[v6.6] UBSAN: array-index-out-of-bounds in dbAllocBits

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 4fc00fe35d46 Linux 6.6.129
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=138fddaa580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c5b35c4db8465904
dashboard link: https://syzkaller.appspot.com/bug?extid=7e9c72fc2a1b79c95dc1
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=178fddaa580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=108e48ba580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b69a43016252/disk-4fc00fe3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/240ac8d2cf70/vmlinux-4fc00fe3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/67c7958e5edb/bzImage-4fc00fe3.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/a5f9147f9781/mount_0.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=14147054580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7e9c72...@syzkaller.appspotmail.com

syz.0.17[5914]: memfd_create() called without MFD_EXEC or MFD_NOEXEC_SEAL set
loop0: detected capacity change from 0 to 32768
================================================================================
UBSAN: array-index-out-of-bounds in fs/jfs/jfs_dmap.c:2257:2
index 10240 is out of range for type 's64[128]' (aka 'long long[128]')
CPU: 1 PID: 5914 Comm: syz.0.17 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
<TASK>
dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
ubsan_epilogue+0xa/0x30 lib/ubsan.c:217
__ubsan_handle_out_of_bounds+0xe3/0xf0 lib/ubsan.c:348
dbAllocBits+0xa04/0xa50 fs/jfs/jfs_dmap.c:2257
dbAllocDmap fs/jfs/jfs_dmap.c:2034 [inline]
dbAllocDmapLev+0x1bd/0x3c0 fs/jfs/jfs_dmap.c:1988
dbAllocCtl+0x148/0x9b0 fs/jfs/jfs_dmap.c:1825
dbAllocAG+0x1e7/0xfe0 fs/jfs/jfs_dmap.c:1353
dbAlloc+0x5aa/0xba0 fs/jfs/jfs_dmap.c:877
dtSplitUp fs/jfs/jfs_dtree.c:982 [inline]
dtInsert+0xb13/0x5de0 fs/jfs/jfs_dtree.c:871
jfs_create+0x734/0xac0 fs/jfs/namei.c:137
lookup_open fs/namei.c:3496 [inline]
open_last_lookups fs/namei.c:3564 [inline]
path_openat+0x12a0/0x3230 fs/namei.c:3794
do_filp_open+0x1f5/0x430 fs/namei.c:3824
do_sys_openat2+0x134/0x1d0 fs/open.c:1421
do_sys_open fs/open.c:1436 [inline]
__do_sys_creat fs/open.c:1514 [inline]
__se_sys_creat fs/open.c:1508 [inline]
__x64_sys_creat+0x90/0xb0 fs/open.c:1508
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f8a5579c799
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fffb9f93f58 EFLAGS: 00000246 ORIG_RAX: 0000000000000055
RAX: ffffffffffffffda RBX: 00007f8a55a15fa0 RCX: 00007f8a5579c799
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000200000000580
RBP: 00007f8a55832bd9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8a55a15fac R14: 00007f8a55a15fa0 R15: 00007f8a55a15fa0
</TASK>
================================================================================


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