linux-kernel - Re: [BUG] io_uring: defer logic based on shared data

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Message-ID: <df3b9edd-86ad-5460-b61b-66707c0fb630@kernel.dk>
Date:   Fri, 25 Oct 2019 10:32:48 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Pavel Begunkov <asml.silence@...il.com>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [BUG] io_uring: defer logic based on shared data

On 10/25/19 10:27 AM, Jens Axboe wrote:
> On 10/25/19 10:21 AM, Pavel Begunkov wrote:
>> On 25/10/2019 19:03, Jens Axboe wrote:
>>> On 10/25/19 3:55 AM, Pavel Begunkov wrote:
>>>> I found 2 problems with __io_sequence_defer().
>>>>
>>>> 1. it uses @sq_dropped, but doesn't consider @cq_overflow
>>>> 2. @sq_dropped and @cq_overflow are write-shared with userspace, so
>>>> it can be maliciously changed.
>>>>
>>>> see sent liburing test (test/defer *_hung()), which left an unkillable
>>>> process for me
>>>
>>> OK, how about the below. I'll split this in two, as it's really two
>>> separate fixes.
>> cached_sq_dropped is good, but I was concerned about cached_cq_overflow.
>> io_cqring_fill_event() can be called in async, so shouldn't we do some
>> synchronisation then?
> 
> We should probably make it an atomic just to be on the safe side, I'll
> update the series.

Here we go, patch 1:

http://git.kernel.dk/cgit/linux-block/commit/?h=for-linus&id=f2a241f596ed9e12b7c8f960e79ccda8053ea294

patch 2:

http://git.kernel.dk/cgit/linux-block/commit/?h=for-linus&id=b7d0297d2df5bfa0d1ecf9d6c66d23676751ef6a

-- 
Jens Axboe