net/ipv6/netfilter/ip6t_NPT.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Copyright (c) 2011, 2012 Patrick McHardy <kaber@trash.net>
   4  */
   5
   6 #include <linux/module.h>
   7 #include <linux/skbuff.h>
   8 #include <linux/ipv6.h>
   9 #include <net/ipv6.h>
  10 #include <linux/netfilter.h>
  11 #include <linux/netfilter_ipv6.h>
  12 #include <linux/netfilter_ipv6/ip6t_NPT.h>
  13 #include <linux/netfilter/x_tables.h>
  14
  15 static int ip6t_npt_checkentry(const struct xt_tgchk_param *par)
  16 {
  17         struct ip6t_npt_tginfo *npt = par->targinfo;
  18         struct in6_addr pfx;
  19         __wsum src_sum, dst_sum;
  20
  21         if (npt->src_pfx_len > 64 || npt->dst_pfx_len > 64)
  22                 return -EINVAL;
  23
  24         /* Ensure that LSB of prefix is zero */
  25         ipv6_addr_prefix(&pfx, &npt->src_pfx.in6, npt->src_pfx_len);
  26         if (!ipv6_addr_equal(&pfx, &npt->src_pfx.in6))
  27                 return -EINVAL;
  28         ipv6_addr_prefix(&pfx, &npt->dst_pfx.in6, npt->dst_pfx_len);
  29         if (!ipv6_addr_equal(&pfx, &npt->dst_pfx.in6))
  30                 return -EINVAL;
  31
  32         src_sum = csum_partial(&npt->src_pfx.in6, sizeof(npt->src_pfx.in6), 0);
  33         dst_sum = csum_partial(&npt->dst_pfx.in6, sizeof(npt->dst_pfx.in6), 0);
  34
  35         npt->adjustment = ~csum_fold(csum_sub(src_sum, dst_sum));
  36         return 0;
  37 }
  38
  39 static bool ip6t_npt_map_pfx(const struct ip6t_npt_tginfo *npt,
  40                              struct in6_addr *addr)
  41 {
  42         unsigned int pfx_len;
  43         unsigned int i, idx;
  44         __be32 mask;
  45         __sum16 sum;
  46
  47         pfx_len = max(npt->src_pfx_len, npt->dst_pfx_len);
  48         for (i = 0; i < pfx_len; i += 32) {
  49                 if (pfx_len - i >= 32)
  50                         mask = 0;
  51                 else
  52                         mask = htonl((1 << (i - pfx_len + 32)) - 1);
  53
  54                 idx = i / 32;
  55                 addr->s6_addr32[idx] &= mask;
  56                 addr->s6_addr32[idx] |= ~mask & npt->dst_pfx.in6.s6_addr32[idx];
  57         }
  58
  59         if (pfx_len <= 48)
  60                 idx = 3;
  61         else {
  62                 for (idx = 4; idx < ARRAY_SIZE(addr->s6_addr16); idx++) {
  63                         if ((__force __sum16)addr->s6_addr16[idx] !=
  64                             CSUM_MANGLED_0)
  65                                 break;
  66                 }
  67                 if (idx == ARRAY_SIZE(addr->s6_addr16))
  68                         return false;
  69         }
  70
  71         sum = ~csum_fold(csum_add(csum_unfold((__force __sum16)addr->s6_addr16[idx]),
  72                                   csum_unfold(npt->adjustment)));
  73         if (sum == CSUM_MANGLED_0)
  74                 sum = 0;
  75         *(__force __sum16 *)&addr->s6_addr16[idx] = sum;
  76
  77         return true;
  78 }
  79
  80 static unsigned int
  81 ip6t_snpt_tg(struct sk_buff *skb, const struct xt_action_param *par)
  82 {
  83         const struct ip6t_npt_tginfo *npt = par->targinfo;
  84
  85         if (!ip6t_npt_map_pfx(npt, &ipv6_hdr(skb)->saddr)) {
  86                 icmpv6_send(skb, ICMPV6_PARAMPROB, ICMPV6_HDR_FIELD,
  87                             offsetof(struct ipv6hdr, saddr));
  88                 return NF_DROP;
  89         }
  90         return XT_CONTINUE;
  91 }
  92
  93 static unsigned int
  94 ip6t_dnpt_tg(struct sk_buff *skb, const struct xt_action_param *par)
  95 {
  96         const struct ip6t_npt_tginfo *npt = par->targinfo;
  97
  98         if (!ip6t_npt_map_pfx(npt, &ipv6_hdr(skb)->daddr)) {
  99                 icmpv6_send(skb, ICMPV6_PARAMPROB, ICMPV6_HDR_FIELD,
 100                             offsetof(struct ipv6hdr, daddr));
 101                 return NF_DROP;
 102         }
 103         return XT_CONTINUE;
 104 }
 105
 106 static struct xt_target ip6t_npt_target_reg[] __read_mostly = {
 107         {
 108                 .name           = "SNPT",
 109                 .table          = "mangle",
 110                 .target         = ip6t_snpt_tg,
 111                 .targetsize     = sizeof(struct ip6t_npt_tginfo),
 112                 .usersize       = offsetof(struct ip6t_npt_tginfo, adjustment),
 113                 .checkentry     = ip6t_npt_checkentry,
 114                 .family         = NFPROTO_IPV6,
 115                 .hooks          = (1 << NF_INET_LOCAL_IN) |
 116                                   (1 << NF_INET_POST_ROUTING),
 117                 .me             = THIS_MODULE,
 118         },
 119         {
 120                 .name           = "DNPT",
 121                 .table          = "mangle",
 122                 .target         = ip6t_dnpt_tg,
 123                 .targetsize     = sizeof(struct ip6t_npt_tginfo),
 124                 .usersize       = offsetof(struct ip6t_npt_tginfo, adjustment),
 125                 .checkentry     = ip6t_npt_checkentry,
 126                 .family         = NFPROTO_IPV6,
 127                 .hooks          = (1 << NF_INET_PRE_ROUTING) |
 128                                   (1 << NF_INET_LOCAL_OUT),
 129                 .me             = THIS_MODULE,
 130         },
 131 };
 132
 133 static int __init ip6t_npt_init(void)
 134 {
 135         return xt_register_targets(ip6t_npt_target_reg,
 136                                    ARRAY_SIZE(ip6t_npt_target_reg));
 137 }
 138
 139 static void __exit ip6t_npt_exit(void)
 140 {
 141         xt_unregister_targets(ip6t_npt_target_reg,
 142                               ARRAY_SIZE(ip6t_npt_target_reg));
 143 }
 144
 145 module_init(ip6t_npt_init);
 146 module_exit(ip6t_npt_exit);
 147
 148 MODULE_LICENSE("GPL");
 149 MODULE_DESCRIPTION("IPv6-to-IPv6 Network Prefix Translation (RFC 6296)");
 150 MODULE_AUTHOR("Patrick McHardy <kaber@trash.net>");
 151 MODULE_ALIAS("ip6t_SNPT");
 152 MODULE_ALIAS("ip6t_DNPT");