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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9#include <linux/module.h>
10#include <linux/skbuff.h>
11#include <linux/netdevice.h>
12#include <linux/route.h>
13#include <net/ip6_fib.h>
14#include <net/ip6_route.h>
15
16#include <linux/netfilter/xt_rpfilter.h>
17#include <linux/netfilter/x_tables.h>
18
19MODULE_LICENSE("GPL");
20MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
21MODULE_DESCRIPTION("Xtables: IPv6 reverse path filter match");
22
23static bool rpfilter_addr_unicast(const struct in6_addr *addr)
24{
25	int addr_type = ipv6_addr_type(addr);
26	return addr_type & IPV6_ADDR_UNICAST;
27}
28
29static bool rpfilter_lookup_reverse6(const struct sk_buff *skb,
30				     const struct net_device *dev, u8 flags)
31{
32	struct rt6_info *rt;
33	struct ipv6hdr *iph = ipv6_hdr(skb);
34	bool ret = false;
35	struct flowi6 fl6 = {
36		.flowi6_iif = LOOPBACK_IFINDEX,
37		.flowlabel = (* (__be32 *) iph) & IPV6_FLOWINFO_MASK,
38		.flowi6_proto = iph->nexthdr,
39		.daddr = iph->saddr,
40	};
41	int lookup_flags;
42
43	if (rpfilter_addr_unicast(&iph->daddr)) {
44		memcpy(&fl6.saddr, &iph->daddr, sizeof(struct in6_addr));
45		lookup_flags = RT6_LOOKUP_F_HAS_SADDR;
46	} else {
47		lookup_flags = 0;
48	}
49
50	fl6.flowi6_mark = flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
51	if ((flags & XT_RPFILTER_LOOSE) == 0) {
52		fl6.flowi6_oif = dev->ifindex;
53		lookup_flags |= RT6_LOOKUP_F_IFACE;
54	}
55
56	rt = (void *) ip6_route_lookup(dev_net(dev), &fl6, lookup_flags);
57	if (rt->dst.error)
58		goto out;
59
60	if (rt->rt6i_flags & (RTF_REJECT|RTF_ANYCAST))
61		goto out;
62
63	if (rt->rt6i_flags & RTF_LOCAL) {
64		ret = flags & XT_RPFILTER_ACCEPT_LOCAL;
65		goto out;
66	}
67
68	if (rt->rt6i_idev->dev == dev || (flags & XT_RPFILTER_LOOSE))
69		ret = true;
70 out:
71	ip6_rt_put(rt);
72	return ret;
73}
74
75static bool rpfilter_is_local(const struct sk_buff *skb)
76{
77	const struct rt6_info *rt = (const void *) skb_dst(skb);
78	return rt && (rt->rt6i_flags & RTF_LOCAL);
79}
80
81static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
82{
83	const struct xt_rpfilter_info *info = par->matchinfo;
84	int saddrtype;
85	struct ipv6hdr *iph;
86	bool invert = info->flags & XT_RPFILTER_INVERT;
87
88	if (rpfilter_is_local(skb))
89		return true ^ invert;
90
91	iph = ipv6_hdr(skb);
92	saddrtype = ipv6_addr_type(&iph->saddr);
93	if (unlikely(saddrtype == IPV6_ADDR_ANY))
94		return true ^ invert; /* not routable: forward path will drop it */
95
96	return rpfilter_lookup_reverse6(skb, par->in, info->flags) ^ invert;
97}
98
99static int rpfilter_check(const struct xt_mtchk_param *par)
100{
101	const struct xt_rpfilter_info *info = par->matchinfo;
102	unsigned int options = ~XT_RPFILTER_OPTION_MASK;
103
104	if (info->flags & options) {
105		pr_info("unknown options encountered");
106		return -EINVAL;
107	}
108
109	if (strcmp(par->table, "mangle") != 0 &&
110	    strcmp(par->table, "raw") != 0) {
111		pr_info("match only valid in the \'raw\' "
112			"or \'mangle\' tables, not \'%s\'.\n", par->table);
113		return -EINVAL;
114	}
115
116	return 0;
117}
118
119static struct xt_match rpfilter_mt_reg __read_mostly = {
120	.name		= "rpfilter",
121	.family		= NFPROTO_IPV6,
122	.checkentry	= rpfilter_check,
123	.match		= rpfilter_mt,
124	.matchsize	= sizeof(struct xt_rpfilter_info),
125	.hooks		= (1 << NF_INET_PRE_ROUTING),
126	.me		= THIS_MODULE
127};
128
129static int __init rpfilter_mt_init(void)
130{
131	return xt_register_match(&rpfilter_mt_reg);
132}
133
134static void __exit rpfilter_mt_exit(void)
135{
136	xt_unregister_match(&rpfilter_mt_reg);
137}
138
139module_init(rpfilter_mt_init);
140module_exit(rpfilter_mt_exit);
141