ipv6: protect protocols not handling ipv4 from v4 connection/bind attempts

Some ipv6 protocols cannot handle ipv4 addresses, so we must not allow
connecting and binding to them. sendmsg logic does already check msg->name
for this but must trust already connected sockets which could be set up
for connection to ipv4 address family.

Per-socket flag ipv6only is of no use here, as it is under users control
by setsockopt.

Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/ipv6.h b/include/net/ipv6.h
index 78d3d51..4f541f1 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -783,6 +783,8 @@
 			   char __user *optval, int __user *optlen);
 
 int ip6_datagram_connect(struct sock *sk, struct sockaddr *addr, int addr_len);
+int ip6_datagram_connect_v6_only(struct sock *sk, struct sockaddr *addr,
+				 int addr_len);
 
 int ipv6_recv_error(struct sock *sk, struct msghdr *msg, int len,
 		    int *addr_len);