linux-kernel - Re: 回复: [syzbot] KASAN: use-after-free Read in io_worker_handle

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Date:   Sat, 22 May 2021 01:55:37 +0100
From:   Pavel Begunkov <asml.silence@...il.com>
To:     "Zhang, Qiang" <Qiang.Zhang@...driver.com>,
        syzbot <syzbot+6cb11ade52aa17095297@...kaller.appspotmail.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "io-uring@...r.kernel.org" <io-uring@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "syzkaller-bugs@...glegroups.com" <syzkaller-bugs@...glegroups.com>
Subject: Re: 回复: [syzbot] KASAN: use-after-free Read in io_worker_handle_work

On 5/21/21 9:45 AM, Zhang, Qiang wrote:
[...]
> It looks like 
> thread iou-wrk-28796 in io-wq(A)  access wqe in the wait queue(data->hash->wait),  but this wqe  has been free due to the destruction of another io-wq(B).
> 
> Should we after wait for all iou-wrk thread exit in the io-wq，  remove wqe from the waiting queue (data->hash->wait).   prevent some one  wqe  belonging to this io-wq , may be still existing in the (data->hash->wait)queue before releasing. 

The guess looks reasonable, it's likely a problem.
Not sure about the diff, it seems racy but I need to
take a closer look to say for sure


> look forward to your opinion.
> 
> --- a/fs/io-wq.c
> +++ b/fs/io-wq.c
> @@ -1003,13 +1003,17 @@ static void io_wq_exit_workers(struct io_wq *wq)
>                 struct io_wqe *wqe = wq->wqes[node];
>  
>                 io_wq_for_each_worker(wqe, io_wq_worker_wake, NULL);
> -               spin_lock_irq(&wq->hash->wait.lock);
> -               list_del_init(&wq->wqes[node]->wait.entry);
> -               spin_unlock_irq(&wq->hash->wait.lock);
>         }
>         rcu_read_unlock();
>         io_worker_ref_put(wq);
>         wait_for_completion(&wq->worker_done);
> +       for_each_node(node) {
> +               struct io_wqe *wqe = wq->wqes[node];
> +
> +               spin_lock_irq(&wq->hash->wait.lock);
> +               list_del_init(&wq->wqes[node]->wait.entry);
> +               spin_unlock_irq(&wq->hash->wait.lock);
> +       }
>         put_task_struct(wq->task);
>         wq->task = NULL;
>  }

-- 
Pavel Begunkov