not, needed by
      clients to provide needed functionality.

   Dbc  Dubious Behavioral Choice.

      Whether allowed by previous specifications or not, an acknowledged
      behavioral variant for which substantive justification is hard to
      perceive.

   Sbt  Should be True.

      Indicate that setting this false has negative consequences of
      which clients and servers need to be aware.



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   Sbf  Should be false.

      Indicate that setting this true has negative consequences of which
      clients and servers need to be aware.

   Mbc  Miscellaneous behavioral choices.

      Describes a set of matters for which previous specifications gave
      no behavioral guidance allowing a range of server behaviors to be
      chosen.

    +================+======+=========================================+
    | Item           | Adv. | Future Dev.                             |
    +================+======+=========================================+
    | ACC4BN_NEINGM  | Vbc  | Convergence desirable but unlikely.     |
    |                |      | Should work to allow client choice.     |
    +----------------+------+-----------------------------------------+
    | ACC4BN_SEPFWX  | Vox  | Will be guided by client needs          |
    +----------------+------+-----------------------------------------+
    | ACC4BN_SEPAFD  | Vox  | Will be guided by client needs          |
    +----------------+------+-----------------------------------------+
    | ACC4BN_SEPDE   | Vox  | Will be guided by client need           |
    +----------------+------+-----------------------------------------+
    | ACC4BN_RNASDI  | Sbf  | Old approach might or might not be      |
    |                |      | implemented                             |
    +----------------+------+-----------------------------------------+
    | ACC4BN_NAD     | Vox  | Will be guided by client needs          |
    +----------------+------+-----------------------------------------+
    | ACC4BN_RNADMOD | Sbt  | Old approach makes no sense.  Will need |
    |                |      | to look at implementations.             |
    +----------------+------+-----------------------------------------+
    | ACC4BN_MBCA    | Sbf  | Would like to get rid of this when we   |
    |                |      | can.                                    |
    +----------------+------+-----------------------------------------+
    | ACC4BN_SMJUST3 | Sbf  | Might be possible to get rid of this.   |
    +----------------+------+-----------------------------------------+
    | ACC4BN_SMOLD   | Sbf  | Would like to get rid of this but       |
    |                |      | can't.                                  |
    +----------------+------+-----------------------------------------+
    | ACC4BN_SMFULL  | Sbt  | Want to get here.  Would take a while.  |
    +----------------+------+-----------------------------------------+
    | ACC4BN_3MASKB  | Vax  | No changes expected.                    |
    +----------------+------+-----------------------------------------+
    | ACC4BN_AUTHWHO | Vbc  | Might not find any implementations.     |
    +----------------+------+-----------------------------------------+
    | ACC4BN_INNO    | Dbc  | Need more than this level of            |
    |                |      | inheritance to support draft-POSIX ACLs |
    +----------------+------+-----------------------------------------+



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    | ACC4BN_IN1BIT  | Upx  | Need at least this level of inheritance |
    |                |      | to support draft-POSIX ACLs             |
    +----------------+------+-----------------------------------------+
    | ACC4BN_INHFULL | Upx  | Sometimes needed for support of draft-  |
    |                |      | POSIX ACLs.                             |
    +----------------+------+-----------------------------------------+
    | ACC4BN_INHAUTO | Vox  | Not sure any implementations exist.     |
    +----------------+------+-----------------------------------------+
    | ACC4BN_INHDEF  | Npx  | Needed for inheritance within draft-    |
    |                |      | POSIX model.                            |
    +----------------+------+-----------------------------------------+
    | ACC4BN_AACPS   | Upx  | Helpful in providing draft-POSIX ACL    |
    |                |      | authorization semantics.                |
    +----------------+------+-----------------------------------------+
    | ACC4BN_OTHWHO  | Dbc  | Special who values with unclear         |
    |                |      | denotation.                             |
    +----------------+------+-----------------------------------------+
    | ACC4BN_DPWHO   | Vox  | Special who values to deal with         |
    |                |      | reverse-slope modes when DENY ACEs are  |
    |                |      | not supported.                          |
    +----------------+------+-----------------------------------------+
    | ACC4BN_RVINV   | Sbf  | Would like to get rid of these.         |
    +----------------+------+-----------------------------------------+
    | ACC4BN_SVTX    | Vbc  | Should be quite common.  Usable even if |
    |                |      | ACLs not supported.                     |
    +----------------+------+-----------------------------------------+
    | ACC4BN_SVTXOLD | Sbf  | Would like to get rid of these.         |
    +----------------+------+-----------------------------------------+
    | ACC4IN_OWNMB   | Vox  | Expect to be common.  If they are all   |
    |                |      | the same, can get rid of this.          |
    +----------------+------+-----------------------------------------+
    | ACC4IN_ODDMB   | Mbc  | Will try to simplify over time.         |
    +----------------+------+-----------------------------------------+
    | ACC4IN_STOREUA | Lux  | Expect some implementations but have    |
    |                |      | not seen any.                           |
    +----------------+------+-----------------------------------------+

              Table 6: Table of Aclchoice Items (with Advice)

13.  Security Considerations

   There are no Security considerations specific to this document.
   Security considerations for NFSv4 as a whole are dealt with in the
   Security Considerations section of [I-D.dnoveck-nfsv4-security].







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14.  IANA Considerations

   This document requires no actions from IANA>

15.  References

15.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8178]  Noveck, D., "Rules for NFSv4 Extensions and Minor
              Versions", RFC 8178, DOI 10.17487/RFC8178, July 2017,
              <https://www.rfc-editor.org/info/rfc8178>.

   [RFC7530]  Haynes, T., Ed. and D. Noveck, Ed., "Network File System
              (NFS) Version 4 Protocol", RFC 7530, DOI 10.17487/RFC7530,
              March 2015, <https://www.rfc-editor.org/info/rfc7530>.

   [RFC7531]  Haynes, T., Ed. and D. Noveck, Ed., "Network File System
              (NFS) Version 4 External Data Representation Standard
              (XDR) Description", RFC 7531, DOI 10.17487/RFC7531, March
              2015, <https://www.rfc-editor.org/info/rfc7531>.

   [RFC8881]  Noveck, D., Ed. and C. Lever, "Network File System (NFS)
              Version 4 Minor Version 1 Protocol", RFC 8881,
              DOI 10.17487/RFC8881, August 2020,
              <https://www.rfc-editor.org/info/rfc8881>.

   [I-D.ietf-nfsv4-rfc5661bis]
              Noveck, D., "Network File System (NFS) Version 4 Minor
              Version 1 Protocol", Work in Progress, Internet-Draft,
              draft-ietf-nfsv4-rfc5661bis-11, 25 June 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-nfsv4-
              rfc5661bis-11>.










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   [I-D.dnoveck-nfsv4-rfc5662bis]
              Noveck, D., "Network File System (NFS) Version 4 Minor
              Version 1 External Data Representation Standard (XDR)
              Description", Work in Progress, Internet-Draft, draft-
              dnoveck-nfsv4-rfc5662bis-06, 23 May 2025,
              <https://datatracker.ietf.org/doc/html/draft-dnoveck-
              nfsv4-rfc5662bis-06>.

   [I-D.dnoveck-nfsv4-security]
              Noveck, D., "Security for the NFSv4 Protocols", Work in
              Progress, Internet-Draft, draft-dnoveck-nfsv4-security-12,
              16 May 2025, <https://datatracker.ietf.org/doc/html/draft-
              dnoveck-nfsv4-security-12>.

