[moderation] [kernel?] KCSAN: data-race in prepare_signal / ptrace_attach (14)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d358e5254674 Merge tag 'for-6.19/dm-changes' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1095a61a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=9230b46da882b43c
dashboard link: https://syzkaller.appspot.com/bug?extid=16fbfb7b2c4b98196060
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
CC: [linux-...@vger.kernel.org ol...@redhat.com]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/4f60a2fdbe51/disk-d358e525.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/127ec1e804fb/vmlinux-d358e525.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2402e3e45961/bzImage-d358e525.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+16fbfb...@syzkaller.appspotmail.com

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

write to 0xffff888104408030 of 4 bytes by task 17687 on cpu 1:
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+0x2ee5/0x3000 arch/x86/include/generated/asm/syscalls_64.h:102
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff888104408030 of 4 bytes by task 17693 on cpu 0:
sig_ignored kernel/signal.c:121 [inline]
prepare_signal+0x450/0x670 kernel/signal.c:935
__send_signal_locked+0x30/0x760 kernel/signal.c:1053
send_signal_locked+0x34e/0x3c0 kernel/signal.c:1216
do_send_sig_info+0x9f/0xf0 kernel/signal.c:1269
do_send_specific+0xca/0x110 kernel/signal.c:4131
do_tkill kernel/signal.c:4152 [inline]
__do_sys_tgkill kernel/signal.c:4171 [inline]
__se_sys_tgkill kernel/signal.c:4165 [inline]
__x64_sys_tgkill+0x127/0x160 kernel/signal.c:4165
x64_sys_call+0x2d22/0x3000 arch/x86/include/generated/asm/syscalls_64.h:235
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xd8/0x2a0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000 -> 0x00000001

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 17693 Comm: syz.5.4942 Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


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