netfilter: nf_conntrack: make event callback registration per-netns

This patch fixes an oops that can be triggered following this recipe:

0) make sure nf_conntrack_netlink and nf_conntrack_ipv4 are loaded.
1) container is started.
2) connect to it via lxc-console.
3) generate some traffic with the container to create some conntrack
   entries in its table.
4) stop the container: you hit one oops because the conntrack table
   cleanup tries to report the destroy event to user-space but the
   per-netns nfnetlink socket has already gone (as the nfnetlink
   socket is per-netns but event callback registration is global).

To fix this situation, we make the ctnl_notifier per-netns so the
callback is registered/unregistered if the container is
created/destroyed.

Alex Bligh and Alexey Dobriyan originally proposed one small patch to
check if the nfnetlink socket is gone in nfnetlink_has_listeners,
but this is a very visited path for events, thus, it may reduce
performance and it looks a bit hackish to check for the nfnetlink
socket only to workaround this situation. As a result, I decided
to follow the bigger path choice, which seems to look nicer to me.

Cc: Alexey Dobriyan <adobriyan@gmail.com>
Reported-by: Alex Bligh <alex@alex.org.uk>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

2 files changed, 70 insertions, 40 deletions

diff --git a/net/netfilter/nf_conntrack_ecache.c b/net/netfilter/nf_conntrack_ecache.c
index 6b368be937c6..b62c4148b921 100644
--- a/net/netfilter/nf_conntrack_ecache.c
+++ b/net/netfilter/nf_conntrack_ecache.c
@@ -27,22 +27,17 @@
 
 static DEFINE_MUTEX(nf_ct_ecache_mutex);
 
-struct nf_ct_event_notifier __rcu *nf_conntrack_event_cb __read_mostly;
-EXPORT_SYMBOL_GPL(nf_conntrack_event_cb);
-
-struct nf_exp_event_notifier __rcu *nf_expect_event_cb __read_mostly;
-EXPORT_SYMBOL_GPL(nf_expect_event_cb);
-
 /* deliver cached events and clear cache entry - must be called with locally
  * disabled softirqs */
 void nf_ct_deliver_cached_events(struct nf_conn *ct)
 {
+        struct net *net = nf_ct_net(ct);
         unsigned long events;
         struct nf_ct_event_notifier *notify;
         struct nf_conntrack_ecache *e;
 
         rcu_read_lock();
-        notify = rcu_dereference(nf_conntrack_event_cb);
+        notify = rcu_dereference(net->ct.nf_conntrack_event_cb);
         if (notify == NULL)
                 goto out_unlock;
 
@@ -83,19 +78,20 @@ out_unlock:
 }
 EXPORT_SYMBOL_GPL(nf_ct_deliver_cached_events);
 
-int nf_conntrack_register_notifier(struct nf_ct_event_notifier *new)
+int nf_conntrack_register_notifier(struct net *net,
+                                   struct nf_ct_event_notifier *new)
 {
         int ret = 0;
         struct nf_ct_event_notifier *notify;
 
         mutex_lock(&nf_ct_ecache_mutex);
-        notify = rcu_dereference_protected(nf_conntrack_event_cb,
+        notify = rcu_dereference_protected(net->ct.nf_conntrack_event_cb,
                                            lockdep_is_held(&nf_ct_ecache_mutex));
         if (notify != NULL) {
                 ret = -EBUSY;
                 goto out_unlock;
         }
-        RCU_INIT_POINTER(nf_conntrack_event_cb, new);
+        RCU_INIT_POINTER(net->ct.nf_conntrack_event_cb, new);
         mutex_unlock(&nf_ct_ecache_mutex);
         return ret;
 
@@ -105,32 +101,34 @@ out_unlock:
 }
 EXPORT_SYMBOL_GPL(nf_conntrack_register_notifier);
 
-void nf_conntrack_unregister_notifier(struct nf_ct_event_notifier *new)
+void nf_conntrack_unregister_notifier(struct net *net,
+                                      struct nf_ct_event_notifier *new)
 {
         struct nf_ct_event_notifier *notify;
 
         mutex_lock(&nf_ct_ecache_mutex);
-        notify = rcu_dereference_protected(nf_conntrack_event_cb,
+        notify = rcu_dereference_protected(net->ct.nf_conntrack_event_cb,
                                            lockdep_is_held(&nf_ct_ecache_mutex));
         BUG_ON(notify != new);
-        RCU_INIT_POINTER(nf_conntrack_event_cb, NULL);
+        RCU_INIT_POINTER(net->ct.nf_conntrack_event_cb, NULL);
         mutex_unlock(&nf_ct_ecache_mutex);
 }
 EXPORT_SYMBOL_GPL(nf_conntrack_unregister_notifier);
 
-int nf_ct_expect_register_notifier(struct nf_exp_event_notifier *new)
+int nf_ct_expect_register_notifier(struct net *net,
+                                   struct nf_exp_event_notifier *new)
 {
         int ret = 0;
         struct nf_exp_event_notifier *notify;
 
         mutex_lock(&nf_ct_ecache_mutex);
-        notify = rcu_dereference_protected(nf_expect_event_cb,
+        notify = rcu_dereference_protected(net->ct.nf_expect_event_cb,
                                            lockdep_is_held(&nf_ct_ecache_mutex));
         if (notify != NULL) {
                 ret = -EBUSY;
                 goto out_unlock;
         }
-        RCU_INIT_POINTER(nf_expect_event_cb, new);
+        RCU_INIT_POINTER(net->ct.nf_expect_event_cb, new);
         mutex_unlock(&nf_ct_ecache_mutex);
         return ret;
 
