[NETFILTER]: Add address family specific checksum helpers

Add checksum operation which takes care of verifying the checksum and
dealing with HW checksum errors and avoids multiple checksum
operations by setting ip_summed to CHECKSUM_UNNECESSARY after
successful verification.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netfilter.h

@@ -285,6 +285,8 @@ extern int skb_make_writable(struct sk_buff **pskb, unsigned int writable_len);
 
 struct nf_afinfo {
 	unsigned short	family;
+	unsigned int	(*checksum)(struct sk_buff *skb, unsigned int hook,
+				    unsigned int dataoff, u_int8_t protocol);
 	void		(*saveroute)(const struct sk_buff *skb,
 				     struct nf_info *info);
 	int		(*reroute)(struct sk_buff **skb,
@@ -298,6 +300,21 @@ static inline struct nf_afinfo *nf_get_afinfo(unsigned short family)
 	return rcu_dereference(nf_afinfo[family]);
 }
 
+static inline unsigned int
+nf_checksum(struct sk_buff *skb, unsigned int hook, unsigned int dataoff,
+	    u_int8_t protocol, unsigned short family)
+{
+	struct nf_afinfo *afinfo;
+	unsigned int csum = 0;
+
+	rcu_read_lock();
+	afinfo = nf_get_afinfo(family);
+	if (afinfo)
+		csum = afinfo->checksum(skb, hook, dataoff, protocol);
+	rcu_read_unlock();
+	return csum;
+}
+
 extern int nf_register_afinfo(struct nf_afinfo *afinfo);
 extern void nf_unregister_afinfo(struct nf_afinfo *afinfo);
 

include/linux/netfilter_ipv4.h

@@ -80,6 +80,8 @@ enum nf_ip_hook_priorities {
 #ifdef __KERNEL__
 extern int ip_route_me_harder(struct sk_buff **pskb);
 extern int ip_xfrm_me_harder(struct sk_buff **pskb);
+extern unsigned int nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
+				   unsigned int dataoff, u_int8_t protocol);
 #endif /*__KERNEL__*/
 
 #endif /*__LINUX_IP_NETFILTER_H*/

include/linux/netfilter_ipv6.h

@@ -73,6 +73,9 @@ enum nf_ip6_hook_priorities {
 };
 
 #ifdef CONFIG_NETFILTER
+extern unsigned int nf_ip6_checksum(struct sk_buff *skb, unsigned int hook,
+				    unsigned int dataoff, u_int8_t protocol);
+
 extern int ipv6_netfilter_init(void);
 extern void ipv6_netfilter_fini(void);
 #else /* CONFIG_NETFILTER */

net/ipv4/netfilter.c

@@ -161,8 +161,41 @@ static int nf_ip_reroute(struct sk_buff **pskb, const struct nf_info *info)
 	return 0;
 }
 
+unsigned int nf_ip_checksum(struct sk_buff *skb, unsigned int hook,
+			    unsigned int dataoff, u_int8_t protocol)
+{
+	struct iphdr *iph = skb->nh.iph;
+	unsigned int csum = 0;
+
+	switch (skb->ip_summed) {
+	case CHECKSUM_HW:
+		if (hook != NF_IP_PRE_ROUTING && hook != NF_IP_LOCAL_IN)
+			break;
+		if ((protocol == 0 && !(u16)csum_fold(skb->csum)) ||
+		    !csum_tcpudp_magic(iph->saddr, iph->daddr,
+			    	       skb->len - dataoff, protocol,
+				       skb->csum)) {
+			skb->ip_summed = CHECKSUM_UNNECESSARY;
+			break;
+		}
+		/* fall through */
+	case CHECKSUM_NONE:
+		if (protocol == 0)
+			skb->csum = 0;
+		else
+			skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
+						       skb->len - dataoff,
+						       protocol, 0);
+		csum = __skb_checksum_complete(skb);
+	}
+	return csum;
+}
+
+EXPORT_SYMBOL(nf_ip_checksum);
+
 static struct nf_afinfo nf_ip_afinfo = {
 	.family		= AF_INET,
+	.checksum	= nf_ip_checksum,
 	.saveroute	= nf_ip_saveroute,
 	.reroute	= nf_ip_reroute,
 	.route_key_size	= sizeof(struct ip_rt_info),

net/ipv6/netfilter.c

@@ -79,8 +79,42 @@ static int nf_ip6_reroute(struct sk_buff **pskb, const struct nf_info *info)
 	return 0;
 }
 
+unsigned int nf_ip6_checksum(struct sk_buff *skb, unsigned int hook,
+			     unsigned int dataoff, u_int8_t protocol)
+{
+	struct ipv6hdr *ip6h = skb->nh.ipv6h;
+	unsigned int csum = 0;
+
+	switch (skb->ip_summed) {
+	case CHECKSUM_HW:
+		if (hook != NF_IP6_PRE_ROUTING && hook != NF_IP6_LOCAL_IN)
+			break;
+		if (!csum_ipv6_magic(&ip6h->saddr, &ip6h->daddr,
+			    	     skb->len - dataoff, protocol,
+				     csum_sub(skb->csum,
+					      skb_checksum(skb, 0,
+							   dataoff, 0)))) {
+			skb->ip_summed = CHECKSUM_UNNECESSARY;
+			break;
+		}
+		/* fall through */
+	case CHECKSUM_NONE:
+		skb->csum = ~csum_ipv6_magic(&ip6h->saddr, &ip6h->daddr,
+					     skb->len - dataoff,
+					     protocol,
+					     csum_sub(0,
+						      skb_checksum(skb, 0,
+							           dataoff, 0)));
+		csum = __skb_checksum_complete(skb);
+	}
+	return csum;
+}
+
+EXPORT_SYMBOL(nf_ip6_checksum);
+
 static struct nf_afinfo nf_ip6_afinfo = {
 	.family		= AF_INET6,
+	.checksum	= nf_ip6_checksum,
 	.saveroute	= nf_ip6_saveroute,
 	.reroute	= nf_ip6_reroute,
 	.route_key_size	= sizeof(struct ip6_rt_info),