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/ip.h>
13#include <net/ip_fib.h>
14#include <net/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("iptables: ipv4 reverse path filter match");
22
23/* don't try to find route from mcast/bcast/zeronet */
24static __be32 rpfilter_get_saddr(__be32 addr)
25{
26 if (ipv4_is_multicast(addr) || ipv4_is_lbcast(addr) ||
27 ipv4_is_zeronet(addr))
28 return 0;
29 return addr;
30}
31
32static bool rpfilter_lookup_reverse(struct net *net, struct flowi4 *fl4,
33 const struct net_device *dev, u8 flags)
34{
35 struct fib_result res;
36
37 if (fib_lookup(net, flp: fl4, res: &res, FIB_LOOKUP_IGNORE_LINKSTATE))
38 return false;
39
40 if (res.type != RTN_UNICAST) {
41 if (res.type != RTN_LOCAL || !(flags & XT_RPFILTER_ACCEPT_LOCAL))
42 return false;
43 }
44 return fib_info_nh_uses_dev(fi: res.fi, dev) || flags & XT_RPFILTER_LOOSE;
45}
46
47static bool
48rpfilter_is_loopback(const struct sk_buff *skb, const struct net_device *in)
49{
50 return skb->pkt_type == PACKET_LOOPBACK || in->flags & IFF_LOOPBACK;
51}
52
53static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
54{
55 const struct xt_rpfilter_info *info;
56 const struct iphdr *iph;
57 struct flowi4 flow;
58 bool invert;
59
60 info = par->matchinfo;
61 invert = info->flags & XT_RPFILTER_INVERT;
62
63 if (rpfilter_is_loopback(skb, in: xt_in(par)))
64 return true ^ invert;
65
66 iph = ip_hdr(skb);
67 if (ipv4_is_zeronet(addr: iph->saddr)) {
68 if (ipv4_is_lbcast(addr: iph->daddr) ||
69 ipv4_is_local_multicast(addr: iph->daddr))
70 return true ^ invert;
71 }
72
73 memset(&flow, 0, sizeof(flow));
74 flow.flowi4_iif = LOOPBACK_IFINDEX;
75 flow.daddr = iph->saddr;
76 flow.saddr = rpfilter_get_saddr(addr: iph->daddr);
77 flow.flowi4_mark = info->flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
78 flow.flowi4_tos = iph->tos & IPTOS_RT_MASK;
79 flow.flowi4_scope = RT_SCOPE_UNIVERSE;
80 flow.flowi4_l3mdev = l3mdev_master_ifindex_rcu(dev: xt_in(par));
81 flow.flowi4_uid = sock_net_uid(net: xt_net(par), NULL);
82
83 return rpfilter_lookup_reverse(net: xt_net(par), fl4: &flow, dev: xt_in(par), flags: info->flags) ^ invert;
84}
85
86static int rpfilter_check(const struct xt_mtchk_param *par)
87{
88 const struct xt_rpfilter_info *info = par->matchinfo;
89 unsigned int options = ~XT_RPFILTER_OPTION_MASK;
90 if (info->flags & options) {
91 pr_info_ratelimited("unknown options\n");
92 return -EINVAL;
93 }
94
95 if (strcmp(par->table, "mangle") != 0 &&
96 strcmp(par->table, "raw") != 0) {
97 pr_info_ratelimited("only valid in \'raw\' or \'mangle\' table, not \'%s\'\n",
98 par->table);
99 return -EINVAL;
100 }
101
102 return 0;
103}
104
105static struct xt_match rpfilter_mt_reg __read_mostly = {
106 .name = "rpfilter",
107 .family = NFPROTO_IPV4,
108 .checkentry = rpfilter_check,
109 .match = rpfilter_mt,
110 .matchsize = sizeof(struct xt_rpfilter_info),
111 .hooks = (1 << NF_INET_PRE_ROUTING),
112 .me = THIS_MODULE
113};
114
115static int __init rpfilter_mt_init(void)
116{
117 return xt_register_match(target: &rpfilter_mt_reg);
118}
119
120static void __exit rpfilter_mt_exit(void)
121{
122 xt_unregister_match(target: &rpfilter_mt_reg);
123}
124
125module_init(rpfilter_mt_init);
126module_exit(rpfilter_mt_exit);
127

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