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(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                 .flowlabel = (* (__be32 *) iph) & IPV6_FLOWINFO_MASK,
  37                 .flowi6_proto = iph->nexthdr,
  38                 .daddr = iph->saddr,
  39         };
  40         int lookup_flags;
  41
  42         if (rpfilter_addr_unicast(&iph->daddr)) {
  43                 memcpy(&fl6.saddr, &iph->daddr, sizeof(struct in6_addr));
  44                 lookup_flags = RT6_LOOKUP_F_HAS_SADDR;
  45         } else {
  46                 lookup_flags = 0;
  47         }
  48
  49         fl6.flowi6_mark = flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
  50         if ((flags & XT_RPFILTER_LOOSE) == 0) {
  51                 fl6.flowi6_oif = dev->ifindex;
  52                 lookup_flags |= RT6_LOOKUP_F_IFACE;
  53         }
  54
  55         rt = (void *) ip6_route_lookup(dev_net(dev), &fl6, lookup_flags);
  56         if (rt->dst.error)
  57                 goto out;
  58
  59         if (rt->rt6i_flags & (RTF_REJECT|RTF_ANYCAST))
  60                 goto out;
  61
  62         if (rt->rt6i_flags & RTF_LOCAL) {
  63                 ret = flags & XT_RPFILTER_ACCEPT_LOCAL;
  64                 goto out;
  65         }
  66
  67         if (rt->rt6i_idev->dev == dev || (flags & XT_RPFILTER_LOOSE))
  68                 ret = true;
  69  out:
  70         ip6_rt_put(rt);
  71         return ret;
  72 }
  73
  74 static bool rpfilter_is_local(const struct sk_buff *skb)
  75 {
  76         const struct rt6_info *rt = (const void *) skb_dst(skb);
  77         return rt && (rt->rt6i_flags & RTF_LOCAL);
  78 }
  79
  80 static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
  81 {
  82         const struct xt_rpfilter_info *info = par->matchinfo;
  83         int saddrtype;
  84         struct ipv6hdr *iph;
  85         bool invert = info->flags & XT_RPFILTER_INVERT;
  86
  87         if (rpfilter_is_local(skb))
  88                 return true ^ invert;
  89
  90         iph = ipv6_hdr(skb);
  91         saddrtype = ipv6_addr_type(&iph->saddr);
  92         if (unlikely(saddrtype == IPV6_ADDR_ANY))
  93                 return true ^ invert; /* not routable: forward path will drop it */
  94
  95         return rpfilter_lookup_reverse6(skb, par->in, info->flags) ^ invert;
  96 }
  97
  98 static int rpfilter_check(const struct xt_mtchk_param *par)
  99 {
 100         const struct xt_rpfilter_info *info = par->matchinfo;
 101         unsigned int options = ~XT_RPFILTER_OPTION_MASK;
 102
 103         if (info->flags & options) {
 104                 pr_info("unknown options encountered");
 105                 return -EINVAL;
 106         }
 107
 108         if (strcmp(par->table, "mangle") != 0 &&
 109             strcmp(par->table, "raw") != 0) {
 110                 pr_info("match only valid in the \'raw\' "
 111                         "or \'mangle\' tables, not \'%s\'.\n", par->table);
 112                 return -EINVAL;
 113         }
 114
 115         return 0;
 116 }
 117
 118 static struct xt_match rpfilter_mt_reg __read_mostly = {
 119         .name           = "rpfilter",
 120         .family         = NFPROTO_IPV6,
 121         .checkentry     = rpfilter_check,
 122         .match          = rpfilter_mt,
 123         .matchsize      = sizeof(struct xt_rpfilter_info),
 124         .hooks          = (1 << NF_INET_PRE_ROUTING),
 125         .me             = THIS_MODULE
 126 };
 127
 128 static int __init rpfilter_mt_init(void)
 129 {
 130         return xt_register_match(&rpfilter_mt_reg);
 131 }
 132
 133 static void __exit rpfilter_mt_exit(void)
 134 {
 135         xt_unregister_match(&rpfilter_mt_reg);
 136 }
 137
 138 module_init(rpfilter_mt_init);
 139 module_exit(rpfilter_mt_exit);