[syzbot] [jfs?] UBSAN: shift-out-of-bounds in dbAllocAG (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 7ea30958b305 Merge tag 'vfs-6.18-rc2.fixes' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10eee5e2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=af9170887d81dea1
dashboard link: https://syzkaller.appspot.com/bug?extid=4b717071f1eecb2972df
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16a64b04580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12c8bdcd980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3e5414d12be0/disk-7ea30958.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f88a30954acd/vmlinux-7ea30958.xz
kernel image: https://storage.googleapis.com/syzbot-assets/aa2283ab9f73/bzImage-7ea30958.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/ffc7d81ee40c/mount_0.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=1585552f980000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4b7170...@syzkaller.appspotmail.com

------------[ cut here ]------------
UBSAN: shift-out-of-bounds in fs/jfs/jfs_dmap.c:1440:48
shift exponent -1 is negative
CPU: 0 UID: 0 PID: 6076 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
ubsan_epilogue+0xa/0x40 lib/ubsan.c:233
__ubsan_handle_shift_out_of_bounds+0x386/0x410 lib/ubsan.c:494
dbAllocAG+0xfc0/0xff0 fs/jfs/jfs_dmap.c:1440
dbAlloc+0x5a8/0xba0 fs/jfs/jfs_dmap.c:877
extBalloc fs/jfs/jfs_extent.c:336 [inline]
extAlloc+0x54a/0xfb0 fs/jfs/jfs_extent.c:127
jfs_get_block+0x346/0xab0 fs/jfs/inode.c:254
__block_write_begin_int+0x6b5/0x1900 fs/buffer.c:2145
block_write_begin+0x8a/0x120 fs/buffer.c:2256
jfs_write_begin+0x35/0x80 fs/jfs/inode.c:306
generic_perform_write+0x29d/0x8c0 mm/filemap.c:4242
generic_file_write_iter+0x118/0x550 mm/filemap.c:4385
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x5d5/0xb40 fs/read_write.c:686
ksys_write+0x14b/0x260 fs/read_write.c:738
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa99272eec9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fffa62c1048 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fa992985fa0 RCX: 00007fa99272eec9
RDX: 0000000000000014 RSI: 0000200000000380 RDI: 0000000000000005
RBP: 00007fa9927b1f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa992985fa0 R14: 00007fa992985fa0 R15: 0000000000000003
</TASK>
---[ end trace ]---


---
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[Pei Xiao]

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index cdfa699cd7c8..9d26c5dc4efd 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -1435,6 +1435,11 @@ dbAllocAG(struct bmap * bmp, int agno, s64 nblocks, int l2nb, s64 * results)
blkno &= ~(MAXL1SIZE - 1);
else /* bmp->db_aglevel == 0 */
blkno &= ~(MAXL0SIZE - 1);
+
+ if (unlikely(budmin < 0)) {
+ WARN_ON_ONCE(1);
+ budmin = 0;
+ }

blkno +=
((s64) (ti - le32_to_cpu(dcp->leafidx))) << budmin;
--
2.25.1

[Pei Xiao]

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

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in dbAllocAG

------------[ cut here ]------------
WARNING: CPU: 1 PID: 6656 at fs/jfs/jfs_dmap.c:1440 dbAllocAG+0xd67/0x1080 fs/jfs/jfs_dmap.c:1440
Modules linked in:
CPU: 1 UID: 0 PID: 6656 Comm: syz.0.22 Not tainted syzkaller #0 PREEMPT_{RT,(full)}

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025

RIP: 0010:dbAllocAG+0xd67/0x1080 fs/jfs/jfs_dmap.c:1440
Code: 89 d8 48 c1 e8 03 42 80 3c 30 00 74 08 48 89 df e8 fe e7 e6 fe 48 8b 3b 48 c7 c6 a0 1a 24 8b e9 d2 f9 ff ff e8 ea 35 85 fe 90 <0f> 0b 90 48 8b 44 24 78 42 0f b6 04 20 84 c0 0f 85 d5 02 00 00 48
RSP: 0018:ffffc90004e4f300 EFLAGS: 00010293
RAX: ffffffff8339c746 RBX: ffff888036d4f000 RCX: ffff88802e0a8000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000100 R11: 0000000000000002 R12: dffffc0000000000
R13: 0000000000000155 R14: 0000000000000000 R15: 00000000000000ff
FS: 00007efe0bfed6c0(0000) GS:ffff888126cc6000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000565151f06950 CR3: 0000000041956000 CR4: 00000000003526f0
Call Trace:
<TASK>

dbAlloc+0x5a8/0xba0 fs/jfs/jfs_dmap.c:877
extBalloc fs/jfs/jfs_extent.c:336 [inline]
extAlloc+0x54a/0xfb0 fs/jfs/jfs_extent.c:127
jfs_get_block+0x346/0xab0 fs/jfs/inode.c:254
__block_write_begin_int+0x6b5/0x1900 fs/buffer.c:2145
block_write_begin+0x8a/0x120 fs/buffer.c:2256
jfs_write_begin+0x35/0x80 fs/jfs/inode.c:306
generic_perform_write+0x29d/0x8c0 mm/filemap.c:4242
generic_file_write_iter+0x118/0x550 mm/filemap.c:4385
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x5d5/0xb40 fs/read_write.c:686
ksys_write+0x14b/0x260 fs/read_write.c:738
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x7efe0c99eec9

Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48

RSP: 002b:00007efe0bfed038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007efe0cbf6090 RCX: 00007efe0c99eec9

RDX: 0000000000000014 RSI: 0000200000000380 RDI: 0000000000000005

RBP: 00007efe0ca21f91 R08: 0000000000000000 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000

R13: 00007efe0cbf6128 R14: 00007efe0cbf6090 R15: 00007ffeba24aff8
</TASK>


Tested on:

commit: 98ac9cc4 Merge tag 'f2fs-fix-6.18-rc2' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1606cb04580000

kernel config: https://syzkaller.appspot.com/x/.config?x=af9170887d81dea1
dashboard link: https://syzkaller.appspot.com/bug?extid=4b717071f1eecb2972df
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=17cfbdcd980000

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

fs/jfs/jfs_dmap.c:1375:27: error: expected ')'


Tested on:

commit: 6f3b6e91 Merge tag 'io_uring-6.18-20251016' of git://g..
git tree: upstream

kernel config: https://syzkaller.appspot.com/x/.config?x=af9170887d81dea1
dashboard link: https://syzkaller.appspot.com/bug?extid=4b717071f1eecb2972df
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=15617542580000