Re: [syzbot] [bcachefs?] KASAN: global-out-of-bounds Read in rcu_pending_exit

syzbot
2025-02-20T18:21:22Z

syzbot has found a reproducer for the following issue on:

HEAD commit: 87a132e73910 Merge tag 'mm-hotfixes-stable-2025-02-19-17-4..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=175775b0580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b7bde34acd8f53b1
dashboard link: https://syzkaller.appspot.com/bug?extid=e733ab672a1b6724c27f
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16d8aba4580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11e1dae4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4a88f50cb21d/disk-87a132e7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d970e0210e8a/vmlinux-87a132e7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9b6329058ef7/bzImage-87a132e7.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/f06af6381842/mount_0.gz

The issue was bisected to:

commit d97de0d017cde0d442c3d144b4f969f43064cc0f
Author: Kent Overstreet <kent.overstreet@linux.dev>
Date: Tue Aug 13 01:31:25 2024 +0000

bcachefs: Make bkey_fsck_err() a wrapper around fsck_err()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=13432ef8580000
final oops: https://syzkaller.appspot.com/x/report.txt?x=10c32ef8580000
console output: https://syzkaller.appspot.com/x/log.txt?x=17432ef8580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e733ab672a1b6724c27f@syzkaller.appspotmail.com
Fixes: d97de0d017cd ("bcachefs: Make bkey_fsck_err() a wrapper around fsck_err()")

------------[ cut here ]------------
==================================================================
BUG: KASAN: global-out-of-bounds in string_nocheck lib/vsprintf.c:632 [inline]
BUG: KASAN: global-out-of-bounds in string+0x229/0x2b0 lib/vsprintf.c:714
Read of size 1 at addr ffffffff8c74c10a by task syz-executor504/5826

CPU: 1 UID: 0 PID: 5826 Comm: syz-executor504 Not tainted 6.14.0-rc3-syzkaller-00079-g87a132e73910 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:408 [inline]
print_report+0x16e/0x5b0 mm/kasan/report.c:521
kasan_report+0x143/0x180 mm/kasan/report.c:634
string_nocheck lib/vsprintf.c:632 [inline]
string+0x229/0x2b0 lib/vsprintf.c:714
vsnprintf+0x8b4/0x1220 lib/vsprintf.c:2843
vprintk_store+0x482/0x1240 kernel/printk/printk.c:2279
vprintk_emit+0x271/0xa10 kernel/printk/printk.c:2408
__warn_printk+0x263/0x360 kernel/panic.c:797
look_up_lock_class+0xdb/0x170 kernel/locking/lockdep.c:938
register_lock_class+0x102/0x980 kernel/locking/lockdep.c:1292
__lock_acquire+0xf3/0x2100 kernel/locking/lockdep.c:5103
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
__raw_spin_lock_irq include/linux/spinlock_api_smp.h:119 [inline]
_raw_spin_lock_irq+0xd3/0x120 kernel/locking/spinlock.c:170
spin_lock_irq include/linux/spinlock.h:376 [inline]
rcu_pending_has_pending_or_armed fs/bcachefs/rcu_pending.c:592 [inline]
rcu_pending_exit+0x13f/0x7a0 fs/bcachefs/rcu_pending.c:610
bch2_fs_btree_key_cache_exit+0x8d1/0x9f0 fs/bcachefs/btree_key_cache.c:778
__bch2_fs_free fs/bcachefs/super.c:569 [inline]
bch2_fs_release+0x206/0x7b0 fs/bcachefs/super.c:624
kobject_cleanup lib/kobject.c:689 [inline]
kobject_release lib/kobject.c:720 [inline]
kref_put include/linux/kref.h:65 [inline]
kobject_put+0x231/0x480 lib/kobject.c:737
deactivate_locked_super+0xc6/0x130 fs/super.c:473
cleanup_mnt+0x41f/0x4b0 fs/namespace.c:1413
task_work_run+0x251/0x310 kernel/task_work.c:227
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:329 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0x13f/0x340 kernel/entry/common.c:218
do_syscall_64+0x100/0x230 arch/x86/entry/common.c:89
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f7e807c2577
Code: 07 00 48 83 c4 08 5b 5d c3 66 2e 0f 1f 84 00 00 00 00 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 a6 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 b8 ff ff ff f7 d8 64 89 02 b8
RSP: 002b:00007ffeee02cd28 EFLAGS: 00000206 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00007f7e807c2577
RDX: 0000000000000000 RSI: 0000000000000009 RDI: 00007ffeee02cde0
RBP: 00007ffeee02cde0 R08: 0000000000000000 R09: 0000000000000000
R10: 00000000ffffffff R11: 0000000000000206 R12: 00007ffeee02de50
R13: 000055557adeb6c0 R14: 431bde82d7b634db R15: 00007ffeee02de70
</TASK>

The buggy address belongs to the variable:
.str+0xa/0x20

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0xc74c
flags: 0xfff00000002000(reserved|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000002000 ffffea000031d308 ffffea000031d308 0000000000000000
raw: 0000000000000000 0000000000000000 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner info is not present (never set?)

Memory state around the buggy address:
ffffffff8c74c000: 00 05 f9 f9 02 f9 f9 f9 06 f9 f9 f9 00 00 00 00
ffffffff8c74c080: f9 f9 f9 f9 00 00 00 00 00 00 00 00 00 00 00 00
>ffffffff8c74c100: 00 01 f9 f9 00 00 00 04 f9 f9 f9 f9 00 00 00 00
^
ffffffff8c74c180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffffffff8c74c200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================

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