Re: [PATCH] io_uring: fix sq array offset calculation

[Jens Axboe <axboe@kernel.dk>]

On 7/17/20 8:05 AM, Jens Axboe wrote:
> On 7/17/20 7:48 AM, Dmitry Vyukov wrote:
>> On Sat, Jul 11, 2020 at 6:16 PM Dmitry Vyukov <dvyukov@google.com> wrote:
>>>
>>> On Sat, Jul 11, 2020 at 5:52 PM Hristo Venev <hristo@venev.name> wrote:
>>>>
>>>> On Sat, 2020-07-11 at 17:31 +0200, Dmitry Vyukov wrote:
>>>>> Looking at the code more, I am not sure how it may not corrupt
>>>>> memory.
>>>>> There definitely should be some combinations where accessing
>>>>> sq_entries*sizeof(u32) more memory won't be OK.
>>>>> May be worth adding a test that allocates all possible sizes for
>>>>> sq/cq
>>>>> and fills both rings.
>>>>
>>>> The layout (after the fix) is roughly as follows:
>>>>
>>>> 1. struct io_rings - ~192 bytes, maybe 256
>>>> 2. cqes - (32 << n) bytes
>>>> 3. sq_array - (4 << n) bytes
>>>>
>>>> The bug was that the sq_array was offset by (4 << n) bytes. I think
>>>> issues can only occur when
>>>>
>>>>     PAGE_ALIGN(192 + (32 << n) + (4 << n) + (4 << n))
>>>>     !=
>>>>     PAGE_ALIGN(192 + (32 << n) + (4 << n))
>>>>
>>>> It looks like this never happens. We got lucky.
>>>
>>> Interesting. CQ entries are larger and we have at least that many of
>>> them as SQ entries. I guess this + power-of-2-pages can make it never
>>> overflow.
>>
>> Hi Jens,
>>
>> I see this patch is in block/for-5.9/io_uring
>> Is this tree merged into linux-next? I don't see it in linux-next yet.
>> Or is it possible to get it into 5.8?
> 
> Yes, that tree is in linux-next, and I'm surprised you don't see it there
> as it's been queued up for almost a week. Are you sure?

I see it in there:

https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/fs/io_uring.c?id=a4968ff8b6314631a73fdc945a66fd8645dfe8cc

-- 
Jens Axboe