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
22 MODULE_LICENSE("GPL");
23 MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
24 MODULE_DESCRIPTION("iptables: ipv4 reverse path filter match");
25
26 /* don't try to find route from mcast/bcast/zeronet */
rpfilter_get_saddr(__be32 addr)27 static __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
rpfilter_lookup_reverse(struct flowi4 * fl4,const struct net_device * dev,u8 flags)35 static 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
rpfilter_mt(const struct sk_buff * skb,struct xt_action_param * par)69 static 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
rpfilter_check(const struct xt_mtchk_param * par)101 static 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
120 static 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
rpfilter_mt_init(void)130 static int __init rpfilter_mt_init(void)
131 {
132 return xt_register_match(&rpfilter_mt_reg);
133 }
134
rpfilter_mt_exit(void)135 static void __exit rpfilter_mt_exit(void)
136 {
137 xt_unregister_match(&rpfilter_mt_reg);
138 }
139
140 module_init(rpfilter_mt_init);
141 module_exit(rpfilter_mt_exit);
142