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

syzbot
2025-10-17T04:35:33Z

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+4b717071f1eecb2972df@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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