netfilter: don't allocate space for decnet hooks unless needed

no need to define hook points if the family isn't supported.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/linux/netfilter.h

@@ -219,9 +219,11 @@ static inline int nf_hook(u_int8_t pf, unsigned int hook, struct net *net,
 	case NFPROTO_BRIDGE:
 		hook_head = rcu_dereference(net->nf.hooks_bridge[hook]);
 		break;
+#if IS_ENABLED(CONFIG_DECNET)
 	case NFPROTO_DECNET:
 		hook_head = rcu_dereference(net->nf.hooks_decnet[hook]);
 		break;
+#endif
 	default:
 		WARN_ON_ONCE(1);
 		break;

include/net/netns/netfilter.h

@@ -21,7 +21,9 @@ struct netns_nf {
 	struct nf_hook_entries __rcu *hooks_ipv6[NF_INET_NUMHOOKS];
 	struct nf_hook_entries __rcu *hooks_arp[NF_ARP_NUMHOOKS];
 	struct nf_hook_entries __rcu *hooks_bridge[NF_INET_NUMHOOKS];
+#if IS_ENABLED(CONFIG_DECNET)
 	struct nf_hook_entries __rcu *hooks_decnet[NF_DN_NUMHOOKS];
+#endif
 #if IS_ENABLED(CONFIG_NF_DEFRAG_IPV4)
 	bool			defrag_ipv4;
 #endif

net/netfilter/core.c

@@ -283,10 +283,12 @@ static struct nf_hook_entries __rcu **nf_hook_entry_head(struct net *net, const
 		if (WARN_ON_ONCE(ARRAY_SIZE(net->nf.hooks_ipv6) <= reg->hooknum))
 			return NULL;
 		return net->nf.hooks_ipv6 + reg->hooknum;
+#if IS_ENABLED(CONFIG_DECNET)
 	case NFPROTO_DECNET:
 		if (WARN_ON_ONCE(ARRAY_SIZE(net->nf.hooks_decnet) <= reg->hooknum))
 			return NULL;
 		return net->nf.hooks_decnet + reg->hooknum;
+#endif
 	default:
 		WARN_ON_ONCE(1);
 		return NULL;
@@ -573,7 +575,9 @@ static int __net_init netfilter_net_init(struct net *net)
 	__netfilter_net_init(net->nf.hooks_ipv6, ARRAY_SIZE(net->nf.hooks_ipv6));
 	__netfilter_net_init(net->nf.hooks_arp, ARRAY_SIZE(net->nf.hooks_arp));
 	__netfilter_net_init(net->nf.hooks_bridge, ARRAY_SIZE(net->nf.hooks_bridge));
+#if IS_ENABLED(CONFIG_DECNET)
 	__netfilter_net_init(net->nf.hooks_decnet, ARRAY_SIZE(net->nf.hooks_decnet));
+#endif
 
 #ifdef CONFIG_PROC_FS
 	net->nf.proc_netfilter = proc_net_mkdir(net, "netfilter",