ipv6: process socket-level control messages in IPv6

Process socket-level control messages by invoking
__sock_cmsg_send in ip6_datagram_send_ctl for control messages on
the SOL_SOCKET layer.

This makes sure whenever ip6_datagram_send_ctl is called for
udp and raw, we also process socket-level control messages.

This is a bit uglier than IPv4, since IPv6 does not have
something like ipcm_cookie. Perhaps we can later create
a control message cookie for IPv6?

Note that this commit interprets new control messages that
were ignored before. As such, this commit does not change
the behavior of IPv6 control messages.

Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c
index 6b54ff3..4f29a4a 100644
--- a/net/l2tp/l2tp_ip6.c
+++ b/net/l2tp/l2tp_ip6.c
@@ -492,6 +492,7 @@
 	struct ip6_flowlabel *flowlabel = NULL;
 	struct dst_entry *dst = NULL;
 	struct flowi6 fl6;
+	struct sockcm_cookie sockc_unused = {0};
 	int addr_len = msg->msg_namelen;
 	int hlimit = -1;
 	int tclass = -1;
@@ -562,9 +563,10 @@
 		memset(opt, 0, sizeof(struct ipv6_txoptions));
 		opt->tot_len = sizeof(struct ipv6_txoptions);
 
-		err = ip6_datagram_send_ctl(sock_net(sk), sk, msg, &fl6, opt,
-					    &hlimit, &tclass, &dontfrag);
-		if (err < 0) {
+                err = ip6_datagram_send_ctl(sock_net(sk), sk, msg, &fl6, opt,
+                                            &hlimit, &tclass, &dontfrag,
+                                            &sockc_unused);
+                if (err < 0) {
 			fl6_sock_release(flowlabel);
 			return err;
 		}