[moderation] [mm?] KCSAN: data-race in copy_process / memcpy_and_pad (2)

[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=1525f992580000
kernel config: https://syzkaller.appspot.com/x/.config?x=9230b46da882b43c
dashboard link: https://syzkaller.appspot.com/bug?extid=e124185ab9c4c2e9a1aa
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
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 lorenzo...@oracle.com mgo...@suse.de mho...@suse.com mi...@redhat.com pet...@infradead.org ros...@goodmis.org rp...@kernel.org sur...@google.com vba...@suse.cz 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/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+e12418...@syzkaller.appspotmail.com

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

write to 0xffff8881001d9638 of 8 bytes by task 76 on cpu 0:
__list_add include/linux/list.h:161 [inline]
list_add_tail include/linux/list.h:191 [inline]
copy_process+0x1c54/0x1ef0 kernel/fork.c:2436
kernel_clone+0x16c/0x5c0 kernel/fork.c:2651
user_mode_thread+0x7d/0xb0 kernel/fork.c:2727
call_usermodehelper_exec_work+0x41/0x160 kernel/umh.c:171
process_one_work kernel/workqueue.c:3257 [inline]
process_scheduled_works+0x4ce/0x9d0 kernel/workqueue.c:3340
worker_thread+0x582/0x770 kernel/workqueue.c:3421
kthread+0x489/0x510 kernel/kthread.c:463
ret_from_fork+0x149/0x290 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

read to 0xffff8881001d9080 of 3264 bytes by task 2 on cpu 1:
memcpy_and_pad+0x48/0x80 lib/string_helpers.c:1007
arch_dup_task_struct+0x2c/0x40 arch/x86/kernel/process.c:108
dup_task_struct+0x6e/0x950 kernel/fork.c:919
copy_process+0x37d/0x1ef0 kernel/fork.c:2052
kernel_clone+0x16c/0x5c0 kernel/fork.c:2651
kernel_thread+0xad/0xe0 kernel/fork.c:2712
create_kthread kernel/kthread.c:486 [inline]
kthreadd+0x28d/0x360 kernel/kthread.c:844
ret_from_fork+0x149/0x290 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 2 Comm: kthreadd Tainted: G W syzkaller #0 PREEMPT(voluntary)
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup