dm: fix use-after-free in dm_put_live_table_bio

dm_put_live_table_bio is called from the end of dm_submit_bio.
However, at this point, the bio may be already finished and the caller
may have freed the bio. Consequently, dm_put_live_table_bio accesses
the stale "bio" pointer.

Fix this bug by loading the bi_opf value and passing it to
dm_get_live_table_bio and dm_put_live_table_bio instead of the bio.

This bug was found by running the lvm2 testsuite with kasan.

Fixes: 563a225 ("dm: introduce dm_{get,put}_live_table_bio called from dm_submit_bio")
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

drivers/md/dm.c

@@ -715,18 +715,18 @@ static void dm_put_live_table_fast(struct mapped_device *md) __releases(RCU)
 }
 
 static inline struct dm_table *dm_get_live_table_bio(struct mapped_device *md,
-						     int *srcu_idx, struct bio *bio)
+						     int *srcu_idx, unsigned bio_opf)
 {
-	if (bio->bi_opf & REQ_NOWAIT)
+	if (bio_opf & REQ_NOWAIT)
 		return dm_get_live_table_fast(md);
 	else
 		return dm_get_live_table(md, srcu_idx);
 }
 
 static inline void dm_put_live_table_bio(struct mapped_device *md, int srcu_idx,
-					 struct bio *bio)
+					 unsigned bio_opf)
 {
-	if (bio->bi_opf & REQ_NOWAIT)
+	if (bio_opf & REQ_NOWAIT)
 		dm_put_live_table_fast(md);
 	else
 		dm_put_live_table(md, srcu_idx);
@@ -1715,8 +1715,9 @@ static void dm_submit_bio(struct bio *bio)
 	struct mapped_device *md = bio->bi_bdev->bd_disk->private_data;
 	int srcu_idx;
 	struct dm_table *map;
+	unsigned bio_opf = bio->bi_opf;
 
-	map = dm_get_live_table_bio(md, &srcu_idx, bio);
+	map = dm_get_live_table_bio(md, &srcu_idx, bio_opf);
 
 	/* If suspended, or map not yet available, queue this IO for later */
 	if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) ||
@@ -1732,7 +1733,7 @@ static void dm_submit_bio(struct bio *bio)
 
 	dm_split_and_process_bio(md, map, bio);
 out:
-	dm_put_live_table_bio(md, srcu_idx, bio);
+	dm_put_live_table_bio(md, srcu_idx, bio_opf);
 }
 
 static bool dm_poll_dm_io(struct dm_io *io, struct io_comp_batch *iob,