dm clone: Fix UAF in clone_dtr()

Dm_clone also has the same UAF problem when dm_resume()
and dm_destroy() are concurrent.

Therefore, cancelling timer again in clone_dtr().

Cc: stable@vger.kernel.org
Fixes: 7431b783 ("dm: add clone target")
Signed-off-by: Luo Meng <luomeng12@huawei.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

drivers/md/dm-clone-target.c

@@ -1958,6 +1958,7 @@ static void clone_dtr(struct dm_target *ti)
 
 	mempool_exit(&clone->hydration_pool);
 	dm_kcopyd_client_destroy(clone->kcopyd_client);
+	cancel_delayed_work_sync(&clone->waker);
 	destroy_workqueue(clone->wq);
 	hash_table_exit(clone);
 	dm_clone_metadata_close(clone->cmd);