Re: [PATCH 5.11] io_uring: NULL files dereference by SQPOLL

Pavel Begunkov
2020-11-07T22:50:47Z

On 07/11/2020 22:28, Jens Axboe wrote:
> On 11/7/20 2:54 PM, Pavel Begunkov wrote:
>> On 07/11/2020 21:18, Pavel Begunkov wrote:
>>> On 07/11/2020 21:16, Pavel Begunkov wrote:
>>>> SQPOLL task may find sqo_task->files == NULL, so
>>>> __io_sq_thread_acquire_files() would left it unset and so all the
>>>> following fails, e.g. attempts to submit. Fail if sqo_task doesn't have
>>>> files.
>>>
>>> Josef, could you try this one?
>>
>> Hmm, as you said it happens often... IIUC there is a drawback with
>> SQPOLL -- after the creator process/thread exits most of subsequent
>> requests will start failing.
>> I'd say from application correctness POV such tasks should exit
>> only after their SQPOLL io_urings got killed.
>
> I don't think there's anything wrong with that - if you submit requests
> and exit before they have completed, then you by definition are not
> caring about the result of them.

Other threads may use it as well thinking that this is fine as
they share mm, files, etc.

1. task1 create io_uring
2. clone(CLONE_FILES|CLONE_VM|...) -> task2
3. task1 exits
4. task2 continues to use io_uring

--
Pavel Begunkov