netfilter: Per network namespace netfilter hooks.

- Add a new set of functions for registering and unregistering per
network namespace hooks.

- Modify the old global namespace hook functions to use the per
network namespace hooks in their implementation, so their remains a
single list that needs to be walked for any hook (this is important
for keeping the hook priority working and for keeping the code
walking the hooks simple).

- Only allow registering the per netdevice hooks in the network
namespace where the network device lives.

- Dynamically allocate the structures in the per network namespace
hook list in nf_register_net_hook, and unregister them in
nf_unregister_net_hook.

Dynamic allocate is required somewhere as the number of network
namespaces are not fixed so we might as well allocate them in the
registration function.

The chain of registered hooks on any list is expected to be small so
the cost of walking that list to find the entry we are unregistering
should also be small.

Performing the management of the dynamically allocated list entries
in the registration and unregistration functions keeps the complexity
from spreading.

Signed-off-by: "Eric W. Biederman" <[e-mail]>

include/linux/netfilter.h

···
 #include <linux/list.h>
 #include <linux/static_key.h>
 #include <linux/netfilter_defs.h>
+#include <linux/netdevice.h>
+#include <net/net_namespace.h>
 
 #ifdef CONFIG_NETFILTER
 static inline int NF_DROP_GETERR(int verdict)
···
 };
 
 /* Function to register/unregister hook points. */
+int nf_register_net_hook(struct net *net, const struct nf_hook_ops *ops);
+void nf_unregister_net_hook(struct net *net, const struct nf_hook_ops *ops);
+int nf_register_net_hooks(struct net *net, const struct nf_hook_ops *reg,
+			  unsigned int n);
+void nf_unregister_net_hooks(struct net *net, const struct nf_hook_ops *reg,
+			     unsigned int n);
+
 int nf_register_hook(struct nf_hook_ops *reg);
 void nf_unregister_hook(struct nf_hook_ops *reg);
 int nf_register_hooks(struct nf_hook_ops *reg, unsigned int n);
···
    need to check permissions yourself! */
 int nf_register_sockopt(struct nf_sockopt_ops *reg);
 void nf_unregister_sockopt(struct nf_sockopt_ops *reg);
-
-extern struct list_head nf_hooks[NFPROTO_NUMPROTO][NF_MAX_HOOKS];
 
 #ifdef HAVE_JUMP_LABEL
 extern struct static_key nf_hooks_needed[NFPROTO_NUMPROTO][NF_MAX_HOOKS];
···
 				 int (*okfn)(struct sock *, struct sk_buff *),
 				 int thresh)
 {
-	struct list_head *nf_hook_list = &nf_hooks[pf][hook];
+	struct net *net = dev_net(indev ? indev : outdev);
+	struct list_head *nf_hook_list = &net->nf.hooks[pf][hook];
 
 	if (nf_hook_list_active(nf_hook_list, pf, hook)) {
 		struct nf_hook_state state;

include/net/netns/netfilter.h

···
 #ifdef CONFIG_SYSCTL
 	struct ctl_table_header *nf_log_dir_header;
 #endif
+	struct list_head hooks[NFPROTO_NUMPROTO][NF_MAX_HOOKS];
 };
 #endif

net/netfilter/core.c

···
 }
 EXPORT_SYMBOL_GPL(nf_unregister_afinfo);
 
-struct list_head nf_hooks[NFPROTO_NUMPROTO][NF_MAX_HOOKS] __read_mostly;
-EXPORT_SYMBOL(nf_hooks);
-
 #ifdef HAVE_JUMP_LABEL
 struct static_key nf_hooks_needed[NFPROTO_NUMPROTO][NF_MAX_HOOKS];
 EXPORT_SYMBOL(nf_hooks_needed);
···
 
 static DEFINE_MUTEX(nf_hook_mutex);
 
