[BUG?] dst reference leak possible in ndisc_send

[Stephen Hemminger <shemminger@vyatta.com>]

This code path looks like it leaks the dst_entry  if xfrm_lookup fails:

static void __ndisc_send(struct net_device *dev,
			 struct neighbour *neigh,
			 const struct in6_addr *daddr,
			 const struct in6_addr *saddr,
			 struct icmp6hdr *icmp6h, const struct in6_addr *target,
			 int llinfo)
{
	struct flowi fl;
	struct dst_entry *dst;
	struct net *net = dev_net(dev);
	struct sock *sk = net->ipv6.ndisc_sk;
	struct sk_buff *skb;
	struct icmp6hdr *hdr;
	struct inet6_dev *idev;
	int len;
	int err;
	u8 *opt, type;

	type = icmp6h->icmp6_type;

	icmpv6_flow_init(sk, &fl, type, saddr, daddr, dev->ifindex);

	dst = icmp6_dst_alloc(dev, neigh, daddr);
	if (!dst)
		return;

	err = xfrm_lookup(&dst, &fl, NULL, 0);
	if (err < 0)
		return;