net/ipv6/netfilter/ip6t_NPT.c

   1 /*
   2  * Copyright (c) 2011, 2012 Patrick McHardy <kaber@trash.net>
   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
   9 #include <linux/module.h>
  10 #include <linux/skbuff.h>
  11 #include <linux/ipv6.h>
  12 #include <net/ipv6.h>
  13 #include <linux/netfilter.h>
  14 #include <linux/netfilter_ipv6.h>
  15 #include <linux/netfilter_ipv6/ip6t_NPT.h>
  16 #include <linux/netfilter/x_tables.h>
  17
  18 static int ip6t_npt_checkentry(const struct xt_tgchk_param *par)
  19 {
  20         struct ip6t_npt_tginfo *npt = par->targinfo;
  21         struct in6_addr pfx;
  22         __wsum src_sum, dst_sum;
  23
  24         if (npt->src_pfx_len > 64 || npt->dst_pfx_len > 64)
  25                 return -EINVAL;
  26
  27         /* Ensure that LSB of prefix is zero */
  28         ipv6_addr_prefix(&pfx, &npt->src_pfx.in6, npt->src_pfx_len);
  29         if (!ipv6_addr_equal(&pfx, &npt->src_pfx.in6))
  30                 return -EINVAL;
  31         ipv6_addr_prefix(&pfx, &npt->dst_pfx.in6, npt->dst_pfx_len);
  32         if (!ipv6_addr_equal(&pfx, &npt->dst_pfx.in6))
  33                 return -EINVAL;
  34
  35         src_sum = csum_partial(&npt->src_pfx.in6, sizeof(npt->src_pfx.in6), 0);
  36         dst_sum = csum_partial(&npt->dst_pfx.in6, sizeof(npt->dst_pfx.in6), 0);
  37
  38         npt->adjustment = ~csum_fold(csum_sub(src_sum, dst_sum));
  39         return 0;
  40 }
  41
  42 static bool ip6t_npt_map_pfx(const struct ip6t_npt_tginfo *npt,
  43                              struct in6_addr *addr)
  44 {
  45         unsigned int pfx_len;
  46         unsigned int i, idx;
  47         __be32 mask;
  48         __sum16 sum;
  49
  50         pfx_len = max(npt->src_pfx_len, npt->dst_pfx_len);
  51         for (i = 0; i < pfx_len; i += 32) {
  52                 if (pfx_len - i >= 32)
  53                         mask = 0;
  54                 else
  55                         mask = htonl((1 << (i - pfx_len + 32)) - 1);
  56
  57                 idx = i / 32;
  58                 addr->s6_addr32[idx] &= mask;
  59                 addr->s6_addr32[idx] |= ~mask & npt->dst_pfx.in6.s6_addr32[idx];
  60         }
  61
  62         if (pfx_len <= 48)
  63                 idx = 3;
  64         else {
  65                 for (idx = 4; idx < ARRAY_SIZE(addr->s6_addr16); idx++) {
  66                         if ((__force __sum16)addr->s6_addr16[idx] !=
  67                             CSUM_MANGLED_0)
  68                                 break;
  69                 }
  70                 if (idx == ARRAY_SIZE(addr->s6_addr16))
  71                         return false;
  72         }
  73
  74         sum = ~csum_fold(csum_add(csum_unfold((__force __sum16)addr->s6_addr16[idx]),
  75                                   csum_unfold(npt->adjustment)));
  76         if (sum == CSUM_MANGLED_0)
  77                 sum = 0;
  78         *(__force __sum16 *)&addr->s6_addr16[idx] = sum;
  79
  80         return true;
  81 }
  82
  83 static unsigned int
  84 ip6t_snpt_tg(struct sk_buff *skb, const struct xt_action_param *par)
  85 {
  86         const struct ip6t_npt_tginfo *npt = par->targinfo;
  87
  88         if (!ip6t_npt_map_pfx(npt, &ipv6_hdr(skb)->saddr)) {
  89                 icmpv6_send(skb, ICMPV6_PARAMPROB, ICMPV6_HDR_FIELD,
  90                             offsetof(struct ipv6hdr, saddr));
  91                 return NF_DROP;
  92         }
  93         return XT_CONTINUE;
  94 }
  95
  96 static unsigned int
  97 ip6t_dnpt_tg(struct sk_buff *skb, const struct xt_action_param *par)
  98 {
  99         const struct ip6t_npt_tginfo *npt = par->targinfo;
 100
 101         if (!ip6t_npt_map_pfx(npt, &ipv6_hdr(skb)->daddr)) {
 102                 icmpv6_send(skb, ICMPV6_PARAMPROB, ICMPV6_HDR_FIELD,
 103                             offsetof(struct ipv6hdr, daddr));
 104                 return NF_DROP;
 105         }
 106         return XT_CONTINUE;
 107 }
 108
 109 static struct xt_target ip6t_npt_target_reg[] __read_mostly = {
 110         {
 111                 .name           = "SNPT",
 112                 .table          = "mangle",
 113                 .target         = ip6t_snpt_tg,
 114                 .targetsize     = sizeof(struct ip6t_npt_tginfo),
 115                 .checkentry     = ip6t_npt_checkentry,
 116                 .family         = NFPROTO_IPV6,
 117                 .hooks          = (1 << NF_INET_LOCAL_IN) |
 118                                   (1 << NF_INET_POST_ROUTING),
 119                 .me             = THIS_MODULE,
 120         },
 121         {
 122                 .name           = "DNPT",
 123                 .table          = "mangle",
 124                 .target         = ip6t_dnpt_tg,
 125                 .targetsize     = sizeof(struct ip6t_npt_tginfo),
 126                 .checkentry     = ip6t_npt_checkentry,
 127                 .family         = NFPROTO_IPV6,
 128                 .hooks          = (1 << NF_INET_PRE_ROUTING) |
 129                                   (1 << NF_INET_LOCAL_OUT),
 130                 .me             = THIS_MODULE,
 131         },
 132 };
 133
 134 static int __init ip6t_npt_init(void)
 135 {
 136         return xt_register_targets(ip6t_npt_target_reg,
 137                                    ARRAY_SIZE(ip6t_npt_target_reg));
 138 }
 139
 140 static void __exit ip6t_npt_exit(void)
 141 {
 142         xt_unregister_targets(ip6t_npt_target_reg,
 143                               ARRAY_SIZE(ip6t_npt_target_reg));
 144 }
 145
 146 module_init(ip6t_npt_init);
 147 module_exit(ip6t_npt_exit);
 148
 149 MODULE_LICENSE("GPL");
 150 MODULE_DESCRIPTION("IPv6-to-IPv6 Network Prefix Translation (RFC 6296)");
 151 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
 152 MODULE_ALIAS("ip6t_SNPT");
 153 MODULE_ALIAS("ip6t_DNPT");