netfilter: nft_ct: add helper set support

this allows to assign connection tracking helpers to
connections via nft objref infrastructure.

The idea is to first specifiy a helper object:

 table ip filter {
    ct helper some-name {
      type "ftp"
      protocol tcp
      l3proto ip
    }
 }

and then assign it via

nft add ... ct helper set "some-name"

helper assignment works for new conntracks only as we cannot expand the
conntrack extension area once it has been committed to the main conntrack
table.

ipv4 and ipv6 protocols are tracked stored separately so
we can also handle families that observe both ipv4 and ipv6 traffic.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/uapi/linux/netfilter/nf_tables.h

@@ -1259,10 +1259,20 @@ enum nft_fib_flags {
 	NFTA_FIB_F_OIF		= 1 << 4,	/* restrict to oif */
 };
 
+enum nft_ct_helper_attributes {
+	NFTA_CT_HELPER_UNSPEC,
+	NFTA_CT_HELPER_NAME,
+	NFTA_CT_HELPER_L3PROTO,
+	NFTA_CT_HELPER_L4PROTO,
+	__NFTA_CT_HELPER_MAX,
+};
+#define NFTA_CT_HELPER_MAX	(__NFTA_CT_HELPER_MAX - 1)
+
 #define NFT_OBJECT_UNSPEC	0
 #define NFT_OBJECT_COUNTER	1
 #define NFT_OBJECT_QUOTA	2
-#define __NFT_OBJECT_MAX	3
+#define NFT_OBJECT_CT_HELPER	3
+#define __NFT_OBJECT_MAX	4
 #define NFT_OBJECT_MAX		(__NFT_OBJECT_MAX - 1)
 
 /**

net/netfilter/nft_ct.c

@@ -32,6 +32,12 @@ struct nft_ct {
 	};
 };
 
+struct nft_ct_helper_obj  {
+	struct nf_conntrack_helper *helper4;
+	struct nf_conntrack_helper *helper6;
+	u8 l4proto;
+};
+
 #ifdef CONFIG_NF_CONNTRACK_ZONES
 static DEFINE_PER_CPU(struct nf_conn *, nft_ct_pcpu_template);
 static unsigned int nft_ct_pcpu_template_refcnt __read_mostly;
@@ -730,6 +736,162 @@ static struct nft_expr_type nft_notrack_type __read_mostly = {
 	.owner		= THIS_MODULE,
 };
 
