netfilter: nf_tables: enable conntrack if NAT chain is registered

Register conntrack hooks if the user adds NAT chains. Users get confused
with the existing behaviour since they will see no packets hitting this
chain until they add the first rule that refers to conntrack.

This patch adds new ->init() and ->free() indirections to chain types
that can be used by NAT chains to invoke the conntrack dependency.

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

include/net/netfilter/nf_tables.h

···
  * 	@owner: module owner
  * 	@hook_mask: mask of valid hooks
  * 	@hooks: array of hook functions
+ *	@init: chain initialization function
+ *	@free: chain release function
  */
 struct nft_chain_type {
 	const char			*name;
···
 	struct module			*owner;
 	unsigned int			hook_mask;
 	nf_hookfn			*hooks[NF_MAX_HOOKS];
+	int				(*init)(struct nft_ctx *ctx);
+	void				(*free)(struct nft_ctx *ctx);
 };
 
 int nft_chain_validate_dependency(const struct nft_chain *chain,

net/ipv4/netfilter/nft_chain_nat_ipv4.c

···
 	return nf_nat_ipv4_local_fn(priv, skb, state, nft_nat_do_chain);
 }
 
+static int nft_nat_ipv4_init(struct nft_ctx *ctx)
+{
+	return nf_ct_netns_get(ctx->net, ctx->family);
+}
+
+static void nft_nat_ipv4_free(struct nft_ctx *ctx)
+{
+	nf_ct_netns_put(ctx->net, ctx->family);
+}
+
 static const struct nft_chain_type nft_chain_nat_ipv4 = {
 	.name		= "nat",
 	.type		= NFT_CHAIN_T_NAT,
···
 		[NF_INET_LOCAL_OUT]	= nft_nat_ipv4_local_fn,
 		[NF_INET_LOCAL_IN]	= nft_nat_ipv4_fn,
 	},
+	.init		= nft_nat_ipv4_init,
+	.free		= nft_nat_ipv4_free,
 };
 
 static int __init nft_chain_nat_init(void)

net/ipv6/netfilter/nft_chain_nat_ipv6.c

···
 	return nf_nat_ipv6_local_fn(priv, skb, state, nft_nat_do_chain);
 }
 
+static int nft_nat_ipv6_init(struct nft_ctx *ctx)
+{
+	return nf_ct_netns_get(ctx->net, ctx->family);
+}
+
+static void nft_nat_ipv6_free(struct nft_ctx *ctx)
+{
+	nf_ct_netns_put(ctx->net, ctx->family);
+}
+
 static const struct nft_chain_type nft_chain_nat_ipv6 = {
 	.name		= "nat",
 	.type		= NFT_CHAIN_T_NAT,
···
 		[NF_INET_LOCAL_OUT]	= nft_nat_ipv6_local_fn,
 		[NF_INET_LOCAL_IN]	= nft_nat_ipv6_fn,
 	},
+	.init		= nft_nat_ipv6_init,
+	.free		= nft_nat_ipv6_free,
 };
 
 static int __init nft_chain_nat_ipv6_init(void)

net/netfilter/nf_tables_api.c

···
 		rcu_assign_pointer(chain->stats, newstats);
 }
 
-static void nf_tables_chain_destroy(struct nft_chain *chain)
+static void nf_tables_chain_destroy(struct nft_ctx *ctx)
 {
+	struct nft_chain *chain = ctx->chain;
+
 	BUG_ON(chain->use > 0);
 
 	if (nft_is_base_chain(chain)) {
 		struct nft_base_chain *basechain = nft_base_chain(chain);
 
+		if (basechain->type->free)
+			basechain->type->free(ctx);
 		module_put(basechain->type->owner);
 		free_percpu(basechain->stats);
 		if (basechain->stats)
···
 		}
 
 		basechain->type = hook.type;
+		if (basechain->type->init)
+			basechain->type->init(ctx);
+
 		chain = &basechain->chain;
 
 		ops		= &basechain->ops;
···
 		if (chain == NULL)
 			return -ENOMEM;
 	}
+	ctx->chain = chain;
+
 	INIT_LIST_HEAD(&chain->rules);
 	chain->handle = nf_tables_alloc_handle(table);
 	chain->table = table;
···
 	if (err < 0)
 		goto err1;
 
-	ctx->chain = chain;
 	err = nft_trans_chain_add(ctx, NFT_MSG_NEWCHAIN);
 	if (err < 0)
 		goto err2;
···
 err2:
 	nf_tables_unregister_hook(net, table, chain);
 err1:
-	nf_tables_chain_destroy(chain);
+	nf_tables_chain_destroy(ctx);
 
 	return err;
 }
···
 		nf_tables_table_destroy(&trans->ctx);
 		break;
 	case NFT_MSG_DELCHAIN:
-		nf_tables_chain_destroy(trans->ctx.chain);
+		nf_tables_chain_destroy(&trans->ctx);
 		break;
 	case NFT_MSG_DELRULE:
 		nf_tables_rule_destroy(&trans->ctx, nft_trans_rule(trans));
···
 		nf_tables_table_destroy(&trans->ctx);
 		break;
 	case NFT_MSG_NEWCHAIN:
-		nf_tables_chain_destroy(trans->ctx.chain);
+		nf_tables_chain_destroy(&trans->ctx);
 		break;
 	case NFT_MSG_NEWRULE:
 		nf_tables_rule_destroy(&trans->ctx, nft_trans_rule(trans));
···
 	}
 	list_del(&ctx->chain->list);
 	ctx->table->use--;
-	nf_tables_chain_destroy(ctx->chain);
+	nf_tables_chain_destroy(ctx);
 
 	return 0;
 }
···
 	struct nft_set *set, *ns;
 	struct nft_ctx ctx = {
 		.net	= net,
+		.family	= NFPROTO_NETDEV,
 	};
 
 	list_for_each_entry_safe(table, nt, &net->nft.tables, list) {
···
 			nft_obj_destroy(obj);
 		}
 		list_for_each_entry_safe(chain, nc, &table->chains, list) {
+			ctx.chain = chain;
 			list_del(&chain->list);
 			table->use--;
-			nf_tables_chain_destroy(chain);
+			nf_tables_chain_destroy(&ctx);
 		}
 		list_del(&table->list);
 		nf_tables_table_destroy(&ctx);