netfilter: conntrack: split resolve_clash function

Followup patch will need a helper function with the 'clashing entries
refer to the identical tuple in both directions' resolution logic.

This patch will add another resolve_clash helper where loser_ct must
not be added to the dying list because it will be inserted into the
table.

Therefore this also moves the stat counters and dying-list insertion
of the losing ct.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_conntrack_core.c

@@ -907,6 +907,39 @@ static void __nf_conntrack_insert_prepare(struct nf_conn *ct)
 		tstamp->start = ktime_get_real_ns();
 }
 
+static int __nf_ct_resolve_clash(struct sk_buff *skb,
+				 struct nf_conntrack_tuple_hash *h)
+{
+	/* This is the conntrack entry already in hashes that won race. */
+	struct nf_conn *ct = nf_ct_tuplehash_to_ctrack(h);
+	enum ip_conntrack_info ctinfo;
+	struct nf_conn *loser_ct;
+
+	loser_ct = nf_ct_get(skb, &ctinfo);
+
+	if (nf_ct_is_dying(ct))
+		return NF_DROP;
+
+	if (!atomic_inc_not_zero(&ct->ct_general.use))
+		return NF_DROP;
+
+	if (((ct->status & IPS_NAT_DONE_MASK) == 0) ||
+	    nf_ct_match(ct, loser_ct)) {
+		struct net *net = nf_ct_net(ct);
+
+		nf_ct_acct_merge(ct, ctinfo, loser_ct);
+		nf_ct_add_to_dying_list(loser_ct);
+		nf_conntrack_put(&loser_ct->ct_general);
+		nf_ct_set(skb, ct, ctinfo);
+
+		NF_CT_STAT_INC(net, insert_failed);
+		return NF_ACCEPT;
+	}
+
+	nf_ct_put(ct);
+	return NF_DROP;
+}
+
 /**
  * nf_ct_resolve_clash - attempt to handle clash without packet drop
  *
@@ -941,31 +974,23 @@ nf_ct_resolve_clash(struct sk_buff *skb, struct nf_conntrack_tuple_hash *h)
 	enum ip_conntrack_info ctinfo;
 	struct nf_conn *loser_ct;
 	struct net *net;
+	int ret;
 
 	loser_ct = nf_ct_get(skb, &ctinfo);
+	net = nf_ct_net(loser_ct);
 
 	l4proto = nf_ct_l4proto_find(nf_ct_protonum(ct));
 	if (!l4proto->allow_clash)
 		goto drop;
 
-	if (nf_ct_is_dying(ct))
-		goto drop;
-
-	if (!atomic_inc_not_zero(&ct->ct_general.use))
-		goto drop;
-
-	if (((ct->status & IPS_NAT_DONE_MASK) == 0) ||
-	    nf_ct_match(ct, loser_ct)) {
-		nf_ct_acct_merge(ct, ctinfo, loser_ct);
-		nf_conntrack_put(&loser_ct->ct_general);
-		nf_ct_set(skb, ct, ctinfo);
-		return NF_ACCEPT;
-	}
+	ret = __nf_ct_resolve_clash(skb, h);
+	if (ret == NF_ACCEPT)
+		return ret;
 
-	nf_ct_put(ct);
 drop:
-	net = nf_ct_net(loser_ct);
+	nf_ct_add_to_dying_list(loser_ct);
 	NF_CT_STAT_INC(net, drop);
+	NF_CT_STAT_INC(net, insert_failed);
 	return NF_DROP;
 }
 
@@ -1034,6 +1059,7 @@ __nf_conntrack_confirm(struct sk_buff *skb)
 
 	if (unlikely(nf_ct_is_dying(ct))) {
 		nf_ct_add_to_dying_list(ct);
+		NF_CT_STAT_INC(net, insert_failed);
 		goto dying;
 	}
 
@@ -1075,11 +1101,9 @@ __nf_conntrack_confirm(struct sk_buff *skb)
 	return NF_ACCEPT;
 
 out:
-	nf_ct_add_to_dying_list(ct);
 	ret = nf_ct_resolve_clash(skb, h);
 dying:
 	nf_conntrack_double_unlock(hash, reply_hash);
-	NF_CT_STAT_INC(net, insert_failed);
 	local_bh_enable();
 	return ret;
 }