1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Copyright (c) 2011 Florian Westphal <fw@strlen.de>
4 */
5#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
6#include <linux/module.h>
7#include <linux/skbuff.h>
8#include <linux/netdevice.h>
9#include <linux/route.h>
10#include <net/ip6_fib.h>
11#include <net/ip6_route.h>
12
13#include <linux/netfilter/xt_rpfilter.h>
14#include <linux/netfilter/x_tables.h>
15
16MODULE_LICENSE("GPL");
17MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
18MODULE_DESCRIPTION("Xtables: IPv6 reverse path filter match");
19
20static bool rpfilter_addr_unicast(const struct in6_addr *addr)
21{
22 int addr_type = ipv6_addr_type(addr);
23 return addr_type & IPV6_ADDR_UNICAST;
24}
25
26static bool rpfilter_addr_linklocal(const struct in6_addr *addr)
27{
28 int addr_type = ipv6_addr_type(addr);
29 return addr_type & IPV6_ADDR_LINKLOCAL;
30}
31
32static bool rpfilter_lookup_reverse6(struct net *net, const struct sk_buff *skb,
33 const struct net_device *dev, u8 flags)
34{
35 struct rt6_info *rt;
36 struct ipv6hdr *iph = ipv6_hdr(skb);
37 bool ret = false;
38 struct flowi6 fl6 = {
39 .flowi6_iif = LOOPBACK_IFINDEX,
40 .flowi6_l3mdev = l3mdev_master_ifindex_rcu(dev),
41 .flowlabel = (* (__be32 *) iph) & IPV6_FLOWINFO_MASK,
42 .flowi6_proto = iph->nexthdr,
43 .flowi6_uid = sock_net_uid(net, NULL),
44 .daddr = iph->saddr,
45 };
46 int lookup_flags;
47
48 if (rpfilter_addr_unicast(addr: &iph->daddr)) {
49 memcpy(&fl6.saddr, &iph->daddr, sizeof(struct in6_addr));
50 lookup_flags = RT6_LOOKUP_F_HAS_SADDR;
51 } else {
52 lookup_flags = 0;
53 }
54
55 fl6.flowi6_mark = flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
56
57 if (rpfilter_addr_linklocal(addr: &iph->saddr)) {
58 lookup_flags |= RT6_LOOKUP_F_IFACE;
59 fl6.flowi6_oif = dev->ifindex;
60 } else if ((flags & XT_RPFILTER_LOOSE) == 0)
61 fl6.flowi6_oif = dev->ifindex;
62
63 rt = (void *)ip6_route_lookup(net, fl6: &fl6, skb, flags: lookup_flags);
64 if (rt->dst.error)
65 goto out;
66
67 if (rt->rt6i_flags & (RTF_REJECT|RTF_ANYCAST))
68 goto out;
69
70 if (rt->rt6i_flags & RTF_LOCAL) {
71 ret = flags & XT_RPFILTER_ACCEPT_LOCAL;
72 goto out;
73 }
74
75 if (rt->rt6i_idev->dev == dev ||
76 l3mdev_master_ifindex_rcu(dev: rt->rt6i_idev->dev) == dev->ifindex ||
77 (flags & XT_RPFILTER_LOOSE))
78 ret = true;
79 out:
80 ip6_rt_put(rt);
81 return ret;
82}
83
84static bool
85rpfilter_is_loopback(const struct sk_buff *skb, const struct net_device *in)
86{
87 return skb->pkt_type == PACKET_LOOPBACK || in->flags & IFF_LOOPBACK;
88}
89
90static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
91{
92 const struct xt_rpfilter_info *info = par->matchinfo;
93 int saddrtype;
94 struct ipv6hdr *iph;
95 bool invert = info->flags & XT_RPFILTER_INVERT;
96
97 if (rpfilter_is_loopback(skb, in: xt_in(par)))
98 return true ^ invert;
99
100 iph = ipv6_hdr(skb);
101 saddrtype = ipv6_addr_type(addr: &iph->saddr);
102 if (unlikely(saddrtype == IPV6_ADDR_ANY))
103 return true ^ invert; /* not routable: forward path will drop it */
104
105 return rpfilter_lookup_reverse6(net: xt_net(par), skb, dev: xt_in(par),
106 flags: info->flags) ^ invert;
107}
108
109static int rpfilter_check(const struct xt_mtchk_param *par)
110{
111 const struct xt_rpfilter_info *info = par->matchinfo;
112 unsigned int options = ~XT_RPFILTER_OPTION_MASK;
113
114 if (info->flags & options) {
115 pr_info_ratelimited("unknown options\n");
116 return -EINVAL;
117 }
118
119 if (strcmp(par->table, "mangle") != 0 &&
120 strcmp(par->table, "raw") != 0) {
121 pr_info_ratelimited("only valid in \'raw\' or \'mangle\' table, not \'%s\'\n",
122 par->table);
123 return -EINVAL;
124 }
125
126 return 0;
127}
128
129static struct xt_match rpfilter_mt_reg __read_mostly = {
130 .name = "rpfilter",
131 .family = NFPROTO_IPV6,
132 .checkentry = rpfilter_check,
133 .match = rpfilter_mt,
134 .matchsize = sizeof(struct xt_rpfilter_info),
135 .hooks = (1 << NF_INET_PRE_ROUTING),
136 .me = THIS_MODULE
137};
138
139static int __init rpfilter_mt_init(void)
140{
141 return xt_register_match(target: &rpfilter_mt_reg);
142}
143
144static void __exit rpfilter_mt_exit(void)
145{
146 xt_unregister_match(target: &rpfilter_mt_reg);
147}
148
149module_init(rpfilter_mt_init);
150module_exit(rpfilter_mt_exit);
151

source code of linux/net/ipv6/netfilter/ip6t_rpfilter.c