em_ipt.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * net/sched/em_ipt.c IPtables matches Ematch
 *
 * (c) 2018 Eyal Birger <eyal.birger@gmail.com>
 */

#include <linux/gfp.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/skbuff.h>
#include <linux/tc_ematch/tc_em_ipt.h>
#include <linux/netfilter.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_ipv4/ip_tables.h>
#include <linux/netfilter_ipv6/ip6_tables.h>
#include <net/pkt_cls.h>

struct em_ipt_match {
	const struct xt_match *match;
	u32 hook;
	u8 nfproto;
	u8 match_data[] __aligned(8);
};

struct em_ipt_xt_match {
	char *match_name;
	int (*validate_match_data)(struct nlattr **tb, u8 mrev);
};

static const struct nla_policy em_ipt_policy[TCA_EM_IPT_MAX + 1] = {
	[TCA_EM_IPT_MATCH_NAME]		= { .type = NLA_STRING,
					    .len = XT_EXTENSION_MAXNAMELEN },
	[TCA_EM_IPT_MATCH_REVISION]	= { .type = NLA_U8 },
	[TCA_EM_IPT_HOOK]		= { .type = NLA_U32 },
	[TCA_EM_IPT_NFPROTO]		= { .type = NLA_U8 },
	[TCA_EM_IPT_MATCH_DATA]		= { .type = NLA_UNSPEC },
};

static int check_match(struct net *net, struct em_ipt_match *im, int mdata_len)
{
	struct xt_mtchk_param mtpar = {};
	union {
		struct ipt_entry e4;
		struct ip6t_entry e6;
	} e = {};

	mtpar.net	= net;
	mtpar.table	= "filter";
	mtpar.hook_mask	= 1 << im->hook;
	mtpar.family	= im->match->family;
	mtpar.match	= im->match;
	mtpar.entryinfo = &e;
	mtpar.matchinfo	= (void *)im->match_data;
	return xt_check_match(&mtpar, mdata_len, 0, 0);
}

static int policy_validate_match_data(struct nlattr **tb, u8 mrev)
{
	if (mrev != 0) {
		pr_err("only policy match revision 0 supported");
		return -EINVAL;
	}

	if (nla_get_u32(tb[TCA_EM_IPT_HOOK]) != NF_INET_PRE_ROUTING) {
		pr_err("policy can only be matched on NF_INET_PRE_ROUTING");
		return -EINVAL;
	}

	return 0;
}

static int addrtype_validate_match_data(struct nlattr **tb, u8 mrev)
{
	if (mrev != 1) {
		pr_err("only addrtype match revision 1 supported");
		return -EINVAL;
	}

	return 0;
}

static const struct em_ipt_xt_match em_ipt_xt_matches[] = {
	{
		.match_name = "policy",
		.validate_match_data = policy_validate_match_data
	},
	{
		.match_name = "addrtype",
		.validate_match_data = addrtype_validate_match_data
	},
	{}
};

static struct xt_match *get_xt_match(struct nlattr **tb)
{
	const struct em_ipt_xt_match *m;
	struct nlattr *mname_attr;
	u8 nfproto, mrev = 0;
	int ret;

	mname_attr = tb[TCA_EM_IPT_MATCH_NAME];
	for (m = em_ipt_xt_matches; m->match_name; m++) {
		if (!nla_strcmp(mname_attr, m->match_name))
			break;
	}

	if (!m->match_name) {
		pr_err("Unsupported xt match");
		return ERR_PTR(-EINVAL);
	}

	if (tb[TCA_EM_IPT_MATCH_REVISION])
		mrev = nla_get_u8(tb[TCA_EM_IPT_MATCH_REVISION]);

	ret = m->validate_match_data(tb, mrev);
	if (ret < 0)
		return ERR_PTR(ret);

	nfproto = nla_get_u8(tb[TCA_EM_IPT_NFPROTO]);
	return xt_request_find_match(nfproto, m->match_name, mrev);
}

static int em_ipt_change(struct net *net, void *data, int data_len,
			 struct tcf_ematch *em)
{
	struct nlattr *tb[TCA_EM_IPT_MAX + 1];
	struct em_ipt_match *im = NULL;
	struct xt_match *match;
	int mdata_len, ret;
	u8 nfproto;

	ret = nla_parse_deprecated(tb, TCA_EM_IPT_MAX, data, data_len,
				   em_ipt_policy, NULL);
	if (ret < 0)
		return ret;

	if (!tb[TCA_EM_IPT_HOOK] || !tb[TCA_EM_IPT_MATCH_NAME] ||
	    !tb[TCA_EM_IPT_MATCH_DATA] || !tb[TCA_EM_IPT_NFPROTO])
		return -EINVAL;

