linux-kernel - Re: [PATCH] io_uring: fix deferred req iovec leak

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Date:   Fri, 7 Feb 2020 00:03:52 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] io_uring: fix deferred req iovec leak

On 06/02/2020 23:58, Jens Axboe wrote:
>>
>> 1. submit a read, which need defer.
>>
>> 2. io_req_defer() allocates ->io and goes io_req_defer_prep() -> io_read_prep().
>> Let #vecs > UIO_FASTIOV, so the prep() in the presence of ->io will allocate iovec.
>> Note: that work.func is left io_wq_submit_work
>>
>> 3. At some point @io_wq calls io_wq_submit_work() -> io_issue_sqe() -> io_read(),
>>
>> 4. actual reading succeeds, and it's coming to finalisation and the following
>> code in particular.
>>
>> if (!io_wq_current_is_worker())
>> 	kfree(iovec);
>>
>> 5. Because we're in io_wq, the cleanup will not be performed, even though we're
>> returning with success. And that's a leak.
>>
>> Do you see anything wrong with it?
> 
> That's my bad, I didn't read the subject fully, this is specific to
> a deferred request. Patch looks good to me, and it cleans it up too
> which is always a nice win!
> 

Great we're agree. Though, it's not only about defer, it's just one example.
The another one is a non-head request, for which io_submit_sqe() allocates ->io,
+ REQ_F_FORCE_ASYNC.

-- 
Pavel Begunkov



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