netfilter: nf_conncount: expose connection list interface

BugLink: https://bugs.launchpad.net/bugs/1811094

This patch provides an interface to maintain the list of connections and
the lookup function to obtain the number of connections in the list.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
(backported from commit 5e5cbc7b)
[mfo: backport: refresh context lines and use older symbol/file names:
 - nf_conntrack_count.h: new file, add include guards.
 - nf_conncount.c -> xt_connlimit.c.
   - nf_conncount_rb -> xt_connlimit_rb
   - nf_conncount_tuple -> xt_connlimit_conn
   - conncount_rb_cachep -> connlimit_rb_cachep
   - conncount_conn_cachep -> connlimit_conn_cachep]
Signed-off-by: Mauricio Faria de Oliveira <mfo@canonical.com>
Acked-by: Khalid Elmously <khalid.elmously@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

include/net/netfilter/nf_conntrack_count.h

+#ifndef _NF_CONNTRACK_COUNT_H
+#define _NF_CONNTRACK_COUNT_H
+
+unsigned int nf_conncount_lookup(struct net *net, struct hlist_head *head,
+				 const struct nf_conntrack_tuple *tuple,
+				 const struct nf_conntrack_zone *zone,
+				 bool *addit);
+
+bool nf_conncount_add(struct hlist_head *head,
+		      const struct nf_conntrack_tuple *tuple);
+
+void nf_conncount_cache_free(struct hlist_head *hhead);
+
+#endif

net/netfilter/xt_connlimit.c

@@ -115,7 +115,7 @@ same_source_net(const union nf_inet_addr *addr,
 	}
 }
 
-static bool add_hlist(struct hlist_head *head,
+bool nf_conncount_add(struct hlist_head *head,
 		      const struct nf_conntrack_tuple *tuple)
 {
 	struct xt_connlimit_conn *conn;
@@ -127,12 +127,12 @@ static bool add_hlist(struct hlist_head *head,
 	hlist_add_head(&conn->node, head);
 	return true;
 }
+EXPORT_SYMBOL_GPL(nf_conncount_add);
 
-static unsigned int check_hlist(struct net *net,
-				struct hlist_head *head,
-				const struct nf_conntrack_tuple *tuple,
-				const struct nf_conntrack_zone *zone,
-				bool *addit)
+unsigned int nf_conncount_lookup(struct net *net, struct hlist_head *head,
+				 const struct nf_conntrack_tuple *tuple,
+				 const struct nf_conntrack_zone *zone,
+				 bool *addit)
 {
 	const struct nf_conntrack_tuple_hash *found;
 	struct xt_connlimit_conn *conn;
@@ -180,6 +180,7 @@ static unsigned int check_hlist(struct net *net,
 
 	return length;
 }
+EXPORT_SYMBOL_GPL(nf_conncount_lookup);
 
 static void tree_nodes_free(struct rb_root *root,
 			    struct xt_connlimit_rb *gc_nodes[],
@@ -226,13 +227,15 @@ count_tree(struct net *net, struct rb_root *root,
 		} else {
 			/* same source network -> be counted! */
 			unsigned int count;
-			count = check_hlist(net, &rbconn->hhead, tuple, zone, &addit);
+
+			count = nf_conncount_lookup(net, &rbconn->hhead, tuple,
+						    zone, &addit);
 
 			tree_nodes_free(root, gc_nodes, gc_count);
 			if (!addit)
 				return count;
 
-			if (!add_hlist(&rbconn->hhead, tuple))
+			if (!nf_conncount_add(&rbconn->hhead, tuple))
 				return 0; /* hotdrop */
 
 			return count + 1;
@@ -242,7 +245,7 @@ count_tree(struct net *net, struct rb_root *root,
 			continue;
 
 		/* only used for GC on hhead, retval and 'addit' ignored */
-		check_hlist(net, &rbconn->hhead, tuple, zone, &addit);
+		nf_conncount_lookup(net, &rbconn->hhead, tuple, zone, &addit);
 		if (hlist_empty(&rbconn->hhead))
 			gc_nodes[gc_count++] = rbconn;
 	}
@@ -392,11 +395,19 @@ static int connlimit_mt_check(const struct xt_mtchk_param *par)
 	return 0;
 }
 
-static void destroy_tree(struct rb_root *r)
+void nf_conncount_cache_free(struct hlist_head *hhead)
 {
 	struct xt_connlimit_conn *conn;
-	struct xt_connlimit_rb *rbconn;
 	struct hlist_node *n;
+
+	hlist_for_each_entry_safe(conn, n, hhead, node)
+		kmem_cache_free(connlimit_conn_cachep, conn);
+}
+EXPORT_SYMBOL_GPL(nf_conncount_cache_free);
+
+static void destroy_tree(struct rb_root *r)
+{
+	struct xt_connlimit_rb *rbconn;
 	struct rb_node *node;
 
 	while ((node = rb_first(r)) != NULL) {
@@ -404,8 +415,7 @@ static void destroy_tree(struct rb_root *r)
 
 		rb_erase(node, r);
 
-		hlist_for_each_entry_safe(conn, n, &rbconn->hhead, node)
-			kmem_cache_free(connlimit_conn_cachep, conn);
+		nf_conncount_cache_free(&rbconn->hhead);
 
 		kmem_cache_free(connlimit_rb_cachep, rbconn);
 	}