Re: [Xen-devel] [PATCH 2/6] xen-netfront: reduce gso_max_size to account for ethernet header

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Mar 25, 2013 at 11:08:18AM +0000, Wei Liu wrote:
> The maximum packet including ethernet header that can be handled by netfront /
> netback wire format is 65535. Reduce gso_max_size accordingly.
> 
> Drop skb and print warning when skb->len > 65535. This can 1) save the effort
> to send malformed packet to netback, 2) help spotting misconfiguration of
> netfront in the future.
> 

Should it also CC stable@xxxxxxxxxxxxxxx?

> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
>  drivers/net/xen-netfront.c |   14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
> index 5527663..3ae9dc1 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 skb->len is too big, drop it and alert user about
> +      * misconfiguration.
> +      */
> +     if (unlikely(skb->len >= (uint16_t)(~0))) {
> +             net_alert_ratelimited(
> +                     "xennet: skb->len = %u, 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)) {
> @@ -1362,6 +1374,8 @@ static struct net_device *xennet_create_dev(struct 
> xenbus_device *dev)
>       SET_ETHTOOL_OPS(netdev, &xennet_ethtool_ops);
>       SET_NETDEV_DEV(netdev, &dev->dev);
>  
> +     netif_set_gso_max_size(netdev, 65535 - ETH_HLEN);
> +
>       np->netdev = netdev;
>  
>       netif_carrier_off(netdev);
> -- 
> 1.7.10.4
> 

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