netfilter: ctnetlink: allow to set expectfn for expectations

This patch allows you to set expectfn which is specifically used
by the NAT side of most of the existing conntrack helpers.

I have added a symbol map that uses a string as key to look up for
the function that is attached to the expectation object. This is
the best solution I came out with to solve this issue.

Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/linux/netfilter/nfnetlink_conntrack.h

···
 	CTA_EXPECT_FLAGS,
 	CTA_EXPECT_CLASS,
 	CTA_EXPECT_NAT,
+	CTA_EXPECT_FN,
 	__CTA_EXPECT_MAX
 };
 #define CTA_EXPECT_MAX (__CTA_EXPECT_MAX - 1)

include/net/netfilter/nf_conntrack_helper.h

···
 				       enum ip_conntrack_info ctinfo,
 				       unsigned int timeout);
 
+struct nf_ct_helper_expectfn {
+	struct list_head head;
+	const char *name;
+	void (*expectfn)(struct nf_conn *ct, struct nf_conntrack_expect *exp);
+};
+
+void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n);
+void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n);
+struct nf_ct_helper_expectfn *
+nf_ct_helper_expectfn_find_by_name(const char *name);
+struct nf_ct_helper_expectfn *
+nf_ct_helper_expectfn_find_by_symbol(const void *symbol);
+
 #endif /*_NF_CONNTRACK_HELPER_H*/

net/ipv4/netfilter/nf_nat_core.c

···
 	.exit = nf_nat_net_exit,
 };
 
+static struct nf_ct_helper_expectfn follow_master_nat = {
+	.name		= "nat-follow-master",
+	.expectfn	= nf_nat_follow_master,
+};
+
 static int __init nf_nat_init(void)
 {
 	size_t i;
···
 
 	l3proto = nf_ct_l3proto_find_get((u_int16_t)AF_INET);
 
+	nf_ct_helper_expectfn_register(&follow_master_nat);
+
 	BUG_ON(nf_nat_seq_adjust_hook != NULL);
 	RCU_INIT_POINTER(nf_nat_seq_adjust_hook, nf_nat_seq_adjust);
 	BUG_ON(nfnetlink_parse_nat_setup_hook != NULL);
···
 	unregister_pernet_subsys(&nf_nat_net_ops);
 	nf_ct_l3proto_put(l3proto);
 	nf_ct_extend_unregister(&nat_extend);
+	nf_ct_helper_expectfn_unregister(&follow_master_nat);
 	RCU_INIT_POINTER(nf_nat_seq_adjust_hook, NULL);
 	RCU_INIT_POINTER(nfnetlink_parse_nat_setup_hook, NULL);
 	RCU_INIT_POINTER(nf_ct_nat_offset, NULL);

net/ipv4/netfilter/nf_nat_h323.c

···
 	return 0;
 }
 
+static struct nf_ct_helper_expectfn q931_nat = {
+	.name		= "Q.931",
+	.expectfn	= ip_nat_q931_expect,
+};
+
+static struct nf_ct_helper_expectfn callforwarding_nat = {
+	.name		= "callforwarding",
+	.expectfn	= ip_nat_callforwarding_expect,
+};
+
 /****************************************************************************/
 static int __init init(void)
 {
···
 	RCU_INIT_POINTER(nat_h245_hook, nat_h245);
 	RCU_INIT_POINTER(nat_callforwarding_hook, nat_callforwarding);
 	RCU_INIT_POINTER(nat_q931_hook, nat_q931);
+	nf_ct_helper_expectfn_register(&q931_nat);
+	nf_ct_helper_expectfn_register(&callforwarding_nat);
 	return 0;
 }
 
···
 	RCU_INIT_POINTER(nat_h245_hook, NULL);
 	RCU_INIT_POINTER(nat_callforwarding_hook, NULL);
 	RCU_INIT_POINTER(nat_q931_hook, NULL);
+	nf_ct_helper_expectfn_unregister(&q931_nat);
+	nf_ct_helper_expectfn_unregister(&callforwarding_nat);
 	synchronize_rcu();
 }
 

net/ipv4/netfilter/nf_nat_sip.c

···
 	return NF_DROP;
 }
 
+static struct nf_ct_helper_expectfn sip_nat = {
+        .name           = "sip",
+        .expectfn       = ip_nat_sip_expected,
+};
+
 static void __exit nf_nat_sip_fini(void)
 {
 	RCU_INIT_POINTER(nf_nat_sip_hook, NULL);
···
 	RCU_INIT_POINTER(nf_nat_sdp_port_hook, NULL);
 	RCU_INIT_POINTER(nf_nat_sdp_session_hook, NULL);
 	RCU_INIT_POINTER(nf_nat_sdp_media_hook, NULL);
+	nf_ct_helper_expectfn_unregister(&sip_nat);
 	synchronize_rcu();
 }
 
