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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
22MODULE_LICENSE("GPL");
23MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
24MODULE_DESCRIPTION("iptables: ipv4 reverse path filter match");
25
26
27static __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
35static 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
69static bool rpfilter_is_local(const struct sk_buff *skb)
70{
71 const struct rtable *rt = skb_rtable(skb);
72 return rt && (rt->rt_flags & RTCF_LOCAL);
73}
74
75static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
76{
77 const struct xt_rpfilter_info *info;
78 const struct iphdr *iph;
79 struct flowi4 flow;
80 bool invert;
81
82 info = par->matchinfo;
83 invert = info->flags & XT_RPFILTER_INVERT;
84
85 if (rpfilter_is_local(skb))
86 return true ^ invert;
87
88 iph = ip_hdr(skb);
89 if (ipv4_is_multicast(iph->daddr)) {
90 if (ipv4_is_zeronet(iph->saddr))
91 return ipv4_is_local_multicast(iph->daddr) ^ invert;
92 flow.flowi4_iif = 0;
93 } else {
94 flow.flowi4_iif = LOOPBACK_IFINDEX;
95 }
96
97 flow.daddr = iph->saddr;
98 flow.saddr = rpfilter_get_saddr(iph->daddr);
99 flow.flowi4_oif = 0;
100 flow.flowi4_mark = info->flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
101 flow.flowi4_tos = RT_TOS(iph->tos);
102 flow.flowi4_scope = RT_SCOPE_UNIVERSE;
103
104 return rpfilter_lookup_reverse(&flow, par->in, info->flags) ^ invert;
105}
106
107static int rpfilter_check(const struct xt_mtchk_param *par)
108{
109 const struct xt_rpfilter_info *info = par->matchinfo;
110 unsigned int options = ~XT_RPFILTER_OPTION_MASK;
111 if (info->flags & options) {
112 pr_info("unknown options encountered");
113 return -EINVAL;
114 }
115
116 if (strcmp(par->table, "mangle") != 0 &&
117 strcmp(par->table, "raw") != 0) {
118 pr_info("match only valid in the \'raw\' "
119 "or \'mangle\' tables, not \'%s\'.\n", par->table);
120 return -EINVAL;
121 }
122
123 return 0;
124}
125
126static struct xt_match rpfilter_mt_reg __read_mostly = {
127 .name = "rpfilter",
128 .family = NFPROTO_IPV4,
129 .checkentry = rpfilter_check,
130 .match = rpfilter_mt,
131 .matchsize = sizeof(struct xt_rpfilter_info),
132 .hooks = (1 << NF_INET_PRE_ROUTING),
133 .me = THIS_MODULE
134};
135
136static int __init rpfilter_mt_init(void)
137{
138 return xt_register_match(&rpfilter_mt_reg);
139}
140
141static void __exit rpfilter_mt_exit(void)
142{
143 xt_unregister_match(&rpfilter_mt_reg);
144}
145
146module_init(rpfilter_mt_init);
147module_exit(rpfilter_mt_exit);
148
