netfilter: conntrack: do not increment two error counters at same time

The /proc interface for nf_conntrack displays the "error" counter as
"icmp_error".

It makes sense to not increment "invalid" when failing to handle an icmp
packet since those are special.

For example, its possible for conntrack to see partial and/or fragmented
packets inside icmp errors.  This should be a separate event and not get
mixed with the "invalid" counter.

Likewise, remove the "error" increment for errors from get_l4proto().
After this, the error counter will only increment for errors coming from
icmp(v6) packet handling.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_core.c

@@ -1725,10 +1725,8 @@ nf_conntrack_handle_icmp(struct nf_conn *tmpl,
 	else
 		return NF_ACCEPT;
 
-	if (ret <= 0) {
+	if (ret <= 0)
 		NF_CT_STAT_INC_ATOMIC(state->net, error);
-		NF_CT_STAT_INC_ATOMIC(state->net, invalid);
-	}
 
 	return ret;
 }
@@ -1813,7 +1811,6 @@ nf_conntrack_in(struct sk_buff *skb, const struct nf_hook_state *state)
 	dataoff = get_l4proto(skb, skb_network_offset(skb), state->pf, &protonum);
 	if (dataoff <= 0) {
 		pr_debug("not prepared to track yet or error occurred\n");
-		NF_CT_STAT_INC_ATOMIC(state->net, error);
 		NF_CT_STAT_INC_ATOMIC(state->net, invalid);
 		ret = NF_ACCEPT;
 		goto out;