draft-ietf-nfsv4-umask-02.txt   draft-ietf-nfsv4-umask-03.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: April 6, 2017 October 03, 2016 Expires: September 4, 2017 March 03, 2017
Allowing inheritable NFSv4 ACLs to override the umask Allowing Inheritable NFSv4 ACLs to Override the Umask
draft-ietf-nfsv4-umask-02 draft-ietf-nfsv4-umask-03
Abstract Abstract
In some environments, inheritable NFSv4 ACLs can be rendered In many important environments, inheritable NFSv4 ACLs can be
ineffective by the application of the per-process umask. This is rendered ineffective by the application of the per-process umask.
easily worked around by transmitting the umask and create mode This can be addressed by transmitting the umask and create mode as
separately, to allow servers to make more intelligent decisions about separate pieces of data, allowing the server to make more intelligent
the new mode of a file. decisions about the permissions to set on new files. 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.
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This Internet-Draft will expire on April 6, 2017. This Internet-Draft will expire on September 4, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2016 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
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described in the Simplified BSD License. described in the Simplified BSD License.
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. mode_umask Attribute . . . . . . . . . . . . . . . . . . . . 3 3. Protocol Extension Considerations . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 4. mode_umask Attribute . . . . . . . . . . . . . . . . . . . . 3
5. Normative References . . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
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). In the absence of inheritable permissions, creation mask (umask), which specifies which permissions must be
the umask specifies which permissions must be turned off when turned off when creating new file system objects.
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 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 ACL to be no more than the permissions granted by the
MODE4_RGRP, MODE4_WGRP, and MODE4_XGRP bits. Servers aiming to MODE4_RGRP, MODE4_WGRP, and MODE4_XGRP bits. Servers aiming to
provide clients with Unix-like chmod behavior may also be motivated provide clients with Unix-like chmod behavior may also be motivated
by the same requirements in [SUSv4]. (See the discussion of by the same requirements in [SUSv4]. (See the discussion of
additional and alternate access control mechanisms in section "4.4 additional and alternate access control mechanisms in section "4.4
File Permissions".) 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. Thus the named users and groups with very restrictive permissions. As a result, inherited ACEs
in an inherited ACL end up being mostly ignored. describing the permissions to be granted to named users and groups
are often ignored. This makes inheritable ACLs useless in some
common cases.
This leads to file permissions which are more restrictive than they Linux solves this problem on local filesystems by ignoring the umask
should be in common cases; permission inheritance over NFSv4 is in the case the parent of the newly-created file has inheritable
broken. ACEs; see [LinuxACL].
To address this problem, a new attribute is proposed which allows the The same solution should work for NFS. However, the NFSv4 protocol
server to apply the umask only when there are no inheritable does not currently give the client a way to transmit the umask of the
permissions. process opening a file. And clients have no way of atomically
checking for inheritable permissions and applying the umask only when
necessary. As a result, the server receives an OPEN with a mode
attribute that already has the umask applied.
3. mode_umask Attribute This document solves the problem by defining a new attribute which
allows the client to transmit umask and the mode specified at file
creation separately, allowing the client to ignore the umask in the
presence of inheritable ACLs. At least in the Linux case, this
allows NFSv4 to provide the same semantics available using local
access.
3. Protocol Extension Considerations
This document presents an extension to minor version 2 of the NFSv4
protocol as described in [nfsv4-versioning]. It describes a new
OPTIONAL feature. NFSv4.2 servers and clients implemented without
knowledge of this extension will continue to interoperate with
clients and servers that are aware of the extension (whether they
support it or not).
Note that [RFC7862] does not define NFSv4.2 as non-extensible, so
that it is considered by [nfsv4-versioning] to be an extensible minor
version. As a result, upon publication of this document as a
Proposed Standard, the extension described herein will effectively be
part of NFSv4.2, even though this document does not update [RFC7862]
or [RFC7863].
4. mode_umask Attribute
struct mode_umask4 { struct mode_umask4 {
mode4 mu_mode; mode4 mu_mode;
mode4 mu_umask; mode4 mu_umask;
}; };
+------------+----+-------------+-----+------------+ +------------+----+-------------+-----+------------+
| Name | Id | Data Type | Acc | Defined in | | Name | Id | Data Type | Acc | Defined in |
+------------+----+-------------+-----+------------+ +------------+----+-------------+-----+------------+
| mode_umask | 81 | mode_umask4 | W | Section 3 | | mode_umask | 81 | mode_umask4 | W | Section 4 |
+------------+----+-------------+-----+------------+ +------------+----+-------------+-----+------------+
Table 1 Table 1
The NFSv4.2 mode_umask attribute is based on the open mode and umask The NFSv4.2 mode_umask attribute is based on the umask and on the
that together determine the mode of a newly created UNIX file. Only mode bits specified at open time, which together determine the mode
the nine low-order mode4 bits of mu_umask are defined. A server MUST of a newly created UNIX file. Only the nine low-order mode4 bits of
return NFS4ERR_INVAL if bits other than those nine are set. mu_umask are defined. A server MUST return NFS4ERR_INVAL if bits
other than those nine are set.
