net: Add l3mdev saddr lookup to raw_sendmsg

ping originated on box through a VRF device is showing up in tcpdump
without a source address:
    $ tcpdump -n -i vrf-blue
    08:58:33.311303 IP 0.0.0.0 > 10.2.2.254: ICMP echo request, id 2834, seq 1, length 64
    08:58:33.311562 IP 10.2.2.254 > 10.2.2.2: ICMP echo reply, id 2834, seq 1, length 64

Add the call to l3mdev_get_saddr to raw_sendmsg.
Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/raw.c

@@ -484,6 +484,7 @@ static int raw_getfrag(void *from, char *to, int offset, int len, int odd,
 static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 {
 	struct inet_sock *inet = inet_sk(sk);
+	struct net *net = sock_net(sk);
 	struct ipcm_cookie ipc;
 	struct rtable *rt = NULL;
 	struct flowi4 fl4;
@@ -543,7 +544,7 @@ static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	ipc.oif = sk->sk_bound_dev_if;
 
 	if (msg->msg_controllen) {
-		err = ip_cmsg_send(sock_net(sk), msg, &ipc, false);
+		err = ip_cmsg_send(net, msg, &ipc, false);
 		if (err)
 			goto out;
 		if (ipc.opt)
@@ -598,6 +599,9 @@ static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 			    (inet->hdrincl ? FLOWI_FLAG_KNOWN_NH : 0),
 			   daddr, saddr, 0, 0);
 
+	if (!saddr && ipc.oif)
+		l3mdev_get_saddr(net, ipc.oif, &fl4);
+
 	if (!inet->hdrincl) {
 		rfv.msg = msg;
 		rfv.hlen = 0;
@@ -608,7 +612,7 @@ static int raw_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	}
 
 	security_sk_classify_flow(sk, flowi4_to_flowi(&fl4));
-	rt = ip_route_output_flow(sock_net(sk), &fl4, sk);
+	rt = ip_route_output_flow(net, &fl4, sk);
 	if (IS_ERR(rt)) {
 		err = PTR_ERR(rt);
 		rt = NULL;