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

From: David Vrabel <[email-masked]>
Date: Mon, 25 Mar 2013 14:23:53 +0000

On 25/03/13 11:08, 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.
[...]
> --- 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))) {

Suggest a #define for this maximum added to include/xen/interface/io/netif.h

David