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 
16 MODULE_LICENSE("GPL");
17 MODULE_AUTHOR("Florian Westphal <fw@strlen.de>");
18 MODULE_DESCRIPTION("Xtables: IPv6 reverse path filter match");
19 
20 static 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 
26 static 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 
32 static 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(&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(&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, skb, 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 || (flags & XT_RPFILTER_LOOSE))
76 		ret = true;
77  out:
78 	ip6_rt_put(rt);
79 	return ret;
80 }
81 
82 static bool
83 rpfilter_is_loopback(const struct sk_buff *skb, const struct net_device *in)
84 {
85 	return skb->pkt_type == PACKET_LOOPBACK || in->flags & IFF_LOOPBACK;
86 }
87 
88 static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
89 {
90 	const struct xt_rpfilter_info *info = par->matchinfo;
91 	int saddrtype;
92 	struct ipv6hdr *iph;
93 	bool invert = info->flags & XT_RPFILTER_INVERT;
94 
95 	if (rpfilter_is_loopback(skb, xt_in(par)))
96 		return true ^ invert;
97 
98 	iph = ipv6_hdr(skb);
99 	saddrtype = ipv6_addr_type(&iph->saddr);
100 	if (unlikely(saddrtype == IPV6_ADDR_ANY))
101 		return true ^ invert; /* not routable: forward path will drop it */
102 
103 	return rpfilter_lookup_reverse6(xt_net(par), skb, xt_in(par),
104 					info->flags) ^ invert;
105 }
106 
107 static 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 
112 	if (info->flags & options) {
113 		pr_info_ratelimited("unknown options\n");
114 		return -EINVAL;
115 	}
116 
117 	if (strcmp(par->table, "mangle") != 0 &&
118 	    strcmp(par->table, "raw") != 0) {
119 		pr_info_ratelimited("only valid in \'raw\' or \'mangle\' table, not \'%s\'\n",
120 				    par->table);
121 		return -EINVAL;
122 	}
123 
124 	return 0;
125 }
126 
127 static struct xt_match rpfilter_mt_reg __read_mostly = {
128 	.name		= "rpfilter",
129 	.family		= NFPROTO_IPV6,
130 	.checkentry	= rpfilter_check,
131 	.match		= rpfilter_mt,
132 	.matchsize	= sizeof(struct xt_rpfilter_info),
133 	.hooks		= (1 << NF_INET_PRE_ROUTING),
134 	.me		= THIS_MODULE
135 };
136 
137 static int __init rpfilter_mt_init(void)
138 {
139 	return xt_register_match(&rpfilter_mt_reg);
140 }
141 
142 static void __exit rpfilter_mt_exit(void)
143 {
144 	xt_unregister_match(&rpfilter_mt_reg);
145 }
146 
147 module_init(rpfilter_mt_init);
148 module_exit(rpfilter_mt_exit);
149