	nfproto = nla_get_u8(tb[TCA_EM_IPT_NFPROTO]);
	switch (nfproto) {
	case NFPROTO_IPV4:
	case NFPROTO_IPV6:
		break;
	default:
		return -EINVAL;
	}

	match = get_xt_match(tb);
	if (IS_ERR(match)) {
		pr_err("unable to load match\n");
		return PTR_ERR(match);
	}

	mdata_len = XT_ALIGN(nla_len(tb[TCA_EM_IPT_MATCH_DATA]));
	im = kzalloc(sizeof(*im) + mdata_len, GFP_KERNEL);
	if (!im) {
		ret = -ENOMEM;
		goto err;
	}

	im->match = match;
	im->hook = nla_get_u32(tb[TCA_EM_IPT_HOOK]);
	im->nfproto = nfproto;
	nla_memcpy(im->match_data, tb[TCA_EM_IPT_MATCH_DATA], mdata_len);

	ret = check_match(net, im, mdata_len);
	if (ret)
		goto err;

	em->datalen = sizeof(*im) + mdata_len;
	em->data = (unsigned long)im;
	return 0;

err:
	kfree(im);
	module_put(match->me);
	return ret;
}

static void em_ipt_destroy(struct tcf_ematch *em)
{
	struct em_ipt_match *im = (void *)em->data;

	if (!im)
		return;

	if (im->match->destroy) {
		struct xt_mtdtor_param par = {
			.net = em->net,
			.match = im->match,
			.matchinfo = im->match_data,
			.family = im->match->family
		};
		im->match->destroy(&par);
	}
	module_put(im->match->me);
	kfree(im);
}

static int em_ipt_match(struct sk_buff *skb, struct tcf_ematch *em,
			struct tcf_pkt_info *info)
{
	const struct em_ipt_match *im = (const void *)em->data;
	struct xt_action_param acpar = {};
	struct net_device *indev = NULL;
	u8 nfproto = im->match->family;
	struct nf_hook_state state;
	int ret;

	switch (tc_skb_protocol(skb)) {
	case htons(ETH_P_IP):
		if (!pskb_network_may_pull(skb, sizeof(struct iphdr)))
			return 0;
		if (nfproto == NFPROTO_UNSPEC)
			nfproto = NFPROTO_IPV4;
		break;
	case htons(ETH_P_IPV6):
		if (!pskb_network_may_pull(skb, sizeof(struct ipv6hdr)))
			return 0;
		if (nfproto == NFPROTO_UNSPEC)
			nfproto = NFPROTO_IPV6;
		break;
	default:
		return 0;
	}

	rcu_read_lock();

	if (skb->skb_iif)
		indev = dev_get_by_index_rcu(em->net, skb->skb_iif);

	nf_hook_state_init(&state, im->hook, nfproto,
			   indev ?: skb->dev, skb->dev, NULL, em->net, NULL);

	acpar.match = im->match;
	acpar.matchinfo = im->match_data;
	acpar.state = &state;

	ret = im->match->match(skb, &acpar);

	rcu_read_unlock();
	return ret;
}

static int em_ipt_dump(struct sk_buff *skb, struct tcf_ematch *em)
{
	struct em_ipt_match *im = (void *)em->data;

	if (nla_put_string(skb, TCA_EM_IPT_MATCH_NAME, im->match->name) < 0)
		return -EMSGSIZE;
	if (nla_put_u32(skb, TCA_EM_IPT_HOOK, im->hook) < 0)
		return -EMSGSIZE;
	if (nla_put_u8(skb, TCA_EM_IPT_MATCH_REVISION, im->match->revision) < 0)
		return -EMSGSIZE;
	if (nla_put_u8(skb, TCA_EM_IPT_NFPROTO, im->nfproto) < 0)
		return -EMSGSIZE;
	if (nla_put(skb, TCA_EM_IPT_MATCH_DATA,
		    im->match->usersize ?: im->match->matchsize,
		    im->match_data) < 0)
		return -EMSGSIZE;

	return 0;
}

static struct tcf_ematch_ops em_ipt_ops = {
	.kind	  = TCF_EM_IPT,
	.change	  = em_ipt_change,
	.destroy  = em_ipt_destroy,
	.match	  = em_ipt_match,
	.dump	  = em_ipt_dump,
	.owner	  = THIS_MODULE,
	.link	  = LIST_HEAD_INIT(em_ipt_ops.link)
};

static int __init init_em_ipt(void)
{
	return tcf_em_register(&em_ipt_ops);
}

static void __exit exit_em_ipt(void)
{
	tcf_em_unregister(&em_ipt_ops);
}

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Eyal Birger <eyal.birger@gmail.com>");
MODULE_DESCRIPTION("TC extended match for IPtables matches");

module_init(init_em_ipt);
module_exit(exit_em_ipt);

MODULE_ALIAS_TCF_EMATCH(TCF_EM_IPT);