-static struct list_head *find_nf_hook_list(const struct nf_hook_ops *reg)
+static struct list_head *find_nf_hook_list(struct net *net,
+					   const struct nf_hook_ops *reg)
 {
 	struct list_head *nf_hook_list = NULL;
 
 	if (reg->pf != NFPROTO_NETDEV)
-		nf_hook_list = &nf_hooks[reg->pf][reg->hooknum];
+		nf_hook_list = &net->nf.hooks[reg->pf][reg->hooknum];
 	else if (reg->hooknum == NF_NETDEV_INGRESS) {
 #ifdef CONFIG_NETFILTER_INGRESS
-		if (reg->dev)
+		if (reg->dev && dev_net(reg->dev) == net)
 			nf_hook_list = &reg->dev->nf_hooks_ingress;
 #endif
 	}
 	return nf_hook_list;
 }
 
-int nf_register_hook(struct nf_hook_ops *reg)
+int nf_register_net_hook(struct net *net, const struct nf_hook_ops *reg)
 {
 	struct list_head *nf_hook_list;
-	struct nf_hook_ops *elem;
+	struct nf_hook_ops *elem, *new;
 
-	nf_hook_list = find_nf_hook_list(reg);
+	new = kzalloc(sizeof(*new), GFP_KERNEL);
+	if (!new)
+		return -ENOMEM;
+
+	new->hook     = reg->hook;
+	new->dev      = reg->dev;
+	new->owner    = reg->owner;
+	new->priv     = reg->priv;
+	new->pf       = reg->pf;
+	new->hooknum  = reg->hooknum;
+	new->priority = reg->priority;
+
+	nf_hook_list = find_nf_hook_list(net, reg);
 	if (!nf_hook_list)
 		return -ENOENT;
 
···
 		if (reg->priority < elem->priority)
 			break;
 	}
-	list_add_rcu(&reg->list, elem->list.prev);
+	list_add_rcu(&new->list, elem->list.prev);
 	mutex_unlock(&nf_hook_mutex);
 #ifdef CONFIG_NETFILTER_INGRESS
 	if (reg->pf == NFPROTO_NETDEV && reg->hooknum == NF_NETDEV_INGRESS)
···
 #endif
 	return 0;
 }
-EXPORT_SYMBOL(nf_register_hook);
+EXPORT_SYMBOL(nf_register_net_hook);
 
-void nf_unregister_hook(struct nf_hook_ops *reg)
+void nf_unregister_net_hook(struct net *net, const struct nf_hook_ops *reg)
 {
+	struct list_head *nf_hook_list;
+	struct nf_hook_ops *elem;
+
+	nf_hook_list = find_nf_hook_list(net, reg);
+	if (!nf_hook_list)
+		return;
+
 	mutex_lock(&nf_hook_mutex);
-	list_del_rcu(&reg->list);
+	list_for_each_entry(elem, nf_hook_list, list) {
+		if ((reg->hook     == elem->hook) &&
+		    (reg->dev      == elem->dev) &&
+		    (reg->owner    == elem->owner) &&
+		    (reg->priv     == elem->priv) &&
+		    (reg->pf       == elem->pf) &&
+		    (reg->hooknum  == elem->hooknum) &&
+		    (reg->priority == elem->priority)) {
+			list_del_rcu(&elem->list);
+			break;
+		}
+	}
 	mutex_unlock(&nf_hook_mutex);
+	if (&elem->list == nf_hook_list) {
+		WARN(1, "nf_unregister_net_hook: hook not found!\n");
+		return;
+	}
 #ifdef CONFIG_NETFILTER_INGRESS
 	if (reg->pf == NFPROTO_NETDEV && reg->hooknum == NF_NETDEV_INGRESS)
 		net_dec_ingress_queue();
···
 	static_key_slow_dec(&nf_hooks_needed[reg->pf][reg->hooknum]);
 #endif
 	synchronize_net();
-	nf_queue_nf_hook_drop(reg);
+	nf_queue_nf_hook_drop(elem);
+	kfree(elem);
+}
+EXPORT_SYMBOL(nf_unregister_net_hook);
+
+int nf_register_net_hooks(struct net *net, const struct nf_hook_ops *reg,
+			  unsigned int n)
+{
+	unsigned int i;
+	int err = 0;
+
+	for (i = 0; i < n; i++) {
+		err = nf_register_net_hook(net, &reg[i]);
+		if (err)
+			goto err;
+	}
+	return err;
+
+err:
+	if (i > 0)
+		nf_unregister_net_hooks(net, reg, i);
+	return err;
+}
+EXPORT_SYMBOL(nf_register_net_hooks);
+
+void nf_unregister_net_hooks(struct net *net, const struct nf_hook_ops *reg,
+			     unsigned int n)
+{
+	while (n-- > 0)
+		nf_unregister_net_hook(net, &reg[n]);
+}
+EXPORT_SYMBOL(nf_unregister_net_hooks);
+
+static LIST_HEAD(nf_hook_list);
+
+int nf_register_hook(struct nf_hook_ops *reg)
+{
+	struct net *net, *last;
+	int ret;
+
+	rtnl_lock();
+	for_each_net(net) {
+		ret = nf_register_net_hook(net, reg);
+		if (ret && ret != -ENOENT)
+			goto rollback;
+	}
+	list_add_tail(&reg->list, &nf_hook_list);
+	rtnl_unlock();
+
+	return 0;
+rollback:
+	last = net;
+	for_each_net(net) {
+		if (net == last)
+			break;
+		nf_unregister_net_hook(net, reg);
+	}
+	rtnl_unlock();
+	return ret;
+}
+EXPORT_SYMBOL(nf_register_hook);
+
+void nf_unregister_hook(struct nf_hook_ops *reg)
+{
+	struct net *net;
+
+	rtnl_lock();
+	list_del(&reg->list);
+	for_each_net(net)
+		nf_unregister_net_hook(net, reg);
+	rtnl_unlock();
 }
 EXPORT_SYMBOL(nf_unregister_hook);
 
