[NETFILTER]: Use conntrack information to determine if packet was NATed

Preparation for IPsec support for NAT:
Use conntrack information instead of saving the saving and comparing the
addresses to determine if a packet was NATed and needs to be rerouted to
make it easier to extend the key.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/netfilter/ip_nat_standalone.c

@@ -162,19 +162,21 @@ ip_nat_in(unsigned int hooknum,
           const struct net_device *out,
           int (*okfn)(struct sk_buff *))
 {
-	u_int32_t saddr, daddr;
+	struct ip_conntrack *ct;
+	enum ip_conntrack_info ctinfo;
 	unsigned int ret;
 
-	saddr = (*pskb)->nh.iph->saddr;
-	daddr = (*pskb)->nh.iph->daddr;
-
 	ret = ip_nat_fn(hooknum, pskb, in, out, okfn);
 	if (ret != NF_DROP && ret != NF_STOLEN
-	    && ((*pskb)->nh.iph->saddr != saddr
-	        || (*pskb)->nh.iph->daddr != daddr)) {
+	    && (ct = ip_conntrack_get(*pskb, &ctinfo)) != NULL) {
+		enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
+
+		if (ct->tuplehash[dir].tuple.src.ip !=
+		    ct->tuplehash[!dir].tuple.dst.ip) {
 			dst_release((*pskb)->dst);
 			(*pskb)->dst = NULL;
 		}
+	}
 	return ret;
 }
 
@@ -200,7 +202,8 @@ ip_nat_local_fn(unsigned int hooknum,
 		const struct net_device *out,
 		int (*okfn)(struct sk_buff *))
 {
-	u_int32_t saddr, daddr;
+	struct ip_conntrack *ct;
+	enum ip_conntrack_info ctinfo;
 	unsigned int ret;
 
 	/* root is playing with raw sockets. */
@@ -208,14 +211,15 @@ ip_nat_local_fn(unsigned int hooknum,
 	    || (*pskb)->nh.iph->ihl * 4 < sizeof(struct iphdr))
 		return NF_ACCEPT;
 
-	saddr = (*pskb)->nh.iph->saddr;
-	daddr = (*pskb)->nh.iph->daddr;
-
 	ret = ip_nat_fn(hooknum, pskb, in, out, okfn);
 	if (ret != NF_DROP && ret != NF_STOLEN
-	    && ((*pskb)->nh.iph->saddr != saddr
-		|| (*pskb)->nh.iph->daddr != daddr))
+	    && (ct = ip_conntrack_get(*pskb, &ctinfo)) != NULL) {
+		enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
+
+		if (ct->tuplehash[dir].tuple.dst.ip !=
+		    ct->tuplehash[!dir].tuple.src.ip)
 			return ip_route_me_harder(pskb) == 0 ? ret : NF_DROP;
+	}
 	return ret;
 }