[moderation] [audit?] KCSAN: data-race in memchr / string (7)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0d97f2067c16 Merge tag 'for-linus' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1713f5cd980000
kernel config: https://syzkaller.appspot.com/x/.config?x=6ffeccb21767c55b
dashboard link: https://syzkaller.appspot.com/bug?extid=c4535ed1abdf56b12a8b
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
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/f0c4fb87563d/disk-0d97f206.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1ed23ffad01d/vmlinux-0d97f206.xz
kernel image: https://storage.googleapis.com/syzbot-assets/93f7c55ce389/bzImage-0d97f206.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c4535e...@syzkaller.appspotmail.com

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

write to 0xffffffff88e581c2 of 1 bytes by task 29 on cpu 1:
string_nocheck lib/vsprintf.c:657 [inline]
string+0x187/0x220 lib/vsprintf.c:735
vsnprintf+0x532/0x890 lib/vsprintf.c:2926
vscnprintf+0x41/0x90 lib/vsprintf.c:2991
printk_sprint+0x30/0x2d0 kernel/printk/printk.c:2189
vprintk_store+0x599/0x860 kernel/printk/printk.c:2309
vprintk_emit+0x10d/0x580 kernel/printk/printk.c:2399
vprintk_default+0x26/0x30 kernel/printk/printk.c:2438
vprintk+0x1d/0x30 kernel/printk/printk_safe.c:82
_printk+0x79/0xa0 kernel/printk/printk.c:2448
kauditd_printk_skb kernel/audit.c:583 [inline]
kauditd_hold_skb+0x1b1/0x1c0 kernel/audit.c:618
kauditd_send_queue+0x273/0x2c0 kernel/audit.c:803
kauditd_thread+0x421/0x630 kernel/audit.c:927
kthread+0x486/0x510 kernel/kthread.c:463
ret_from_fork+0x122/0x1b0 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffffffff88e581c2 of 1 bytes by task 27980 on cpu 0:
memchr+0x28/0x50 lib/string.c:809
memchr include/linux/fortify-string.h:739 [inline]
count_lines kernel/printk/printk_ringbuffer.c:1815 [inline]
copy_data kernel/printk/printk_ringbuffer.c:1861 [inline]
prb_read kernel/printk/printk_ringbuffer.c:1954 [inline]
_prb_read_valid+0x65d/0x920 kernel/printk/printk_ringbuffer.c:2131
prb_read_valid_info+0x66/0x90 kernel/printk/printk_ringbuffer.c:2238
do_syslog+0x6e2/0x7e0 kernel/printk/printk.c:1826
__do_sys_syslog kernel/printk/printk.c:1850 [inline]
__se_sys_syslog kernel/printk/printk.c:1848 [inline]
__x64_sys_syslog+0x41/0x50 kernel/printk/printk.c:1848
x64_sys_call+0x2f45/0x3000 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: 0x29 -> 0x6d

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 27980 Comm: syz.9.5827 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
==================================================================


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