@@ -140,15 +138,16 @@ out_unlock:
 }
 EXPORT_SYMBOL_GPL(nf_ct_expect_register_notifier);
 
-void nf_ct_expect_unregister_notifier(struct nf_exp_event_notifier *new)
+void nf_ct_expect_unregister_notifier(struct net *net,
+                                      struct nf_exp_event_notifier *new)
 {
         struct nf_exp_event_notifier *notify;
 
         mutex_lock(&nf_ct_ecache_mutex);
-        notify = rcu_dereference_protected(nf_expect_event_cb,
+        notify = rcu_dereference_protected(net->ct.nf_expect_event_cb,
                                            lockdep_is_held(&nf_ct_ecache_mutex));
         BUG_ON(notify != new);
-        RCU_INIT_POINTER(nf_expect_event_cb, NULL);
+        RCU_INIT_POINTER(net->ct.nf_expect_event_cb, NULL);
         mutex_unlock(&nf_ct_ecache_mutex);
 }
 EXPORT_SYMBOL_GPL(nf_ct_expect_unregister_notifier);
diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index e58aa9b1fe8a..ef21b221f036 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -4,7 +4,7 @@
  * (C) 2001 by Jay Schulist <jschlst@samba.org>
  * (C) 2002-2006 by Harald Welte <laforge@gnumonks.org>
  * (C) 2003 by Patrick Mchardy <kaber@trash.net>
- * (C) 2005-2008 by Pablo Neira Ayuso <pablo@netfilter.org>
+ * (C) 2005-2011 by Pablo Neira Ayuso <pablo@netfilter.org>
  *
  * Initial connection tracking via netlink development funded and
  * generally made possible by Network Robots, Inc. (www.networkrobots.com)
@@ -2163,6 +2163,54 @@ MODULE_ALIAS("ip_conntrack_netlink");
 MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_CTNETLINK);
 MODULE_ALIAS_NFNL_SUBSYS(NFNL_SUBSYS_CTNETLINK_EXP);
 
+static int __net_init ctnetlink_net_init(struct net *net)
+{
+#ifdef CONFIG_NF_CONNTRACK_EVENTS
+        int ret;
+
+        ret = nf_conntrack_register_notifier(net, &ctnl_notifier);
+        if (ret < 0) {
+                pr_err("ctnetlink_init: cannot register notifier.\n");
+                goto err_out;
+        }
+
+        ret = nf_ct_expect_register_notifier(net, &ctnl_notifier_exp);
+        if (ret < 0) {
+                pr_err("ctnetlink_init: cannot expect register notifier.\n");
+                goto err_unreg_notifier;
+        }
+#endif
+        return 0;
+
+#ifdef CONFIG_NF_CONNTRACK_EVENTS
+err_unreg_notifier:
+        nf_conntrack_unregister_notifier(net, &ctnl_notifier);
+err_out:
+        return ret;
+#endif
+}
+
+static void ctnetlink_net_exit(struct net *net)
+{
+#ifdef CONFIG_NF_CONNTRACK_EVENTS
+        nf_ct_expect_unregister_notifier(net, &ctnl_notifier_exp);
+        nf_conntrack_unregister_notifier(net, &ctnl_notifier);
+#endif
+}
+
+static void __net_exit ctnetlink_net_exit_batch(struct list_head *net_exit_list)
+{
+        struct net *net;
+
+        list_for_each_entry(net, net_exit_list, exit_list)
+                ctnetlink_net_exit(net);
+}
+
+static struct pernet_operations ctnetlink_net_ops = {
+        .init           = ctnetlink_net_init,
+        .exit_batch     = ctnetlink_net_exit_batch,
+};
+
 static int __init ctnetlink_init(void)
 {
         int ret;
@@ -2180,28 +2228,15 @@ static int __init ctnetlink_init(void)
                 goto err_unreg_subsys;
         }
 
-#ifdef CONFIG_NF_CONNTRACK_EVENTS
-        ret = nf_conntrack_register_notifier(&ctnl_notifier);
-        if (ret < 0) {
-                pr_err("ctnetlink_init: cannot register notifier.\n");
+        if (register_pernet_subsys(&ctnetlink_net_ops)) {
+                pr_err("ctnetlink_init: cannot register pernet operations\n");
                 goto err_unreg_exp_subsys;
         }
 
-        ret = nf_ct_expect_register_notifier(&ctnl_notifier_exp);
-        if (ret < 0) {
-                pr_err("ctnetlink_init: cannot expect register notifier.\n");
-                goto err_unreg_notifier;
-        }
-#endif
-
         return 0;
 
-#ifdef CONFIG_NF_CONNTRACK_EVENTS
-err_unreg_notifier:
-        nf_conntrack_unregister_notifier(&ctnl_notifier);
 err_unreg_exp_subsys:
         nfnetlink_subsys_unregister(&ctnl_exp_subsys);
-#endif
 err_unreg_subsys:
         nfnetlink_subsys_unregister(&ctnl_subsys);
 err_out:
@@ -2213,11 +2248,7 @@ static void __exit ctnetlink_exit(void)
         pr_info("ctnetlink: unregistering from nfnetlink.\n");
 
         nf_ct_remove_userspace_expectations();
-#ifdef CONFIG_NF_CONNTRACK_EVENTS
-        nf_ct_expect_unregister_notifier(&ctnl_notifier_exp);
-        nf_conntrack_unregister_notifier(&ctnl_notifier);
-#endif
-
+        unregister_pernet_subsys(&ctnetlink_net_ops);
         nfnetlink_subsys_unregister(&ctnl_exp_subsys);
         nfnetlink_subsys_unregister(&ctnl_subsys);
 }