+static int nft_ct_helper_obj_init(const struct nft_ctx *ctx,
+				  const struct nlattr * const tb[],
+				  struct nft_object *obj)
+{
+	struct nft_ct_helper_obj *priv = nft_obj_data(obj);
+	struct nf_conntrack_helper *help4, *help6;
+	char name[NF_CT_HELPER_NAME_LEN];
+	int family = ctx->afi->family;
+
+	if (!tb[NFTA_CT_HELPER_NAME] || !tb[NFTA_CT_HELPER_L4PROTO])
+		return -EINVAL;
+
+	priv->l4proto = nla_get_u8(tb[NFTA_CT_HELPER_L4PROTO]);
+	if (!priv->l4proto)
+		return -ENOENT;
+
+	nla_strlcpy(name, tb[NFTA_CT_HELPER_NAME], sizeof(name));
+
+	if (tb[NFTA_CT_HELPER_L3PROTO])
+		family = ntohs(nla_get_be16(tb[NFTA_CT_HELPER_L3PROTO]));
+
+	help4 = NULL;
+	help6 = NULL;
+
+	switch (family) {
+	case NFPROTO_IPV4:
+		if (ctx->afi->family == NFPROTO_IPV6)
+			return -EINVAL;
+
+		help4 = nf_conntrack_helper_try_module_get(name, family,
+							   priv->l4proto);
+		break;
+	case NFPROTO_IPV6:
+		if (ctx->afi->family == NFPROTO_IPV4)
+			return -EINVAL;
+
+		help6 = nf_conntrack_helper_try_module_get(name, family,
+							   priv->l4proto);
+		break;
+	case NFPROTO_NETDEV: /* fallthrough */
+	case NFPROTO_BRIDGE: /* same */
+	case NFPROTO_INET:
+		help4 = nf_conntrack_helper_try_module_get(name, NFPROTO_IPV4,
+							   priv->l4proto);
+		help6 = nf_conntrack_helper_try_module_get(name, NFPROTO_IPV6,
+							   priv->l4proto);
+		break;
+	default:
+		return -EAFNOSUPPORT;
+	}
+
+	/* && is intentional; only error if INET found neither ipv4 or ipv6 */
+	if (!help4 && !help6)
+		return -ENOENT;
+
+	priv->helper4 = help4;
+	priv->helper6 = help6;
+
+	return 0;
+}
+
+static void nft_ct_helper_obj_destroy(struct nft_object *obj)
+{
+	struct nft_ct_helper_obj *priv = nft_obj_data(obj);
+
+	if (priv->helper4)
+		module_put(priv->helper4->me);
+	if (priv->helper6)
+		module_put(priv->helper6->me);
+}
+
+static void nft_ct_helper_obj_eval(struct nft_object *obj,
+				   struct nft_regs *regs,
+				   const struct nft_pktinfo *pkt)
+{
+	const struct nft_ct_helper_obj *priv = nft_obj_data(obj);
+	struct nf_conn *ct = (struct nf_conn *)skb_nfct(pkt->skb);
+	struct nf_conntrack_helper *to_assign = NULL;
+	struct nf_conn_help *help;
+
+	if (!ct ||
+	    nf_ct_is_confirmed(ct) ||
+	    nf_ct_is_template(ct) ||
+	    priv->l4proto != nf_ct_protonum(ct))
+		return;
+
+	switch (nf_ct_l3num(ct)) {
+	case NFPROTO_IPV4:
+		to_assign = priv->helper4;
+		break;
+	case NFPROTO_IPV6:
+		to_assign = priv->helper6;
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		return;
+	}
+
+	if (!to_assign)
+		return;
+
+	if (test_bit(IPS_HELPER_BIT, &ct->status))
+		return;
+
+	help = nf_ct_helper_ext_add(ct, to_assign, GFP_ATOMIC);
+	if (help) {
+		rcu_assign_pointer(help->helper, to_assign);
+		set_bit(IPS_HELPER_BIT, &ct->status);
+	}
+}
+
+static int nft_ct_helper_obj_dump(struct sk_buff *skb,
+				  struct nft_object *obj, bool reset)
+{
+	const struct nft_ct_helper_obj *priv = nft_obj_data(obj);
+	const struct nf_conntrack_helper *helper = priv->helper4;
+	u16 family;
+
+	if (nla_put_string(skb, NFTA_CT_HELPER_NAME, helper->name))
+		return -1;
+
+	if (nla_put_u8(skb, NFTA_CT_HELPER_L4PROTO, priv->l4proto))
+		return -1;
+
+	if (priv->helper4 && priv->helper6)
+		family = NFPROTO_INET;
+	else if (priv->helper6)
+		family = NFPROTO_IPV6;
+	else
+		family = NFPROTO_IPV4;
+
+	if (nla_put_be16(skb, NFTA_CT_HELPER_L3PROTO, htons(family)))
+		return -1;
+
+	return 0;
+}
+
+static const struct nla_policy nft_ct_helper_policy[NFTA_CT_HELPER_MAX + 1] = {
+	[NFTA_CT_HELPER_NAME] = { .type = NLA_STRING,
+				  .len = NF_CT_HELPER_NAME_LEN - 1 },
+	[NFTA_CT_HELPER_L3PROTO] = { .type = NLA_U16 },
+	[NFTA_CT_HELPER_L4PROTO] = { .type = NLA_U8 },
+};
+
+static struct nft_object_type nft_ct_helper_obj __read_mostly = {
+	.type		= NFT_OBJECT_CT_HELPER,
+	.size		= sizeof(struct nft_ct_helper_obj),
+	.maxattr	= NFTA_CT_HELPER_MAX,
+	.policy		= nft_ct_helper_policy,
+	.eval		= nft_ct_helper_obj_eval,
+	.init		= nft_ct_helper_obj_init,
+	.destroy	= nft_ct_helper_obj_destroy,
+	.dump		= nft_ct_helper_obj_dump,
+	.owner		= THIS_MODULE,
+};
+
 static int __init nft_ct_module_init(void)
 {
 	int err;
@@ -744,7 +906,14 @@ static int __init nft_ct_module_init(void)
 	if (err < 0)
 		goto err1;
 
+	err = nft_register_obj(&nft_ct_helper_obj);
+	if (err < 0)
+		goto err2;
+
 	return 0;
+
+err2:
+	nft_unregister_expr(&nft_notrack_type);
 err1:
 	nft_unregister_expr(&nft_ct_type);
 	return err;
@@ -752,6 +921,7 @@ static int __init nft_ct_module_init(void)
 
 static void __exit nft_ct_module_exit(void)
 {
+	nft_unregister_obj(&nft_ct_helper_obj);
 	nft_unregister_expr(&nft_notrack_type);
 	nft_unregister_expr(&nft_ct_type);
 }
@@ -763,3 +933,4 @@ MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
 MODULE_ALIAS_NFT_EXPR("ct");
 MODULE_ALIAS_NFT_EXPR("notrack");
+MODULE_ALIAS_NFT_OBJ(NFT_OBJECT_CT_HELPER);