Re: [Xen-devel] [PATCH 2/4] xen-netfront: drop skb when skb->len > 65535

[Nick Pegg <npegg@xxxxxxxxxx>]

On 3/18/13 6:35 AM, Wei Liu wrote:
> The `size' field of Xen network wire format is uint16_t, anything bigger than
> 65535 will cause overflow.
> 
> 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..8c3d065 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;
>  
> +     /*
> +      * wire 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)(~0))) {
> +             net_alert_ratelimited(
> +                     "xennet: skb->len = %d, too big for wire 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)) {
> 

I have tested this patch on a 3.7.10 DomU and have confirmed that it
works for the test case that Wei came up with (set MTU to 100 on DomU,
run iperf). I haven't come across any other ways to cause this to
happen, so my testing isn't very thorough.


-Nick

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel