[syzbot] [ocfs2?] UBSAN: array-index-out-of-bounds in ocfs2_grow_tree

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0048fbb4011e Merge tag 'locking-futex-2025-12-10' of git:/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16457992580000
kernel config: https://syzkaller.appspot.com/x/.config?x=de48dccdf203ea90
dashboard link: https://syzkaller.appspot.com/bug?extid=7c93eb455e59ca14c7cd
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-0048fbb4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d7e936edc53d/vmlinux-0048fbb4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/84b695b1f82c/bzImage-0048fbb4.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+7c93eb...@syzkaller.appspotmail.com

------------[ cut here ]------------
UBSAN: array-index-out-of-bounds in fs/ocfs2/alloc.c:1090:9
index -1 is out of range for type 'struct ocfs2_extent_rec[] __counted_by(l_count)' (aka 'struct ocfs2_extent_rec[]')
CPU: 0 UID: 0 PID: 5338 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
ubsan_epilogue+0xa/0x40 lib/ubsan.c:233
__ubsan_handle_out_of_bounds+0xe9/0xf0 lib/ubsan.c:455
ocfs2_sum_rightmost_rec fs/ocfs2/alloc.c:1090 [inline]
ocfs2_shift_tree_depth fs/ocfs2/alloc.c:1412 [inline]
ocfs2_grow_tree+0x35af/0x3dc0 fs/ocfs2/alloc.c:1560
ocfs2_insert_extent+0xb54/0x15a0 fs/ocfs2/alloc.c:4755
ocfs2_add_clusters_in_btree+0x64f/0xf50 fs/ocfs2/alloc.c:4857
ocfs2_add_inode_data+0xce/0x120 fs/ocfs2/file.c:550
ocfs2_write_cluster fs/ocfs2/aops.c:1115 [inline]
ocfs2_write_cluster_by_desc+0x547/0x1cf0 fs/ocfs2/aops.c:1219
ocfs2_write_begin_nolock+0x3180/0x4300 fs/ocfs2/aops.c:1796
ocfs2_write_begin+0x1bb/0x310 fs/ocfs2/aops.c:1884
generic_perform_write+0x2c5/0x900 mm/filemap.c:4314
ocfs2_file_write_iter+0x1582/0x1cf0 fs/ocfs2/file.c:2469
new_sync_write fs/read_write.c:593 [inline]
vfs_write+0x5c9/0xb30 fs/read_write.c:686
ksys_write+0x145/0x250 fs/read_write.c:738
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6962b8f7c9
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:00007f6963a6b038 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f6962de6090 RCX: 00007f6962b8f7c9
RDX: 0000000000000140 RSI: 0000000000000000 RDI: 0000000000000005
RBP: 00007f6962c13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6962de6128 R14: 00007f6962de6090 R15: 00007ffc0ec42858
</TASK>
---[ end trace ]---


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