15.2.  Informative References

   [RFC3010]  Shepler, S., Callaghan, B., Robinson, D., Thurlow, R.,
              Beame, C., Eisler, M., and D. Noveck, "NFS version 4
              Protocol", RFC 3010, DOI 10.17487/RFC3010, December 2000,
              <https://www.rfc-editor.org/info/rfc3010>.

   [RFC3530]  Shepler, S., Callaghan, B., Robinson, D., Thurlow, R.,
              Beame, C., Eisler, M., and D. Noveck, "Network File System
              (NFS) version 4 Protocol", RFC 3530, DOI 10.17487/RFC3530,
              April 2003, <https://www.rfc-editor.org/info/rfc3530>.

   [RFC8257]  Bensley, S., Thaler, D., Balasubramanian, P., Eggert, L.,
              and G. Judd, "Data Center TCP (DCTCP): TCP Congestion
              Control for Data Centers", RFC 8257, DOI 10.17487/RFC8257,
              October 2017, <https://www.rfc-editor.org/info/rfc8257>.

   [RFC8276]  Naik, M. and M. Eshel, "File System Extended Attributes in
              NFSv4", RFC 8276, DOI 10.17487/RFC8276, December 2017,
              <https://www.rfc-editor.org/info/rfc8276>.

   [I-D.rmacklem-nfsv4-posix-acls]
              Macklem, R., "POSIX Draft ACL support for Network File
              System Version 4, Minor Version 2", Work in Progress,
              Internet-Draft, draft-rmacklem-nfsv4-posix-acls-12, 12
              June 2025, <https://datatracker.ietf.org/doc/html/draft-
              rmacklem-nfsv4-posix-acls-12>.

   [Grünbacher]
              Grünbacher, A., "POSIX Access Control Lists on Linux",
              USENIX 2003 Annual Technical Conference Proceedings, June
              2003.





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Appendix A.  Issues for which Consensus Needs to be Ascertained

A.1.  List of Issues

   This section helps to keep track of specific changes which the author
   has made or intends to make to deal with ACL-related issues that
   appear in RFCs 7530 and 8881.  The changes listed here exclude those
   which are clearly editorial but includes some that the author
   believes are editorial but for which the issues are sufficiently
   complicated that working group consensus on the issue is probably
   necessary.

   These changes are presented in the table below, organized into a set
   of "Consensus Items" identified by the numeric code appearing in
   annotations in the proposed document text.  For each such item, a
   type code is assigned with separate sets of code define for pending
   items and for those which are no longer pending.

   The following codes are defined for pending consensus items:

   *  "NM" denotes a change which is new material that is not purely
      editorial and thus requires Working Group consensus for eventual
      publication.

   *  "BE" denotes a change which the author believes is editorial but
      for which the change is sufficiently complex that the judgment is
      best confirmed by the Working Group.

   *  "BC" denotes a change which is a substantive change that the
      author believes is correct.  This does not exclude the possibility
      of compatibility issues becoming an issue but is used to indicate
      that the author believes any such issues are unlikely to prevent
      its eventual acceptance.

   *  "CI" denotes a change for which the potential for compatibility
      issues is a major concern with the expected result that working
      group discussion of change will focus on clarifying our knowledge
      of how existing clients and server deal with the issue and how
      they might be affected by the change or the change modified to
      accommodate them.

   *  "NS" denotes a change which represents the author's best effort to
      resolve a difficulty but for which the author is not yet confident
      that it will be adopted in its present form, principally because
      of the possibility of troublesome compatibility issues.






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   *  "NE" denotes change based on an existing issue in the spec but for
      which the replacement text is incomplete and needs further
      elaboration.

   *  "WI" denotes a potential change based on an existing issue in the
      spec but for which replacement text is not yet available because
      further working group input is necessary before drafting.  It is
      expected that replacement text will be available in a later draft
      once that discussion is done.

   *  "LD" denotes a potential change based on an existing issue in the
      spec but for which replacement text is not yet available due to
      the press of time.  It is expected that replacement text will be
      available in a later draft.

   *  "EV" denote a potential change which is tentative or incomplete
      because further details need to be provide or because the author
      is unsure that he has a correct explanation of the issue.  It is
      expected that replacement text will be available in a later draft.

   The following codes are defined for consensus items which are no
   longer pending.

   *  "RT" designates a former item which has been retired, because it
      has been merged with another one or otherwise organized out of
      existence.

      Such items no longer are referred to the document source although
      the item id is never reassigned.  They are no longer counted among
      the set of total items.

   *  "CA" designates a former item for which consensus has been
      achieved in the judgment of the author, although not by any
      official process.

      Items reaching this state are effected in the document source
      including the deletion of annotations and the elimination of
      obsoleted previous treatments.

      Items in this state are still counted among the total of item but
      are no longer considered pending

   *  "CV" designates a former item for which consensus has been
      achieved and formally verified.

      Items in this state are not counted among the item totals.  They
      may be kept in the table but only to indicate that the item id is
      still reserved.



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   *  "DR" designates a former item which has been dropped, because it
      appears that working group acceptance of it, even with some
      modification, is unlikely.

      Such items no longer are referred to the document source although
      the item id is never reassigned.  They are no longer counted among
      the set of total items.

   When asterisk is appended to a state of "NM", "BC" or "BE" it that
   there has been adequate working group discussion leading one to
   reasonably expect it will be adopted, without major change, in a
   subsequent document revision.

   Such general acceptance is not equivalent to a formal working group
   consensus and it not expected to result in major changes to the draft
   document,

   On the other hand, once there is a working group consensus with
   regard to a particular issue, the document will be modified to remove
   associated annotations, with the previously conditional text
   appearing just as other document text does.  The issue will remain in
   this table as a non-pending item.  It will be mentioned in Appendix A
   of [I-D.dnoveck-nfsv4-security], to summarize the changes that have
   been made.

   It is to be expected that these designations will change as
   discussion proceeds and new document versions are published.  It is
   hoped that most such shifts will be upward in the above list or
   result in the deletion of a pending item, by reaching a consensus to
   accept or reject it.  This would enable, once all items are dealt
   with, an eventual request for publication as an RFC, with this
   appendix having been deleted.

   The consensus items in the following table can be divided into three
   groups, based on the associated numeric id.

   *  Those with ids less than 62 were created as part of the security
      document and transferred to this one as part of the document
      split.

   *  Those with ids between 62 and 65 are the result of splitting items
      created as part of the security document that now address issues
      in both documents

   *  Those with id 100 and above were created after the document split.
      In most case, there is no connection to material within the
      security document.




