From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH net-next-2.6 8/9] jme: Don't show UDP Checksum error if
 HW misjudged
Date: Sun, 13 Feb 2011 20:43:00 -0800 (PST)
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From: "Guo-Fu Tseng" <cooldavid@cooldavid.org>
Date: Mon, 14 Feb 2011 12:27:41 +0800

> @@ -956,8 +956,27 @@ jme_disable_rx_engine(struct jme_adapter *jme)
>  	jme_mac_rxclk_off(jme);
>  }
>  
> +static u16
> +jme_udpsum(struct sk_buff *skb)
> +{
> +	u16 csum = 0xFFFFu;
> +
> +	if (skb->protocol != htons(ETH_P_IP))
> +		return csum;
> +	skb_set_network_header(skb, ETH_HLEN);
> +	if (ip_hdr(skb)->protocol != IPPROTO_UDP)
> +		return csum;
> +	skb_set_transport_header(skb,
> +			ETH_HLEN + (ip_hdr(skb)->ihl << 2));
> +	csum = udp_hdr(skb)->check;
> +	skb_reset_transport_header(skb);
> +	skb_reset_network_header(skb);
> +
> +	return csum;
> +}

You need to validate the packet length in all of these packet header
accesses, otherwise you're potentially looking at garbage.