dm cache: Fix UAF in destroy()

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

Therefore, cancelling timer again in destroy().

Cc: stable@vger.kernel.org
Fixes: c6b4fcba ("dm: add cache target")
Signed-off-by: Luo Meng <luomeng12@huawei.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

drivers/md/dm-cache-target.c

@@ -1887,6 +1887,7 @@ static void destroy(struct cache *cache)
 	if (cache->prison)
 		dm_bio_prison_destroy_v2(cache->prison);
 
+	cancel_delayed_work_sync(&cache->waker);
 	if (cache->wq)
 		destroy_workqueue(cache->wq);