Re: [Xen-devel] [PATCH net 2/4] xen-netback: Fix releasing frag_list skbs in error path

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Jul 17, 2014 at 08:09:50PM +0100, Zoltan Kiss wrote:
> When the grant operations failed, the skb is freed up eventually, and it tries
> to release the frags, if there is any. For the main skb nr_frags is set to 0 
> to
> avoid this, but on the frag_list it iterates through the frags array, and 
> tries
> to call put_page on the page pointer which contains garbage at that time.
> 
> Signed-off-by: Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>
> Reported-by: Armin Zentai <armin.zentai@xxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
> ---
> diff --git a/drivers/net/xen-netback/netback.c 
> b/drivers/net/xen-netback/netback.c
> index 604ff71..e9ffb05 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -1522,6 +1522,11 @@ static int xenvif_tx_submit(struct xenvif_queue *queue)
>               /* Check the remap error code. */
>               if (unlikely(xenvif_tx_check_gop(queue, skb, &gop_map, 
> &gop_copy))) {

It's worth adding a comment here saying that all those pages have been
freed in xenvif_tx_check_gop so that we don't leak any page even if we
manually set nr_frags to 0.

Wei.

>                       skb_shinfo(skb)->nr_frags = 0;
> +                     if (skb_has_frag_list(skb)) {
> +                             struct sk_buff *nskb =
> +                                             skb_shinfo(skb)->frag_list;
> +                             skb_shinfo(nskb)->nr_frags = 0;
> +                     }
>                       kfree_skb(skb);
>                       continue;
>               }

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