In the Linux kernel, the following vulnerability has been resolved:

FS:JFS:UBSAN:array-index-out-of-bounds in dbAdjTree

Syzkaller reported the following issue:

UBSAN: array-index-out-of-bounds in fs/jfs/jfs_dmap.c:2867:6
index 196694 is out of range for type ‘s8[1365]’ (aka ‘signed char[1365]’)
CPU: 1 PID: 109 Comm: jfsCommit Not tainted 6.6.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/04/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
ubsan_epilogue lib/ubsan.c:217 [inline]
__ubsan_handle_out_of_bounds+0x11c/0x150 lib/ubsan.c:348
dbAdjTree+0x474/0x4f0 fs/jfs/jfs_dmap.c:2867
dbJoin+0x210/0x2d0 fs/jfs/jfs_dmap.c:2834
dbFreeBits+0x4eb/0xda0 fs/jfs/jfs_dmap.c:2331
dbFreeDmap fs/jfs/jfs_dmap.c:2080 [inline]
dbFree+0x343/0x650 fs/jfs/jfs_dmap.c:402
txFreeMap+0x798/0xd50 fs/jfs/jfs_txnmgr.c:2534
txUpdateMap+0x342/0x9e0
txLazyCommit fs/jfs/jfs_txnmgr.c:2664 [inline]
jfs_lazycommit+0x47a/0xb70 fs/jfs/jfs_txnmgr.c:2732
kthread+0x2d3/0x370 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304
</TASK>

Kernel panic - not syncing: UBSAN: panic_on_warn set …
CPU: 1 PID: 109 Comm: jfsCommit Not tainted 6.6.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/04/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1e7/0x2d0 lib/dump_stack.c:106
panic+0x30f/0x770 kernel/panic.c:340
check_panic_on_warn+0x82/0xa0 kernel/panic.c:236
ubsan_epilogue lib/ubsan.c:223 [inline]
__ubsan_handle_out_of_bounds+0x13c/0x150 lib/ubsan.c:348
dbAdjTree+0x474/0x4f0 fs/jfs/jfs_dmap.c:2867
dbJoin+0x210/0x2d0 fs/jfs/jfs_dmap.c:2834
dbFreeBits+0x4eb/0xda0 fs/jfs/jfs_dmap.c:2331
dbFreeDmap fs/jfs/jfs_dmap.c:2080 [inline]
dbFree+0x343/0x650 fs/jfs/jfs_dmap.c:402
txFreeMap+0x798/0xd50 fs/jfs/jfs_txnmgr.c:2534
txUpdateMap+0x342/0x9e0
txLazyCommit fs/jfs/jfs_txnmgr.c:2664 [inline]
jfs_lazycommit+0x47a/0xb70 fs/jfs/jfs_txnmgr.c:2732
kthread+0x2d3/0x370 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304
</TASK>
Kernel Offset: disabled
Rebooting in 86400 seconds…

The issue is caused when the value of lp becomes greater than
CTLTREESIZE which is the max size of stree. Adding a simple check
solves this issue.

Dave:
As the function returns a void, good error handling
would require a more intrusive code reorganization, so I modified
Osama’s patch at use WARN_ON_ONCE for lack of a cleaner option.

The patch is tested via syzbot.