netfilter: x_tables: add xt_find_table

This will be used to obtain the xt_table struct given address family and
table name.

Followup patches will reduce the number of direct accesses to the xt_table
structures via net->ipv{4,6}.ip(6)table_{nat,mangle,...} pointers, then
remove them.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/linux/netfilter/x_tables.h

@@ -322,6 +322,7 @@ struct xt_target *xt_request_find_target(u8 af, const char *name, u8 revision);
 int xt_find_revision(u8 af, const char *name, u8 revision, int target,
 		     int *err);
 
+struct xt_table *xt_find_table(struct net *net, u8 af, const char *name);
 struct xt_table *xt_find_table_lock(struct net *net, u_int8_t af,
 				    const char *name);
 struct xt_table *xt_request_find_table_lock(struct net *net, u_int8_t af,

net/netfilter/x_tables.c

@@ -1199,6 +1199,23 @@ void xt_free_table_info(struct xt_table_info *info)
 }
 EXPORT_SYMBOL(xt_free_table_info);
 
+struct xt_table *xt_find_table(struct net *net, u8 af, const char *name)
+{
+	struct xt_pernet *xt_net = net_generic(net, xt_pernet_id);
+	struct xt_table *t;
+
+	mutex_lock(&xt[af].mutex);
+	list_for_each_entry(t, &xt_net->tables[af], list) {
+		if (strcmp(t->name, name) == 0) {
+			mutex_unlock(&xt[af].mutex);
+			return t;
+		}
+	}
+	mutex_unlock(&xt[af].mutex);
+	return NULL;
+}
+EXPORT_SYMBOL(xt_find_table);
+
 /* Find table by name, grabs mutex & ref.  Returns ERR_PTR on error. */
 struct xt_table *xt_find_table_lock(struct net *net, u_int8_t af,
 				    const char *name)