netfilter: limit the length of the helper name

This is necessary in order to have an upper bound for Netlink
message calculation, which is not a problem at all, as there
are no helpers with a longer name.
Signed-off-by: Holger Eitzenberger <holger@eitzenberger.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>

include/net/netfilter/nf_conntrack_helper.h

@@ -14,6 +14,8 @@
 
 struct module;
 
+#define NF_CT_HELPER_NAME_LEN	16
+
 struct nf_conntrack_helper
 {
 	struct hlist_node hnode;	/* Internal use. */

net/netfilter/nf_conntrack_helper.c

@@ -142,6 +142,7 @@ int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 
 	BUG_ON(me->expect_policy == NULL);
 	BUG_ON(me->expect_class_max >= NF_CT_MAX_EXPECT_CLASSES);
+	BUG_ON(strlen(me->name) > NF_CT_HELPER_NAME_LEN - 1);
 
 	mutex_lock(&nf_ct_helper_mutex);
 	hlist_add_head_rcu(&me->hnode, &nf_ct_helper_hash[h]);