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 net *net, struct flowi4 *fl4,
36 const struct net_device *dev, u8 flags)
37{
38 struct fib_result res;
39 int ret __maybe_unused;
40
41 if (fib_lookup(net, fl4, &res, FIB_LOOKUP_IGNORE_LINKSTATE))
42 return false;
43
44 if (res.type != RTN_UNICAST) {
45 if (res.type != RTN_LOCAL || !(flags & XT_RPFILTER_ACCEPT_LOCAL))
46 return false;
47 }
48 return fib_info_nh_uses_dev(res.fi, dev) || flags & XT_RPFILTER_LOOSE;
49}
50
51static bool
52rpfilter_is_loopback(const struct sk_buff *skb, const struct net_device *in)
53{
54 return skb->pkt_type == PACKET_LOOPBACK || in->flags & IFF_LOOPBACK;
55}
56
57static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
58{
59 const struct xt_rpfilter_info *info;
60 const struct iphdr *iph;
61 struct flowi4 flow;
62 bool invert;
63
64 info = par->matchinfo;
65 invert = info->flags & XT_RPFILTER_INVERT;
66
67 if (rpfilter_is_loopback(skb, xt_in(par)))
68 return true ^ invert;
69
70 iph = ip_hdr(skb);
71 if (ipv4_is_zeronet(iph->saddr)) {
72 if (ipv4_is_lbcast(iph->daddr) ||
73 ipv4_is_local_multicast(iph->daddr))
74 return true ^ invert;
75 }
76
77 memset(&flow, 0, sizeof(flow));
78 flow.flowi4_iif = LOOPBACK_IFINDEX;
79 flow.daddr = iph->saddr;
80 flow.saddr = rpfilter_get_saddr(iph->daddr);
81 flow.flowi4_mark = info->flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
82 flow.flowi4_tos = RT_TOS(iph->tos);
83 flow.flowi4_scope = RT_SCOPE_UNIVERSE;
84
85 return rpfilter_lookup_reverse(xt_net(par), &flow, xt_in(par), info->flags) ^ invert;
86}
87
88static int rpfilter_check(const struct xt_mtchk_param *par)
89{
90 const struct xt_rpfilter_info *info = par->matchinfo;
91 unsigned int options = ~XT_RPFILTER_OPTION_MASK;
92 if (info->flags & options) {
93 pr_info_ratelimited("unknown options\n");
94 return -EINVAL;
95 }
96
97 if (strcmp(par->table, "mangle") != 0 &&
98 strcmp(par->table, "raw") != 0) {
99 pr_info_ratelimited("only valid in \'raw\' or \'mangle\' table, not \'%s\'\n",
100 par->table);
101 return -EINVAL;
102 }
103
104 return 0;
105}
106
107static struct xt_match rpfilter_mt_reg __read_mostly = {
108 .name = "rpfilter",
109 .family = NFPROTO_IPV4,
110 .checkentry = rpfilter_check,
111 .match = rpfilter_mt,
112 .matchsize = sizeof(struct xt_rpfilter_info),
113 .hooks = (1 << NF_INET_PRE_ROUTING),
114 .me = THIS_MODULE
115};
116
117static int __init rpfilter_mt_init(void)
118{
119 return xt_register_match(&rpfilter_mt_reg);
120}
121
122static void __exit rpfilter_mt_exit(void)
123{
124 xt_unregister_match(&rpfilter_mt_reg);
125}
126
127module_init(rpfilter_mt_init);
128module_exit(rpfilter_mt_exit);
129