[v6.6] KASAN: null-ptr-deref Read in get_empty_nodes

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0a805b6ea8cd Linux 6.6.116
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=17523412580000
kernel config: https://syzkaller.appspot.com/x/.config?x=12606d4b8832c7e4
dashboard link: https://syzkaller.appspot.com/bug?extid=13bc02acf427225c620c
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: https://storage.googleapis.com/syzbot-assets/13874446b4b2/disk-0a805b6e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/69a5e59e1ade/vmlinux-0a805b6e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/322c0711f976/bzImage-0a805b6e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+13bc02...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: null-ptr-deref in instrument_atomic_read include/linux/instrumented.h:68 [inline]
BUG: KASAN: null-ptr-deref in _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
BUG: KASAN: null-ptr-deref in set_buffer_journal_new fs/reiserfs/reiserfs.h:2833 [inline]
BUG: KASAN: null-ptr-deref in get_empty_nodes+0x525/0x8c0 fs/reiserfs/fix_node.c:901
Read of size 8 at addr 0000000000000000 by task syz.0.201/6871

CPU: 1 PID: 6871 Comm: syz.0.201 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
<TASK>
dump_stack_lvl+0x16c/0x230 lib/dump_stack.c:106
kasan_report+0x117/0x150 mm/kasan/report.c:581
check_region_inline mm/kasan/generic.c:-1 [inline]
kasan_check_range+0x288/0x290 mm/kasan/generic.c:187
instrument_atomic_read include/linux/instrumented.h:68 [inline]
_test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
set_buffer_journal_new fs/reiserfs/reiserfs.h:2833 [inline]
get_empty_nodes+0x525/0x8c0 fs/reiserfs/fix_node.c:901
fix_nodes+0x1e52/0x82e0 fs/reiserfs/fix_node.c:2663
reiserfs_insert_item+0x9a1/0xbe0 fs/reiserfs/stree.c:2238
indirect2direct+0x596/0x9c0 fs/reiserfs/tail_conversion.c:283
maybe_indirect_to_direct fs/reiserfs/stree.c:1585 [inline]
reiserfs_cut_from_item+0x78b/0x1f10 fs/reiserfs/stree.c:1692
reiserfs_do_truncate+0xa3d/0x1340 fs/reiserfs/stree.c:1971
reiserfs_truncate_file+0x37a/0x7c0 fs/reiserfs/inode.c:2306
reiserfs_setattr+0xc0c/0x11a0 fs/reiserfs/inode.c:3392
notify_change+0xb0d/0xe10 fs/attr.c:499
do_truncate+0x19b/0x220 fs/open.c:66
do_sys_ftruncate+0x325/0x3d0 fs/open.c:194
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fb28638f6c9
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:00007fb287170038 EFLAGS: 00000246 ORIG_RAX: 000000000000004d
RAX: ffffffffffffffda RBX: 00007fb2865e6180 RCX: 00007fb28638f6c9
RDX: 0000000000000000 RSI: 0000000000000f88 RDI: 0000000000000004
RBP: 00007fb286411f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb2865e6218 R14: 00007fb2865e6180 R15: 00007ffcecc90f98
</TASK>
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup