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

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Date:   Thu, 27 Apr 2023 12:42:43 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Tudor Cretu <tudor.cretu@....com>, io-uring@...r.kernel.org
Cc:     =axboe@...nel.dk, asml.silence@...il.com, kevin.brodsky@....com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] io_uring/kbuf: Fix size for shared buffer ring

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@....com>
> ---
>  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@...il.com>
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?

-- 
Jens Axboe