draft-ietf-nfsv4-umask-03.txt   draft-ietf-nfsv4-umask-04.txt 
NFSv4 J. Fields NFSv4 J. Fields
Internet-Draft A. Gruenbacher Internet-Draft A. Gruenbacher
Intended status: Standards Track Red Hat Intended status: Standards Track Red Hat
Expires: September 4, 2017 March 03, 2017 Expires: January 21, 2018 July 20, 2017
Allowing Inheritable NFSv4 ACLs to Override the Umask Allowing Inheritable NFSv4 Access Control Entries to Override the Umask
draft-ietf-nfsv4-umask-03 draft-ietf-nfsv4-umask-04
Abstract Abstract
In many important environments, inheritable NFSv4 ACLs can be In many environments, inheritable NFSv4 Access Control Entries (ACEs)
rendered ineffective by the application of the per-process umask. can be rendered ineffective by the application of the per-process
This can be addressed by transmitting the umask and create mode as umask. This can be addressed by transmitting the umask and create
separate pieces of data, allowing the server to make more intelligent mode as separate pieces of data, allowing the server to make more
decisions about the permissions to set on new files. This document intelligent decisions about the permissions to set on new files.
proposes a protocol extension which accomplishes that. This document proposes a protocol extension which accomplishes that.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 4, 2017. This Internet-Draft will expire on January 21, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 17 skipping to change at page 2, line 17
Table of Contents Table of Contents
1. Conventions Used in This Document . . . . . . . . . . . . . . 2 1. Conventions Used in This Document . . . . . . . . . . . . . . 2
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 2 2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 2
3. Protocol Extension Considerations . . . . . . . . . . . . . . 3 3. Protocol Extension Considerations . . . . . . . . . . . . . . 3
4. mode_umask Attribute . . . . . . . . . . . . . . . . . . . . 3 4. mode_umask Attribute . . . . . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5 7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 6 7.2. Informative References . . . . . . . . . . . . . . . . . 5
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 6 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Conventions Used in This Document 1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Problem Statement 2. Problem Statement
On Unix-like systems, each process is associated with a file mode On Unix-like systems, each process is associated with a file mode
creation mask (umask), which specifies which permissions must be creation mask (umask), which specifies which permissions must be
turned off when creating new file system objects. turned off when creating new file system objects.
When applying the mode, section 6.4.1.1 of [RFC7530] recommends that When applying the mode, section 6.4.1.1 of [RFC7530] recommends that
servers SHOULD restrict permissions granted to any user or group servers SHOULD restrict permissions granted to any user or group
named in the ACL to be no more than the permissions granted by the named in the Access Control List (ACL) to be no more than the
MODE4_RGRP, MODE4_WGRP, and MODE4_XGRP bits. Servers aiming to permissions granted by the MODE4_RGRP, MODE4_WGRP, and MODE4_XGRP
provide clients with Unix-like chmod behavior may also be motivated bits. Servers aiming to provide clients with Unix-like chmod
by the same requirements in [SUSv4]. (See the discussion of behavior may also be motivated by the same requirements in [SUSv4].
additional and alternate access control mechanisms in section "4.4 (See the discussion of additional and alternate access control
File Permissions" of that document.) mechanisms in section "4.4 File Permissions" of that document.)
On many existing installations, all ordinary users by default use the On many existing installations, all ordinary users by default use the
same effective group ID. To prevent granting all users full access same effective group ID. To prevent granting all users full access
to each other's files, such installations usually default to a umask to each other's files, such installations usually default to a umask
with very restrictive permissions. As a result, inherited ACEs with very restrictive permissions. As a result, inherited ACL
describing the permissions to be granted to named users and groups entries (inheritable ACEs) describing the permissions to be granted
are often ignored. This makes inheritable ACLs useless in some to named users and groups are often ignored. This makes inheritable
common cases. ACEs useless in some common cases.
Linux solves this problem on local filesystems by ignoring the umask Linux solves this problem on local filesystems by ignoring the umask
in the case the parent of the newly-created file has inheritable in the case the parent of the newly-created file has inheritable
ACEs; see [LinuxACL]. ACEs; see [LinuxACL].
The same solution should work for NFS. However, the NFSv4 protocol The same solution should work for NFS. However, the NFSv4 protocol
does not currently give the client a way to transmit the umask of the does not currently give the client a way to transmit the umask of the
process opening a file. And clients have no way of atomically process opening a file. And clients have no way of atomically
checking for inheritable permissions and applying the umask only when checking for inheritable permissions and applying the umask only when
necessary. As a result, the server receives an OPEN with a mode necessary. As a result, the server receives an OPEN with a mode
attribute that already has the umask applied. attribute that already has the umask applied.
This document solves the problem by defining a new attribute which This document solves the problem by defining a new attribute which
allows the client to transmit umask and the mode specified at file allows the client to transmit umask and the mode specified at file
creation separately, allowing the client to ignore the umask in the creation separately, allowing the client to ignore the umask in the
presence of inheritable ACLs. At least in the Linux case, this presence of inheritable ACEs. At least in the Linux case, this
allows NFSv4 to provide the same semantics available using local allows NFSv4 to provide the same semantics available using local
access. access.
