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

[Jens Axboe <axboe@kernel.dk>]

On 7/11/20 3:31 AM, Dmitry Vyukov wrote:
> rings_size() sets sq_offset to the total size of the rings
> (the returned value which is used for memory allocation).
> This is wrong: sq array should be located within the rings,
> not after them. Set sq_offset to where it should be.
> 
> Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
> Cc: io-uring@vger.kernel.org
> Cc: Hristo Venev <hristo@venev.name>
> Fixes: 75b28affdd6a ("io_uring: allocate the two rings together")
> 
> ---
> This looks so wrong and yet io_uring works.
> So I am either missing something very obvious here,
> or io_uring worked only due to lucky side-effects
> of rounding size to power-of-2 number of pages
> (which gave it enough slack at the end),
> maybe reading/writing some unrelated memory
> with some sizes.
> If I am wrong, please poke my nose into what I am not seeing.
> Otherwise, we probably need to CC stable as well.

Well that's a noodle scratcher, it's definitely been working fine,
and I've never seen any out-of-bounds on any of the testing I do.
I regularly run anything with KASAN enabled too.

In any case, the patch is obviously correct, I'll queue it up.

-- 
Jens Axboe