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_addr_linklocal(const struct in6_addr *addr)
  30 {
  31         int addr_type = ipv6_addr_type(addr);
  32         return addr_type & IPV6_ADDR_LINKLOCAL;
  33 }
  34
  35 static bool rpfilter_lookup_reverse6(struct net *net, const struct sk_buff *skb,
  36                                      const struct net_device *dev, u8 flags)
  37 {
  38         struct rt6_info *rt;
  39         struct ipv6hdr *iph = ipv6_hdr(skb);
  40         bool ret = false;
  41         struct flowi6 fl6 = {
  42                 .flowi6_iif = LOOPBACK_IFINDEX,
  43                 .flowlabel = (* (__be32 *) iph) & IPV6_FLOWINFO_MASK,
  44                 .flowi6_proto = iph->nexthdr,
  45                 .daddr = iph->saddr,
  46         };
  47         int lookup_flags;
  48
  49         if (rpfilter_addr_unicast(&iph->daddr)) {
  50                 memcpy(&fl6.saddr, &iph->daddr, sizeof(struct in6_addr));
  51                 lookup_flags = RT6_LOOKUP_F_HAS_SADDR;
  52         } else {
  53                 lookup_flags = 0;
  54         }
  55
  56         fl6.flowi6_mark = flags & XT_RPFILTER_VALID_MARK ? skb->mark : 0;
  57
  58         if (rpfilter_addr_linklocal(&iph->saddr)) {
  59                 lookup_flags |= RT6_LOOKUP_F_IFACE;
  60                 fl6.flowi6_oif = dev->ifindex;
  61         } else if ((flags & XT_RPFILTER_LOOSE) == 0)
  62                 fl6.flowi6_oif = dev->ifindex;
  63
  64         rt = (void *) ip6_route_lookup(net, &fl6, lookup_flags);
  65         if (rt->dst.error)
  66                 goto out;
  67
  68         if (rt->rt6i_flags & (RTF_REJECT|RTF_ANYCAST))
  69                 goto out;
  70
  71         if (rt->rt6i_flags & RTF_LOCAL) {
  72                 ret = flags & XT_RPFILTER_ACCEPT_LOCAL;
  73                 goto out;
  74         }
  75
  76         if (rt->rt6i_idev->dev == dev || (flags & XT_RPFILTER_LOOSE))
  77                 ret = true;
  78  out:
  79         ip6_rt_put(rt);
  80         return ret;
  81 }
  82
  83 static bool
  84 rpfilter_is_loopback(const struct sk_buff *skb, const struct net_device *in)
  85 {
  86         return skb->pkt_type == PACKET_LOOPBACK || in->flags & IFF_LOOPBACK;
  87 }
  88
  89 static bool rpfilter_mt(const struct sk_buff *skb, struct xt_action_param *par)
  90 {
  91         const struct xt_rpfilter_info *info = par->matchinfo;
  92         int saddrtype;
  93         struct ipv6hdr *iph;
  94         bool invert = info->flags & XT_RPFILTER_INVERT;
  95
  96         if (rpfilter_is_loopback(skb, xt_in(par)))
  97                 return true ^ invert;
  98
  99         iph = ipv6_hdr(skb);
 100         saddrtype = ipv6_addr_type(&iph->saddr);
 101         if (unlikely(saddrtype == IPV6_ADDR_ANY))
 102                 return true ^ invert; /* not routable: forward path will drop it */
 103
 104         return rpfilter_lookup_reverse6(xt_net(par), skb, xt_in(par),
 105                                         info->flags) ^ invert;
 106 }
 107
 108 static int rpfilter_check(const struct xt_mtchk_param *par)
 109 {
 110         const struct xt_rpfilter_info *info = par->matchinfo;
 111         unsigned int options = ~XT_RPFILTER_OPTION_MASK;
 112
 113         if (info->flags & options) {
 114                 pr_info("unknown options encountered");
 115                 return -EINVAL;
 116         }
 117
 118         if (strcmp(par->table, "mangle") != 0 &&
 119             strcmp(par->table, "raw") != 0) {
 120                 pr_info("match only valid in the \'raw\' "
 121                         "or \'mangle\' tables, not \'%s\'.\n", par->table);
 122                 return -EINVAL;
 123         }
 124
 125         return 0;
 126 }
 127
 128 static struct xt_match rpfilter_mt_reg __read_mostly = {
 129         .name           = "rpfilter",
 130         .family         = NFPROTO_IPV6,
 131         .checkentry     = rpfilter_check,
 132         .match          = rpfilter_mt,
 133         .matchsize      = sizeof(struct xt_rpfilter_info),
 134         .hooks          = (1 << NF_INET_PRE_ROUTING),
 135         .me             = THIS_MODULE
 136 };
 137
 138 static int __init rpfilter_mt_init(void)
 139 {
 140         return xt_register_match(&rpfilter_mt_reg);
 141 }
 142
 143 static void __exit rpfilter_mt_exit(void)
 144 {
 145         xt_unregister_match(&rpfilter_mt_reg);
 146 }
 147
 148 module_init(rpfilter_mt_init);
 149 module_exit(rpfilter_mt_exit);