netfilter: reduce size of hook entry point locations

struct net contains:

struct nf_hook_entries __rcu *hooks[NFPROTO_NUMPROTO][NF_MAX_HOOKS];

which store the hook entry point locations for the various protocol
families and the hooks.

Using array results in compact c code when doing accesses, i.e.
  x = rcu_dereference(net->nf.hooks[pf][hook]);

but its also wasting a lot of memory, as most families are
not used.

So split the array into those families that are used, which
are only 5 (instead of 13).  In most cases, the 'pf' argument is
constant, i.e. gcc removes switch statement.

struct net before:
 /* size: 5184, cachelines: 81, members: 46 */
after:
 /* size: 4672, cachelines: 73, members: 46 */
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/linux/netfilter.h

@@ -195,7 +195,7 @@ static inline int nf_hook(u_int8_t pf, unsigned int hook, struct net *net,
 			  struct net_device *indev, struct net_device *outdev,
 			  int (*okfn)(struct net *, struct sock *, struct sk_buff *))
 {
-	struct nf_hook_entries *hook_head;
+	struct nf_hook_entries *hook_head = NULL;
 	int ret = 1;
 
 #ifdef HAVE_JUMP_LABEL
@@ -206,7 +206,27 @@ static inline int nf_hook(u_int8_t pf, unsigned int hook, struct net *net,
 #endif
 
 	rcu_read_lock();
-	hook_head = rcu_dereference(net->nf.hooks[pf][hook]);
+	switch (pf) {
+	case NFPROTO_IPV4:
+		hook_head = rcu_dereference(net->nf.hooks_ipv4[hook]);
+		break;
+	case NFPROTO_IPV6:
+		hook_head = rcu_dereference(net->nf.hooks_ipv6[hook]);
+		break;
+	case NFPROTO_ARP:
+		hook_head = rcu_dereference(net->nf.hooks_arp[hook]);
+		break;
+	case NFPROTO_BRIDGE:
+		hook_head = rcu_dereference(net->nf.hooks_bridge[hook]);
+		break;
+	case NFPROTO_DECNET:
+		hook_head = rcu_dereference(net->nf.hooks_decnet[hook]);
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		break;
+	}
+
 	if (hook_head) {
 		struct nf_hook_state state;
 

include/net/netns/netfilter.h

@@ -17,7 +17,11 @@ struct netns_nf {
 #ifdef CONFIG_SYSCTL
 	struct ctl_table_header *nf_log_dir_header;
 #endif
-	struct nf_hook_entries __rcu *hooks[NFPROTO_NUMPROTO][NF_MAX_HOOKS];
+	struct nf_hook_entries __rcu *hooks_ipv4[NF_MAX_HOOKS];
+	struct nf_hook_entries __rcu *hooks_ipv6[NF_MAX_HOOKS];
+	struct nf_hook_entries __rcu *hooks_arp[NF_MAX_HOOKS];
+	struct nf_hook_entries __rcu *hooks_bridge[NF_MAX_HOOKS];
+	struct nf_hook_entries __rcu *hooks_decnet[NF_MAX_HOOKS];
 #if IS_ENABLED(CONFIG_NF_DEFRAG_IPV4)
 	bool			defrag_ipv4;
 #endif

net/bridge/br_netfilter_hooks.c

@@ -991,7 +991,7 @@ int br_nf_hook_thresh(unsigned int hook, struct net *net,
 	unsigned int i;
 	int ret;
 
