[PATCH 2/6] [PATCH] helper load-on-demand support for ctnetlink

[Pablo Neira Ayuso <pablo@netfilter.org>]

This patch adds on-request module loading for helpers via ctnetlink.
To do so, we release the locks, load the module and check. If the
helper is present, then it returns EAGAIN to re-start the operation.
With this patch, we support explicit and implicit helper assignment.

This patch also modifies nfnetlink to handle EAGAIN appropriately.
This all is based on a suggestion from Patrick McHardy.

This patch also provides a refactorized function to lookup-and-set
the connection tracking helper. The function removes the exported
symbol __nf_ct_helper_find as it has not clients anymore.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---

 include/linux/netfilter/nfnetlink.h         |    3 +
 include/net/netfilter/nf_conntrack_helper.h |    5 +-
 net/netfilter/nf_conntrack_core.c           |   28 +---------
 net/netfilter/nf_conntrack_helper.c         |   33 +++++++++++-
 net/netfilter/nf_conntrack_netlink.c        |   73 ++++++++++++++++++++++++---
 net/netfilter/nfnetlink.c                   |   12 +++-
 6 files changed, 111 insertions(+), 43 deletions(-)

diff --git a/include/linux/netfilter/nfnetlink.h b/include/linux/netfilter/nfnetlink.h
index 0d8424f..7d8e045 100644
--- a/include/linux/netfilter/nfnetlink.h
+++ b/include/linux/netfilter/nfnetlink.h
@@ -78,6 +78,9 @@ extern int nfnetlink_send(struct sk_buff *skb, u32 pid, unsigned group,
 			  int echo);
 extern int nfnetlink_unicast(struct sk_buff *skb, u_int32_t pid, int flags);
 
+extern void nfnl_lock(void);
+extern void nfnl_unlock(void);
+
 #define MODULE_ALIAS_NFNL_SUBSYS(subsys) \
 	MODULE_ALIAS("nfnetlink-subsys-" __stringify(subsys))
 
diff --git a/include/net/netfilter/nf_conntrack_helper.h b/include/net/netfilter/nf_conntrack_helper.h
index f8060ab..8eebf6e 100644
--- a/include/net/netfilter/nf_conntrack_helper.h
+++ b/include/net/netfilter/nf_conntrack_helper.h
@@ -39,9 +39,6 @@ struct nf_conntrack_helper
 };
 
 extern struct nf_conntrack_helper *
-__nf_ct_helper_find(const struct nf_conntrack_tuple *tuple);
-
-extern struct nf_conntrack_helper *
 __nf_conntrack_helper_find_byname(const char *name);
 
 extern int nf_conntrack_helper_register(struct nf_conntrack_helper *);
@@ -49,6 +46,8 @@ extern void nf_conntrack_helper_unregister(struct nf_conntrack_helper *);
 
 extern struct nf_conn_help *nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp);
 
+extern int __nf_ct_set_helper(struct nf_conn *ct, gfp_t flags);
+
 static inline struct nf_conn_help *nfct_help(const struct nf_conn *ct)
 {
 	return nf_ct_ext_find(ct, NF_CT_EXT_HELPER);
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 27de3c7..54e35f3 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -581,14 +581,7 @@ init_conntrack(struct net *net,
 		nf_conntrack_get(&ct->master->ct_general);
 		NF_CT_STAT_INC(net, expect_new);
 	} else {
-		struct nf_conntrack_helper *helper;
-
-		helper = __nf_ct_helper_find(&repl_tuple);
-		if (helper) {
-			help = nf_ct_helper_ext_add(ct, GFP_ATOMIC);
-			if (help)
-				rcu_assign_pointer(help->helper, helper);
-		}
+		__nf_ct_set_helper(ct, GFP_ATOMIC);
 		NF_CT_STAT_INC(net, new);
 	}
 
@@ -765,7 +758,6 @@ void nf_conntrack_alter_reply(struct nf_conn *ct,
 			      const struct nf_conntrack_tuple *newreply)
 {
 	struct nf_conn_help *help = nfct_help(ct);
-	struct nf_conntrack_helper *helper;
 