The mode_umask attribute is only meaningful for operations that The mode_umask attribute is only meaningful for operations that
create objects (CREATE and OPEN); the server SHOULD reject it for create objects (CREATE and OPEN); in other operations that take
other operations that take fattr4 arguments. fattr4 arguments, the server MUST reject it with NFS4ERR_INVAL.
The server MUST ignore any mode attribute set in the same operation The server MUST return NFS4ERR_INVAL if the client attempts to set
as mode_umask. both mode and mode_umask in the same operation.
When the server supports the mode_umask attribute, a client creating When the server supports the mode_umask attribute, a client creating
a file should use mode_umask in place of mode, with mu_mode set to a file should use mode_umask in place of mode, with mu_mode set to
the unmodified mode provided by the user, and mu_umask set to the the unmodified mode provided by the user, and mu_umask set to the
umask of the requesting process. umask of the requesting process.
The server then uses mode_umask as follows: The server then uses mode_umask as follows:
o On a server that supports ACL attributes, if an object inherits o On a server that supports ACL attributes, if an object inherits
any ACEs from its parent directory, mu_mode SHOULD be used, and any ACEs from its parent directory, mu_mode SHOULD be used, and
mu_umask ignored. mu_umask ignored.
o Otherwise, mu_umask MUST be used to limit the mode: all bits in o Otherwise, mu_umask MUST be used to limit the mode: all bits in
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
to use for creating the object becomes (mu_mode & ~mu_umask) assigned to the new object becomes (mu_mode & ~mu_umask) instead.
instead.
4. 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 SHOULD 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 common practice; permissions in the form of a "POSIX" default ACL is of long standing
there are no known security concerns. The "POSIX" default ACL and has not given rise to security issues. The "POSIX" default ACL
mechanism and the mechanism of inheriting permissions in NFSv4 is mechanism and the mechanism for permission inheritance in NFSv4 are
equivalent for this purpose. equivalent from a security perspective.
5. Normative References 6. IANA Considerations
This document does not require any actions by IANA.
7. References
7.1. Normative References
[LEGAL] IETF Trust, "Legal Provisions Relating to IETF Documents", [LEGAL] IETF Trust, "Legal Provisions Relating to IETF Documents",
November 2008, <http://trustee.ietf.org/docs/ November 2008, <http://trustee.ietf.org/docs/
IETF-Trust-License-Policy.pdf>. IETF-Trust-License-Policy.pdf>.
[POSIX-1003.1e] [nfsv4-versioning]
Portable Applications Standards Committee of the IEEE Noveck, D., "Rules for NFSv4 Extensions and Minor
Compute Society, "POSIX 1003.1e Withdrawn Draft 17", Versions", draft-ietf-nfsv4-versioning-08 (work in
October 1997. 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", [RFC4506] Eisler, M., "XDR: External Data Representation Standard",
STD 67, RFC 4506, May 2006. STD 67, RFC 4506, May 2006.
[RFC5661] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed., [RFC5661] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
"Network File System (NFS) Version 4 Minor Version 1 "Network File System (NFS) Version 4 Minor Version 1
Protocol", RFC 5661, January 2010. Protocol", RFC 5661, January 2010.
[RFC5662] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed., [RFC5662] Shepler, S., Ed., Eisler, M., Ed., and D. Noveck, Ed.,
"Network File System (NFS) Version 4 Minor Version 1 "Network File System (NFS) Version 4 Minor Version 1
External Data Representation Standard (XDR) Description", External Data Representation Standard (XDR) Description",
RFC 5662, January 2010. 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
Version 2 Protocol", RFC 7862, November 2016.
[RFC7863] Haynes, T., "Network File System (NFS) Version 4 Minor
Version 2 External Data Representation Standard (XDR)
Description", RFC 7863, November 2016.
[SUSv4] The Open Group, "Single UNIX Specification Version 4", [SUSv4] The Open Group, "Single UNIX Specification Version 4",
2013. 2013.
7.2. Informative References
[LinuxACL]
Gruenbacher, A., "ACL(5) - Access Control Lists", Linux
man pages ACL(5), March 2002, <http://kernel.org/doc/man-
pages/online/pages/man5/acl.5.html>.
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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