netfilter: don't allocate space for arp/bridge hooks unless needed

no need to define hook points if the family isn't supported.
Because we need these hooks for either nftables, arp/ebtables
or the 'call-iptables' hack we have in the bridge layer add two
new dependencies, NETFILTER_FAMILY_{ARP,BRIDGE}, and have the
users select them.

Signed-off-by: Florian Westphal <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/linux/netfilter.h

···
 		hook_head = rcu_dereference(net->nf.hooks_ipv6[hook]);
 		break;
 	case NFPROTO_ARP:
+#ifdef CONFIG_NETFILTER_FAMILY_ARP
 		hook_head = rcu_dereference(net->nf.hooks_arp[hook]);
+#endif
 		break;
 	case NFPROTO_BRIDGE:
+#ifdef CONFIG_NETFILTER_FAMILY_BRIDGE
 		hook_head = rcu_dereference(net->nf.hooks_bridge[hook]);
+#endif
 		break;
 #if IS_ENABLED(CONFIG_DECNET)
 	case NFPROTO_DECNET:

include/net/netns/netfilter.h

···
 #endif
 	struct nf_hook_entries __rcu *hooks_ipv4[NF_INET_NUMHOOKS];
 	struct nf_hook_entries __rcu *hooks_ipv6[NF_INET_NUMHOOKS];
+#ifdef CONFIG_NETFILTER_FAMILY_ARP
 	struct nf_hook_entries __rcu *hooks_arp[NF_ARP_NUMHOOKS];
+#endif
+#ifdef CONFIG_NETFILTER_FAMILY_BRIDGE
 	struct nf_hook_entries __rcu *hooks_bridge[NF_INET_NUMHOOKS];
+#endif
 #if IS_ENABLED(CONFIG_DECNET)
 	struct nf_hook_entries __rcu *hooks_decnet[NF_DN_NUMHOOKS];
 #endif

net/Kconfig

···
 	depends on BRIDGE
 	depends on NETFILTER && INET
 	depends on NETFILTER_ADVANCED
+	select NETFILTER_FAMILY_BRIDGE
 	default m
 	---help---
 	  Enabling this option will let arptables resp. iptables see bridged

net/bridge/netfilter/Kconfig

···
 #
 menuconfig NF_TABLES_BRIDGE
 	depends on BRIDGE && NETFILTER && NF_TABLES
+	select NETFILTER_FAMILY_BRIDGE
 	tristate "Ethernet Bridge nf_tables support"
 
 if NF_TABLES_BRIDGE
···
 menuconfig BRIDGE_NF_EBTABLES
 	tristate "Ethernet Bridge tables (ebtables) support"
 	depends on BRIDGE && NETFILTER && NETFILTER_XTABLES
+	select NETFILTER_FAMILY_BRIDGE
 	help
 	  ebtables is a general, extensible frame/packet identification
 	  framework. Say 'Y' or 'M' here if you want to do Ethernet

net/ipv4/netfilter/Kconfig

···
 
 config NF_TABLES_ARP
 	tristate "ARP nf_tables support"
+	select NETFILTER_FAMILY_ARP
 	help
 	  This option enables the ARP support for nf_tables.
 
···
 config IP_NF_ARPTABLES
 	tristate "ARP tables support"
 	select NETFILTER_XTABLES
+	select NETFILTER_FAMILY_ARP
 	depends on NETFILTER_ADVANCED
 	help
 	  arptables is a general, extensible packet identification framework.

net/netfilter/Kconfig

···
 config NETFILTER_NETLINK
 	tristate
 
+config NETFILTER_FAMILY_BRIDGE
+	bool
+
+config NETFILTER_FAMILY_ARP
+	bool
+
 config NETFILTER_NETLINK_ACCT
 tristate "Netfilter NFACCT over NFNETLINK interface"
 	depends on NETFILTER_ADVANCED

net/netfilter/core.c

···
 	switch (reg->pf) {
 	case NFPROTO_NETDEV:
 		break;
+#ifdef CONFIG_NETFILTER_FAMILY_ARP
 	case NFPROTO_ARP:
 		if (WARN_ON_ONCE(ARRAY_SIZE(net->nf.hooks_arp) <= reg->hooknum))
 			return NULL;
 		return net->nf.hooks_arp + reg->hooknum;
+#endif
+#ifdef CONFIG_NETFILTER_FAMILY_BRIDGE
 	case NFPROTO_BRIDGE:
 		if (WARN_ON_ONCE(ARRAY_SIZE(net->nf.hooks_bridge) <= reg->hooknum))
 			return NULL;
 		return net->nf.hooks_bridge + reg->hooknum;
+#endif
 	case NFPROTO_IPV4:
 		if (WARN_ON_ONCE(ARRAY_SIZE(net->nf.hooks_ipv4) <= reg->hooknum))
 			return NULL;
···
 {
 	__netfilter_net_init(net->nf.hooks_ipv4, ARRAY_SIZE(net->nf.hooks_ipv4));
 	__netfilter_net_init(net->nf.hooks_ipv6, ARRAY_SIZE(net->nf.hooks_ipv6));
+#ifdef CONFIG_NETFILTER_FAMILY_ARP
 	__netfilter_net_init(net->nf.hooks_arp, ARRAY_SIZE(net->nf.hooks_arp));
+#endif
+#ifdef CONFIG_NETFILTER_FAMILY_BRIDGE
 	__netfilter_net_init(net->nf.hooks_bridge, ARRAY_SIZE(net->nf.hooks_bridge));
+#endif
 #if IS_ENABLED(CONFIG_DECNET)
 	__netfilter_net_init(net->nf.hooks_decnet, ARRAY_SIZE(net->nf.hooks_decnet));
 #endif

net/netfilter/nf_queue.c

···
 static struct nf_hook_entries *nf_hook_entries_head(const struct net *net, u8 pf, u8 hooknum)
 {
 	switch (pf) {
+#ifdef CONFIG_NETFILTER_FAMILY_BRIDGE
 	case NFPROTO_BRIDGE:
 		return rcu_dereference(net->nf.hooks_bridge[hooknum]);
+#endif
 	case NFPROTO_IPV4:
 		return rcu_dereference(net->nf.hooks_ipv4[hooknum]);
 	case NFPROTO_IPV6: