Allowing inheritable NFSv4 ACLs to override the umask
draft-ietf-nfsv4-umask-01

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Last updated 2016-09-30
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NFSv4                                                          J. Fields
Internet-Draft                                            A. Gruenbacher
Intended status: Informational                                   Red Hat
Expires: April 3, 2017                                September 30, 2016

         Allowing inheritable NFSv4 ACLs to override the umask
                       draft-ietf-nfsv4-umask-01

Abstract

   In some environments, inheritable NFSv4 ACLs can be rendered
   ineffective by the application of the per-process umask.  This is
   easily worked around by transmitting the umask and create mode
   separately, to allow servers to make more intelligent decisions about
   the new mode of a file.

Status of This Memo

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   This Internet-Draft will expire on April 3, 2017.

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Table of Contents

   1.  Conventions Used in This Document . . . . . . . . . . . . . .   2
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   2
   3.  mode_umask Attribute  . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Conventions Used in This Document

   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 described in [RFC2119].

2.  Problem Statement

   On Unix-like systems, each process is associated with a file mode
   creation mask (umask).  In the absence of inheritable permissions,
   the umask specifies which permissions must be turned off when
   creating new file system objects.  With "POSIX" Access Control Lists
   [POSIX-1003.1e], in the presence of inheritable permissions, the
   umask must be ignored.  Other Access Control List implementations on
   Unix-like systems may ignore the umask in a similar way.

   The NFSv4 protocol currently does not include the umask concept;
   applying the umask is left to clients.  Unfortunately, clients have
   no way of atomically checking for inheritable permissions and
   applying the umask only when necessary.  Instead, they err on the
   safe side and always apply the umask.  Thus the mode the server
   receives in an OPEN already has the umask applied.

   When applying the mode, section 6.4.1.1 of [RFC7530] recommends that
   servers SHOULD restrict permissions granted to any user or group
   named in the ACL to be no more than the permissions granted by the
   MODE4_RGRP, MODE4_WGRP, and MODE4_XGRP bits.  Servers aiming to
   provide clients with Unix-like chmod behavior may also be motivated
   by the same requirements in [SUSv4].  (See the discussion of
   additional and alternate access control mechanisms in section "4.4
   File Permissions".)

   On many existing installations, all ordinary users by default use the
   same effective group ID.  To prevent granting all users full access
   to each other's files, such installations usually default to a umask
   with very restrictive permissions.  Thus the named users and groups
   in an inherited ACL end up being mostly ignored.

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   This leads to file permissions which are more restrictive than they
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