Re: [syzbot] [kernel?] KASAN: slab-use-after-free Read in thread_group_cputime

[Jens Axboe <axboe@kernel.dk>]

On 1/10/25 7:13 AM, Pavel Begunkov wrote:
> On 1/10/25 13:56, Dmitry Vyukov wrote:
>> On Fri, 10 Jan 2025 at 14:51, syzbot
>> <syzbot+3d92cfcfa84070b0a470@syzkaller.appspotmail.com> wrote:
>>>
>>> Hello,
>>>
>>> syzbot found the following issue on:
>>>
>>> HEAD commit:    ccb98ccef0e5 Merge tag 'platform-drivers-x86-v6.13-4' of g..
>>> git tree:       upstream
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=1377fac4580000
>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=1c541fa8af5c9cc7
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=3d92cfcfa84070b0a470
>>> 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/6e96673b1b94/disk-ccb98cce.raw.xz
>>> vmlinux: https://storage.googleapis.com/syzbot-assets/528385411880/vmlinux-ccb98cce.xz
>>> kernel image: https://storage.googleapis.com/syzbot-assets/b061a4d50538/bzImage-ccb98cce.xz
>>>
>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>> Reported-by: syzbot+3d92cfcfa84070b0a470@syzkaller.appspotmail.com
>>>
>>> ==================================================================
>>> BUG: KASAN: slab-use-after-free in thread_group_cputime+0x409/0x700 kernel/sched/cputime.c:341
>>> Read of size 8 at addr ffff88803578c510 by task syz.2.3223/27552
>>>
>>> CPU: 1 UID: 0 PID: 27552 Comm: syz.2.3223 Not tainted 6.13.0-rc5-syzkaller-00004-gccb98ccef0e5 #0
>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
>>> Call Trace:
>>>   <TASK>
>>>   __dump_stack lib/dump_stack.c:94 [inline]
>>>   dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
>>>   print_address_description mm/kasan/report.c:378 [inline]
>>>   print_report+0x169/0x550 mm/kasan/report.c:489
>>>   kasan_report+0x143/0x180 mm/kasan/report.c:602
>>>   thread_group_cputime+0x409/0x700 kernel/sched/cputime.c:341
>>>   thread_group_cputime_adjusted+0xa6/0x340 kernel/sched/cputime.c:639
>>>   getrusage+0x1000/0x1340 kernel/sys.c:1863
>>>   io_uring_show_fdinfo+0xdfe/0x1770 io_uring/fdinfo.c:197
>>
>> This looks to be more likely an io-uring issue rather than cputime.c
>>
>> #syz set subsystems: io-uring
>>
>> +maintainers
> 
> Thanks. It probably needs something like below.
> 
> diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c
> index 6df5e649c413..5768e31e99b1 100644
> --- a/io_uring/sqpoll.c
> +++ b/io_uring/sqpoll.c
> @@ -268,8 +268,12 @@ static int io_sq_thread(void *data)
>         DEFINE_WAIT(wait);
> 
>         /* offload context creation failed, just exit */
> -       if (!current->io_uring)
> +       if (!current->io_uring) {
> +               mutex_lock(&sqd->lock);
> +               sqd->thread = NULL;
> +               mutex_unlock(&sqd->lock);
>                 goto err_out;
> +       }
> 
>         snprintf(buf, sizeof(buf), "iou-sqp-%d", sqd->task_pid);
>         set_task_comm(current, buf);

Indeed - can you send that out and I can include it in this weeks pull?

-- 
Jens Axboe