Revision as of 09:10, 15 July 2013

SSSD CIFS plugin

Summary

During the F20 development cycle, the SSSD will provide an ID-mapping plugin for cifs-utils so that Windows SIDs can be mapped onto POSIX IDs and/or names without requiring Winbind and using the same code as the SSSD uses for identity information.

Owner

Name: Sumit Bose, Jakub Hrozek
Email: sbose@redhat.com, jhrozek@redhat.com
Release notes owner:

Current status

Targeted release: Fedora 20
Last updated: 2013-07-12
Tracker bug: <will be assigned by the Wrangler>

Detailed Description

When working with files on a CIFS share, mapping between Windows SIDs and POSIX IDs might be required in some situations like modifying the ACLs. In recent versions, the cifs-util package introduced a plugin interface that allows different libraries to handle the ID mapping. Currently only Winbind provides such plugin (see file idmapwb.c in cifs-utils tree). The goal of this change is to provide a similar plugin using SSSD's ID mapping library so that the same method of ID mapping is used and Winbind is not required at all. The upstream design page that includes deeper technical details can be found in the SSSD Trac . The progress of the work can also be tracked in the upstream ticket #1534.

Benefit to Fedora

Fedora already defaults to configuring the SSSD to access identity information from Windows servers via realmd and Enterprise Login support. Using the same software for ID mapping when accessing CIFS shares makes sense from both correctness point of view (the same method would be used to convert SID to ID or names) and reducing the dependency footprint.

Scope

The SSSD would provide a plugin for the cifs-utils package as described in the upstream design page. The cifs-utils package would then switch to using the SSSD plugin instead of the one provided by Winbind. The change on the cifs-utils side should amount to changing a symlink.

Proposal owners:
- SSSD needs to create a plugin that matches the interface used by cifs-utils.
- This plugin would be packaged as a separate subpackage

Other developers:
- The cifs-utils package would switch to managing which ID mapping plugin it uses with the use of alternatives (rhbz #984088)
Release engineering:
- No mass rebuild would be required.
- The cifs-utils package would Require the new SSSD plugin and indirectly its dependencies which would be primarily the libsss_idmap library

Policies and guidelines:
- No new policy guidelies

Upgrade/compatibility impact

No existing functionality should be lost. Resolving SIDs to IDs and names should work as it used to.

How To Test

Testing with getcifsacl

If there is no plugin for the CIFS client utilities or the plugin cannot resolve the SIDs to names getcifsacl will only show the SID strings in the output:

# getcifsacl /tmp/bla/Users/Administrator/Desktop/putty.exe 
REVISION:0x1
CONTROL:0x8004
OWNER:S-1-5-32-544
GROUP:S-1-5-21-3090815309-2627318493-3395719201-513
ACL:S-1-5-18:ALLOWED/0x0/FULL
ACL:S-1-5-32-544:ALLOWED/0x0/FULL
ACL:S-1-5-21-3090815309-2627318493-3395719201-500:ALLOWED/0x0/FULL

With the plugin, the output would resolve the SIDs to human-readable names:

# getcifsacl /tmp/bla/Users/Administrator/Desktop/putty.exe 
REVISION:0x1
CONTROL:0x8004
OWNER:BUILTIN\Administrators
GROUP:AD18\Domain Users
ACL:S-1-5-18:ALLOWED/0x0/FULL
ACL:BUILTIN\Administrators:ALLOWED/0x0/FULL
ACL:AD18\Administrator:ALLOWED/0x0/FULL

Testing with cifsacl option to mount.cifs

If the cifsacl mount option is used the cifs kernel module will call cifs.idmap to translate the Windows SIDs into the corresponding UIDs/GIDs of the client system so that the ownership of the files in the mounted file system is not mapped to the user how mounted the file system, but corresponds to the owning user and group of the Windows domain.

User Experience

N/A (not a System Wide Change)

Dependencies

cifs-utils would grow dependency of this new plugin

Contingency Plan

Contingency mechanism: revert the symlink change made to cifs-utils.
Contingency deadline: N/A
Blocks release? No

Documentation

So far only the design page is available.

Release Notes

@@ Line 78: / Line 78: @@
 * Proposal owners:
 ** SSSD needs to create a plugin that matches the interface used by cifs-utils.
+** This plugin would be packaged as a separate subpackage
 <!-- What work do the feature owners have to accomplish to complete the feature in time for release?  Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?-->
 * Other developers: <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
-** The cifs-utils package would switch the default ID mapping plugin by pointing the <code>/etc/cifs-utils/idmap-plugin</code> symlink to the new plugin provided by the SSSD.
 <!-- What work do other developers have to accomplish to complete the feature in time for release?  Is it a large change affecting many parts of the distribution or is it a very isolated change? What are those changes?-->
+** The cifs-utils package would switch to managing which ID mapping plugin it uses with the use of alternatives ([https://bugzilla.redhat.com/show_bug.cgi?id=984088 rhbz #984088])
 * Release engineering: <!-- REQUIRED FOR SYSTEM WIDE CHANGES -->
 ** No mass rebuild would be required.
@@ Line 116: / Line 116: @@
 ==== Testing with getcifsacl ====
-If there is no plugin for the CIFS client utilities or the plugin cannot resolve the SIDs to names getcifsacl will only show the SID strings in the outout:
+If there is no plugin for the CIFS client utilities or the plugin cannot resolve the SIDs to names getcifsacl will only show the SID strings in the output:
   # getcifsacl /tmp/bla/Users/Administrator/Desktop/putty.exe

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