From: Dmitry Vyukov <[email protected]>
To: Jens Axboe <[email protected]>
Cc: Necip Fazil Yildiran <[email protected]>,
[email protected], Hristo Venev <[email protected]>
Subject: Re: [PATCH] io_uring: fix sq array offset calculation
Date: Sat, 11 Jul 2020 17:31:06 +0200 [thread overview]
Message-ID: <CACT4Y+YGwr+1k=rsJhMsnyQL4C+S2s9t7Cz5Axwc9fO5Ap4HbQ@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>
On Sat, Jul 11, 2020 at 5:16 PM Jens Axboe <[email protected]> wrote:
>
> 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 <[email protected]>
> > Cc: [email protected]
> > Cc: Hristo Venev <[email protected]>
> > 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.
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.
next prev parent reply other threads:[~2020-07-11 15:31 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-11 9:31 [PATCH] io_uring: fix sq array offset calculation Dmitry Vyukov
2020-07-11 9:37 ` Hristo Venev
2020-07-11 15:15 ` Jens Axboe
2020-07-11 15:31 ` Dmitry Vyukov [this message]
2020-07-11 15:36 ` Jens Axboe
2020-07-11 15:47 ` Jens Axboe
2020-07-11 15:52 ` Hristo Venev
2020-07-11 15:55 ` Jens Axboe
2020-07-11 15:56 ` Hristo Venev
2020-07-11 16:16 ` Dmitry Vyukov
2020-07-17 13:48 ` Dmitry Vyukov
2020-07-17 14:05 ` Jens Axboe
2020-07-17 14:08 ` Jens Axboe
2020-07-17 14:08 ` Dmitry Vyukov
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