Subject: Re: linux-next: Tree for Aug 7

From: Phil Sutter <[email-masked]>
Date: Fri, 9 Aug 2013 15:58:49 +0200

On Wed, Aug 07, 2013 at 04:36:21PM -0700, David Miller wrote:
> From: David Miller <[email-masked]>
> Date: Wed, 07 Aug 2013 16:27:48 -0700 (PDT)
> 
> > Look, I'm going to fix this myself, because I'm pretty tired of
> > waiting for the obvious fix.
> 
> Someone please test this:
> 
> diff --git a/include/linux/etherdevice.h b/include/linux/etherdevice.h
> index c623861..afc02a6 100644
> --- a/include/linux/etherdevice.h
> +++ b/include/linux/etherdevice.h
> @@ -29,6 +29,7 @@
>  
>  #ifdef __KERNEL__
>  extern __be16		eth_type_trans(struct sk_buff *skb, struct net_device *dev);
> +extern __be16		__eth_type_trans(struct sk_buff *skb, struct net_device *dev);
>  extern const struct header_ops eth_header_ops;
>  
>  extern int eth_header(struct sk_buff *skb, struct net_device *dev,
> diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
> index be1f64d..35dc1be 100644
> --- a/net/ethernet/eth.c
> +++ b/net/ethernet/eth.c
> @@ -146,6 +146,45 @@ int eth_rebuild_header(struct sk_buff *skb)
>  EXPORT_SYMBOL(eth_rebuild_header);
>  
>  /**
> + * __eth_type_trans - only determine the packet's protocol ID.
> + * @skb: packet
> + * @dev: device
> + */
> +__be16 __eth_type_trans(struct sk_buff *skb, struct net_device *dev)
> +{
> +	struct ethhdr *eth = (struct ethhdr *) skb->data;
> +
> +	/*
> +	 * Some variants of DSA tagging don't have an ethertype field
> +	 * at all, so we check here whether one of those tagging
> +	 * variants has been configured on the receiving interface,
> +	 * and if so, set skb->protocol without looking at the packet.
> +	 */
> +	if (netdev_uses_dsa_tags(dev))
> +		return htons(ETH_P_DSA);
> +	if (netdev_uses_trailer_tags(dev))
> +		return htons(ETH_P_TRAILER);
> +
> +	if (ntohs(eth->h_proto) >= ETH_P_802_3_MIN)
> +		return eth->h_proto;
> +
> +	/*
> +	 *      This is a magic hack to spot IPX packets. Older Novell breaks
> +	 *      the protocol design and runs IPX over 802.3 without an 802.2 LLC
> +	 *      layer. We look for FFFF which isn't a used 802.2 SSAP/DSAP. This
> +	 *      won't work for fault tolerant netware but does for the rest.
> +	 */
> +	if (skb->len >= 2 && *(unsigned short *)(skb->data) == 0xFFFF)
> +		return htons(ETH_P_802_3);
> +
> +	/*
> +	 *      Real 802.2 LLC
> +	 */
> +	return htons(ETH_P_802_2);
> +}
> +EXPORT_SYMBOL(__eth_type_trans);
> +
> +/**
>   * eth_type_trans - determine the packet's protocol ID.
>   * @skb: received socket data
>   * @dev: receiving network device
> @@ -184,33 +223,7 @@ __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
>  			skb->pkt_type = PACKET_OTHERHOST;
>  	}
>  
> -	/*
> -	 * Some variants of DSA tagging don't have an ethertype field
> -	 * at all, so we check here whether one of those tagging
> -	 * variants has been configured on the receiving interface,
> -	 * and if so, set skb->protocol without looking at the packet.
> -	 */
> -	if (netdev_uses_dsa_tags(dev))
> -		return htons(ETH_P_DSA);
> -	if (netdev_uses_trailer_tags(dev))
> -		return htons(ETH_P_TRAILER);
> -
> -	if (ntohs(eth->h_proto) >= ETH_P_802_3_MIN)
> -		return eth->h_proto;
> -
> -	/*
> -	 *      This is a magic hack to spot IPX packets. Older Novell breaks
> -	 *      the protocol design and runs IPX over 802.3 without an 802.2 LLC
> -	 *      layer. We look for FFFF which isn't a used 802.2 SSAP/DSAP. This
> -	 *      won't work for fault tolerant netware but does for the rest.
> -	 */
> -	if (skb->len >= 2 && *(unsigned short *)(skb->data) == 0xFFFF)
> -		return htons(ETH_P_802_3);
> -
> -	/*
> -	 *      Real 802.2 LLC
> -	 */
> -	return htons(ETH_P_802_2);
> +	return __eth_type_trans(skb, dev);
>  }
>  EXPORT_SYMBOL(eth_type_trans);
>  
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index 0c0f6c9..ec8e1c3 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -2003,7 +2003,7 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
>  			return err;
>  
>  		if (dev->type == ARPHRD_ETHER)
> -			skb->protocol = eth_type_trans(skb, dev);
> +			skb->protocol = __eth_type_trans(skb, dev);
>  
>  		data += dev->hard_header_len;
>  		to_write -= dev->hard_header_len;
> @@ -2332,13 +2332,13 @@ static int packet_snd(struct socket *sock,
>  	sock_tx_timestamp(sk, &skb_shinfo(skb)->tx_flags);
>  
>  	if (dev->type == ARPHRD_ETHER) {
> -		skb->protocol = eth_type_trans(skb, dev);
> +		skb->protocol = __eth_type_trans(skb, dev);
>  		if (skb->protocol == htons(ETH_P_8021Q))
>  			reserve += VLAN_HLEN;
>  	} else {
>  		skb->protocol = proto;
> -		skb->dev = dev;
>  	}
> +	skb->dev = dev;
>  
>  	if (!gso_type && (len > dev->mtu + reserve + extra_len)) {
>  		err = -EMSGSIZE;

The problem with this patch is __eth_type_trans() assuming the MAC
header at skb->data which might be correct in the most cases, but not
when called from eth_type_trans() as the later sets skb->data to after
the ethernet header (which was the problem from the beginning).

Best wishes, Phil