[PATCH v3] jfs: UBSAN: shift-out-of-bounds in dbFindBits

[Matt Jan <zoo868e@gmail.com>]

Return immediately if the needed free bits span a full word to avoid
out-of-bounds shifting.

#syz test

Reported-by: syzbot+9e90a1c5eedb9dc4c6cc@syzkaller.appspotmail.com
Signed-off-by: Matt Jan <zoo868e@gmail.com>
---
Changes in v3: Return the result earlier instead of assert it
Changes in v2: Test if the patch resolve the issue through syzbot and
reference the reporter.

 fs/jfs/jfs_dmap.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index 974ecf5e0d95..45b7a393b769 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -3012,6 +3012,11 @@ static int dbFindBits(u32 word, int l2nb)
 	int bitno, nb;
 	u32 mask;
 
+	/* return immediately if the number of free bits is a word
+	 */
+	if (l2nb == BUDMIN)
+		return (!!word) << BUDMIN;
+
 	/* get the number of bits.
 	 */
 	nb = 1 << l2nb;
-- 
2.25.1