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
19 MODULE_LICENSE("GPL");
20 MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
21 MODULE_DESCRIPTION("iptables: ipv4 reverse path filter match");
22
23 /* don't try to find route from mcast/bcast/zeronet */
24 static __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
32 static 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 int ret __maybe_unused;
37
38 if (fib_lookup(net, fl4, &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(res.fi, dev) || flags & XT_RPFILTER_LOOSE;
46 }
47
48 static bool
49 rpfilter_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
54 static 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, xt_in(par)))
65 return true ^ invert;
66
67 iph = ip_hdr(skb);
68 if (ipv4_is_zeronet(iph->saddr)) {
69 if (ipv4_is_lbcast(iph->daddr) ||
70 ipv4_is_local_multicast(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(iph->daddr);
78 flow.flowi4_mark = info->flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
79 flow.flowi4_tos = iph->tos & IPTOS_RT_MASK;
80 flow.flowi4_scope = RT_SCOPE_UNIVERSE;
81 flow.flowi4_oif = l3mdev_master_ifindex_rcu(xt_in(par));
82
83 return rpfilter_lookup_reverse(xt_net(par), &flow, xt_in(par), info->flags) ^ invert;
84 }
85
86 static 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
105 static 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
115 static int __init rpfilter_mt_init(void)
116 {
117 return xt_register_match(&rpfilter_mt_reg);
118 }
119
120 static void __exit rpfilter_mt_exit(void)
121 {
122 xt_unregister_match(&rpfilter_mt_reg);
123 }
124
125 module_init(rpfilter_mt_init);
126 module_exit(rpfilter_mt_exit);
127
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