On Tue, 2023-08-08 at 15:31 +0200, Christian Brauner wrote:

On Tue, Aug 08, 2023 at 07:34:20AM -0400, Jeff Layton wrote:

quoted

From: David Howells <dhowells@redhat.com>

When NFS superblocks are created by automounting, their LSM parameters
aren't set in the fs_context struct prior to sget_fc() being called,
leading to failure to match existing superblocks.

This bug leads to messages like the following appearing in dmesg when
fscache is enabled:

    NFS: Cache volume key already in use (nfs,4.2,2,108,106a8c0,1,,,,100000,100000,2ee,3a98,1d4c,3a98,1)

Fix this by adding a new LSM hook to load fc->security for submount
creation.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Fixes: 9bc61ab18b1d ("vfs: Introduce fs_context, switch vfs_kern_mount() to it.")
Fixes: 779df6a5480f ("NFS: Ensure security label is set for root inode)
Tested-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>

I've made a significant number of changes since Casey acked this. It
might be a good idea to drop his Acked-by (unless he wants to chime in
and ask us to keep it).

Thanks,
Jeff

quoted

Acked-by: "Christian Brauner (Microsoft)" <brauner@kernel.org>
Link: https://lore.kernel.org/r/165962680944.3334508.6610023900349142034.stgit@warthog.procyon.org.uk/ (local) # v1
Link: https://lore.kernel.org/r/165962729225.3357250.14350728846471527137.stgit@warthog.procyon.org.uk/ (local) # v2
Link: https://lore.kernel.org/r/165970659095.2812394.6868894171102318796.stgit@warthog.procyon.org.uk/ (local) # v3
Link: https://lore.kernel.org/r/166133579016.3678898.6283195019480567275.stgit@warthog.procyon.org.uk/ (local) # v4
Link: https://lore.kernel.org/r/217595.1662033775@warthog.procyon.org.uk/ (local) # v5
---
ver #2)
- Added Smack support
- Made LSM parameter extraction dependent on reference != NULL.

ver #3)
- Made LSM parameter extraction dependent on fc->purpose ==
   FS_CONTEXT_FOR_SUBMOUNT.  Shouldn't happen on FOR_RECONFIGURE.

ver #4)
- When doing a FOR_SUBMOUNT mount, don't set the root label in SELinux or Smack.

ver #5)
- Removed unused variable.
- Only allocate smack_mnt_opts if we're dealing with a submount.

ver #6)
- Rebase onto v6.5.0-rc4
- Link to v6: https://lore.kernel.org/r/20230802-master-v6-1-45d48299168b@kernel.org (local)

ver #7)
- Drop lsm_set boolean
- Link to v7: https://lore.kernel.org/r/20230804-master-v7-1-5d4e48407298@kernel.org (local)

ver #8)
- Remove spurious semicolon in smack_fs_context_init
- Make fs_context_init take a superblock as reference instead of dentry
- WARN_ON_ONCE's when fc->purpose != FS_CONTEXT_FOR_SUBMOUNT
- Call the security hook from fs_context_for_submount instead of alloc_fs_context
- Link to v8: https://lore.kernel.org/r/20230807-master-v8-1-54e249595f10@kernel.org (local)

ver #9)
- rename *_fs_context_init to *_fs_context_submount
- remove checks for FS_CONTEXT_FOR_SUBMOUNT and NULL reference pointers
- fix prototype on smack_fs_context_submount

Thanks, this looks good from my perspective. If it looks fine to LSM
folks as well I can put it with the rest of the super work for this
cycle or it can go through the LSM tree.

-- 
Jeff Layton [off-list ref]