Fix tcon use-after-free and NULL ptr deref.
Customer system crashes with the following kernel log:
[462233.169868] CIFS VFS: Cancelling wait for mid 4894753 cmd: 14 => a QUERY DIR
[462233.228045] CIFS VFS: cifs_put_smb_ses: Session Logoff failure rc=-4
[462233.305922] CIFS VFS: cifs_put_smb_ses: Session Logoff failure rc=-4
[462233.306205] CIFS VFS: cifs_put_smb_ses: Session Logoff failure rc=-4
[462233.347060] CIFS VFS: cifs_put_smb_ses: Session Logoff failure rc=-4
[462233.347107] CIFS VFS: Close unmatched open
[462233.347113] BUG: unable to handle kernel NULL pointer dereference at 0000000000000038
...
[exception RIP: cifs_put_tcon+0xa0] (this is doing tcon->ses->server)
#6 [...] smb2_cancelled_close_fid at ... [cifs]
#7 [...] process_one_work at ...
#8 [...] worker_thread at ...
#9 [...] kthread at ...
The most likely explanation we have is:
* When we put the last reference of a tcon (refcount=0), we close the
cached share root handle.
* If closing a handle is interupted, SMB2_close() will
queue a SMB2_close() in a work thread.
* The queued object keeps a tcon ref so we bump the tcon
refcount, jumping from 0 to 1.
* We reach the end of cifs_put_tcon(), we free the tcon object despite
it now having a refcount of 1.
* The queued work now runs, but the tcon, ses & server was freed in
the meantime resulting in a crash.
THREAD 1
========
cifs_put_tcon => tcon refcount reach 0
SMB2_tdis
close_shroot_lease
close_shroot_lease_locked => if cached root has lease && refcount reach 0
smb2_close_cached_fid => if cached root valid
SMB2_close => retry close in a worker thread if interrupted
smb2_handle_cancelled_close
__smb2_handle_cancelled_close => !! tcon refcount bump 0 => 1 !!
INIT_WORK(&cancelled->work, smb2_cancelled_close_fid);
queue_work(cifsiod_wq, &cancelled->work) => queue work
tconInfoFree(tcon); ==> freed!
cifs_put_smb_ses(ses); ==> freed!
THREAD 2 (workqueue)
========
smb2_cancelled_close_fid
SMB2_close(0, cancelled->tcon, ...); => use-after-free of tcon
cifs_put_tcon(cancelled->tcon); => tcon refcount reach 0 second time
*CRASH*
Fixes: d9191319358d ("CIFS: Close cached root handle only if it has a lease")
Signed-off-by: Aurelien Aptel <aaptel@xxxxxxxx>
---
fs/cifs/smb2misc.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/fs/cifs/smb2misc.c b/fs/cifs/smb2misc.c
index 0511aaf451d4..965276aeffcf 100644
--- a/fs/cifs/smb2misc.c
+++ b/fs/cifs/smb2misc.c
@@ -766,6 +766,12 @@ smb2_handle_cancelled_close(struct cifs_tcon *tcon, __u64 persistent_fid,
cifs_dbg(FYI, "%s: tc_count=%d\n", __func__, tcon->tc_count);
spin_lock(&cifs_tcp_ses_lock);
+ if (tcon->tc_count <= 0) {
+ spin_unlock(&cifs_tcp_ses_lock);
+ cifs_dbg(VFS, "tcon is closing, skipping async close retry of fid %llu %llu\n",
+ persistent_fid, volatile_fid);
+ return 0;
+ }
tcon->tc_count++;
spin_unlock(&cifs_tcp_ses_lock);
--
2.16.4
