netfilter: ctnetlink: helper modules load-on-demand support

This patch adds module loading for helpers via ctnetlink.

* Creation path: We support explicit and implicit helper assignation. For
  the explicit case, we try to load the module. If the module is correctly
  loaded and the helper is present, we return EAGAIN to re-start the
  creation. Otherwise, we return EOPNOTSUPP.
* Update path: release the spin lock, load the module and check. If it is
  present, then return EAGAIN to re-start the update.

This patch 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>
Signed-off-by: Patrick McHardy <kaber@trash.net>

3 files changed, 93 insertions, 37 deletions

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 622d7c671cb7..1e649fb9e0df 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -588,14 +588,7 @@ 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_try_assign_helper(ct, GFP_ATOMIC);
                 NF_CT_STAT_INC(net, new);
         }
 
@@ -772,7 +765,6 @@ 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));
@@ -785,23 +777,7 @@ 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_try_assign_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 9c06b9f86ad4..9e4b74b95ce8 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 +93,35 @@ 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_try_assign_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);
+                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_try_assign_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 49a04fa0becc..4f6486cfd337 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -917,8 +917,22 @@ 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_MODULES
+                spin_unlock_bh(&nf_conntrack_lock);
+
+                if (request_module("nfct-helper-%s", helpname) < 0) {
+                        spin_lock_bh(&nf_conntrack_lock);
+                        return -EOPNOTSUPP;
+                }
+
+                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)
@@ -1082,7 +1096,6 @@ 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);
@@ -1097,16 +1110,55 @@ 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_MODULES
+                        if (request_module("nfct-helper-%s", helpname) < 0) {
+                                err = -EOPNOTSUPP;
+                                goto err;
+                        }
+
+                        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_try_assign_helper(ct, GFP_ATOMIC);
+                if (err < 0) {
                         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]) {