net: make ipv6 PKTINFO honour freebind

This just makes it possible to spoof source IPv6 address on a socket
without having to create and bind a new socket for every source IP
we wish to spoof.
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/datagram.c

@@ -654,7 +654,7 @@ int datagram_send_ctl(struct net *net, struct sock *sk,
 
 			if (addr_type != IPV6_ADDR_ANY) {
 				int strict = __ipv6_addr_src_scope(addr_type) <= IPV6_ADDR_SCOPE_LINKLOCAL;
-				if (!inet_sk(sk)->transparent &&
+				if (!(inet_sk(sk)->freebind || inet_sk(sk)->transparent) &&
 				    !ipv6_chk_addr(net, &src_info->ipi6_addr,
 						   strict ? dev : NULL, 0))
 					err = -EINVAL;