[PATCH 5.10/5.15] jfs: add check if log->bdev is NULL in lbmStartIO()

[Mikhail Ukhin]

Fuzzing of 5.10 stable branch shows NULL pointer dereference happens in 
lbmStartIO() on log->bdev pointer. The reason for bdev being NULL is the 
JFS_NOINTEGRITY flag is set on mount of this fs. When this flag is enabled,
it results in the open_dummy_log function being called, which initializes a
new dummy_log, but does not assign a value to bdev.

The error is fixed in 5.18 by commit
07888c665b405b1cd3577ddebfeb74f4717a84c4.
Backport of this commit is too intrusive, so it is more reasonable to apply
a small patch to fix this issue.

Found by Linux Verification Center (linuxtesting.org) with syzkaller.

Signed-off-by: Mikhail Ukhin <mish.uxin2012@xxxxxxxxx>
Signed-off-by: Mikhail Ivanov <iwanov-23@xxxxx>
Signed-off-by: Pavel Koshutin <koshutin.pavel@xxxxxxxxx>
Signed-off-by: Artem Sadovnikov <ancowi69@xxxxxxxxx>
---
 fs/jfs/jfs_logmgr.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/jfs/jfs_logmgr.c b/fs/jfs/jfs_logmgr.c
index 78fd136ac13b..d6f0fea96ba1 100644
--- a/fs/jfs/jfs_logmgr.c
+++ b/fs/jfs/jfs_logmgr.c
@@ -1983,7 +1983,8 @@ static int lbmRead(struct jfs_log * log, int pn, struct lbuf ** bpp)
 	bio = bio_alloc(GFP_NOFS, 1);
 
 	bio->bi_iter.bi_sector = bp->l_blkno << (log->l2bsize - 9);
-	bio_set_dev(bio, log->bdev);
+	if (log->bdev != NULL)
+		bio_set_dev(bio, log->bdev);
 
 	bio_add_page(bio, bp->l_page, LOGPSIZE, bp->l_offset);
 	BUG_ON(bio->bi_iter.bi_size != LOGPSIZE);
@@ -2127,7 +2128,8 @@ static void lbmStartIO(struct lbuf * bp)
 
 	bio = bio_alloc(GFP_NOFS, 1);
 	bio->bi_iter.bi_sector = bp->l_blkno << (log->l2bsize - 9);
-	bio_set_dev(bio, log->bdev);
+	if (log->bdev != NULL)
+		bio_set_dev(bio, log->bdev);
 
 	bio_add_page(bio, bp->l_page, LOGPSIZE, bp->l_offset);
 	BUG_ON(bio->bi_iter.bi_size != LOGPSIZE);
-- 
2.25.1