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Linux/net/ipv6/netfilter/ip6t_NPT.c

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  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");
154 

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