net/ipv6: Create a neigh_lookup for FIB entries

The router discovery code has a FIB entry and wants to validate the
gateway has a neighbor entry. Refactor the existing dst_neigh_lookup
for IPv6 and create a new function that takes the gateway and device
and returns a neighbor entry. Use the new function in
ndisc_router_discovery to validate the gateway.
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip6_route.h

@@ -279,4 +279,7 @@ static inline bool rt6_duplicate_nexthop(struct rt6_info *a, struct rt6_info *b)
 	       !lwtunnel_cmp_encap(a->fib6_nh.nh_lwtstate, b->fib6_nh.nh_lwtstate);
 }
 
+struct neighbour *ip6_neigh_lookup(const struct in6_addr *gw,
+				   struct net_device *dev, struct sk_buff *skb,
+				   const void *daddr);
 #endif

net/ipv6/ndisc.c

@@ -1276,7 +1276,9 @@ static void ndisc_router_discovery(struct sk_buff *skb)
 	rt = rt6_get_dflt_router(net, &ipv6_hdr(skb)->saddr, skb->dev);
 
 	if (rt) {
-		neigh = dst_neigh_lookup(&rt->dst, &ipv6_hdr(skb)->saddr);
+		neigh = ip6_neigh_lookup(&rt->fib6_nh.nh_gw,
+					 rt->fib6_nh.nh_dev, NULL,
+					  &ipv6_hdr(skb)->saddr);
 		if (!neigh) {
 			ND_PRINTK(0, err,
 				  "RA: %s got default router without neighbour\n",
@@ -1304,7 +1306,9 @@ static void ndisc_router_discovery(struct sk_buff *skb)
 			return;
 		}
 
-		neigh = dst_neigh_lookup(&rt->dst, &ipv6_hdr(skb)->saddr);
+		neigh = ip6_neigh_lookup(&rt->fib6_nh.nh_gw,
+					 rt->fib6_nh.nh_dev, NULL,
+					  &ipv6_hdr(skb)->saddr);
 		if (!neigh) {
 			ND_PRINTK(0, err,
 				  "RA: %s got default router without neighbour\n",

net/ipv6/route.c

@@ -182,12 +182,10 @@ static void rt6_uncached_list_flush_dev(struct net *net, struct net_device *dev)
 	}
 }
 
-static inline const void *choose_neigh_daddr(struct rt6_info *rt,
+static inline const void *choose_neigh_daddr(const struct in6_addr *p,
 					     struct sk_buff *skb,
 					     const void *daddr)
 {
-	struct in6_addr *p = &rt->rt6i_gateway;
-
 	if (!ipv6_addr_any(p))
 		return (const void *) p;
 	else if (skb)
@@ -195,18 +193,27 @@ static inline const void *choose_neigh_daddr(struct rt6_info *rt,
 	return daddr;
 }
 
-static struct neighbour *ip6_neigh_lookup(const struct dst_entry *dst,
+struct neighbour *ip6_neigh_lookup(const struct in6_addr *gw,
+				   struct net_device *dev,
 				   struct sk_buff *skb,
 				   const void *daddr)
 {
-	struct rt6_info *rt = (struct rt6_info *) dst;
 	struct neighbour *n;
 
-	daddr = choose_neigh_daddr(rt, skb, daddr);
-	n = __ipv6_neigh_lookup(dst->dev, daddr);
+	daddr = choose_neigh_daddr(gw, skb, daddr);
+	n = __ipv6_neigh_lookup(dev, daddr);
 	if (n)
 		return n;
-	return neigh_create(&nd_tbl, daddr, dst->dev);
+	return neigh_create(&nd_tbl, daddr, dev);
+}
+
+static struct neighbour *ip6_dst_neigh_lookup(const struct dst_entry *dst,
+					      struct sk_buff *skb,
+					      const void *daddr)
+{
+	const struct rt6_info *rt = container_of(dst, struct rt6_info, dst);
+
+	return ip6_neigh_lookup(&rt->rt6i_gateway, dst->dev, skb, daddr);
 }
 
 static void ip6_confirm_neigh(const struct dst_entry *dst, const void *daddr)
@@ -214,7 +221,7 @@ static void ip6_confirm_neigh(const struct dst_entry *dst, const void *daddr)
 	struct net_device *dev = dst->dev;
 	struct rt6_info *rt = (struct rt6_info *)dst;
 
-	daddr = choose_neigh_daddr(rt, NULL, daddr);
+	daddr = choose_neigh_daddr(&rt->rt6i_gateway, NULL, daddr);
 	if (!daddr)
 		return;
 	if (dev->flags & (IFF_NOARP | IFF_LOOPBACK))
@@ -239,7 +246,7 @@ static struct dst_ops ip6_dst_ops_template = {
 	.update_pmtu		=	ip6_rt_update_pmtu,
 	.redirect		=	rt6_do_redirect,
 	.local_out		=	__ip6_local_out,
-	.neigh_lookup		=	ip6_neigh_lookup,
+	.neigh_lookup		=	ip6_dst_neigh_lookup,
 	.confirm_neigh		=	ip6_confirm_neigh,
 };
 
@@ -269,7 +276,7 @@ static struct dst_ops ip6_dst_blackhole_ops = {
 	.update_pmtu		=	ip6_rt_blackhole_update_pmtu,
 	.redirect		=	ip6_rt_blackhole_redirect,
 	.cow_metrics		=	dst_cow_metrics_generic,
-	.neigh_lookup		=	ip6_neigh_lookup,
+	.neigh_lookup		=	ip6_dst_neigh_lookup,
 };
 
 static const u32 ip6_template_metrics[RTAX_MAX] = {