ipv4: Add a socket release callback for datagram sockets

This implements a socket release callback function to check
if the socket cached route got invalid during the time
we owned the socket. The function is used from udp, raw
and ping sockets.
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip.h

@@ -143,6 +143,8 @@ static inline struct sk_buff *ip_finish_skb(struct sock *sk, struct flowi4 *fl4)
 extern int		ip4_datagram_connect(struct sock *sk, 
 					     struct sockaddr *uaddr, int addr_len);
 
+extern void ip4_datagram_release_cb(struct sock *sk);
+
 struct ip_reply_arg {
 	struct kvec iov[1];   
 	int	    flags;

net/ipv4/datagram.c

@@ -85,3 +85,28 @@ int ip4_datagram_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 	return err;
 }
 EXPORT_SYMBOL(ip4_datagram_connect);
+
+void ip4_datagram_release_cb(struct sock *sk)
+{
+	const struct inet_sock *inet = inet_sk(sk);
+	const struct ip_options_rcu *inet_opt;
+	__be32 daddr = inet->inet_daddr;
+	struct flowi4 fl4;
+	struct rtable *rt;
+
+	if (! __sk_dst_get(sk) || __sk_dst_check(sk, 0))
+		return;
+
+	rcu_read_lock();
+	inet_opt = rcu_dereference(inet->inet_opt);
+	if (inet_opt && inet_opt->opt.srr)
+		daddr = inet_opt->opt.faddr;
+	rt = ip_route_output_ports(sock_net(sk), &fl4, sk, daddr,
+				   inet->inet_saddr, inet->inet_dport,
+				   inet->inet_sport, sk->sk_protocol,
+				   RT_CONN_FLAGS(sk), sk->sk_bound_dev_if);
+	if (!IS_ERR(rt))
+		__sk_dst_set(sk, &rt->dst);
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL_GPL(ip4_datagram_release_cb);

net/ipv4/ping.c

@@ -738,6 +738,7 @@ struct proto ping_prot = {
 	.recvmsg =	ping_recvmsg,
 	.bind =		ping_bind,
 	.backlog_rcv =	ping_queue_rcv_skb,
+	.release_cb =	ip4_datagram_release_cb,
 	.hash =		ping_v4_hash,
 	.unhash =	ping_v4_unhash,
 	.get_port =	ping_v4_get_port,

net/ipv4/raw.c

@@ -894,6 +894,7 @@ struct proto raw_prot = {
 	.recvmsg	   = raw_recvmsg,
 	.bind		   = raw_bind,
 	.backlog_rcv	   = raw_rcv_skb,
+	.release_cb	   = ip4_datagram_release_cb,
 	.hash		   = raw_hash_sk,
 	.unhash		   = raw_unhash_sk,
 	.obj_size	   = sizeof(struct raw_sock),

net/ipv4/udp.c

@@ -1952,6 +1952,7 @@ struct proto udp_prot = {
 	.recvmsg	   = udp_recvmsg,
 	.sendpage	   = udp_sendpage,
 	.backlog_rcv	   = __udp_queue_rcv_skb,
+	.release_cb	   = ip4_datagram_release_cb,
 	.hash		   = udp_lib_hash,
 	.unhash		   = udp_lib_unhash,
 	.rehash		   = udp_v4_rehash,