···
 EXPORT_SYMBOL(nf_nat_decode_session_hook);
 #endif
 
+static int nf_register_hook_list(struct net *net)
+{
+	struct nf_hook_ops *elem;
+	int ret;
+
+	rtnl_lock();
+	list_for_each_entry(elem, &nf_hook_list, list) {
+		ret = nf_register_net_hook(net, elem);
+		if (ret && ret != -ENOENT)
+			goto out_undo;
+	}
+	rtnl_unlock();
+	return 0;
+
+out_undo:
+	list_for_each_entry_continue_reverse(elem, &nf_hook_list, list)
+		nf_unregister_net_hook(net, elem);
+	rtnl_unlock();
+	return ret;
+}
+
+static void nf_unregister_hook_list(struct net *net)
+{
+	struct nf_hook_ops *elem;
+
+	rtnl_lock();
+	list_for_each_entry(elem, &nf_hook_list, list)
+		nf_unregister_net_hook(net, elem);
+	rtnl_unlock();
+}
+
 static int __net_init netfilter_net_init(struct net *net)
 {
+	int i, h, ret;
+
+	for (i = 0; i < ARRAY_SIZE(net->nf.hooks); i++) {
+		for (h = 0; h < NF_MAX_HOOKS; h++)
+			INIT_LIST_HEAD(&net->nf.hooks[i][h]);
+	}
+
 #ifdef CONFIG_PROC_FS
 	net->nf.proc_netfilter = proc_net_mkdir(net, "netfilter",
 						net->proc_net);
···
 		return -ENOMEM;
 	}
 #endif
-	return 0;
+	ret = nf_register_hook_list(net);
+	if (ret)
+		remove_proc_entry("netfilter", net->proc_net);
+
+	return ret;
 }
 
 static void __net_exit netfilter_net_exit(struct net *net)
 {
+	nf_unregister_hook_list(net);
 	remove_proc_entry("netfilter", net->proc_net);
 }
 
···
 
 int __init netfilter_init(void)
 {
-	int i, h, ret;
-
-	for (i = 0; i < ARRAY_SIZE(nf_hooks); i++) {
-		for (h = 0; h < NF_MAX_HOOKS; h++)
-			INIT_LIST_HEAD(&nf_hooks[i][h]);
-	}
+	int ret;
 
 	ret = register_pernet_subsys(&netfilter_net_ops);
 	if (ret < 0)