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