[moderation] [kernel?] KCSAN: data-race in memchr / number (4)

Hello,

syzbot found the following issue on:

HEAD commit: 9afe652958c3 Merge tag 'x86_urgent_for_6.16-rc3' of git://..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=129f9e82580000
kernel config: https://syzkaller.appspot.com/x/.config?x=25d7df3a6a1d1ea6
dashboard link: https://syzkaller.appspot.com/bug?extid=f8211c5c8f80af6b7c0e
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
CC: [[email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected]]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/e970c17d447e/disk-9afe6529.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3eeb72064f16/vmlinux-9afe6529.xz
kernel image: https://storage.googleapis.com/syzbot-assets/dec9f2e49870/bzImage-9afe6529.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]

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

write to 0xffffffff88e6366c of 1 bytes by task 10069 on cpu 0:
number+0x6af/0xab0 lib/vsprintf.c:545
vsnprintf+0x691/0x890 lib/vsprintf.c:2838
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
__show_regs+0xd6/0x440 arch/x86/kernel/process_64.c:90
show_regs_if_on_stack arch/x86/kernel/dumpstack.c:165 [inline]
show_trace_log_lvl+0x423/0x560 arch/x86/kernel/dumpstack.c:298
__dump_stack+0x1d/0x30 lib/dump_stack.c:94
dump_stack_lvl+0xe8/0x140 lib/dump_stack.c:120
dump_stack+0x15/0x1b lib/dump_stack.c:129
fail_dump lib/fault-inject.c:73 [inline]
should_fail_ex+0x265/0x280 lib/fault-inject.c:174
should_fail+0xb/0x20 lib/fault-inject.c:184
should_fail_usercopy+0x1a/0x20 lib/fault-inject-usercopy.c:37
strncpy_from_user+0x25/0x230 lib/strncpy_from_user.c:118
import_xattr_name fs/xattr.c:591 [inline]
setxattr_copy fs/xattr.c:611 [inline]
path_setxattrat+0xeb/0x310 fs/xattr.c:701
__do_sys_fsetxattr fs/xattr.c:761 [inline]
__se_sys_fsetxattr fs/xattr.c:758 [inline]
__x64_sys_fsetxattr+0x6b/0x80 fs/xattr.c:758
x64_sys_call+0x2f7c/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:191
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

read to 0xffffffff88e6366c of 1 bytes by task 10065 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
find_first_fitting_seq+0x1b1/0x320 kernel/printk/printk.c:1589
syslog_print_all+0x111/0x3a0 kernel/printk/printk.c:1721
do_syslog+0x2fd/0x7e0 kernel/printk/printk.c:1799
__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: 0x36 -> 0x30

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 10065 Comm: syz.2.2447 Not tainted 6.16.0-rc2-syzkaller-00024-g9afe652958c3 #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================


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