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   +===+====+====================+=====================================+
   |#  |Type| ...References...   | Substance                           |
   +===+====+====================+=====================================+
   |3  |BE  | #3a in S 7.2       | Conversion of mask bit descriptions |
   |   |    |                    | from being about "permissions" to   |
   |   |    |                    | being about the action permitted,   |
   |   |    |                    | denied, or specified as being       |
   |   |    |                    | audited or generating alarms.       |
   +---+----+--------------------+-------------------------------------+
   |4  |CI  | #4a in S 2.3       | Elimination of uses of SHOULD       |
   |   |    |                    | believed inappropriate in the       |
   |   |    | #4c in S 7.2       | descriptions of ACEs and            |
   |   |    |                    | clarification of ongoing use of     |
   |   |    | #4d in S 7.2.1     | SHOULD.                             |
   |   |    |                    |                                     |
   |   |    | #4e in S 7.2.4     |                                     |
   |   |    |                    |                                     |
   |   |    | #4f in S 7.2.5     |                                     |
   |   |    |                    |                                     |
   |   |    | #4g in S 7.3.1     |                                     |
   +---+----+--------------------+-------------------------------------+
   |5  |NE  | #5a in S 7.2       | Changes needed in treatment of      |
   |   |    |                    | ACCESS, including the following:    |
   |   |    | #5b in S 7.2.1     |                                     |
   |   |    |                    | *  ACCESS is listed as an operation |
   |   |    |                    |    in all cases in which one of the |
   |   |    |                    |    bits returned by the operation   |
   |   |    |                    |    could be affected.               |
   |   |    |                    |                                     |
   |   |    |                    | *  There is now explicit indication |
   |   |    |                    |    of which bit(s) returned by      |
   |   |    |                    |    ACCESS might be affected.        |
   |   |    |                    |                                     |
   |   |    |                    | *  There is now a discussion of     |
   |   |    |                    |    differences between the effect   |
   |   |    |                    |    on authorization and that on     |
   |   |    |                    |    other uses of the associated     |
   |   |    |                    |    mask bits for ACEs not connected |
   |   |    |                    |    with authorization.              |
   |   |    |                    |                                     |
   |   |    |                    |    Given the inability of the       |
   |   |    |                    |    server to determine which bits   |
   |   |    |                    |    are being tested by the client,  |
   |   |    |                    |    determining when success or      |
   |   |    |                    |    failure has occurred is          |
   |   |    |                    |    impossible.  As a result it      |
   |   |    |                    |    appears best to given the server |
   |   |    |                    |    freedom, in any particular case, |



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   |   |    |                    |    to decide whether an ACCESS has  |
   |   |    |                    |    succeeded or failed in           |
   |   |    |                    |    determining whether it           |
   |   |    |                    |    constitutes a recordable event.  |
   |   |    |                    |                                     |
   +---+----+--------------------+-------------------------------------+
   |7  |BE  | #7a in S 7.2.1     | Clarification of relationship       |
   |   |    |                    | between READ_DATA and EXECUTE.      |
   |   |    | #7b in S 7.2.4     |                                     |
   +---+----+--------------------+-------------------------------------+
   |8  |CI  | #8a in S 7.2.1     | Revised discussion of relationship  |
   |   |    |                    | between WRITE_DATA and APPEND_DATA. |
   |   |    | #8b in S 7.2.4     |                                     |
   |   |    |                    |                                     |
   |   |    | #8c in S 7.2.5     |                                     |
   +---+----+--------------------+-------------------------------------+
   |9  |CI  | #9a in S 7.2.1     | Clarification of how ADD_DIRECTORY  |
   |   |    |                    | relates to RENAME.                  |
   |   |    | #9b in S 7.2.5     |                                     |
   |   |    |                    | We are assuming that the cross-     |
   |   |    |                    | directory and within-directory      |
   |   |    |                    | cases need to be treated            |
   |   |    |                    | differently.                        |
   +---+----+--------------------+-------------------------------------+
   |10 |WI  | #10a in S 7.2.8    | Possible revisions in handling of   |
   |   |    |                    | the masks WRITE_RETENTION and       |
   |   |    |                    | WRITE_RETENTION_HOLD.               |
   +---+----+--------------------+-------------------------------------+
   |11 |CI  | #11a in S 7.2.8    | Explicit recommendation and         |
   |   |    |                    | requirements for mask granularity,  |
   |   |    |                    | replacing the previous treatment    |
   |   |    |                    | which gave the server license to    |
   |   |    |                    | ignore most of the previous         |
   |   |    |                    | section, placing clients in an      |
   |   |    |                    | unfortunate situation.              |
   +---+----+--------------------+-------------------------------------+
   |12 |BC  | #12a in S 4.6      | Revised treatment of directory      |
   |   |    |                    | entry deletion.                     |
   |   |    | #12b in S 5.6      |                                     |
   |   |    |                    |                                     |
   |   |    | #12c in S 7.2.15   |                                     |
   |   |    |                    |                                     |
   |   |    | #12d in S 7.2.16   |                                     |
   |   |    |                    |                                     |
   |   |    | #12e in S 7.2.16   |                                     |
   +---+----+--------------------+-------------------------------------+
   |13 |BC  | #13a in 7.3        | Attempt to put some reasonable      |
   |   |    |                    | limits on possible non-support (or  |



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   |   |    | #13b in 7.3.1      | variations in the support provided) |
   |   |    |                    | for the ACE flags.  This is to      |
   |   |    | #13c in 7.3.2      | replace a situation in which the    |
   |   |    |                    | client has no real way to deal with |
   |   |    | #13d in 7.3.2.1    | the freedom granted to server       |
   |   |    |                    | implementations.                    |
   +---+----+--------------------+-------------------------------------+
   |14 |BC  | #14a in S 4        | Explicit discussion and use of the  |
   |   |    |                    | case in which aclsupport is not     |
   |   |    | #14b in S 4.5      | supported.                          |
   |   |    |                    |                                     |
   |   |    | #14c in S 6.1      |                                     |
   |   |    |                    |                                     |
   |   |    | #14d in S 6.2      |                                     |
   +---+----+--------------------+-------------------------------------+
   |15 |BC  | #15a in S 4.5      | Handling of the proper relationship |
   |   |    |                    | between support for ALLOW and DENY  |
   |   |    |                    | ACEs.                               |
   +---+----+--------------------+-------------------------------------+
   |16 |NM  | #16a in S 4.4      | Discussion of coherence of acl,     |
   |   |    |                    | sacl, and dacl attributes.          |
   +---+----+--------------------+-------------------------------------+
   |26 |CI  | #26a in S 10.2     | Decide how ACEs with who values     |
   |   |    |                    | other than OWNER@, Group, or        |
   |   |    | #26b in S 10.7.3   | EVERYONE@ are be dealt with when    |
   |   |    |                    | setting mode.                       |
   |   |    | #26c in S 10.7.4   |                                     |
   |   |    |                    |                                     |
   |   |    | #26d in S 10.7.5   |                                     |
   |   |    |                    |                                     |
   |   |    | #26e in S 10.7.6   |                                     |
   +---+----+--------------------+-------------------------------------+
   |27 |CI  | #27a in S 10.2     | Concerns the possible existence of  |
   |   |    |                    | multiple methods of computing a     |
   |   |    | #27b in S 10.3     | mode from an acl that clients can   |
   |   |    |                    | depend on, and the proper           |
   |   |    | #27c in S 10.4     | relationship among these methods.   |
   |   |    |                    |                                     |
   |   |    | #27d in S 10.5     |                                     |
   +---+----+--------------------+-------------------------------------+
   |28 |WI  | #28a in S 10.2     | Decide how to address flags in      |
   |   |    |                    | mapping to/from reverse- slope      |
   |   |    | #28b in S 10.3     | modes.                              |
   |   |    |                    |                                     |
   |   |    | #28 in S 10.7.3    |                                     |
   +---+----+--------------------+-------------------------------------+
   |29 |BC  | #29 in S 10.7.3    | Address the coordination of mode    |
   |   |    |                    | and ACL-based attributes in a       |



