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

From: Dave Kleikamp
Date: Fri Aug 23 2024 - 14:16:49 EST


On 7/9/24 7:12PM, Remington Brasga wrote:
Fix issue with UBSAN throwing shift-out-of-bounds warning.

Reported-by: syzbot+e38d703eeb410b17b473@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Remington Brasga <rbrasga@xxxxxxx>
---
When nb = 32, `mask = mask >> nb` or shorthand `mask >>= nb` throws
shift-out-of-bounds warning.
`mask = (mask >> nb)` removes that warning.

Looks good. Applied.

Shaggy


Link to the syzbot bug report: https://lore.kernel.org/all/0000000000006fc563061cbc7f9c@xxxxxxxxxx/T/

fs/jfs/jfs_dmap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index cb3cda1390ad..636aae946e84 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -3020,7 +3020,7 @@ static int dbFindBits(u32 word, int l2nb)
/* scan the word for nb free bits at nb alignments.
*/
- for (bitno = 0; mask != 0; bitno += nb, mask >>= nb) {
+ for (bitno = 0; mask != 0; bitno += nb, mask = (mask >> nb)) {
if ((mask & word) == mask)
break;
}