 	/* Should be unconfirmed, so not in hash table yet */
 	NF_CT_ASSERT(!nf_ct_is_confirmed(ct));
@@ -778,23 +770,7 @@ void nf_conntrack_alter_reply(struct nf_conn *ct,
 		return;
 
 	rcu_read_lock();
-	helper = __nf_ct_helper_find(newreply);
-	if (helper == NULL) {
-		if (help)
-			rcu_assign_pointer(help->helper, NULL);
-		goto out;
-	}
-
-	if (help == NULL) {
-		help = nf_ct_helper_ext_add(ct, GFP_ATOMIC);
-		if (help == NULL)
-			goto out;
-	} else {
-		memset(&help->help, 0, sizeof(help->help));
-	}
-
-	rcu_assign_pointer(help->helper, helper);
-out:
+	__nf_ct_set_helper(ct, GFP_ATOMIC);
 	rcu_read_unlock();
 }
 EXPORT_SYMBOL_GPL(nf_conntrack_alter_reply);
diff --git a/net/netfilter/nf_conntrack_helper.c b/net/netfilter/nf_conntrack_helper.c
index 9c06b9f..86cdbde 100644
--- a/net/netfilter/nf_conntrack_helper.c
+++ b/net/netfilter/nf_conntrack_helper.c
@@ -44,7 +44,7 @@ static unsigned int helper_hash(const struct nf_conntrack_tuple *tuple)
 		(__force __u16)tuple->src.u.all) % nf_ct_helper_hsize;
 }
 
-struct nf_conntrack_helper *
+static struct nf_conntrack_helper *
 __nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
 {
 	struct nf_conntrack_helper *helper;
@@ -62,7 +62,6 @@ __nf_ct_helper_find(const struct nf_conntrack_tuple *tuple)
 	}
 	return NULL;
 }
-EXPORT_SYMBOL_GPL(__nf_ct_helper_find);
 
 struct nf_conntrack_helper *
 __nf_conntrack_helper_find_byname(const char *name)
@@ -94,6 +93,36 @@ struct nf_conn_help *nf_ct_helper_ext_add(struct nf_conn *ct, gfp_t gfp)
 }
 EXPORT_SYMBOL_GPL(nf_ct_helper_ext_add);
 
+int __nf_ct_set_helper(struct nf_conn *ct, gfp_t flags)
+{
+	int ret = 0;
+	struct nf_conntrack_helper *helper;
+	struct nf_conn_help *help = nfct_help(ct);
+
+	helper = __nf_ct_helper_find(&ct->tuplehash[IP_CT_DIR_REPLY].tuple);
+	if (helper == NULL) {
+		if (help)
+			rcu_assign_pointer(help->helper, NULL);
+		ret = -ENOENT;
+		goto out;
+	}
+
+	if (help == NULL) {
+		help = nf_ct_helper_ext_add(ct, flags);
+		if (help == NULL) {
+			ret = -ENOMEM;
+			goto out;
+		}
+	} else {
+		memset(&help->help, 0, sizeof(help->help));
+	}
+
+	rcu_assign_pointer(help->helper, helper);
+out:
+	return ret;
+}
+EXPORT_SYMBOL_GPL(__nf_ct_set_helper);
+
 static inline int unhelp(struct nf_conntrack_tuple_hash *i,
 			 const struct nf_conntrack_helper *me)
 {
diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index b7a6be8..8621b48 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -952,8 +952,23 @@ ctnetlink_change_helper(struct nf_conn *ct, struct nlattr *cda[])
 	}
 
 	helper = __nf_conntrack_helper_find_byname(helpname);
-	if (helper == NULL)
+	if (helper == NULL) {
+#ifdef CONFIG_KMOD
+		spin_unlock_bh(&nf_conntrack_lock);
+		nfnl_unlock();
+		if (request_module("nfct-helper-%s", helpname) < 0) {
+			nfnl_lock();
+			spin_lock_bh(&nf_conntrack_lock);
+			return -EOPNOTSUPP;
+		}
+		nfnl_lock();
+		spin_lock_bh(&nf_conntrack_lock);
+		helper = __nf_conntrack_helper_find_byname(helpname);
+		if (helper)
+			return -EAGAIN;
+#endif
 		return -EOPNOTSUPP;
+	}
 