-	e = rcu_dereference(net->nf.hooks[NFPROTO_BRIDGE][hook]);
+	e = rcu_dereference(net->nf.hooks_bridge[hook]);
 	if (!e)
 		return okfn(net, sk, skb);
 

net/netfilter/core.c

@@ -264,8 +264,23 @@ static void *__nf_hook_entries_try_shrink(struct nf_hook_entries __rcu **pp)
 
 static struct nf_hook_entries __rcu **nf_hook_entry_head(struct net *net, const struct nf_hook_ops *reg)
 {
-	if (reg->pf != NFPROTO_NETDEV)
-		return net->nf.hooks[reg->pf]+reg->hooknum;
+	switch (reg->pf) {
+	case NFPROTO_NETDEV:
+		break;
+	case NFPROTO_ARP:
+		return net->nf.hooks_arp + reg->hooknum;
+	case NFPROTO_BRIDGE:
+		return net->nf.hooks_bridge + reg->hooknum;
+	case NFPROTO_IPV4:
+		return net->nf.hooks_ipv4 + reg->hooknum;
+	case NFPROTO_IPV6:
+		return net->nf.hooks_ipv6 + reg->hooknum;
+	case NFPROTO_DECNET:
+		return net->nf.hooks_decnet + reg->hooknum;
+	default:
+		WARN_ON_ONCE(1);
+		return NULL;
+	}
 
 #ifdef CONFIG_NETFILTER_INGRESS
 	if (reg->hooknum == NF_NETDEV_INGRESS) {
@@ -534,14 +549,21 @@ void (*nf_nat_decode_session_hook)(struct sk_buff *, struct flowi *);
 EXPORT_SYMBOL(nf_nat_decode_session_hook);
 #endif
 
-static int __net_init netfilter_net_init(struct net *net)
+static void __net_init __netfilter_net_init(struct nf_hook_entries *e[NF_MAX_HOOKS])
 {
-	int i, h;
+	int h;
 
-	for (i = 0; i < ARRAY_SIZE(net->nf.hooks); i++) {
-		for (h = 0; h < NF_MAX_HOOKS; h++)
-			RCU_INIT_POINTER(net->nf.hooks[i][h], NULL);
-	}
+	for (h = 0; h < NF_MAX_HOOKS; h++)
+		RCU_INIT_POINTER(e[h], NULL);
+}
+
+static int __net_init netfilter_net_init(struct net *net)
+{
+	__netfilter_net_init(net->nf.hooks_ipv4);
+	__netfilter_net_init(net->nf.hooks_ipv6);
+	__netfilter_net_init(net->nf.hooks_arp);
+	__netfilter_net_init(net->nf.hooks_bridge);
+	__netfilter_net_init(net->nf.hooks_decnet);
 
 #ifdef CONFIG_PROC_FS
 	net->nf.proc_netfilter = proc_net_mkdir(net, "netfilter",

net/netfilter/nf_queue.c

@@ -201,6 +201,23 @@ static unsigned int nf_iterate(struct sk_buff *skb,
 	return NF_ACCEPT;
 }
 
+static struct nf_hook_entries *nf_hook_entries_head(const struct net *net, u8 pf, u8 hooknum)
+{
+	switch (pf) {
+	case NFPROTO_BRIDGE:
+		return rcu_dereference(net->nf.hooks_bridge[hooknum]);
+	case NFPROTO_IPV4:
+		return rcu_dereference(net->nf.hooks_ipv4[hooknum]);
+	case NFPROTO_IPV6:
+		return rcu_dereference(net->nf.hooks_ipv6[hooknum]);
+	default:
+		WARN_ON_ONCE(1);
+		return NULL;
+	}
+
+	return NULL;
+}
+
 /* Caller must hold rcu read-side lock */
 void nf_reinject(struct nf_queue_entry *entry, unsigned int verdict)
 {
@@ -216,12 +233,12 @@ void nf_reinject(struct nf_queue_entry *entry, unsigned int verdict)
 	net = entry->state.net;
 	pf = entry->state.pf;
 
-	hooks = rcu_dereference(net->nf.hooks[pf][entry->state.hook]);
+	hooks = nf_hook_entries_head(net, pf, entry->state.hook);
 
 	nf_queue_entry_release_refs(entry);
 
 	i = entry->hook_index;
-	if (WARN_ON_ONCE(i >= hooks->num_hook_entries)) {
+	if (WARN_ON_ONCE(!hooks || i >= hooks->num_hook_entries)) {
 		kfree_skb(skb);
 		kfree(entry);
 		return;