tipc: add replicast peer discovery

Automatically learn UDP remote IP addresses of communicating peers by
looking at the source IP address of incoming TIPC link configuration
messages (neighbor discovery).

This makes configuration slightly easier and removes the problematic
scenario where a node receives directly addressed neighbor discovery
messages sent using replicast which the node cannot "reply" to using
mutlicast, leaving the link FSM in a limbo state.

Signed-off-by: Richard Alpe <richard.alpe@ericsson.com>
Reviewed-by: Jon Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/udp_media.c

@@ -254,6 +254,26 @@ static int tipc_udp_send_msg(struct net *net, struct sk_buff *skb,
 	return err;
 }
 
+static bool tipc_udp_is_known_peer(struct tipc_bearer *b,
+				   struct udp_media_addr *addr)
+{
+	struct udp_replicast *rcast, *tmp;
+	struct udp_bearer *ub;
+
+	ub = rcu_dereference_rtnl(b->media_ptr);
+	if (!ub) {
+		pr_err_ratelimited("UDP bearer instance not found\n");
+		return false;
+	}
+
+	list_for_each_entry_safe(rcast, tmp, &ub->rcast.list, list) {
+		if (!memcmp(&rcast->addr, addr, sizeof(struct udp_media_addr)))
+			return true;
+	}
+
+	return false;
+}
+
 static int tipc_udp_rcast_add(struct tipc_bearer *b,
 			      struct udp_media_addr *addr)
 {
@@ -281,29 +301,83 @@ static int tipc_udp_rcast_add(struct tipc_bearer *b,
 	return 0;
 }
 
+static int tipc_udp_rcast_disc(struct tipc_bearer *b, struct sk_buff *skb)
+{
+	struct udp_media_addr src = {0};
+	struct udp_media_addr *dst;
+
+	dst = (struct udp_media_addr *)&b->bcast_addr.value;
+	if (tipc_udp_is_mcast_addr(dst))
+		return 0;
+
+	src.port = udp_hdr(skb)->source;
+
+	if (ip_hdr(skb)->version == 4) {
+		struct iphdr *iphdr = ip_hdr(skb);
+
+		src.proto = htons(ETH_P_IP);
+		src.ipv4.s_addr = iphdr->saddr;
+		if (ipv4_is_multicast(iphdr->daddr))
+			return 0;
+#if IS_ENABLED(CONFIG_IPV6)
+	} else if (ip_hdr(skb)->version == 6) {
+		struct ipv6hdr *iphdr = ipv6_hdr(skb);
+
+		src.proto = htons(ETH_P_IPV6);
+		src.ipv6 = iphdr->saddr;
+		if (ipv6_addr_is_multicast(&iphdr->daddr))
+			return 0;
+#endif
+	} else {
+		return 0;
+	}
+
+	if (likely(tipc_udp_is_known_peer(b, &src)))
+		return 0;
+
+	return tipc_udp_rcast_add(b, &src);
+}
+
 /* tipc_udp_recv - read data from bearer socket */
 static int tipc_udp_recv(struct sock *sk, struct sk_buff *skb)
 {
 	struct udp_bearer *ub;
 	struct tipc_bearer *b;
+	struct tipc_msg *hdr;
+	int err;
 
 	ub = rcu_dereference_sk_user_data(sk);
 	if (!ub) {
 		pr_err_ratelimited("Failed to get UDP bearer reference");
-		kfree_skb(skb);
-		return 0;
+		goto out;
 	}
-
 	skb_pull(skb, sizeof(struct udphdr));
+	hdr = buf_msg(skb);
+
 	rcu_read_lock();
 	b = rcu_dereference_rtnl(ub->bearer);
+	if (!b)
+		goto rcu_out;
 
 	if (b && test_bit(0, &b->up)) {
 		tipc_rcv(sock_net(sk), skb, b);
 		rcu_read_unlock();
 		return 0;
 	}
+
+	if (unlikely(msg_user(hdr) == LINK_CONFIG)) {
+		err = tipc_udp_rcast_disc(b, skb);
+		if (err)
+			goto rcu_out;
+	}
+
+	tipc_rcv(sock_net(sk), skb, b);
 	rcu_read_unlock();
+	return 0;
+
+rcu_out:
+	rcu_read_unlock();
+out:
 	kfree_skb(skb);
 	return 0;
 }
@@ -398,6 +472,9 @@ int tipc_udp_nl_bearer_add(struct tipc_bearer *b, struct nlattr *attr)
 		return -EINVAL;
 	}
 
+	if (tipc_udp_is_known_peer(b, &addr))
+		return 0;
+
 	return tipc_udp_rcast_add(b, &addr);
 }