ceph: don't try fill file_lock on unsuccessful GETFILELOCK reply

When ceph_mdsc_do_request returns an error, we can't assume that the
filelock_reply pointer will be set. Only try to fetch fields out of
the r_reply_info when it returns success.

Cc: stable@vger.kernel.org
Reported-by: Hector Martin <hector@marcansoft.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/locks.c

@@ -111,8 +111,7 @@ static int ceph_lock_message(u8 lock_type, u16 operation, struct inode *inode,
 		req->r_wait_for_completion = ceph_lock_wait_for_completion;
 
 	err = ceph_mdsc_do_request(mdsc, inode, req);
-
-	if (operation == CEPH_MDS_OP_GETFILELOCK) {
+	if (!err && operation == CEPH_MDS_OP_GETFILELOCK) {
 		fl->fl_pid = -le64_to_cpu(req->r_reply_info.filelock_reply->pid);
 		if (CEPH_LOCK_SHARED == req->r_reply_info.filelock_reply->type)
 			fl->fl_type = F_RDLCK;