netfilter: af_info: add 'strict' parameter to limit lookup to .oif

ipv6 fib lookup can set RT6_LOOKUP_F_IFACE flag to restrict search
to an interface, but this flag cannot be set via struct flowi.

Also, it cannot be set via ip6_route_output: this function uses the
passed sock struct to determine if this flag is required
(by testing for nonzero sk_bound_dev_if).

Work around this by passing in an artificial struct sk in case
'strict' argument is true.

This is required to replace the rt6_lookup call in xt_addrtype.c with
nf_afinfo->route().

Signed-off-by: Florian Westphal <[e-mail]>
Acked-by: David S. Miller <[e-mail]>
Signed-off-by: Patrick McHardy <[e-mail]>

include/linux/netfilter.h

···
 					    unsigned int len,
 					    u_int8_t protocol);
 	int		(*route)(struct net *net, struct dst_entry **dst,
-				 struct flowi *fl);
+				 struct flowi *fl, bool strict);
 	void		(*saveroute)(const struct sk_buff *skb,
 				     struct nf_queue_entry *entry);
 	int		(*reroute)(struct sk_buff *skb,

net/ipv4/netfilter.c

···
 }
 
 static int nf_ip_route(struct net *net, struct dst_entry **dst,
-		       struct flowi *fl)
+		       struct flowi *fl, bool strict __always_unused)
 {
 	struct rtable *rt = ip_route_output_key(net, &fl->u.ip4);
 	if (IS_ERR(rt))

net/ipv6/netfilter.c

···
 }
 
 static int nf_ip6_route(struct net *net, struct dst_entry **dst,
-			struct flowi *fl)
+			struct flowi *fl, bool strict)
 {
-	*dst = ip6_route_output(net, NULL, &fl->u.ip6);
+	static const struct ipv6_pinfo fake_pinfo;
+	static const struct inet_sock fake_sk = {
+		/* makes ip6_route_output set RT6_LOOKUP_F_IFACE: */
+		.sk.sk_bound_dev_if = 1,
+		.pinet6 = (struct ipv6_pinfo *) &fake_pinfo,
+	};
+	const void *sk = strict ? &fake_sk : NULL;
+
+	*dst = ip6_route_output(net, sk, &fl->u.ip6);
 	return (*dst)->error;
 }
 

net/netfilter/nf_conntrack_h323_main.c

···
 		memset(&fl2, 0, sizeof(fl2));
 		fl2.daddr = dst->ip;
 		if (!afinfo->route(&init_net, (struct dst_entry **)&rt1,
-				   flowi4_to_flowi(&fl1))) {
+				   flowi4_to_flowi(&fl1), false)) {
 			if (!afinfo->route(&init_net, (struct dst_entry **)&rt2,
-					   flowi4_to_flowi(&fl2))) {
+					   flowi4_to_flowi(&fl2), false)) {
 				if (rt1->rt_gateway == rt2->rt_gateway &&
 				    rt1->dst.dev  == rt2->dst.dev)
 					ret = 1;
···
 		memset(&fl2, 0, sizeof(fl2));
 		ipv6_addr_copy(&fl2.daddr, &dst->in6);
 		if (!afinfo->route(&init_net, (struct dst_entry **)&rt1,
-				   flowi6_to_flowi(&fl1))) {
+				   flowi6_to_flowi(&fl1), false)) {
 			if (!afinfo->route(&init_net, (struct dst_entry **)&rt2,
-					   flowi6_to_flowi(&fl2))) {
+					   flowi6_to_flowi(&fl2), false)) {
 				if (!memcmp(&rt1->rt6i_gateway, &rt2->rt6i_gateway,
 					    sizeof(rt1->rt6i_gateway)) &&
 				    rt1->dst.dev == rt2->dst.dev)

net/netfilter/xt_TCPMSS.c

···
 	rcu_read_lock();
 	ai = nf_get_afinfo(family);
 	if (ai != NULL)
-		ai->route(&init_net, (struct dst_entry **)&rt, &fl);
+		ai->route(&init_net, (struct dst_entry **)&rt, &fl, false);
 	rcu_read_unlock();
 
 	if (rt != NULL) {