dm-verity: correctly handle dm_bufio_client_create() failure

[ Upstream commit 119f4f0 ]

If either of the calls to dm_bufio_client_create() in verity_fec_ctr()
fails, then dm_bufio_client_destroy() is later called with an ERR_PTR()
argument.  That causes a crash.  Fix this.

Fixes: a739ff3 ("dm verity: add support for forward error correction")
Cc: stable@vger.kernel.org
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Eric Biggers

drivers/md/dm-verity-fec.c

@@ -533,9 +533,9 @@ void verity_fec_dtr(struct dm_verity *v)
 	mempool_exit(&f->output_pool);
 	kmem_cache_destroy(f->cache);
 
-	if (f->data_bufio)
+	if (!IS_ERR_OR_NULL(f->data_bufio))
 		dm_bufio_client_destroy(f->data_bufio);
-	if (f->bufio)
+	if (!IS_ERR_OR_NULL(f->bufio))
 		dm_bufio_client_destroy(f->bufio);
 
 	if (f->dev)