mptcp: pm nl: support IPv4 mapped in v6 addresses

On one side, we can allow the creation of subflows between v4 mapped in
v6 and v4 addresses. For that we look for v4mapped addresses between the
local address we want to select and the remote one.

On the other side, we also properly deal with received v4mapped
addresses, either announced ones or set via Netlink.

Fixes: 01cacb0 ("mptcp: add netlink-based PM")
Closes: #122
Co-developed-by: Geliang Tang <[email protected]>
Signed-off-by: Geliang Tang <[email protected]>
Signed-off-by: Matthieu Baerts <[email protected]>

net/mptcp/pm_netlink.c

@@ -60,15 +60,20 @@ static bool addresses_equal(const struct mptcp_addr_info *a,
 {
 	bool addr_equals = false;
 
-	if (a->family != b->family)
-		return false;
-
-	if (a->family == AF_INET)
-		addr_equals = a->addr.s_addr == b->addr.s_addr;
+	if (a->family == b->family) {
+		if (a->family == AF_INET)
+			addr_equals = a->addr.s_addr == b->addr.s_addr;
 #if IS_ENABLED(CONFIG_MPTCP_IPV6)
-	else
-		addr_equals = !ipv6_addr_cmp(&a->addr6, &b->addr6);
+		else
+			addr_equals = !ipv6_addr_cmp(&a->addr6, &b->addr6);
+	} else if (a->family == AF_INET) {
+		if (ipv6_addr_v4mapped(&b->addr6))
+			addr_equals = a->addr.s_addr == b->addr6.s6_addr32[3];
+	} else if (b->family == AF_INET) {
+		if (ipv6_addr_v4mapped(&a->addr6))
+			addr_equals = a->addr6.s6_addr32[3] == b->addr.s_addr;
 #endif
+	}
 
 	if (!addr_equals)
 		return false;
@@ -133,22 +138,33 @@ static bool lookup_subflow_by_saddr(const struct list_head *list,
 }
 
 static struct mptcp_pm_addr_entry *
-select_local_address(const struct pm_nl_pernet *pernet,
-		     struct mptcp_sock *msk)
+select_local_address(const struct pm_nl_pernet *pernet, struct mptcp_sock *msk)
 {
 	struct mptcp_pm_addr_entry *entry, *ret = NULL;
+	struct mptcp_addr_info remote = { 0 };
+
+	remote_address((struct sock_common *)msk, &remote);
 
 	rcu_read_lock();
 	__mptcp_flush_join_list(msk);
 	list_for_each_entry_rcu(entry, &pernet->local_addr_list, list) {
 		if (!(entry->addr.flags & MPTCP_PM_ADDR_FLAG_SUBFLOW))
 			continue;
 
+		if (entry->addr.family != remote.family) {
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+			if ((entry->addr.family == AF_INET &&
+			     !ipv6_addr_v4mapped(&remote.addr6)) ||
+			    (remote.family == AF_INET &&
+			     !ipv6_addr_v4mapped(&entry->addr.addr6)))
+#endif
+				continue;
+		}
+
 		/* avoid any address already in use by subflows and
 		 * pending join
 		 */
-		if (entry->addr.family == ((struct sock *)msk)->sk_family &&
-		    !lookup_subflow_by_saddr(&msk->conn_list, &entry->addr)) {
+		if (!lookup_subflow_by_saddr(&msk->conn_list, &entry->addr)) {
 			ret = entry;
 			break;
 		}