1/*
2 * Copyright (c) 2011 Florian Westphal <fw@strlen.de>
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License version 2 as
6 * published by the Free Software Foundation.
7 *
8 * based on fib_frontend.c; Author: Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
9 */
10#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
11#include <linux/module.h>
12#include <linux/skbuff.h>
13#include <linux/netdevice.h>
14#include <linux/ip.h>
15#include <net/ip.h>
16#include <net/ip_fib.h>
17#include <net/route.h>
18
19#include <linux/netfilter/xt_rpfilter.h>
20#include <linux/netfilter/x_tables.h>
21
22MODULE_LICENSE("GPL");
23MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
24MODULE_DESCRIPTION("iptables: ipv4 reverse path filter match");
25
26/* don't try to find route from mcast/bcast/zeronet */
27static __be32 rpfilter_get_saddr(__be32 addr)
28{
29	if (ipv4_is_multicast(addr) || ipv4_is_lbcast(addr) ||
30	    ipv4_is_zeronet(addr))
31		return 0;
32	return addr;
33}
34
35static bool rpfilter_lookup_reverse(struct flowi4 *fl4,
36				const struct net_device *dev, u8 flags)
37{
38	struct fib_result res;
39	bool dev_match;
40	struct net *net = dev_net(dev);
41	int ret __maybe_unused;
42
43	if (fib_lookup(net, fl4, &res))
44		return false;
45
46	if (res.type != RTN_UNICAST) {
47		if (res.type != RTN_LOCAL || !(flags & XT_RPFILTER_ACCEPT_LOCAL))
48			return false;
49	}
50	dev_match = false;
51#ifdef CONFIG_IP_ROUTE_MULTIPATH
52	for (ret = 0; ret < res.fi->fib_nhs; ret++) {
53		struct fib_nh *nh = &res.fi->fib_nh[ret];
54
55		if (nh->nh_dev == dev) {
56			dev_match = true;
57			break;
58		}
59	}
60#else
61	if (FIB_RES_DEV(res) == dev)
62		dev_match = true;
63#endif
64	if (dev_match || flags & XT_RPFILTER_LOOSE)
65		return FIB_RES_NH(res).nh_scope <= RT_SCOPE_HOST;
66	return dev_match;
67}
68
69static bool rpfilter_is_local(const struct sk_buff *skb)
70{
71	const struct rtable *rt = skb_rtable(skb);
72	return rt && (rt->rt_flags & RTCF_LOCAL);
73}
74
75static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
76{
77	const struct xt_rpfilter_info *info;
78	const struct iphdr *iph;
79	struct flowi4 flow;
80	bool invert;
81
82	info = par->matchinfo;
83	invert = info->flags & XT_RPFILTER_INVERT;
84
85	if (rpfilter_is_local(skb))
86		return true ^ invert;
87
88	iph = ip_hdr(skb);
89	if (ipv4_is_multicast(iph->daddr)) {
90		if (ipv4_is_zeronet(iph->saddr))
91			return ipv4_is_local_multicast(iph->daddr) ^ invert;
92	}
93	flow.flowi4_iif = LOOPBACK_IFINDEX;
94	flow.daddr = iph->saddr;
95	flow.saddr = rpfilter_get_saddr(iph->daddr);
96	flow.flowi4_oif = 0;
97	flow.flowi4_mark = info->flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
98	flow.flowi4_tos = RT_TOS(iph->tos);
99	flow.flowi4_scope = RT_SCOPE_UNIVERSE;
100
101	return rpfilter_lookup_reverse(&flow, par->in, info->flags) ^ invert;
102}
103
104static int rpfilter_check(const struct xt_mtchk_param *par)
105{
106	const struct xt_rpfilter_info *info = par->matchinfo;
107	unsigned int options = ~XT_RPFILTER_OPTION_MASK;
108	if (info->flags & options) {
109		pr_info("unknown options encountered");
110		return -EINVAL;
111	}
112
113	if (strcmp(par->table, "mangle") != 0 &&
114	    strcmp(par->table, "raw") != 0) {
115		pr_info("match only valid in the \'raw\' "
116			"or \'mangle\' tables, not \'%s\'.\n", par->table);
117		return -EINVAL;
118	}
119
120	return 0;
121}
122
123static struct xt_match rpfilter_mt_reg __read_mostly = {
124	.name		= "rpfilter",
125	.family		= NFPROTO_IPV4,
126	.checkentry	= rpfilter_check,
127	.match		= rpfilter_mt,
128	.matchsize	= sizeof(struct xt_rpfilter_info),
129	.hooks		= (1 << NF_INET_PRE_ROUTING),
130	.me		= THIS_MODULE
131};
132
133static int __init rpfilter_mt_init(void)
134{
135	return xt_register_match(&rpfilter_mt_reg);
136}
137
138static void __exit rpfilter_mt_exit(void)
139{
140	xt_unregister_match(&rpfilter_mt_reg);
141}
142
143module_init(rpfilter_mt_init);
144module_exit(rpfilter_mt_exit);
145