···
 	RCU_INIT_POINTER(nf_nat_sdp_port_hook, ip_nat_sdp_port);
 	RCU_INIT_POINTER(nf_nat_sdp_session_hook, ip_nat_sdp_session);
 	RCU_INIT_POINTER(nf_nat_sdp_media_hook, ip_nat_sdp_media);
+	nf_ct_helper_expectfn_register(&sip_nat);
 	return 0;
 }
 

net/netfilter/nf_conntrack_helper.c

···
 	}
 }
 
+static LIST_HEAD(nf_ct_helper_expectfn_list);
+
+void nf_ct_helper_expectfn_register(struct nf_ct_helper_expectfn *n)
+{
+	spin_lock_bh(&nf_conntrack_lock);
+	list_add_rcu(&n->head, &nf_ct_helper_expectfn_list);
+	spin_unlock_bh(&nf_conntrack_lock);
+}
+EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_register);
+
+void nf_ct_helper_expectfn_unregister(struct nf_ct_helper_expectfn *n)
+{
+	spin_lock_bh(&nf_conntrack_lock);
+	list_del_rcu(&n->head);
+	spin_unlock_bh(&nf_conntrack_lock);
+}
+EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_unregister);
+
+struct nf_ct_helper_expectfn *
+nf_ct_helper_expectfn_find_by_name(const char *name)
+{
+	struct nf_ct_helper_expectfn *cur;
+	bool found = false;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
+		if (!strcmp(cur->name, name)) {
+			found = true;
+			break;
+		}
+	}
+	rcu_read_unlock();
+	return found ? cur : NULL;
+}
+EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_name);
+
+struct nf_ct_helper_expectfn *
+nf_ct_helper_expectfn_find_by_symbol(const void *symbol)
+{
+	struct nf_ct_helper_expectfn *cur;
+	bool found = false;
+
+	rcu_read_lock();
+	list_for_each_entry_rcu(cur, &nf_ct_helper_expectfn_list, head) {
+		if (cur->expectfn == symbol) {
+			found = true;
+			break;
+		}
+	}
+	rcu_read_unlock();
+	return found ? cur : NULL;
+}
+EXPORT_SYMBOL_GPL(nf_ct_helper_expectfn_find_by_symbol);
+
 int nf_conntrack_helper_register(struct nf_conntrack_helper *me)
 {
 	unsigned int h = helper_hash(&me->tuple);

net/netfilter/nf_conntrack_netlink.c

···
 	struct nlattr *nest_parms;
 	struct nf_conntrack_tuple nat_tuple = {};
 #endif
+	struct nf_ct_helper_expectfn *expfn;
+
 	if (timeout < 0)
 		timeout = 0;
 
···
 		if (helper)
 			NLA_PUT_STRING(skb, CTA_EXPECT_HELP_NAME, helper->name);
 	}
+	expfn = nf_ct_helper_expectfn_find_by_symbol(exp->expectfn);
+	if (expfn != NULL)
+		NLA_PUT_STRING(skb, CTA_EXPECT_FN, expfn->name);
 
 	return 0;
 
···
 	[CTA_EXPECT_FLAGS]	= { .type = NLA_U32 },
 	[CTA_EXPECT_CLASS]	= { .type = NLA_U32 },
 	[CTA_EXPECT_NAT]	= { .type = NLA_NESTED },
+	[CTA_EXPECT_FN]		= { .type = NLA_NUL_STRING },
 };
 
 static int
···
 		} else
 			exp->flags = 0;
 	}
+	if (cda[CTA_EXPECT_FN]) {
+		const char *name = nla_data(cda[CTA_EXPECT_FN]);
+		struct nf_ct_helper_expectfn *expfn;
+
+		expfn = nf_ct_helper_expectfn_find_by_name(name);
+		if (expfn == NULL) {
+			err = -EINVAL;
+			goto err_out;
+		}
+		exp->expectfn = expfn->expectfn;
+	} else
+		exp->expectfn = NULL;
 
 	exp->class = class;
-	exp->expectfn = NULL;
 	exp->master = ct;
 	exp->helper = helper;
 	memcpy(&exp->tuple, &tuple, sizeof(struct nf_conntrack_tuple));