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_mt(const struct sk_buff *skb, struct xt_action_param *par)
 70{
 71	const struct xt_rpfilter_info *info;
 72	const struct iphdr *iph;
 73	struct flowi4 flow;
 74	bool invert;
 75
 76	info = par->matchinfo;
 77	invert = info->flags & XT_RPFILTER_INVERT;
 78
 79	if (par->in->flags & IFF_LOOPBACK)
 80		return true ^ invert;
 81
 82	iph = ip_hdr(skb);
 83	if (ipv4_is_multicast(iph->daddr)) {
 84		if (ipv4_is_zeronet(iph->saddr))
 85			return ipv4_is_local_multicast(iph->daddr) ^ invert;
 86		flow.flowi4_iif = 0;
 87	} else {
 88		flow.flowi4_iif = dev_net(par->in)->loopback_dev->ifindex;
 89	}
 90
 91	flow.daddr = iph->saddr;
 92	flow.saddr = rpfilter_get_saddr(iph->daddr);
 93	flow.flowi4_oif = 0;
 94	flow.flowi4_mark = info->flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
 95	flow.flowi4_tos = RT_TOS(iph->tos);
 96	flow.flowi4_scope = RT_SCOPE_UNIVERSE;
 97
 98	return rpfilter_lookup_reverse(&flow, par->in, info->flags) ^ invert;
 99}
100
101static int rpfilter_check(const struct xt_mtchk_param *par)
102{
103	const struct xt_rpfilter_info *info = par->matchinfo;
104	unsigned int options = ~XT_RPFILTER_OPTION_MASK;
105	if (info->flags & options) {
106		pr_info("unknown options encountered");
107		return -EINVAL;
108	}
109
110	if (strcmp(par->table, "mangle") != 0 &&
111	    strcmp(par->table, "raw") != 0) {
112		pr_info("match only valid in the \'raw\' "
113			"or \'mangle\' tables, not \'%s\'.\n", par->table);
114		return -EINVAL;
115	}
116
117	return 0;
118}
119
120static struct xt_match rpfilter_mt_reg __read_mostly = {
121	.name		= "rpfilter",
122	.family		= NFPROTO_IPV4,
123	.checkentry	= rpfilter_check,
124	.match		= rpfilter_mt,
125	.matchsize	= sizeof(struct xt_rpfilter_info),
126	.hooks		= (1 << NF_INET_PRE_ROUTING),
127	.me		= THIS_MODULE
128};
129
130static int __init rpfilter_mt_init(void)
131{
132	return xt_register_match(&rpfilter_mt_reg);
133}
134
135static void __exit rpfilter_mt_exit(void)
136{
137	xt_unregister_match(&rpfilter_mt_reg);
138}
139
140module_init(rpfilter_mt_init);
141module_exit(rpfilter_mt_exit);