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 <net/inet_dscp.h>
12 #include <linux/ip.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 
20 MODULE_LICENSE("GPL");
21 MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
22 MODULE_DESCRIPTION("iptables: ipv4 reverse path filter match");
23 
24 /* don't try to find route from mcast/bcast/zeronet */
25 static __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 
33 static 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, 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 = inet_dscp_to_dsfield(ip4h_dscp(iph));
80 	flow.flowi4_scope = RT_SCOPE_UNIVERSE;
81 	flow.flowi4_l3mdev = l3mdev_master_ifindex_rcu(xt_in(par));
82 	flow.flowi4_uid = sock_net_uid(xt_net(par), NULL);
83 
84 	return rpfilter_lookup_reverse(xt_net(par), &flow, xt_in(par), info->flags) ^ invert;
85 }
86 
87 static 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 
106 static 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 
116 static int __init rpfilter_mt_init(void)
117 {
118 	return xt_register_match(&rpfilter_mt_reg);
119 }
120 
121 static void __exit rpfilter_mt_exit(void)
122 {
123 	xt_unregister_match(&rpfilter_mt_reg);
124 }
125 
126 module_init(rpfilter_mt_init);
127 module_exit(rpfilter_mt_exit);
128