1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (c) 2011 Florian Westphal <fw@strlen.de>
4 *
5 * based on fib_frontend.c; Author: Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
6 */
7#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
8#include <linux/module.h>
9#include <linux/skbuff.h>
10#include <linux/netdevice.h>
11#include <linux/ip.h>
12#include <net/flow.h>
13#include <net/ip.h>
14#include <net/ip_fib.h>
15#include <net/route.h>
16
17#include <linux/netfilter/xt_rpfilter.h>
18#include <linux/netfilter/x_tables.h>
19
20MODULE_LICENSE("GPL");
21MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
22MODULE_DESCRIPTION("iptables: ipv4 reverse path filter match");
23
24/* don't try to find route from mcast/bcast/zeronet */
25static __be32 rpfilter_get_saddr(__be32 addr)
26{
27 if (ipv4_is_multicast(addr) || ipv4_is_lbcast(addr) ||
28 ipv4_is_zeronet(addr))
29 return 0;
30 return addr;
31}
32
33static bool rpfilter_lookup_reverse(struct net *net, struct flowi4 *fl4,
34 const struct net_device *dev, u8 flags)
35{
36 struct fib_result res;
37
38 if (fib_lookup(net, flp: fl4, res: &res, FIB_LOOKUP_IGNORE_LINKSTATE))
39 return false;
40
41 if (res.type != RTN_UNICAST) {
42 if (res.type != RTN_LOCAL || !(flags & XT_RPFILTER_ACCEPT_LOCAL))
43 return false;
44 }
45 return fib_info_nh_uses_dev(fi: res.fi, dev) || flags & XT_RPFILTER_LOOSE;
46}
47
48static bool
49rpfilter_is_loopback(const struct sk_buff *skb, const struct net_device *in)
50{
51 return skb->pkt_type == PACKET_LOOPBACK || in->flags & IFF_LOOPBACK;
52}
53
54static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
55{
56 const struct xt_rpfilter_info *info;
57 const struct iphdr *iph;
58 struct flowi4 flow;
59 bool invert;
60
61 info = par->matchinfo;
62 invert = info->flags & XT_RPFILTER_INVERT;
63
64 if (rpfilter_is_loopback(skb, in: xt_in(par)))
65 return true ^ invert;
66
67 iph = ip_hdr(skb);
68 if (ipv4_is_zeronet(addr: iph->saddr)) {
69 if (ipv4_is_lbcast(addr: iph->daddr) ||
70 ipv4_is_local_multicast(addr: iph->daddr))
71 return true ^ invert;
72 }
73
74 memset(&flow, 0, sizeof(flow));
75 flow.flowi4_iif = LOOPBACK_IFINDEX;
76 flow.daddr = iph->saddr;
77 flow.saddr = rpfilter_get_saddr(addr: iph->daddr);
78 flow.flowi4_mark = info->flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
79 flow.flowi4_dscp = ip4h_dscp(ip4h: iph);
80 flow.flowi4_scope = RT_SCOPE_UNIVERSE;
81 flow.flowi4_l3mdev = l3mdev_master_ifindex_rcu(dev: xt_in(par));
82 flow.flowi4_uid = sock_net_uid(net: xt_net(par), NULL);
83
84 return rpfilter_lookup_reverse(net: xt_net(par), fl4: &flow, dev: xt_in(par), flags: info->flags) ^ invert;
85}
86
87static int rpfilter_check(const struct xt_mtchk_param *par)
88{
89 const struct xt_rpfilter_info *info = par->matchinfo;
90 unsigned int options = ~XT_RPFILTER_OPTION_MASK;
91 if (info->flags & options) {
92 pr_info_ratelimited("unknown options\n");
93 return -EINVAL;
94 }
95
96 if (strcmp(par->table, "mangle") != 0 &&
97 strcmp(par->table, "raw") != 0) {
98 pr_info_ratelimited("only valid in \'raw\' or \'mangle\' table, not \'%s\'\n",
99 par->table);
100 return -EINVAL;
101 }
102
103 return 0;
104}
105
106static struct xt_match rpfilter_mt_reg __read_mostly = {
107 .name = "rpfilter",
108 .family = NFPROTO_IPV4,
109 .checkentry = rpfilter_check,
110 .match = rpfilter_mt,
111 .matchsize = sizeof(struct xt_rpfilter_info),
112 .hooks = (1 << NF_INET_PRE_ROUTING),
113 .me = THIS_MODULE
114};
115
116static int __init rpfilter_mt_init(void)
117{
118 return xt_register_match(target: &rpfilter_mt_reg);
119}
120
121static void __exit rpfilter_mt_exit(void)
122{
123 xt_unregister_match(target: &rpfilter_mt_reg);
124}
125
126module_init(rpfilter_mt_init);
127module_exit(rpfilter_mt_exit);
128

source code of linux/net/ipv4/netfilter/ipt_rpfilter.c