 	if (help) {
 		if (help->helper == helper)
@@ -1117,7 +1132,6 @@ ctnetlink_create_conntrack(struct nlattr *cda[],
 {
 	struct nf_conn *ct;
 	int err = -EINVAL;
-	struct nf_conn_help *help;
 	struct nf_conntrack_helper *helper;
 
 	ct = nf_conntrack_alloc(&init_net, otuple, rtuple, GFP_KERNEL);
@@ -1132,16 +1146,57 @@ ctnetlink_create_conntrack(struct nlattr *cda[],
 	ct->status |= IPS_CONFIRMED;
 
 	rcu_read_lock();
-	helper = __nf_ct_helper_find(rtuple);
-	if (helper) {
-		help = nf_ct_helper_ext_add(ct, GFP_ATOMIC);
-		if (help == NULL) {
+ 	if (cda[CTA_HELP]) {
+ 		char *helpname;
+ 
+ 		err = ctnetlink_parse_help(cda[CTA_HELP], &helpname);
+ 		if (err < 0) {
+			rcu_read_unlock();
+			goto err;
+		}
+
+		helper = __nf_conntrack_helper_find_byname(helpname);
+		if (helper == NULL) {
+			rcu_read_unlock();
+#ifdef CONFIG_KMOD
+			nfnl_unlock();
+			if (request_module("nfct-helper-%s", helpname) < 0) {
+				nfnl_lock();
+				err = -EOPNOTSUPP;
+				goto err;
+			}
+			nfnl_lock();
+			rcu_read_lock();
+			helper = __nf_conntrack_helper_find_byname(helpname);
+			if (helper) {
+				rcu_read_unlock();
+				err = -EAGAIN;
+				goto err;
+			}
+			rcu_read_unlock();
+#endif
+			err = -EOPNOTSUPP;
+			goto err;
+		} else {
+			struct nf_conn_help *help;
+
+			help = nf_ct_helper_ext_add(ct, GFP_ATOMIC);
+			if (help == NULL) {
+				rcu_read_unlock();
+				err = -ENOMEM;
+				goto err;
+			}
+
+			/* not in hash table yet so not strictly necessary */
+			rcu_assign_pointer(help->helper, helper);
+		}
+	} else {
+		/* try an implicit helper assignation */
+		err = __nf_ct_set_helper(ct, GFP_ATOMIC);
+		if (err == -ENOMEM) {
 			rcu_read_unlock();
-			err = -ENOMEM;
 			goto err;
 		}
-		/* not in hash table yet so not strictly necessary */
-		rcu_assign_pointer(help->helper, helper);
 	}
 
 	if (cda[CTA_STATUS]) {
diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
index b75c9c4..4739f9f 100644
--- a/net/netfilter/nfnetlink.c
+++ b/net/netfilter/nfnetlink.c
@@ -44,15 +44,17 @@ static struct sock *nfnl = NULL;
 static const struct nfnetlink_subsystem *subsys_table[NFNL_SUBSYS_COUNT];
 static DEFINE_MUTEX(nfnl_mutex);
 
-static inline void nfnl_lock(void)
+void nfnl_lock(void)
 {
 	mutex_lock(&nfnl_mutex);
 }
+EXPORT_SYMBOL_GPL(nfnl_lock);
 
-static inline void nfnl_unlock(void)
+void nfnl_unlock(void)
 {
 	mutex_unlock(&nfnl_mutex);
 }
+EXPORT_SYMBOL_GPL(nfnl_unlock);
 
 int nfnetlink_subsys_register(const struct nfnetlink_subsystem *n)
 {
@@ -132,6 +134,7 @@ static int nfnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 		return 0;
 
 	type = nlh->nlmsg_type;
+replay:
 	ss = nfnetlink_get_subsys(type);
 	if (!ss) {
 #ifdef CONFIG_KMOD
@@ -165,7 +168,10 @@ static int nfnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 		} else
 			return -EINVAL;
 
-		return nc->call(nfnl, skb, nlh, cda);
+		err = nc->call(nfnl, skb, nlh, cda);
+		if (err == -EAGAIN)
+			goto replay;
+		return err;
 	}
 }