[moderation] [kernel?] KCSAN: data-race in memcpy_and_pad / release_task

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c0c9379f235d Merge tag 'usb-6.16-rc1' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17b8e20c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b473f115729830aa
dashboard link: https://syzkaller.appspot.com/bug?extid=d06247460da822ececd6
compiler: Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
CC: [linux-...@vger.kernel.org]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/5e69bdb57e13/disk-c0c9379f.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/2af7036e5167/vmlinux-c0c9379f.xz
kernel image: https://storage.googleapis.com/syzbot-assets/00cdb2f97fc4/bzImage-c0c9379f.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d06247...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in memcpy_and_pad / release_task

write to 0xffff8881199204c8 of 8 bytes by task 3037 on cpu 0:
__list_del include/linux/list.h:195 [inline]
__list_del_entry include/linux/list.h:218 [inline]
list_del_rcu include/linux/rculist.h:168 [inline]
__unhash_process kernel/exit.c:148 [inline]
__exit_signal kernel/exit.c:211 [inline]
release_task+0x6f9/0xb60 kernel/exit.c:266
wait_task_zombie kernel/exit.c:1266 [inline]
wait_consider_task+0x113f/0x1650 kernel/exit.c:1493
do_wait_pid kernel/exit.c:1632 [inline]
__do_wait+0x34a/0x510 kernel/exit.c:1667
do_wait+0xb7/0x260 kernel/exit.c:1708
kernel_wait4+0x16b/0x1e0 kernel/exit.c:1867
__do_sys_wait4 kernel/exit.c:1895 [inline]
__se_sys_wait4 kernel/exit.c:1891 [inline]
__x64_sys_wait4+0x91/0x120 kernel/exit.c:1891
x64_sys_call+0x26c8/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:62
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 0xffff888119920000 of 3200 bytes by task 5444 on cpu 1:
memcpy_and_pad+0x48/0x80 lib/string_helpers.c:1007
arch_dup_task_struct+0x2c/0x40 arch/x86/kernel/process.c:98
dup_task_struct+0x83/0x6a0 kernel/fork.c:873
copy_process+0x399/0x1fe0 kernel/fork.c:1999
kernel_clone+0x16c/0x5b0 kernel/fork.c:2599
__do_sys_clone3 kernel/fork.c:2903 [inline]
__se_sys_clone3+0x1c2/0x200 kernel/fork.c:2882
__x64_sys_clone3+0x31/0x40 kernel/fork.c:2882
x64_sys_call+0x10c9/0x2fb0 arch/x86/include/generated/asm/syscalls_64.h:436
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

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 5444 Comm: syz.2.544 Not tainted 6.15.0-syzkaller-13473-gc0c9379f235d #0 PREEMPT(voluntary)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
==================================================================


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