dm cache: fix flushing uninitialized delayed_work on cache_ctr error

An unexpected WARN_ON from flush_work() may occur when cache creation
fails, caused by destroying the uninitialized delayed_work waker in the
error path of cache_create(). For example, the warning appears on the
superblock checksum error.

Reproduce steps:

dmsetup create cmeta --table "0 8192 linear /dev/sdc 0"
dmsetup create cdata --table "0 65536 linear /dev/sdc 8192"
dmsetup create corig --table "0 524288 linear /dev/sdc 262144"
dd if=/dev/urandom of=/dev/mapper/cmeta bs=4k count=1 oflag=direct
dmsetup create cache --table "0 524288 cache /dev/mapper/cmeta \
/dev/mapper/cdata /dev/mapper/corig 128 2 metadata2 writethrough smq 0"

Kernel logs:

(snip)
WARNING: CPU: 0 PID: 84 at kernel/workqueue.c:4178 __flush_work+0x5d4/0x890

Fix by pulling out the cancel_delayed_work_sync() from the constructor's
error path. This patch doesn't affect the use-after-free fix for
concurrent dm_resume and dm_destroy (commit 6a459d8 ("dm cache: Fix
UAF in destroy()")) as cache_dtr is not changed.

Signed-off-by: Ming-Hung Tsai <[email protected]>
Fixes: 6a459d8 ("dm cache: Fix UAF in destroy()")
Cc: [email protected]
Signed-off-by: Mikulas Patocka <[email protected]>
Acked-by: Joe Thornber <[email protected]>

Author: mingnus

drivers/md/dm-cache-target.c

@@ -1905,16 +1905,13 @@ static void check_migrations(struct work_struct *ws)
  * This function gets called on the error paths of the constructor, so we
  * have to cope with a partially initialised struct.
  */
-static void destroy(struct cache *cache)
+static void __destroy(struct cache *cache)
 {
-	unsigned int i;
-
 	mempool_exit(&cache->migration_pool);
 
 	if (cache->prison)
 		dm_bio_prison_destroy_v2(cache->prison);
 
-	cancel_delayed_work_sync(&cache->waker);
 	if (cache->wq)
 		destroy_workqueue(cache->wq);
 
@@ -1942,13 +1939,22 @@ static void destroy(struct cache *cache)
 	if (cache->policy)
 		dm_cache_policy_destroy(cache->policy);
 
+	bioset_exit(&cache->bs);
+
+	kfree(cache);
+}
+
+static void destroy(struct cache *cache)
+{
+	unsigned int i;
+
+	cancel_delayed_work_sync(&cache->waker);
+
 	for (i = 0; i < cache->nr_ctr_args ; i++)
 		kfree(cache->ctr_args[i]);
 	kfree(cache->ctr_args);
 
-	bioset_exit(&cache->bs);
-
-	kfree(cache);
+	__destroy(cache);
 }
 
 static void cache_dtr(struct dm_target *ti)
@@ -2561,7 +2567,7 @@ static int cache_create(struct cache_args *ca, struct cache **result)
 	*result = cache;
 	return 0;
 bad:
-	destroy(cache);
+	__destroy(cache);
 	return r;
 }
 
@@ -2612,7 +2618,7 @@ static int cache_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 
 	r = copy_ctr_args(cache, argc - 3, (const char **)argv + 3);
 	if (r) {
-		destroy(cache);
+		__destroy(cache);
 		goto out;
 	}