[PATCH 2/5] dm cache: fix flushing uninitialized delayed_work on cache_ctr error

[Ming-Hung Tsai]

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 6a459d8edbdb ("dm cache: Fix
UAF in destroy()")) as cache_dtr is not changed.

Signed-off-by: Ming-Hung Tsai <mt...@redhat.com>
Fixes: 6a459d8edbdb ("dm cache: Fix UAF in destroy()")
---
 drivers/md/dm-cache-target.c | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 90772b42c234..68e9a1abd303 100644
--- a/drivers/md/dm-cache-target.c
+++ b/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;
        }
 
-- 
2.47.0