[PATCH 5.15.y] jfs: Fix shift-out-of-bounds in dbDiscardAG

[PATCH 5.15.y] jfs: Fix shift-out-of-bounds in dbDiscardAG

[Zhi Yang]

From: Pei Li <peili.dev@gmail.com>

commit 7063b80268e2593e58bee8a8d709c2f3ff93e2f2 upstream.

When searching for the next smaller log2 block, BLKSTOL2() returned 0,
causing shift exponent -1 to be negative.

This patch fixes the issue by exiting the loop directly when negative
shift is found.

Reported-by: syzbot+61be3359d2ee3467e7e4@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=61be3359d2ee3467e7e4
Signed-off-by: Pei Li <peili.dev@gmail.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Signed-off-by: Zhi Yang <Zhi.Yang@windriver.com>
Signed-off-by: He Zhe <zhe.he@windriver.com>
---
Build test passed.
---
 fs/jfs/jfs_dmap.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index e6cbe4c982c5..0d314fac32ca 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -1694,6 +1694,8 @@ s64 dbDiscardAG(struct inode *ip, int agno, s64 minlen)
 		} else if (rc == -ENOSPC) {
 			/* search for next smaller log2 block */
 			l2nb = BLKSTOL2(nblocks) - 1;
+			if (unlikely(l2nb < 0))
+				break;
 			nblocks = 1LL << l2nb;
 		} else {
 			/* Trim any already allocated blocks */
-- 
2.34.1

Re: [PATCH 5.15.y] jfs: Fix shift-out-of-bounds in dbDiscardAG

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

✅ All tests passed successfully. No issues detected.
No action required from the submitter.

The upstream commit SHA1 provided is correct: 7063b80268e2593e58bee8a8d709c2f3ff93e2f2

WARNING: Author mismatch between patch and upstream commit:
Backport author: Zhi Yang<Zhi.Yang@eng.windriver.com>
Commit author: Pei Li<peili.dev@gmail.com>

Status in newer kernel trees:
6.14.y | Present (exact SHA1)
6.13.y | Present (exact SHA1)
6.12.y | Present (exact SHA1)
6.6.y | Present (different SHA1: f650148b4394)
6.1.y | Present (different SHA1: bd04a149e3a2)

Note: The patch differs from the upstream commit:
---
1:  7063b80268e25 ! 1:  d8916f054bb95 jfs: Fix shift-out-of-bounds in dbDiscardAG
    @@ Metadata
      ## Commit message ##
         jfs: Fix shift-out-of-bounds in dbDiscardAG
     
    +    commit 7063b80268e2593e58bee8a8d709c2f3ff93e2f2 upstream.
    +
         When searching for the next smaller log2 block, BLKSTOL2() returned 0,
         causing shift exponent -1 to be negative.
     
    @@ Commit message
         Closes: https://syzkaller.appspot.com/bug?extid=61be3359d2ee3467e7e4
         Signed-off-by: Pei Li <peili.dev@gmail.com>
         Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
    +    Signed-off-by: Zhi Yang <Zhi.Yang@windriver.com>
    +    Signed-off-by: He Zhe <zhe.he@windriver.com>
     
      ## fs/jfs/jfs_dmap.c ##
     @@ fs/jfs/jfs_dmap.c: s64 dbDiscardAG(struct inode *ip, int agno, s64 minlen)
---

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-5.15.y       |  Success    |  Success   |