l2tp: Use inet_sk_init_flowi4() in l2tp_ip_sendmsg().

Use inet_sk_init_flowi4() to automatically initialise the flowi4
structure in l2tp_ip_sendmsg() instead of passing parameters manually
to ip_route_output_ports().

Override ->daddr with the value passed in the msghdr structure if
provided.

Signed-off-by: Guillaume Nault <[email protected]>
Reviewed-by: James Chapman <[email protected]>
Link: https://patch.msgid.link/2ff22a3560c5050228928456662b80b9c84a8fe4.1734357769.git.gnault@redhat.com
Signed-off-by: Jakub Kicinski <[email protected]>

Author: Guillaume Nault

net/l2tp/l2tp_ip.c

@@ -425,7 +425,6 @@ static int l2tp_ip_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	int rc;
 	struct inet_sock *inet = inet_sk(sk);
 	struct rtable *rt = NULL;
-	struct flowi4 *fl4;
 	int connected = 0;
 	__be32 daddr;
 
@@ -455,7 +454,6 @@ static int l2tp_ip_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		if (sk->sk_state != TCP_ESTABLISHED)
 			goto out;
 
-		daddr = inet->inet_daddr;
 		connected = 1;
 	}
 
@@ -482,29 +480,24 @@ static int l2tp_ip_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		goto error;
 	}
 
-	fl4 = &inet->cork.fl.u.ip4;
 	if (connected)
 		rt = dst_rtable(__sk_dst_check(sk, 0));
 
 	rcu_read_lock();
 	if (!rt) {
-		const struct ip_options_rcu *inet_opt;
+		struct flowi4 *fl4 = &inet->cork.fl.u.ip4;
 
-		inet_opt = rcu_dereference(inet->inet_opt);
+		inet_sk_init_flowi4(inet, fl4);
 
-		/* Use correct destination address if we have options. */
-		if (inet_opt && inet_opt->opt.srr)
-			daddr = inet_opt->opt.faddr;
+		/* Overwrite ->daddr if msg->msg_name was provided */
+		if (!connected)
+			fl4->daddr = daddr;
 
 		/* If this fails, retransmit mechanism of transport layer will
 		 * keep trying until route appears or the connection times
 		 * itself out.
 		 */
-		rt = ip_route_output_ports(sock_net(sk), fl4, sk,
-					   daddr, inet->inet_saddr,
-					   inet->inet_dport, inet->inet_sport,
-					   sk->sk_protocol, ip_sock_rt_tos(sk),
-					   sk->sk_bound_dev_if);
+		rt = ip_route_output_flow(sock_net(sk), fl4, sk);
 		if (IS_ERR(rt))
 			goto no_route;
 		if (connected) {