l2tp: close sessions in ip socket destroy callback

l2tp_core hooks UDP's .destroy handler to gain advance warning of a tunnel
socket being closed from userspace.  We need to do the same thing for
IP-encapsulation sockets.
Signed-off-by: Tom Parkin <tparkin@katalix.com>
Signed-off-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/l2tp/l2tp_ip.c

@@ -228,10 +228,16 @@ static void l2tp_ip_close(struct sock *sk, long timeout)
 static void l2tp_ip_destroy_sock(struct sock *sk)
 {
 	struct sk_buff *skb;
+	struct l2tp_tunnel *tunnel = l2tp_sock_to_tunnel(sk);
 
 	while ((skb = __skb_dequeue_tail(&sk->sk_write_queue)) != NULL)
 		kfree_skb(skb);
 
+	if (tunnel) {
+		l2tp_tunnel_closeall(tunnel);
+		sock_put(sk);
+	}
+
 	sk_refcnt_debug_dec(sk);
 }
 

net/l2tp/l2tp_ip6.c

@@ -241,10 +241,17 @@ static void l2tp_ip6_close(struct sock *sk, long timeout)
 
 static void l2tp_ip6_destroy_sock(struct sock *sk)
 {
+	struct l2tp_tunnel *tunnel = l2tp_sock_to_tunnel(sk);
+
 	lock_sock(sk);
 	ip6_flush_pending_frames(sk);
 	release_sock(sk);
 
+	if (tunnel) {
+		l2tp_tunnel_closeall(tunnel);
+		sock_put(sk);
+	}
+
 	inet6_destroy_sock(sk);
 }