ksmbd: fix use-after-free in smb2_lock

commit 84d2d16 upstream.

If smb_lock->zero_len has value, ->llist of smb_lock is not delete and
flock is old one. It will cause use-after-free on error handling
routine.

Cc: [email protected]
Reported-by: Norbert Szetei <[email protected]>
Tested-by: Norbert Szetei <[email protected]>
Signed-off-by: Namjae Jeon <[email protected]>
Signed-off-by: Steve French <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
(cherry picked from commit 8573571)

Author: namjaejeon

fs/smb/server/smb2pdu.c

@@ -7442,13 +7442,13 @@ int smb2_lock(struct ksmbd_work *work)
 		}
 
 no_check_cl:
+		flock = smb_lock->fl;
+		list_del(&smb_lock->llist);
+
 		if (smb_lock->zero_len) {
 			err = 0;
 			goto skip;
 		}
-
-		flock = smb_lock->fl;
-		list_del(&smb_lock->llist);
 retry:
 		rc = vfs_lock_file(filp, smb_lock->cmd, flock, NULL);
 skip: