openvswitch: support asymmetric conntrack

The openvswitch module shares a common conntrack and NAT infrastructure
exposed via netfilter.  It's possible that a packet needs both SNAT and
DNAT manipulation, due to e.g. tuple collision.  Netfilter can support
this because it runs through the NAT table twice - once on ingress and
again after egress.  The openvswitch module doesn't have such capability.

Like netfilter hook infrastructure, we should run through NAT twice to
keep the symmetry.

Fixes: 05752523e5 ("openvswitch: Interface with NAT.")
Signed-off-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/openvswitch/conntrack.c

@@ -903,6 +903,17 @@ static int ovs_ct_nat(struct net *net, struct sw_flow_key *key,
 	}
 	err = ovs_ct_nat_execute(skb, ct, ctinfo, &info->range, maniptype);
 
+	if (err == NF_ACCEPT &&
+	    ct->status & IPS_SRC_NAT && ct->status & IPS_DST_NAT) {
+		if (maniptype == NF_NAT_MANIP_SRC)
+			maniptype = NF_NAT_MANIP_DST;
+		else
+			maniptype = NF_NAT_MANIP_SRC;
+
+		err = ovs_ct_nat_execute(skb, ct, ctinfo, &info->range,
+					 maniptype);
+	}
+
 	/* Mark NAT done if successful and update the flow key. */
 	if (err == NF_ACCEPT)
 		ovs_nat_update_key(key, skb, maniptype);