CIFS: fix deadlock in cached root handling

commit 7e5a70ad88b1e6f6d9b934b2efb41afff496820f upstream.

Prevent deadlock between open_shroot() and
cifs_mark_open_files_invalid() by releasing the lock before entering
SMB2_open, taking it again after and checking if we still need to use
the result.

Link: https://lore.kernel.org/linux-cifs/684ed01c-cbca-2716-bc28-b0a59a0f8521@prodrive-technologies.com/T/#u
Fixes: 3d4ef9a15343 ("smb3: fix redundant opens on root")
Signed-off-by: Aurelien Aptel <aaptel@suse.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
CC: Stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index cc9e846..094be40 100644 (file)
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -553,7 +553,50 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
        oparams.fid = pfid;
        oparams.reconnect = false;
 
+       /*
+        * We do not hold the lock for the open because in case
+        * SMB2_open needs to reconnect, it will end up calling
+        * cifs_mark_open_files_invalid() which takes the lock again
+        * thus causing a deadlock
+        */
+       mutex_unlock(&tcon->crfid.fid_mutex);
        rc = SMB2_open(xid, &oparams, &srch_path, &oplock, NULL, NULL, NULL);
+       mutex_lock(&tcon->crfid.fid_mutex);
+
+       /*
+        * Now we need to check again as the cached root might have
+        * been successfully re-opened from a concurrent process
+        */
+
+       if (tcon->crfid.is_valid) {
+               /* work was already done */
+
+               /* stash fids for close() later */
+               struct cifs_fid fid = {
+                       .persistent_fid = pfid->persistent_fid,
+                       .volatile_fid = pfid->volatile_fid,
+               };
+
+               /*
+                * Caller expects this func to set pfid to a valid
+                * cached root, so we copy the existing one and get a
+                * reference
+                */
+               memcpy(pfid, tcon->crfid.fid, sizeof(*pfid));
+               kref_get(&tcon->crfid.refcount);
+
+               mutex_unlock(&tcon->crfid.fid_mutex);
+
+               if (rc == 0) {
+                       /* close extra handle outside of critical section */
+                       SMB2_close(xid, tcon, fid.persistent_fid,
+                                  fid.volatile_fid);
+               }
+               return 0;
+       }
+
+       /* Cached root is still invalid, continue normaly */
+
        if (rc == 0) {
                memcpy(tcon->crfid.fid, pfid, sizeof(struct cifs_fid));
                tcon->crfid.tcon = tcon;
@@ -561,6 +604,7 @@ int open_shroot(unsigned int xid, struct cifs_tcon *tcon, struct cifs_fid *pfid)
                kref_init(&tcon->crfid.refcount);
                kref_get(&tcon->crfid.refcount);
        }
+
        mutex_unlock(&tcon->crfid.fid_mutex);
        return rc;
 }