net/ipv6/netfilter/ip6t_rpfilter.c

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