Re: [PATCH net-next 4/6] xdp: add multi-buff support to xdp_return_{buff/frame}

[Jesper Dangaard Brouer]

On Wed, 19 Aug 2020 15:13:49 +0200
Lorenzo Bianconi <lore...@kernel.org> wrote:

> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 884f140fc3be..006b24b5d276 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -370,19 +370,55 @@ static void __xdp_return(void *data, struct 
> xdp_mem_info *mem, bool napi_direct)
>  
>  void xdp_return_frame(struct xdp_frame *xdpf)
>  {
> +     struct skb_shared_info *sinfo;
> +     int i;
> +
>       __xdp_return(xdpf->data, &xdpf->mem, false);

There is a use-after-free race here.  The xdpf->data contains the
shared_info (xdp_get_shared_info_from_frame(xdpf)). Thus you cannot
free/return the page and use this data area below.

> +     if (!xdpf->mb)
> +             return;
> +
> +     sinfo = xdp_get_shared_info_from_frame(xdpf);
> +     for (i = 0; i < sinfo->nr_frags; i++) {
> +             struct page *page = skb_frag_page(&sinfo->frags[i]);
> +
> +             __xdp_return(page_address(page), &xdpf->mem, false);
> +     }
>  }
>  EXPORT_SYMBOL_GPL(xdp_return_frame);
>  
>  void xdp_return_frame_rx_napi(struct xdp_frame *xdpf)
>  {
> +     struct skb_shared_info *sinfo;
> +     int i;
> +
>       __xdp_return(xdpf->data, &xdpf->mem, true);

Same issue.

> +     if (!xdpf->mb)
> +             return;
> +
> +     sinfo = xdp_get_shared_info_from_frame(xdpf);
> +     for (i = 0; i < sinfo->nr_frags; i++) {
> +             struct page *page = skb_frag_page(&sinfo->frags[i]);
> +
> +             __xdp_return(page_address(page), &xdpf->mem, true);
> +     }
>  }
>  EXPORT_SYMBOL_GPL(xdp_return_frame_rx_napi);
>  
>  void xdp_return_buff(struct xdp_buff *xdp)
>  {
> +     struct skb_shared_info *sinfo;
> +     int i;
> +
>       __xdp_return(xdp->data, &xdp->rxq->mem, true);

Same issue.

> +     if (!xdp->mb)
> +             return;
> +
> +     sinfo = xdp_get_shared_info_from_buff(xdp);
> +     for (i = 0; i < sinfo->nr_frags; i++) {
> +             struct page *page = skb_frag_page(&sinfo->frags[i]);
> +
> +             __xdp_return(page_address(page), &xdp->rxq->mem, true);
> +     }
>  }



-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer