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

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Message-ID: <7243f420-58c5-60e4-6c8f-c16a90766c0c@gmail.com>
Date:   Sun, 23 May 2021 21:07:36 +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 5/22/21 1:55 AM, Pavel Begunkov wrote:
> 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

It looks sensible, please send a patch


>> 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