[moderation] [kernel?] KCSAN: data-race in get_signal / ptrace_attach (8)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ac3fd01e4c1e Linux 6.18-rc7
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1610b8b4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=655255e3ef31c19b
dashboard link: https://syzkaller.appspot.com/bug?extid=aa76b57099e518972841
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [linux-...@vger.kernel.org lu...@kernel.org pet...@infradead.org tg...@linutronix.de]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0b87e3335067/disk-ac3fd01e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5d86405bc71d/vmlinux-ac3fd01e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5cdf269de51b/bzImage-ac3fd01e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+aa76b5...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in get_signal / ptrace_attach

write to 0xffff88811ad66330 of 4 bytes by task 16548 on cpu 0:
ptrace_attach+0x26c/0x590 kernel/ptrace.c:462
__do_sys_ptrace kernel/ptrace.c:1405 [inline]
__se_sys_ptrace+0x146/0x2c0 kernel/ptrace.c:1387
__x64_sys_ptrace+0x55/0x70 kernel/ptrace.c:1387
x64_sys_call+0x2870/0x3000 arch/x86/include/generated/asm/syscalls_64.h:102
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 0xffff88811ad66330 of 4 bytes by task 16549 on cpu 1:
get_signal+0x3a0/0xf70 kernel/signal.c:2919
arch_do_signal_or_restart+0x96/0x440 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop kernel/entry/common.c:40 [inline]
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
irqentry_exit_to_user_mode+0x5b/0xa0 kernel/entry/common.c:73
irqentry_exit+0x12/0x50 kernel/entry/common.c:191
asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618

value changed: 0x00000000 -> 0x00000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 16549 Comm: syz.8.4231 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
==================================================================


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