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Linux/net/ipv6/netfilter/ip6t_NPT.c

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  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");
153 

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