[moderation] [mm?] KCSAN: data-race in copy_process / memcpy_and_pad (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: a0c83177734a Merge tag 'drm-fixes-2026-03-21' of https://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=146f2ada580000
kernel config: https://syzkaller.appspot.com/x/.config?x=3a78dd265deac3a9
dashboard link: https://syzkaller.appspot.com/bug?extid=6a8474e85c8b2af6410d
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [Liam.H...@oracle.com ak...@linux-foundation.org bse...@google.com da...@kernel.org dietmar....@arm.com juri....@redhat.com ke...@kernel.org linux-...@vger.kernel.org linu...@kvack.org l...@kernel.org mgo...@suse.de mho...@suse.com mi...@redhat.com pet...@infradead.org ros...@goodmis.org rp...@kernel.org sur...@google.com vba...@kernel.org vincent...@linaro.org vsch...@redhat.com]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/41a0e5c919b7/disk-a0c83177.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/70408718214e/vmlinux-a0c83177.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b610cc9ea81f/bzImage-a0c83177.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6a8474...@syzkaller.appspotmail.com

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

write to 0xffff888100232758 of 8 bytes by task 24103 on cpu 1:
__list_add include/linux/list.h:161 [inline]
list_add_tail include/linux/list.h:191 [inline]
copy_process+0x1e05/0x20b0 kernel/fork.c:2438
kernel_clone+0x16b/0x5d0 kernel/fork.c:2653
user_mode_thread+0x9c/0xd0 kernel/fork.c:2729
call_usermodehelper_exec_work+0x41/0x160 kernel/umh.c:171
process_one_work kernel/workqueue.c:3276 [inline]
process_scheduled_works+0x513/0xa10 kernel/workqueue.c:3359
worker_thread+0x58a/0x780 kernel/workqueue.c:3440
kthread+0x22a/0x280 kernel/kthread.c:436
ret_from_fork+0x150/0x360 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

read to 0xffff888100232180 of 3328 bytes by task 2 on cpu 0:
memcpy_and_pad+0x48/0x80 lib/string_helpers.c:1008
arch_dup_task_struct+0x2c/0x40 arch/x86/kernel/process.c:108
dup_task_struct+0x6e/0x950 kernel/fork.c:920
copy_process+0x37e/0x20b0 kernel/fork.c:2050
kernel_clone+0x16b/0x5d0 kernel/fork.c:2653
kernel_thread+0xe5/0x120 kernel/fork.c:2714
create_kthread kernel/kthread.c:459 [inline]
kthreadd+0x25b/0x320 kernel/kthread.c:817
ret_from_fork+0x150/0x360 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 UID: 0 PID: 2 Comm: kthreadd Tainted: G W syzkaller #0 PREEMPT(full)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
==================================================================


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