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   |   |    |                    | unified way for all minor versions. |
   +---+----+--------------------+-------------------------------------+
   |30 |CI  | #30a in S 10.7.1   | New proposed treatment of setting   |
   |   |    |                    | mode incorporating some             |
   |   |    | #30b in S 10.7.2   | consequences of anticipated         |
   |   |    |                    | decisions regarding other consensus |
   |   |    | #30c in S 10.7.3   | items (#26, #28, #29)               |
   |   |    |                    |                                     |
   |   |    | #30d in S 10.7.4   |                                     |
   |   |    |                    |                                     |
   |   |    | #30e in S 10.7.5   |                                     |
   |   |    |                    |                                     |
   |   |    | #30f in S 10.7.6   |                                     |
   +---+----+--------------------+-------------------------------------+
   |31 |WI  | #31a in S 10.7.3   | Need to deal with mask bits         |
   |   |    |                    | ACE4_READ_ATTRIBUTES,               |
   |   |    |                    | ACE4_WRITE_RETENTION,               |
   |   |    |                    | ACE4_WRITE_RETENTION_HOLD,          |
   |   |    |                    | ACE4_READ_ACL to reflect the        |
   |   |    |                    | semantics of the mode attribute.    |
   +---+----+--------------------+-------------------------------------+
   |50 |BC  | #50a in S 4.6      | Revise handling of "special" who    |
   |   |    |                    | values, making it clear for which   |
   |   |    | #50b in S 7.3.3    | ones "special" is a euphemism for   |
   |   |    |                    | "semantics-challenged".             |
   |   |    | #50c in S 7.3.3.1  |                                     |
   |   |    |                    |                                     |
   |   |    | #50d in S 7.3.3.2  |                                     |
   +---+----+--------------------+-------------------------------------+
   |51 |BC  | #51a in S 7.3.3    | Clarify the handling of the group   |
   |   |    |                    | bit for the special who values.     |
   +---+----+--------------------+-------------------------------------+
   |61 |RT  | #61a in S 4.3      | Proposal to distinguish support for |
   |   |    |                    | UNIX and NFSv4 ACLS, depending on   |
   |   |    | #61b in S 4.5      | the results returned by the         |
   |   |    |                    | Aclsupport attribute.               |
   |   |    | #61c in S 4.8      |                                     |
   |   |    |                    | Modified to be conditional on the   |
   |   |    | #61d in S 6        | absence of Aclchoice attribute      |
   |   |    |                    | because of the need to effectively  |
   |   |    | #61e in S 6.2      | handle hybrids.                     |
   |   |    |                    |                                     |
   |   |    | #61f in S 10.4     | Many previous instances of this     |
   |   |    |                    | item now include Item #105 as well, |
   |   |    | #61g in S 10.5     | since Aclchoice, when supported,    |
   |   |    |                    | replaces the attempt to infer the   |
   |   |    |                    | semantic model based on material    |
   |   |    |                    | available in earlier minor          |



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   |   |    |                    | versions.                           |
   +---+----+--------------------+-------------------------------------+
   |62 |NE  | #62a in S 5.3      | New/revised description of the role |
   |   |    |                    | of the "sticky bit" for             |
   |   |    | #62b in S 7.2.2    | directories, with respect to ACL/   |
   |   |    |                    | ACE handling.                       |
   |   |    |                    |                                     |
   |   |    |                    | Needs to be considered together     |
   |   |    |                    | with Item #6 in the security        |
   |   |    |                    | document proper.                    |
   +---+----+--------------------+-------------------------------------+
   |63 |CI  | #63a in S 10.1     | Revised description of co-          |
   |   |    |                    | ordination of acl and mode          |
   |   |    | #63b in S 10.2     | attributes to apply to NFSv4 as a   |
   |   |    |                    | whole.  While this includes many    |
   |   |    | #63d in S 10.8     | aspects of the shift to be more     |
   |   |    |                    | specific about the co-ordination    |
   |   |    | #63e in S 10.10    | requirements including addressing   |
   |   |    |                    | apparently unmotivated uses of the  |
   |   |    | #63f in S 10.11    | terms "SHOULD" and "SHOULD NOT", it |
   |   |    |                    | excludes some arguably related      |
   |   |    |                    | matters dealt with as Consensus     |
   |   |    |                    | Items #26 and #27.                  |
   |   |    |                    |                                     |
   |   |    |                    | Needs to be considered together     |
   |   |    |                    | with Item #25 in the security       |
   |   |    |                    | document proper.                    |
   +---+----+--------------------+-------------------------------------+
   |64 |WI  | #64a in S 5.1      | Discussion of issues related to the |
   |   |    |                    | scope of the UNIX ACL model and the |
   |   |    |                    | provisions made to handle it.       |
   |   |    |                    |                                     |
   |   |    |                    | Needs to be considered together     |
   |   |    |                    | with Item #56 in the security       |
   |   |    |                    | document proper.                    |
   +---+----+--------------------+-------------------------------------+
   |65 |NS  | #65a 4.4           | Designation of the Acl, Dacl, and   |
   |   |    |                    | Sacl attributes as Experimental in  |
   |   |    | #65b 4.7           | previous specifications even though |
   |   |    |                    | still formally OPTIONAL.            |
   |   |    | #65c 4.8           |                                     |
   |   |    |                    | Note that this is separate from the |
   |   |    |                    | possibility of sufficiently         |
   |   |    |                    | clarifying the description of the   |
   |   |    |                    | acl, dacl, and sacl attributes to   |
   |   |    |                    | make the Experimental designation   |
   |   |    |                    | unnecessary, or providing other     |
   |   |    |                    | means of semantic model discovery,  |



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   |   |    |                    | which will be covered as Item #110. |
   |   |    |                    |                                     |
   |   |    |                    | Needs to be considered together     |
   |   |    |                    | with Item #58 in the security       |
   |   |    |                    | document proper.                    |
   +---+----+--------------------+-------------------------------------+
   |101|NM  | #101a in S 7.2.4   | Inclusion of the action of READLINK |
   |   |    |                    | as authorized by ACE4_READ_DATA     |
   +---+----+--------------------+-------------------------------------+
   |102|NE  | #102a in S 7.2     | Mask bits have to be dealt with     |
   |   |    |                    | that are not simply finer-grained   |
   |   |    | #102b in S 7.2.7   | correlates of one of the three      |
   |   |    |                    | POSIX privilege bits or of          |
   |   |    |                    | ownership.                          |
   +---+----+--------------------+-------------------------------------+
   |103|NM  | #103a in S 7.2     | Classification of masks bits based  |
   |   |    |                    | on relationship to permission bits  |
   |   |    | #103b in S 7.2.5   | and existence of implementations.   |
   +---+----+--------------------+-------------------------------------+
   |104|NE  | #104a in S 1       | Presentation of UNIX ACLs as the    |
   |   |    |                    | basis of the feature, rather than   |
   |   |    | #104b in S 1.2     | the possibly aspirational NFSv4     |
   |   |    |                    | ACLs                                |
   |   |    | #104c in S 3       |                                     |
   |   |    |                    | Includes work to track the possible |
   |   |    | #104d in S 3.2     | deletion of Extension features that |
   |   |    |                    | were never implemented, where the   |
   |   |    | #104e in S 3.3     | WG agrees.                          |
   |   |    |                    |                                     |
   |   |    | #104d in S 3.1     |                                     |
   |   |    |                    |                                     |
   |   |    | #104d in S 3.1     |                                     |
   |   |    |                    |                                     |
   |   |    | #104f in S 3.5     |                                     |
   |   |    |                    |                                     |
   |   |    | #104g in S 5       |                                     |
   |   |    |                    |                                     |
   |   |    | #104h in S 5.4     |                                     |
   |   |    |                    |                                     |
   |   |    | #104i in S 5.1     |                                     |
   +---+----+--------------------+-------------------------------------+
   |105|NE  | #105a in S 1       | Support for discovery of ACL        |
   |   |    |                    | extensions using the Aclchoice      |
   |   |    | #105b in S 1.2     | attribute or by using inference     |
   |   |    |                    | rules, to help in those case in     |
   |   |    | #105c in S 3       | which it is not supported.          |
   |   |    |                    |                                     |
   |   |    | #105d in S 3.2     | Includes necessary restrictions on  |



