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 <pablo@netfilter.org>

2 files changed, 72 insertions, 1 deletions

diff --git a/net/netfilter/nf_conntrack_helper.c b/net/netfilter/nf_conntrack_helper.c
index bbe23baa19b..436b7cb79ba 100644
--- a/net/netfilter/nf_conntrack_helper.c
+++ b/net/netfilter/nf_conntrack_helper.c
@@ -181,6 +181,60 @@ void nf_ct_helper_destroy(struct nf_conn *ct)
 	}
 }
 
+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);
diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index 845c8ca2856..b8827e8a11f 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -1679,6 +1679,8 @@ ctnetlink_exp_dump_expect(struct sk_buff *skb,
 	struct nlattr *nest_parms;
 	struct nf_conntrack_tuple nat_tuple = {};
 #endif
+	struct nf_ct_helper_expectfn *expfn;
+
 	if (timeout < 0)
 		timeout = 0;
 
@@ -1722,6 +1724,9 @@ ctnetlink_exp_dump_expect(struct sk_buff *skb,
 		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;
 
@@ -1881,6 +1886,7 @@ static const struct nla_policy exp_nla_policy[CTA_EXPECT_MAX+1] = {
 	[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
@@ -2182,9 +2188,20 @@ ctnetlink_create_expect(struct net *net, u16 zone,
 		} 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));