1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * Copyright (c) 2011 Florian Westphal <[email protected]>
4 *
5 * based on fib_frontend.c; Author: Alexey Kuznetsov, <[email protected]>
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 <[email protected]>");
22 MODULE_DESCRIPTION("iptables: ipv4 reverse path filter match");
23
24 /* don't try to find route from mcast/bcast/zeronet */
rpfilter_get_saddr(__be32 addr)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
rpfilter_lookup_reverse(struct net * net,struct flowi4 * fl4,const struct net_device * dev,u8 flags)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
rpfilter_is_loopback(const struct sk_buff * skb,const struct net_device * in)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
rpfilter_mt(const struct sk_buff * skb,struct xt_action_param * par)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
rpfilter_check(const struct xt_mtchk_param * par)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
rpfilter_mt_init(void)116 static int __init rpfilter_mt_init(void)
117 {
118 return xt_register_match(&rpfilter_mt_reg);
119 }
120
rpfilter_mt_exit(void)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