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   |   |    |                    | server semantics to enable useful   |
   |   |    | #105e in S 3.5     | support to be provide when          |
   |   |    |                    | Aclchoice is not supported (e.g.,   |
   |   |    | #105f in S 4.6     | in NFSv4.0)                         |
   |   |    |                    |                                     |
   |   |    | #105g in S 4.8     | Presumes Item #104 has been         |
   |   |    |                    | implemented as well.                |
   |   |    | #105h in S 5       |                                     |
   |   |    |                    |                                     |
   |   |    | #105i in S 5.1     |                                     |
   |   |    |                    |                                     |
   |   |    | #105j in S 5.4     |                                     |
   |   |    |                    |                                     |
   |   |    | #105k in S 5.5     |                                     |
   |   |    |                    |                                     |
   |   |    | #105l in S 5.6     |                                     |
   |   |    |                    |                                     |
   |   |    | #105m in S 6       |                                     |
   |   |    |                    |                                     |
   |   |    | #105n in S 6.1     |                                     |
   |   |    |                    |                                     |
   |   |    | #105o in S 6.2     |                                     |
   |   |    |                    |                                     |
   |   |    | #105p in S 7.1.2   |                                     |
   |   |    |                    |                                     |
   |   |    | #105q in S 7.1.3   |                                     |
   |   |    |                    |                                     |
   |   |    | #105r in S 7.3.2   |                                     |
   |   |    |                    |                                     |
   |   |    | #105s in S         |                                     |
   |   |    | 7.3.3.1            |                                     |
   |   |    |                    |                                     |
   |   |    | #105t in S 10.3    |                                     |
   |   |    |                    |                                     |
   |   |    | #105u in S 10.7.3  |                                     |
   |   |    |                    |                                     |
   |   |    | #105v in S 12.3    |                                     |
   +---+----+--------------------+-------------------------------------+
   |106|BC  | #106a in S 7.2.4   | More detail about cases in which    |
   |   |    |                    | OPEN is affected by ACE mask bits,  |
   |   |    | #106b in S 7.2.5   | including the dependence on the     |
   |   |    |                    | type of OPEN.                       |
   +---+----+--------------------+-------------------------------------+
   |107|BC  | #107a in S 7.2.4   | More detail about use of            |
   |   |    |                    | ACE4_WRITE_DATA and the dependence  |
   |   |    | #107b in S 7.2.5   | on the support for finer-grained    |
   |   |    |                    | bits in descriptions of ACE mask    |
   |   |    |                    | bits.                               |



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   +---+----+--------------------+-------------------------------------+
   |108|BC  |                    | Distinguish mask bit treatments     |
   |   |    |                    | depending on the type of the        |
   |   |    |                    | objects                             |
   +---+----+--------------------+-------------------------------------+
   |109|BC  |                    | More detail about cases in which    |
   |   |    |                    | RENAME is affected by ACE mask bits |
   |   |    |                    | including the dependence on the     |
   |   |    |                    | directories for which the mask      |
   |   |    |                    | bits, distinguishing the within-    |
   |   |    |                    | directory and cross-directory       |
   |   |    |                    | cases, and dealing appropriately    |
   |   |    |                    | with the rename-over case.          |
   +---+----+--------------------+-------------------------------------+
   |110|NM  | #110a in S 4.5     | Make explicit reference to the ACL  |
   |   |    |                    | semantics provided by the server,   |
   |   |    | #110b in S 4.8     | assuming this can be known somehow, |
   |   |    |                    | rather than by hand-wavily assuming |
   |   |    | #110c in S 6       | that clients will somehow get by.   |
   |   |    |                    |                                     |
   |   |    | #110d in S 6.1     | Assumes that Item #61 or #105 is    |
   |   |    |                    | present or some replacement.        |
   |   |    | #110f in S 10.3    |                                     |
   |   |    |                    |                                     |
   |   |    | #110g in S 10.5    |                                     |
   +---+----+--------------------+-------------------------------------+
   |111|WI  | #111a in S 7.2     | Needs to be considered together     |
   |   |    |                    | with Item #66 in the security       |
   |   |    | #111b in S 7.2.4   | document which deal with parallel   |
   |   |    |                    | issues regarding POSIX-based        |
   |   |    | #111c in S 7.2.5   | authorization.                      |
   |   |    |                    |                                     |
   |   |    | #111d in S 7.2.7   | Addresses more substantively the    |
   |   |    |                    | handling of the mask bits           |
   |   |    |                    | ACE4_{READ,WRITE}_NAMED_ATTRIBUTES. |
   |   |    |                    |                                     |
   |   |    |                    | Part of the eventual necessary      |
   |   |    |                    | resolution, most likely best        |
   |   |    |                    | deferred until we learn about an    |
   |   |    |                    | actual implementation, will need to |
   |   |    |                    | tackle seriously the question of    |
   |   |    |                    | whether ACE4_WRITE_NAMED_ATTRIBUTES |
   |   |    |                    | is somehow a finer-grained variant  |
   |   |    |                    | of the write privilege bits.  While |
   |   |    |                    | this is arguable despite it refers  |
   |   |    |                    | to a different object, the          |
   |   |    |                    | corresponding issue with regard to  |
   |   |    |                    | ACE4_READ_NAMED_ATTRIBUTES is more  |



