Re: [Xen-devel] [PATCH] xen-netfront: drop skb when skb->len > 65535

[Wei Liu <wei.liu2@xxxxxxxxxx>]

Oops, I made a mistake in Konrad's address.

Please remove the wrong address in future CC.


Wei.


On Fri, 2013-03-01 at 16:31 +0000, Wei Liu wrote:
> The `size' field of Xen network wired format is uint16_t, anything bigger than
> 65535 will cause overflow.
> 
> The punishment introduced by XSA-39 is quite harsh - DomU is disconnected when
> it's discovered to be sending corrupted skbs. However, it looks like Linux
> kernel will generate some bad skbs sometimes, so drop those skbs before
> sending to over netback to avoid being disconnected.
> 
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
>  drivers/net/xen-netfront.c |   12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index 5527663..284059b 100644
> --- a/drivers/net/xen-netfront.c
> +++ b/drivers/net/xen-netfront.c
> @@ -547,6 +547,18 @@ static int xennet_start_xmit(struct sk_buff *skb, struct 
> net_device *dev)
>       unsigned int len = skb_headlen(skb);
>       unsigned long flags;
>  
> +     /*
> +      * wired format of xen_netif_tx_request only supports skb->len
> +      * < 64K, because size field in xen_netif_tx_request is
> +      * uint16_t.
> +      */
> +     if (unlikely(skb->len > (uint16_t)(~((uint16_t)0)))) {
> +             net_alert_ratelimited(
> +                     "xennet: skb->len = %d, too big for wired format\n",
> +                     skb->len);
> +             goto drop;
> +     }
> +
>       slots = DIV_ROUND_UP(offset + len, PAGE_SIZE) +
>               xennet_count_skb_frag_slots(skb);
>       if (unlikely(slots > MAX_SKB_FRAGS + 1)) {



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