ip6t_rpfilter.c

  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(&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 ||
 76	    l3mdev_master_ifindex_rcu(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, xt_in(par)))
 98		return true ^ invert;
 99
100	iph = ipv6_hdr(skb);
101	saddrtype = ipv6_addr_type(&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(xt_net(par), skb, xt_in(par),
106					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(&rpfilter_mt_reg);
142}
143
144static void __exit rpfilter_mt_exit(void)
145{
146	xt_unregister_match(&rpfilter_mt_reg);
147}
148
149module_init(rpfilter_mt_init);
150module_exit(rpfilter_mt_exit);