SSSD CIFS plugin
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.
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.
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
- Policies and guidelines:
- No new policy guidelies
- 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 (https://bugzilla.redhat.com/show_bug.cgi?id=984087 rhbz #984087):
# 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.
N/A (not a System Wide Change)
- cifs-utils would grow dependency of this new plugin
- Contingency mechanism: revert the symlink change made to cifs-utils.
- Contingency deadline: N/A
- Blocks release? No
So far only the design page is available.