[moderation] [audit?] KCSAN: data-race in memchr / string (6)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 2c4a1f3fe03e Merge tag 'bpf-fixes' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1686d9d4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f437300db311c188
dashboard link: https://syzkaller.appspot.com/bug?extid=3984271db8fa10af29b7
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
CC: [au...@vger.kernel.org epa...@redhat.com linux-...@vger.kernel.org pa...@paul-moore.com]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/655e44254540/disk-2c4a1f3f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0b107f49d633/vmlinux-2c4a1f3f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1ae745fedaa8/bzImage-2c4a1f3f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+398427...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in memchr / string

write to 0xffffffff88e5385b of 1 bytes by task 29 on cpu 0:
string_nocheck lib/vsprintf.c:643 [inline]
string+0x187/0x220 lib/vsprintf.c:721
vsnprintf+0x532/0x890 lib/vsprintf.c:2874
vscnprintf+0x41/0x90 lib/vsprintf.c:2939
printk_sprint+0x30/0x2d0 kernel/printk/printk.c:2216
vprintk_store+0x599/0x860 kernel/printk/printk.c:2336
vprintk_emit+0x178/0x650 kernel/printk/printk.c:2426
vprintk_default+0x26/0x30 kernel/printk/printk.c:2465
vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
_printk+0x79/0xa0 kernel/printk/printk.c:2475
kauditd_printk_skb kernel/audit.c:546 [inline]
kauditd_hold_skb+0x1b1/0x1c0 kernel/audit.c:581
kauditd_send_queue+0x273/0x2c0 kernel/audit.c:766
kauditd_thread+0x421/0x630 kernel/audit.c:890
kthread+0x486/0x510 kernel/kthread.c:464
ret_from_fork+0xda/0x150 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffffff88e5385b of 1 bytes by task 19606 on cpu 1:
memchr+0x28/0x50 lib/string.c:809
_Z6memchrPKvU25pass_dynamic_object_size0im include/linux/fortify-string.h:739 [inline]
count_lines kernel/printk/printk_ringbuffer.c:1797 [inline]
copy_data kernel/printk/printk_ringbuffer.c:1843 [inline]
prb_read kernel/printk/printk_ringbuffer.c:1936 [inline]
_prb_read_valid+0x65d/0x920 kernel/printk/printk_ringbuffer.c:2113
prb_read_valid_info+0x66/0x90 kernel/printk/printk_ringbuffer.c:2219
do_syslog+0x6e2/0x7e0 kernel/printk/printk.c:1853
__do_sys_syslog kernel/printk/printk.c:1877 [inline]
__se_sys_syslog kernel/printk/printk.c:1875 [inline]
__x64_sys_syslog+0x41/0x50 kernel/printk/printk.c:1875
x64_sys_call+0x2ea0/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:104
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd2/0x200 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x45 -> 0x36

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 19606 Comm: syz.0.6195 Not tainted 6.16.0-rc1-syzkaller-00010-g2c4a1f3fe03e #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.