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   |   |    |                    | troublesome in that it is a finer-  |
   |   |    |                    | grained variant of the or of two    |
   |   |    |                    | privilege bits: R and X.            |
   +---+----+--------------------+-------------------------------------+
   |112|WI  | #112a in S 7.2.8   | Address the validity/utility of     |
   |   |    |                    | ACE4_READ_ATTRIBUTES.  This might   |
   |   |    |                    | be unnecessary, if Aclchoice were   |
   |   |    |                    | implemented, since non-support      |
   |   |    |                    | would be a available as an option   |
   |   |    |                    | likely to be commonly chosen.       |
   +---+----+--------------------+-------------------------------------+
   |113|NE  |                    | Clarify how ACE mask bits defined   |
   |   |    |                    | in Section 7.2.5 are to be dealt    |
   |   |    |                    | with by clients when the server     |
   |   |    |                    | does not support those mask bits,   |
   |   |    |                    | as might be the case when the       |
   |   |    |                    | server supports the UNIX ACL model. |
   +---+----+--------------------+-------------------------------------+
   |114|NM  | #114a in S 1.2     | Clarify the goals of the document   |
   |   |    |                    | as part of the rfc5661bis effort,   |
   |   |    |                    | given that we might be unable to    |
   |   |    |                    | undo the damage created by the      |
   |   |    |                    | earlier approach taken and          |
   |   |    |                    | subsequent decades of neglect.      |
   +---+----+--------------------+-------------------------------------+
   |115|CI  |                    | Create a separate bit, if           |
   |   |    |                    | necessary, to govern the            |
   |   |    |                    | authorization approach used in      |
   |   |    |                    | draft-POSIX ACLs, in which an ACE   |
   |   |    |                    | is not allowed to partially satisfy |
   |   |    |                    | an authorization request.           |
   +---+----+--------------------+-------------------------------------+
   |116|NM  | #116a in S 5.3     | Create behavioral restrictions in   |
   |   |    |                    | the form of residual SHOULDs, to    |
   |   |    |                    | provide ensure proper support for   |
   |   |    |                    | clients when Aclchoice is not       |
   |   |    |                    | available.  The focus will be on    |
   |   |    |                    | UNIX-oriented clients although      |
   |   |    |                    | better support for other clients    |
   |   |    |                    | should be considered.               |
   +---+----+--------------------+-------------------------------------+
   |117|NM  | #117a in Abstr.    | Clearly distinguish the UNIX and    |
   |   |    |                    | draft-POSIX ACL models,             |
   |   |    | #117b in S 1       | distinguishing clearly those        |
   |   |    |                    | elements of the latter that are     |
   |   |    | #117c in S 1.2     | allowed behavioral variants with    |
   |   |    |                    | the NFSv4 ACL model and those that  |
   |   |    | #117d in S 1.3     | cannot be made so within the        |



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   |   |    |                    | context of this respecification     |
   |   |    | #117e in S 3.2     | effort.  the core UNIX model        |
   |   |    |                    |                                     |
   |   |    | #117f in S 3.4     |                                     |
   |   |    |                    |                                     |
   |   |    | #117g in S 3.6     |                                     |
   |   |    |                    |                                     |
   |   |    | #117h in S 5.1     |                                     |
   |   |    |                    |                                     |
   |   |    | #117i in S 5.2     |                                     |
   |   |    |                    |                                     |
   |   |    | #117j in S         |                                     |
   |   |    | 7.3.3.1            |                                     |
   |   |    |                    |                                     |
   |   |    | #117k in S 12.3    |                                     |
   +---+----+--------------------+-------------------------------------+
   |118|NM  | #118a in S 4.1.3   | Clarify issues related to proper    |
   |   |    |                    | denotation of the absence of ACLs   |
   |   |    | #118b in S 4.4     | when interrogating or setting ACL-  |
   |   |    |                    | related attributes.                 |
   |   |    | #118c in S 4.7     |                                     |
   |   |    |                    | The current proposal is to use      |
   |   |    | #118d in S 4.8     | empty ace arrays.  It is possible   |
   |   |    |                    | that this approach will result in   |
   |   |    |                    | controversy.                        |
   |   |    |                    |                                     |
   |   |    |                    | Regardless of that choice, this     |
   |   |    |                    | issue needs to be addressed         |
   |   |    |                    | somehow.                            |
   +---+----+--------------------+-------------------------------------+

                                  Table 7

   The following table summarizes the issues in each particular state.

















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                +==============+=====+====================+
                | Type         | Cnt | Detail             |
                +==============+=====+====================+
                | BC           | 11  | 12, 13, 14, 15     |
                |              |     |                    |
                |              |     | 29, 50, 51         |
                |              |     |                    |
                |              |     | 106, 107, 108, 108 |
                +--------------+-----+--------------------+
                | BE           | 2   | 3, 7               |
                +--------------+-----+--------------------+
                | CI           | 9   | 4, 8, 9, 11        |
                |              |     |                    |
                |              |     | 26, 27, 30, 63     |
                |              |     |                    |
                |              |     | 115                |
                +--------------+-----+--------------------+
                | NE           | 6   | 5, 62, 102, 104    |
                |              |     |                    |
                |              |     | 105, 113           |
                +--------------+-----+--------------------+
                | NM           | 8   | 16, 101, 103, 110  |
                |              |     |                    |
                |              |     | 114, 116, 117, 118 |
                +--------------+-----+--------------------+
                | NS           | 1   | 65                 |
                +--------------+-----+--------------------+
                | WI           | 6   | 10, 28, 31, 64     |
                |              |     |                    |
                |              |     | 111, 112           |
                +--------------+-----+--------------------+
                | Non-terminal | 43  | BC, BE, CI, NE     |
                |              |     |                    |
                |              |     | NM, NS, WS         |
                +--------------+-----+--------------------+
                | RT           | 1   | 61                 |
                +--------------+-----+--------------------+
                | Terminal     | 1   | RT                 |
                +--------------+-----+--------------------+
                | All          | 44  | Grand total for    |
                |              |     | above table.       |
                +--------------+-----+--------------------+

                                  Table 8







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A.2.  Issue Changes

A.2.1.  Issue Changes Until Acls-01

   When the acls document was split form the overall security document
   the Consensus items related to ACLs were moved over, with their
   original item number from that document to this.  In addition, five
   items that affected text in both documents were split and had new
   item numbers assigned for the acl-related portion of the item.

   In addition, as a result of work to make server semantics more
   visible to the client, a substantial number of new issues, with item
   numbers over one hundred were added.

   As a result, there were forty unresolved Consensus items in acls-01.

A.2.2.  Issue Changes In Acls-02

   As a result of a review of existing consensus items the following
   changes were made:

   *  Items #100 and #111 were merged.

   *  A new Item #114 was created.  It deals with document goals.

   *  A new Item #115 was created.  It deals with the partial-
      authorization-prohibition in the semantics of draft-POSIX ACLs.

   *  A new Item #116 was created.  It deals with possible server
      behavior restrictions to ensure proper support to clients.

   *  A new Item #117 was created.  It deals with better handling of the
      draft-POSIX ACL model

   As a result, there are now forty-two unresolved Consensus items in
   acls-02.

A.2.3.  Issue Changes In Acls-05

   As a result of changes made in acl-05:

   *  The substance of item #117 was changed as it became clear that the
      issues previously associated with it could not be addressed as
      part of the respecification effort.

      Nevertheless, the new version of the item addresses the same gaps
      in the original specifications and is suitably treated as a
      replacement.



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   *  A new item, #118, was added to deal with the representation of the
      absence of an acl as a value of an ACL-related attribute.

   As a result, there are now forty-three unresolved Consensus items in
   acls-05.

A.3.  Issue Priorities

   As a result of the history of this document, there are two important
   classes of issues that should be dealt with expeditiously to allow us
   to make progress on this document and complete the rfc5661bis effort,
   despite the plethora of problems in the specification of ACL in
   exiting standard-track documents.

   *  There a large set of issues whose discussion is now long overdue,
      as a result of lack of working group discussion of the issues
      raised by the existing approach to specification of this feature.

      Thirteen of these issues listed in Table 9 should be non-
      controversial making it desirable we get these out of the way in
      order to focus on more difficult matters.

   *  Another set of important issues are of more recent origin and
      reflect the important need, previously unaddressed, is to
      recognize OPTIONAL features and behavioral variants and make these
      choices accessible to clients.

