net: sched: add em_ipt ematch for calling xtables matches

The commit a new tc ematch for using netfilter xtable matches.

This allows early classification as well as mirroning/redirecting traffic
based on logic implemented in netfilter extensions.

Current supported use case is classification based on the incoming IPSec
state used during decpsulation using the 'policy' iptables extension
(xt_policy).

The module dynamically fetches the netfilter match module and calls
it using a fake xt_action_param structure based on validated userspace
provided parameters.

As the xt_policy match does not access skb->data, no skb modifications
are needed on match.

Signed-off-by: Eyal Birger <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/uapi/linux/pkt_cls.h

···
 #define	TCF_EM_VLAN		6
 #define	TCF_EM_CANID		7
 #define	TCF_EM_IPSET		8
-#define	TCF_EM_MAX		8
+#define	TCF_EM_IPT		9
+#define	TCF_EM_MAX		9
 
 enum {
 	TCF_EM_PROG_TC

include/uapi/linux/tc_ematch/tc_em_ipt.h

···
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef __LINUX_TC_EM_IPT_H
+#define __LINUX_TC_EM_IPT_H
+
+#include <linux/types.h>
+#include <linux/pkt_cls.h>
+
+enum {
+	TCA_EM_IPT_UNSPEC,
+	TCA_EM_IPT_HOOK,
+	TCA_EM_IPT_MATCH_NAME,
+	TCA_EM_IPT_MATCH_REVISION,
+	TCA_EM_IPT_NFPROTO,
+	TCA_EM_IPT_MATCH_DATA,
+	__TCA_EM_IPT_MAX
+};
+
+#define TCA_EM_IPT_MAX (__TCA_EM_IPT_MAX - 1)
+
+#endif

net/sched/Kconfig

···
 	  To compile this code as a module, choose M here: the
 	  module will be called em_ipset.
 
+config NET_EMATCH_IPT
+	tristate "IPtables Matches"
+	depends on NET_EMATCH && NETFILTER && NETFILTER_XTABLES
+	---help---
+	  Say Y here to be able to classify packets based on iptables
+	  matches.
+	  Current supported match is "policy" which allows packet classification
+	  based on IPsec policy that was used during decapsulation
+
+	  To compile this code as a module, choose M here: the
+	  module will be called em_ipt.
+
 config NET_CLS_ACT
 	bool "Actions"
 	select NET_CLS

net/sched/Makefile

···
 obj-$(CONFIG_NET_EMATCH_TEXT)	+= em_text.o
 obj-$(CONFIG_NET_EMATCH_CANID)	+= em_canid.o
 obj-$(CONFIG_NET_EMATCH_IPSET)	+= em_ipset.o
+obj-$(CONFIG_NET_EMATCH_IPT)	+= em_ipt.o

net/sched/em_ipt.c

···
+/*
+ * net/sched/em_ipt.c IPtables matches Ematch
+ *
+ * (c) 2018 Eyal Birger <[e-mail]>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#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 match_data[0] __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 const struct em_ipt_xt_match em_ipt_xt_matches[] = {
+	{
+		.match_name = "policy",
+		.validate_match_data = policy_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;
+
+	ret = nla_parse(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;
+
+	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]);
+	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((void *)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;
+	struct nf_hook_state state;
+	int ret;
+
+	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, im->match->family,
+			   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->match->family) < 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 <[e-mail]>");
+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);