Re: [syzbot] [perf?] KCSAN: data-race in _free_event / perf_pending_task (2)

[Dmitry Vyukov]

On Mon, 14 Oct 2024 at 08:09, syzbot
<syzbot+e75157f5b04f8ff40e17@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    87d6aab2389e Merge tag 'for_linus' of git://git.kernel.org..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=10104f9f980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=a2f7ae2f221e9eae
> dashboard link: https://syzkaller.appspot.com/bug?extid=e75157f5b04f8ff40e17
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/cce40536bdc3/disk-87d6aab2.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/479edc06c8d8/vmlinux-87d6aab2.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/9d377c65ffca/bzImage-87d6aab2.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+e75157f5b04f8ff40e17@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> ==================================================================
> BUG: KCSAN: data-race in _free_event / perf_pending_task
>
> write to 0xffff8881155361e8 of 4 bytes by task 9574 on cpu 1:
>  perf_pending_task+0xe8/0x220 kernel/events/core.c:6976
>  task_work_run+0x13a/0x1a0 kernel/task_work.c:228
>  resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
>  exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
>  syscall_exit_to_user_mode+0xbe/0x130 kernel/entry/common.c:218
>  do_syscall_64+0xd6/0x1c0 arch/x86/entry/common.c:89
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> read to 0xffff8881155361e8 of 4 bytes by task 9573 on cpu 0:
>  perf_pending_task_sync kernel/events/core.c:5302 [inline]

+Marco, IIRC we assumed event->pending_work should only be accessed by
the owner task.
Here it's concurrently modified/changed. The other task calls
task_work_cancel on current based on the valus of this field, this
looks bad.

>  _free_event+0x3d/0xa10 kernel/events/core.c:5326
>  put_event kernel/events/core.c:5454 [inline]
>  perf_event_release_kernel+0x61a/0x670 kernel/events/core.c:5579
>  perf_release+0x1f/0x30 kernel/events/core.c:5589
>  __fput+0x17a/0x6d0 fs/file_table.c:431
>  ____fput+0x1c/0x30 fs/file_table.c:459
>  task_work_run+0x13a/0x1a0 kernel/task_work.c:228
>  resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
>  exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
>  __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
>  syscall_exit_to_user_mode+0xbe/0x130 kernel/entry/common.c:218
>  do_syscall_64+0xd6/0x1c0 arch/x86/entry/common.c:89
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> value changed: 0x7ad100bf -> 0x00000000
>
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 0 UID: 0 PID: 9573 Comm: syz.3.2265 Tainted: G        W          6.12.0-rc2-syzkaller-00006-g87d6aab2389e #0
> Tainted: [W]=WARN
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
> ==================================================================
>
>
> ---
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