      Eight of these issues listed in Table 10 need to be prioritized so
      that the working group has a clearly understood shared
      understanding of the general approach being taken towards ACLs.

    +======+==========================================================+
    | Item | Discussion                                               |
    +======+==========================================================+
    | 4    | Resolving cases in which SHOULD is used inappropriately. |
    |      |                                                          |
    |      | Most or all of these are cases in which the definition   |
    |      | in [RFC2119] is not adhered to.                          |
    |      |                                                          |
    |      | Might be some controversy about the replacement in       |
    |      | specific cases, but we need to isolate any disagreements |
    |      | so that we can focus on resolving them.                  |
    +------+----------------------------------------------------------+
    | 7    | Clarification of READ vs. Execute.                       |
    |      |                                                          |
    |      | Believe this is editorial and expect the working group   |
    |      | to agree.                                                |
    +------+----------------------------------------------------------+



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    | 8    | Clarification of Write vs, Append                        |
    |      |                                                          |
    |      | The previous concern about possible compatible issues is |
    |      | no longer relevant since there is an Aclchoice flag for  |
    |      | this, so that all previously valid approaches remain     |
    |      | valid.                                                   |
    +------+----------------------------------------------------------+
    | 14   | Deals with the case of Aclsupport not being supported.   |
    |      |                                                          |
    |      | Fixing this gap should be uncontroversial.               |
    +------+----------------------------------------------------------+
    | 15   | Fix relationship of support for ALLOW and SENY.          |
    |      |                                                          |
    |      | What is there is clearly bogus.  Can be sure my          |
    |      | replacement is better but there may people who want      |
    |      | something else.                                          |
    +------+----------------------------------------------------------+
    | 16   | Coherence requirements for acl, sacl, dacl.              |
    |      |                                                          |
    |      | Although this is new material, it is unlikely to         |
    |      | generate controversy.  I think the new text merely       |
    |      | clarifies existing expectations                          |
    +------+----------------------------------------------------------+
    | 27   | Multiple methods of computing mode.                      |
    |      |                                                          |
    |      | There is likely to be controversy about details but it   |
    |      | seems that a least two methods will be required,         |
    |      | especially since the protocol has been that way from the |
    |      | beginning.                                               |
    +------+----------------------------------------------------------+
    | 29   | Making sure that the co-ordination requirements for      |
    |      | modes and ACLs apply to all minor versions.              |
    |      |                                                          |
    |      | There is some text that suggests otherwise but if the    |
    |      | same requirements do not hold, it is hard to see what    |
    |      | can be said or how clients could be asked to deal with   |
    |      | the resulting vacuum.                                    |
    +------+----------------------------------------------------------+
    | 30   | New proposed treatment of setting mode incorporating     |
    |      | some consequences of anticipated decisions regarding     |
    |      | other consensus items (#26, #28, #29)                    |
    |      |                                                          |
    |      | There might be objections and this could change but the  |
    |      | existing confusion cannot continue as it has.            |
    +------+----------------------------------------------------------+
    | 50   | Handling of special "who" values.                        |
    |      |                                                          |
    |      | Expect a big yawn and difficulty getting comments but    |



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    |      | controversy is unlikely.                                 |
    +------+----------------------------------------------------------+
    | 51   | Clarify the handling of the group bit for the special    |
    |      | who values.                                              |
    |      |                                                          |
    |      | Need to resolved somehow.                                |
    +------+----------------------------------------------------------+
    | 101  | Inclusion of the action of READLINK as authorized by     |
    |      | ACE4_READ_DATA                                           |
    |      |                                                          |
    |      | Can't imagine any controversy about this.                |
    +------+----------------------------------------------------------+

            Table 9: Issues For Which Resolution is Long Overdue

     +======+========================================================+
     | Item | Discussion                                             |
     +======+========================================================+
     | 64   | Clarification of the role, scope, and handling of the  |
     |      | UNIX ACL model.                                        |
     |      |                                                        |
     |      | It is important to be clear about this because the     |
     |      | existing specs, while making great efforts to allow    |
     |      | use of this model, are very unclear about the scope of |
     |      | that model or the range of behaviors to be supported.  |
     |      |                                                        |
     |      | The decision of make this model the required core of   |
     |      | supported has raised the importance of this issue.     |
     +------+--------------------------------------------------------+
     | 102  | Handling of orphan mask bits.                          |
     |      |                                                        |
     |      | Discussion may turn up some useful suggestions.  In    |
     |      | any case, the working group has to make decisions      |
     |      | about each of these as was not done when they entered  |
     |      | the protocol in RFC3010.                               |
     +------+--------------------------------------------------------+
     | 104  | UNIX ACLs as basic.                                    |
     |      |                                                        |
     |      | Might be controversial but the issue needs to be       |
     |      | discussed regardless.                                  |
     +------+--------------------------------------------------------+
     | 105  | Aclchoice attribute.                                   |
     |      |                                                        |
     |      | Expect a lot of controversy, but the inability of      |
     |      | clients to determine the presence of extensions needs  |
     |      | to be addressed somehow.                               |
     +------+--------------------------------------------------------+
     | 109  | More detail about cases in which RENAME is affected by |



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     |      | ACE mask bits including the dependence on the          |
     |      | directories for which the mask bits, distinguishing    |
     |      | the within-directory and cross-directory cases, and    |
     |      | dealing appropriately with the rename-over case.       |
     |      |                                                        |
     |      | Can't see what would be controversial here.            |
     |      | Nevertheless, working group feedback is expected to be |
     |      | helpful.                                               |
     +------+--------------------------------------------------------+
     | 110  | Make explicit reference to the ACL semantics provided  |
     |      | by the server, assuming this can be known somehow,     |
     |      | rather than by hand-wavily assuming that clients will  |
     |      | somehow get by.                                        |
     |      |                                                        |
     |      | Could be a shock for some but the issue needs to be    |
     |      | clearly understood and a decision made.                |
     +------+--------------------------------------------------------+
     | 113  | Clarify how ACE mask bits defined in Section 7.2.5 are |
     |      | to be dealt with by clients when the server does not   |
     |      | support those mask bits, as might be the case when he  |
     |      | server supports the UNIX ACL model.                    |
     |      |                                                        |
     |      | Don't expect much controversy on this.                 |
     +------+--------------------------------------------------------+
     | 114  | Clarify the goals of the document as part of the       |
     |      | rfc5661bis effort, given that we might be unable to    |
     |      | undo the damage created by the earlier approach taken  |
     |      | and subsequent decades of neglect.                     |
     |      |                                                        |
     |      | Expect controversy which is precisely why we need to   |
     |      | have this discussion instead of putting it off         |
     |      | repeatedly.                                            |
     +------+--------------------------------------------------------+
     | 117  | Make changes to better describe the needs relating to  |
     |      | the support of draft-POSIX ACLs.                       |
     |      |                                                        |
     |      | The scope of these changes has changed recently do     |
     |      | that the needs cannot be addressed as part of the      |
     |      | respecification effort.                                |
     |      |                                                        |
     |      | Expect this discussion to focus other ways of          |
     |      | addressing draft-POSIX ACL support in NFv4.2           |
     |      | extensions, as discussed in Appendix C.  Those matters |
     |      | are not part of this consensus item, however.          |
     +------+--------------------------------------------------------+
     | 118  | Make changes to clearly describe how the absence of an |
     |      | ACL is represented when interrogating an ACL-related   |
     |      | attribute or when setting one in order to delete an    |



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     |      | ACL.                                                   |
     |      |                                                        |
     |      | There might be controversy about the proper form but   |
     |      | we need to be clear that there is such a form,         |
     |      | particularly to allow the future support of multiple   |
     |      | ACL models.                                            |
     +------+--------------------------------------------------------+

      Table 10: Issues that need to be addressed soon to set direction

Appendix B.  Prospective Aclchoice Changes

B.1.  Possible Simplifications

   Simplification  of following items is likely to be necessary:

   *  The handling of ACC4IN_ODDMB could be simplified once we had more
      information on the actual range of behavioral variation shown by
      existing server implementations.

