--- a/net/ipv6/datagram.c
+++ b/net/ipv6/datagram.c
@@ -146,10 +146,12 @@ int __ip6_datagram_connect(struct sock *sk, struct sockaddr *uaddr,
 	struct sockaddr_in6	*usin = (struct sockaddr_in6 *) uaddr;
 	struct inet_sock	*inet = inet_sk(sk);
 	struct ipv6_pinfo	*np = inet6_sk(sk);
-	struct in6_addr		*daddr;
+	struct in6_addr		*daddr, old_daddr;
+	__be32			fl6_flowlabel = 0;
+	__be32			old_fl6_flowlabel;
+	__be32			old_dport;
 	int			addr_type;
 	int			err;
-	__be32			fl6_flowlabel = 0;
 
 	if (usin->sin6_family == AF_INET) {
 		if (__ipv6_only_sock(sk))
@@ -238,9 +240,13 @@ int __ip6_datagram_connect(struct sock *sk, struct sockaddr *uaddr,
 		}
 	}
 
+	/* save the current peer information before updating it */
+	old_daddr = sk->sk_v6_daddr;
+	old_fl6_flowlabel = np->flow_label;
+	old_dport = inet->inet_dport;
+
 	sk->sk_v6_daddr = *daddr;
 	np->flow_label = fl6_flowlabel;
-
 	inet->inet_dport = usin->sin6_port;
 
 	/*
@@ -250,11 +256,12 @@ int __ip6_datagram_connect(struct sock *sk, struct sockaddr *uaddr,
 
 	err = ip6_datagram_dst_update(sk, true);
 	if (err) {
-		/* Reset daddr and dport so that udp_v6_early_demux()
-		 * fails to find this socket
+		/* Restore the socket peer info, to keep it consistent with
+		 * the old socket state
 		 */
-		memset(&sk->sk_v6_daddr, 0, sizeof(sk->sk_v6_daddr));
-		inet->inet_dport = 0;
+		sk->sk_v6_daddr = old_daddr;
+		np->flow_label = old_fl6_flowlabel;
+		inet->inet_dport = old_dport;
 		goto out;
 	}
 
diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index 83421c6f0bef..49d0791c50e2 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1049,7 +1049,8 @@ static int l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb,
 	/* Queue the packet to IP for output */
 	skb->ignore_df = 1;
 #if IS_ENABLED(CONFIG_IPV6)
-	if (tunnel->sock->sk_family == PF_INET6 && !tunnel->v4mapped)
+	if (tunnel->sock->sk_family == PF_INET6 &&
+	    !ipv6_addr_v4mapped(&tunnel->sock->sk_v6_daddr))
 		error = inet6_csk_xmit(tunnel->sock, skb, NULL);
 	else
 #endif
@@ -1131,7 +1132,8 @@ int l2tp_xmit_skb(struct l2tp_session *session, struct sk_buff *skb, int hdr_len
 
 		/* Calculate UDP checksum if configured to do so */
 #if IS_ENABLED(CONFIG_IPV6)
-		if (sk->sk_family == PF_INET6 && !tunnel->v4mapped)
+		if (sk->sk_family == PF_INET6 &&
+		    ipv6_addr_v4mapped(&sk->sk_v6_daddr))
 			udp6_set_csum(udp_get_no_check6_tx(sk),
 				      skb, &inet6_sk(sk)->saddr,
 				      &sk->sk_v6_daddr, udp_len);
@@ -1449,6 +1451,13 @@ int l2tp_tunnel_create(struct net *net, int fd, int version, u32 tunnel_id, u32
 			err = -EINVAL;
 			goto err;
 		}
+
+		/* Reject unconnected sockets */
+		if (sock->sk->sk_state != TCP_ESTABLISHED) {
+			pr_err("tunl %u: sock fd=%d is unconnected\n",
+			       tunnel_id, fd);
+			goto err;
+		}
 	}
 
 	sk = sock->sk;