af_netlink: Add needed scm_destroy after scm_send.

scm_send occasionally allocates state in the scm_cookie, so I have
modified netlink_sendmsg to guarantee that when scm_send succeeds
scm_destory will be called to free that state.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Reviewed-by: Daniel Lezcano <daniel.lezcano@free.fr>
Acked-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netlink/af_netlink.c

@@ -1323,19 +1323,23 @@ static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	if (msg->msg_flags&MSG_OOB)
 		return -EOPNOTSUPP;
 
-	if (NULL == siocb->scm)
+	if (NULL == siocb->scm) {
 		siocb->scm = &scm;
+		memset(&scm, 0, sizeof(scm));
+	}
 	err = scm_send(sock, msg, siocb->scm);
 	if (err < 0)
 		return err;
 
 	if (msg->msg_namelen) {
+		err = -EINVAL;
 		if (addr->nl_family != AF_NETLINK)
-			return -EINVAL;
+			goto out;
 		dst_pid = addr->nl_pid;
 		dst_group = ffs(addr->nl_groups);
+		err =  -EPERM;
 		if (dst_group && !netlink_capable(sock, NL_NONROOT_SEND))
-			return -EPERM;
+			goto out;
 	} else {
 		dst_pid = nlk->dst_pid;
 		dst_group = nlk->dst_group;
@@ -1387,6 +1391,7 @@ static int netlink_sendmsg(struct kiocb *kiocb, struct socket *sock,
 	err = netlink_unicast(sk, skb, dst_pid, msg->msg_flags&MSG_DONTWAIT);
 
 out:
+	scm_destroy(siocb->scm);
 	return err;
 }