   *  There are a number of ACE mask bits that look likely to be deleted
      at some point.  These include ACE4_READ_ATTRIBUTES and others for
      which no server implementation has been brought to the working
      group's attention.

      To delete these it would be necessary to make an assessment of
      client need leading to a Consensus.

   Work on these two areas is likely to be mutually reinforcing since
   the a reduction in the number of attributes to be reported within
   ODDMB will make it easier to classify the implementations of the
   rest.  After all, in the likely event that some of these bits have
   only a signed server implementation, there is no possibility of
   behavioral variants.

B.2.  Possible Additions

   Excluding those connected with Aclchoice simplification, there are
   two likely sources of potential additions in subsequent drafts and
   minor versions:

   *  Discovery of new behavioral variants in existing server
      implementations.

      While it could be argued that many of these are instance of
      flawed, non-compliant implementations, the general tenor of
      existing specifications may make it difficult to put existing
      implementations outside the set of acceptable choices.



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      In view of the need to accommodate file system implementations
      with widely varying heritages, the most likely way of dealing with
      divergent implementations is to treat them as behavioral variants
      and deal with the groups advice/recommendations in Section 12.3.

   *  The potential need for finer authorization granularity.

      Although there is a need for removal of granularity overshoot,
      there may be need for additional granularity to deal with new
      functionality such as extended attributes

Appendix C.  Future Handling of Draft POSIX ACLs

   Because of the large semantic differences between the NFSv4 and
   draft-POSIX ACL models, the use of mapping between these two models
   needs substantial supplementation in order to:

   (A)  Support ACL inheritance using the default ACL model.

   (B)  Make it clear that, when both are supported, which authorization
        model a given ACL requires.

   (C)  Provide the ability to specify the mask which is often needed in
        many draft-POSIX ACLs.

   The following ways of accomplishing these ends have been considered:

   *  Defining new ACE types to address (B) and (C) while addressing (A)
      by defining a new default-dacl attribute.

      This would have the advantage of expanding the NFsv4 model to
      include the draft-POSIX model as a sub-model and enabling the
      default ACL approach to inheritance to be used more widely.

   *  Defining separate access-acl and default-acl attributes, oriented
      to the existing structure of draft-POSIX ACLs as described in
      [Grünbacher].  Such an approach is described in
      [I-D.rmacklem-nfsv4-posix-acls].

      This has the advantage of being more comprehensible and usable to
      those that have experience with draft-POSIX ACLs, whether locally
      or via a sideband protocol associated with NFSsv3

Appendix D.  Possible Future Extensions

   There are a number of likely extensions that might need to be
   considered in a later minor version.




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   These include the possible Addition of ACE mask bits controlling the
   authorization of the interrogation and modification of extended
   attributes, as discussed in Appendix D.1.

D.1.  Finer-grained Authorization Support For Extended Attributes

   Currently, authorization for the modification or interrogation of
   extended attributes, is handled in a coarse-grained fashion:

   *  Authorization of the modification of these attributes is
      controlled by the write permission bit if there is no ACL.

      When there is an ACL, authorization is controlled by a single ACE
      mask bit: ACE4_ADD_FILE in the case of directories and
      ACE_WRITE_DATA in the case of other types of objects.

   *  Authorization of the interrogation of these attributes is
      controlled by either read permission bit or the execute permission
      bit if there is no ACL.

      When there is an ACL, authorization is controlled by a the
      allowance associated with the or of two ACE mask bits.

      The first is ACE4_LIST_DIRECTORY in the case of directories and
      ACE_WRITE_DATA in the case of other types of objects.

      The second is ACE4_EXECUTE.

   It needs to be considered whether it is worthwhile to provide finer-
   grained authorization in a fashion similar to the way in which
   reading and writing of named attributes is controlled, i.e., with
   separate ACE mask bits ACE4_READ_NAMED_ATTRIBUTES and
   ACE4_WRITE_NAMED_ATTRIBUTES.

   It is worth noting that the current situation is inconsistent in that
   [RFC8276] defines extensions to ACCESS "to provide fine-grained
   access control to query or modify extended attributes", there are no
   fine-grained ways to control how these bits are set.

   The following possibilities need to be considered:

   *  Creation of new mask bits ACE4_READ_XATTR and ACE4_WRITE_XATTR
      parallelling ACE4_READ_NAMED_ATTRIBUTES and
      ACE4_WRITE_NAMED_ATTRIBUTES with similar mappings when not
      supported.

   *  Creation of new mask bits ACE4_READ_XATTR, ACE4_WRITE_XATTR, and
      ACE4_LIST_XATTR matching the set of new ACCESS bits.



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D.2.  Client Choice Regarding Mode Display

   While the existing handling of this issue make this a matter of
   server choice, it is really not clear why the server's choices have
   any relevance here.

   When a file has an ACL, it controls file authorization and the mode's
   role is limited to providing a value for display.  Given this fact,
   it is unclear why the server's preferences in the matter have any
   real relevance and that, since this does not have any effect on what
   other clients see, the choice of what to do for display is not up to
   the requesting client.

   If the client continues to interrogate the mode attribute there is no
   way to avoid the server's preferences in this becoming controlling,
   for no good reason.

   A new read-only per-object attribute which we will call modeinfo
   could provide separate information regarding the permissions of named
   user and groups, allowing the actual reported to the client-side API
   a mater of client choice, as it should be.

Acknowledgments

   The author wishes to thank Tom Haynes for his helpful suggestion to
   deal with security for all NFSv4 minor versions in the same document.
   The benefits of this approach have been even more apparent in dealing
   with the issues associated with ACL description.

   The author wishes to thank Bruce Fields for his helpful comments
   regarding ACL support which had a major role in the evolution of this
   document.

   The author wishes to thank Rick Macklem, Trond Myklebust, and Chuck
   Lever for their help in clarifying and addressing issues relating to
   POSIX ACL support.

RFC Editor Notes

   [RFC Editor: please remove this section prior to publishing this
   document as an RFC]

   [RFC Editor: prior to publishing this document as an RFC, please
   replace all occurrences of RFCTBD10 with RFCxxxx where xxxx is the
   RFC number of this document]






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   [RFC Editor: prior to publishing this document as an RFC, please
   replace all occurrences of RFCTBD20 with RFCyyyy where yyyy is the
   RFC number of the document providing an overall description of NFSv4
   security, currently expected to result from completion of the
   document referenced in [I-D.dnoveck-nfsv4-security] or a document
   replacing that one.

Author's Address

   David Noveck (editor)
   NetApp
   201 Jones Road, Suite 16
   Waltham, MA 02451
   United States of America
   Phone: +1-781-572-8038
   Email: davenoveck@gmail.com



































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