netfilter: nf_conntrack_ipv6: Plug sk_buff leak in fragment handling

In commit 4cdd3408 ("netfilter: nf_conntrack_ipv6: improve fragmentation
handling"), an sk_buff leak was introduced when dealing with reassembled
packets by grabbing a reference to the original skb instead of the
reassembled skb.  At this point, the leak only impacted conntracks with an
associated helper.

In commit 58a317f1 ("netfilter: ipv6: add IPv6 NAT support"), the bug was
expanded to include all reassembled packets with unconfirmed conntracks.

Fix this by grabbing a reference to the proper reassembled skb.  This
closes netfilter bugzilla #823.
Signed-off-by: NPhil Oester <kernel@linuxace.com>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>

net/ipv6/netfilter/nf_conntrack_l3proto_ipv6.c

@@ -204,7 +204,7 @@ static unsigned int __ipv6_conntrack_in(struct net *net,
 		if (ct != NULL && !nf_ct_is_untracked(ct)) {
 			help = nfct_help(ct);
 			if ((help && help->helper) || !nf_ct_is_confirmed(ct)) {
-				nf_conntrack_get_reasm(skb);
+				nf_conntrack_get_reasm(reasm);
 				NF_HOOK_THRESH(NFPROTO_IPV6, hooknum, reasm,
 					       (struct net_device *)in,
 					       (struct net_device *)out,