Public bug reported:
[Impact]
Currently when the client creates a cifsFileInfo structure for
a newly opened file, it allocates a list of byte-range locks
with a pointer to the new cfile and attaches this list to the
inode's lock list. The latter happens before initializing all
other fields, e.g. cfile->tlink. Thus a partially initialized
cifsFileInfo structure becomes available to other threads that
walk through the inode's lock list. One example of such a thread
may be an oplock break worker thread that tries to push all
cached byte-range locks. This causes NULL-pointer dereference
in smb2_push_mandatory_locks() when accessing cfile->tlink:
[598428.945633] BUG: kernel NULL pointer dereference, address: 0000000000000038
...
[598428.945749] Workqueue: cifsoplockd cifs_oplock_break [cifs]
[598428.945793] RIP: 0010:smb2_push_mandatory_locks+0xd6/0x5a0 [cifs]
...
[598428.945834] Call Trace:
[598428.945870] ? cifs_revalidate_mapping+0x45/0x90 [cifs]
[598428.945901] cifs_oplock_break+0x13d/0x450 [cifs]
[598428.945909] process_one_work+0x1db/0x380
[598428.945914] worker_thread+0x4d/0x400
[598428.945921] kthread+0x104/0x140
[598428.945925] ? process_one_work+0x380/0x380
[598428.945931] ? kthread_park+0x80/0x80
[598428.945937] ret_from_fork+0x35/0x40
[Test Case]
TBD.
[Fix]
Backport commit 6f582b273ec23332074d970a7fb25bef835df71f ("CIFS: Fix
NULL-pointer dereference in smb2_push_mandatory_locks")
[Regression Potential]
Low. The patch is fairly simple and it's tagged for stable kernels. In
fact it is already in some of the released upstream stable kernels.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: Incomplete
** Affects: linux (Ubuntu Xenial)
Importance: Undecided
Status: Incomplete
** Affects: linux (Ubuntu Bionic)
Importance: Undecided
Status: Incomplete
** Affects: linux (Ubuntu Disco)
Importance: Undecided
Status: Incomplete
** Affects: linux (Ubuntu Eoan)
Importance: Undecided
Status: Incomplete
** Also affects: linux (Ubuntu Focal)
Importance: Undecided
Status: New
** Also affects: linux (Ubuntu Bionic)
Importance: Undecided
Status: New
** Also affects: linux (Ubuntu Eoan)
Importance: Undecided
Status: New
** Also affects: linux (Ubuntu Xenial)
Importance: Undecided
Status: New
** Also affects: linux (Ubuntu Disco)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1856949
Title:
cifs: kernel NULL pointer dereference, address: 0000000000000038
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