Re: [PATCH] io_uring/kbuf: Fix size for shared buffer ring

[Tudor Cretu]

On 27-04-2023 19:42, Jens Axboe wrote:
> On 4/27/23 8:31 AM, Tudor Cretu wrote:
> > The size of the ring is the product of ring_entries and the size of
> > struct io_uring_buf. Using struct_size is equivalent to
> >    (ring_entries + 1) * sizeof(struct io_uring_buf)
> > and generates an off-by-one error. Fix it by using size_mul directly.
> >
> > Signed-off-by: Tudor Cretu <tudor.cretu@xxxxxxx>
> > ---
> >   io_uring/kbuf.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
> > index 4a6401080c1f..9770757c89a0 100644
> > --- a/io_uring/kbuf.c
> > +++ b/io_uring/kbuf.c
> > @@ -505,7 +505,7 @@ int io_register_pbuf_ring(struct io_ring_ctx *ctx, void __user *arg)
> >   	}
> >   
> >   	pages = io_pin_pages(reg.ring_addr,
> > -			     struct_size(br, bufs, reg.ring_entries),
> > +			     size_mul(sizeof(struct io_uring_buf), reg.ring_entries),
> >   			     &nr_pages);
> >   	if (IS_ERR(pages)) {
> >   		kfree(free_bl);
>
> Looking into this again, and some bells ringing in the back of my head,
> we do have:
>
> commit 48ba08374e779421ca34bd14b4834aae19fc3e6a
> Author: Wojciech Lukowicz <wlukowicz01@xxxxxxxxx>
> Date:   Sat Feb 18 18:41:41 2023 +0000
>
>      io_uring: fix size calculation when registering buf ring
>
> which should have fixed that issue. What kernel version are you looking at?

Hi Jens,

Thank you for your message. Indeed I was looking at a slightly older 
version of the kernel. Apologies for the noise!

Kind regards,
Tudor

>