3. Protocol Extension Considerations 3. Protocol Extension Considerations
This document presents an extension to minor version 2 of the NFSv4 This document presents an extension to minor version 2 of the NFSv4
protocol as described in [nfsv4-versioning]. It describes a new protocol as described in [nfsv4-versioning]. It describes a new
OPTIONAL feature. NFSv4.2 servers and clients implemented without OPTIONAL feature. NFSv4.2 servers and clients implemented without
knowledge of this extension will continue to interoperate with knowledge of this extension will continue to interoperate with
clients and servers that are aware of the extension (whether they clients and servers that are aware of the extension (whether they
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the mode MUST be turned off which are set in the umask; the mode the mode MUST be turned off which are set in the umask; the mode
assigned to the new object becomes (mu_mode & ~mu_umask) instead. assigned to the new object becomes (mu_mode & ~mu_umask) instead.
5. Security Considerations 5. Security Considerations
The mode_umask attribute shifts to the server the decision about when The mode_umask attribute shifts to the server the decision about when
to apply the umask. Because the server MUST apply the umask if there to apply the umask. Because the server MUST apply the umask if there
are no inheritable permissions, the traditional semantics are are no inheritable permissions, the traditional semantics are
preserved in the absence of a permission inheritance mechanism. The preserved in the absence of a permission inheritance mechanism. The
only relaxation of permissions comes in the case servers follow the only relaxation of permissions comes in the case servers follow the
RECOMMENDATION that they ignore the umask in the presence of recommendation that they ignore the umask in the presence of
inheritable permissions. inheritable permissions.
The practice of ignoring the umask when there are inheritable The practice of ignoring the umask when there are inheritable
permissions in the form of a "POSIX" default ACL is of long standing permissions in the form of a "POSIX" default ACL is of long standing
and has not given rise to security issues. The "POSIX" default ACL and has not given rise to security issues. The "POSIX" default ACL
mechanism and the mechanism for permission inheritance in NFSv4 are mechanism and the mechanism for permission inheritance in NFSv4 are
equivalent from a security perspective. equivalent from a security perspective.
6. IANA Considerations 6. IANA Considerations
This document does not require any actions by IANA. This document does not require any actions by IANA.
7. References 7. References
7.1. Normative References 7.1. Normative References
[LEGAL] IETF Trust, "Legal Provisions Relating to IETF Documents",
November 2008, <http://trustee.ietf.org/docs/
IETF-Trust-License-Policy.pdf>.
[nfsv4-versioning] [nfsv4-versioning]
Noveck, D., "Rules for NFSv4 Extensions and Minor Noveck, D., "Rules for NFSv4 Extensions and Minor
Versions", draft-ietf-nfsv4-versioning-08 (work in Versions", draft-ietf-nfsv4-versioning-08 (work in
progress), December 2016. progress), December 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", March 1997. Requirement Levels", March 1997.
[RFC4506] Eisler, M., "XDR: External Data Representation Standard",
STD 67, RFC 4506, May 2006.
[RFC5661] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
"Network File System (NFS) Version 4 Minor Version 1
Protocol", RFC 5661, January 2010.
[RFC5662] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
"Network File System (NFS) Version 4 Minor Version 1
External Data Representation Standard (XDR) Description",
RFC 5662, January 2010.
[RFC7530] Haynes, T. and D. Noveck, "Network File System (NFS) [RFC7530] Haynes, T. and D. Noveck, "Network File System (NFS)
version 4 Protocol", RFC 7530, March 2015. version 4 Protocol", RFC 7530, March 2015.
[RFC7862] Haynes, T., "Network File System (NFS) Version 4 Minor [RFC7862] Haynes, T., "Network File System (NFS) Version 4 Minor
Version 2 Protocol", RFC 7862, November 2016. Version 2 Protocol", RFC 7862, November 2016.
[RFC7863] Haynes, T., "Network File System (NFS) Version 4 Minor [RFC7863] Haynes, T., "Network File System (NFS) Version 4 Minor
Version 2 External Data Representation Standard (XDR) Version 2 External Data Representation Standard (XDR)
Description", RFC 7863, November 2016. Description", RFC 7863, November 2016.
[SUSv4] The Open Group, "Single UNIX Specification Version 4",
2013.
7.2. Informative References 7.2. Informative References
[LinuxACL] [LinuxACL]
Gruenbacher, A., "ACL(5) - Access Control Lists", Linux Gruenbacher, A., "ACL(5) - Access Control Lists", Linux
man pages ACL(5), March 2002, <http://kernel.org/doc/man- man pages ACL(5), March 2002, <http://kernel.org/doc/man-
pages/online/pages/man5/acl.5.html>. pages/online/pages/man5/acl.5.html>.
[SUSv4] The Open Group, "Single UNIX Specification Version 4",
2013.
Appendix A. Acknowledgments Appendix A. Acknowledgments
Thanks to Dave Noveck and Trond Myklebust for review. Thanks to Dave Noveck and Trond Myklebust for review.
Authors' Addresses Authors' Addresses
J. Bruce Fields J. Bruce Fields
Red Hat, Inc. Red Hat, Inc.
Email: bfields@redhat.com Email: bfields@redhat.com
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