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

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Message-ID: <20130325165637.GA25740@phenom.dumpdata.com>
Date:	Mon, 25 Mar 2013 12:56:37 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Wei Liu <wei.liu2@...rix.com>
Cc:	xen-devel@...ts.xen.org, netdev@...r.kernel.org,
	ian.campbell@...rix.com, annie.li@...cle.com,
	david.vrabel@...rix.com
Subject: Re: [PATCH 2/6] xen-netfront: reduce gso_max_size to account for
 ethernet header

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@...r.kernel.org?

> Signed-off-by: Wei Liu <wei.liu2@...rix.com>
> ---
>  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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