net/ipv4/netfilter/nf_nat_rule.c

   1 /* (C) 1999-2001 Paul `Rusty' Russell
   2  * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
   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 /* Everything about the rules for NAT. */
  10 #include <linux/types.h>
  11 #include <linux/ip.h>
  12 #include <linux/netfilter.h>
  13 #include <linux/netfilter_ipv4.h>
  14 #include <linux/module.h>
  15 #include <linux/kmod.h>
  16 #include <linux/skbuff.h>
  17 #include <linux/proc_fs.h>
  18 #include <net/checksum.h>
  19 #include <net/route.h>
  20 #include <linux/bitops.h>
  21
  22 #include <linux/netfilter_ipv4/ip_tables.h>
  23 #include <net/netfilter/nf_nat.h>
  24 #include <net/netfilter/nf_nat_core.h>
  25 #include <net/netfilter/nf_nat_rule.h>
  26
  27 #define NAT_VALID_HOOKS ((1 << NF_INET_PRE_ROUTING) | \
  28                          (1 << NF_INET_POST_ROUTING) | \
  29                          (1 << NF_INET_LOCAL_OUT))
  30
  31 static struct
  32 {
  33         struct ipt_replace repl;
  34         struct ipt_standard entries[3];
  35         struct ipt_error term;
  36 } nat_initial_table __initdata = {
  37         .repl = {
  38                 .name = "nat",
  39                 .valid_hooks = NAT_VALID_HOOKS,
  40                 .num_entries = 4,
  41                 .size = sizeof(struct ipt_standard) * 3 + sizeof(struct ipt_error),
  42                 .hook_entry = {
  43                         [NF_INET_PRE_ROUTING] = 0,
  44                         [NF_INET_POST_ROUTING] = sizeof(struct ipt_standard),
  45                         [NF_INET_LOCAL_OUT] = sizeof(struct ipt_standard) * 2
  46                 },
  47                 .underflow = {
  48                         [NF_INET_PRE_ROUTING] = 0,
  49                         [NF_INET_POST_ROUTING] = sizeof(struct ipt_standard),
  50                         [NF_INET_LOCAL_OUT] = sizeof(struct ipt_standard) * 2
  51                 },
  52         },
  53         .entries = {
  54                 IPT_STANDARD_INIT(NF_ACCEPT),   /* PRE_ROUTING */
  55                 IPT_STANDARD_INIT(NF_ACCEPT),   /* POST_ROUTING */
  56                 IPT_STANDARD_INIT(NF_ACCEPT),   /* LOCAL_OUT */
  57         },
  58         .term = IPT_ERROR_INIT,                 /* ERROR */
  59 };
  60
  61 static struct xt_table __nat_table = {
  62         .name           = "nat",
  63         .valid_hooks    = NAT_VALID_HOOKS,
  64         .lock           = __RW_LOCK_UNLOCKED(__nat_table.lock),
  65         .me             = THIS_MODULE,
  66         .af             = AF_INET,
  67 };
  68 static struct xt_table *nat_table;
  69
  70 /* Source NAT */
  71 static unsigned int ipt_snat_target(struct sk_buff *skb,
  72                                     const struct net_device *in,
  73                                     const struct net_device *out,
  74                                     unsigned int hooknum,
  75                                     const struct xt_target *target,
  76                                     const void *targinfo)
  77 {
  78         struct nf_conn *ct;
  79         enum ip_conntrack_info ctinfo;
  80         const struct nf_nat_multi_range_compat *mr = targinfo;
  81
  82         NF_CT_ASSERT(hooknum == NF_INET_POST_ROUTING);
  83
  84         ct = nf_ct_get(skb, &ctinfo);
  85
  86         /* Connection must be valid and new. */
  87         NF_CT_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED ||
  88                             ctinfo == IP_CT_RELATED + IP_CT_IS_REPLY));
  89         NF_CT_ASSERT(out);
  90
  91         return nf_nat_setup_info(ct, &mr->range[0], IP_NAT_MANIP_SRC);
  92 }
  93
  94 /* Before 2.6.11 we did implicit source NAT if required. Warn about change. */
  95 static void warn_if_extra_mangle(__be32 dstip, __be32 srcip)
  96 {
  97         static int warned = 0;
  98         struct flowi fl = { .nl_u = { .ip4_u = { .daddr = dstip } } };
  99         struct rtable *rt;
 100
 101         if (ip_route_output_key(&init_net, &rt, &fl) != 0)
 102                 return;
 103
 104         if (rt->rt_src != srcip && !warned) {
 105                 printk("NAT: no longer support implicit source local NAT\n");
 106                 printk("NAT: packet src %u.%u.%u.%u -> dst %u.%u.%u.%u\n",
 107                        NIPQUAD(srcip), NIPQUAD(dstip));
 108                 warned = 1;
 109         }
 110         ip_rt_put(rt);
 111 }
 112
 113 static unsigned int ipt_dnat_target(struct sk_buff *skb,
 114                                     const struct net_device *in,
 115                                     const struct net_device *out,
 116                                     unsigned int hooknum,
 117                                     const struct xt_target *target,
 118                                     const void *targinfo)
 119 {
 120         struct nf_conn *ct;
 121         enum ip_conntrack_info ctinfo;
 122         const struct nf_nat_multi_range_compat *mr = targinfo;
 123
 124         NF_CT_ASSERT(hooknum == NF_INET_PRE_ROUTING ||
 125                      hooknum == NF_INET_LOCAL_OUT);
 126
 127         ct = nf_ct_get(skb, &ctinfo);
 128
 129         /* Connection must be valid and new. */
 130         NF_CT_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED));
 131
 132         if (hooknum == NF_INET_LOCAL_OUT &&
 133             mr->range[0].flags & IP_NAT_RANGE_MAP_IPS)
 134                 warn_if_extra_mangle(ip_hdr(skb)->daddr,
 135                                      mr->range[0].min_ip);
 136
 137         return nf_nat_setup_info(ct, &mr->range[0], IP_NAT_MANIP_DST);
 138 }
 139
 140 static bool ipt_snat_checkentry(const char *tablename,
 141                                 const void *entry,
 142                                 const struct xt_target *target,
 143                                 void *targinfo,
 144                                 unsigned int hook_mask)
 145 {
 146         const struct nf_nat_multi_range_compat *mr = targinfo;
 147
 148         /* Must be a valid range */
 149         if (mr->rangesize != 1) {
 150                 printk("SNAT: multiple ranges no longer supported\n");
 151                 return false;
 152         }
 153         return true;
 154 }
 155
 156 static bool ipt_dnat_checkentry(const char *tablename,
 157                                 const void *entry,
 158                                 const struct xt_target *target,
 159                                 void *targinfo,
 160                                 unsigned int hook_mask)
 161 {
 162         const struct nf_nat_multi_range_compat *mr = targinfo;
 163
 164         /* Must be a valid range */
 165         if (mr->rangesize != 1) {
 166                 printk("DNAT: multiple ranges no longer supported\n");
 167                 return false;
 168         }
 169         return true;
 170 }
 171
 172 unsigned int
 173 alloc_null_binding(struct nf_conn *ct, unsigned int hooknum)
 174 {
 175         /* Force range to this IP; let proto decide mapping for
 176            per-proto parts (hence not IP_NAT_RANGE_PROTO_SPECIFIED).
 177            Use reply in case it's already been mangled (eg local packet).
 178         */
 179         __be32 ip
 180                 = (HOOK2MANIP(hooknum) == IP_NAT_MANIP_SRC
 181                    ? ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3.ip
 182                    : ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.u3.ip);
 183         struct nf_nat_range range
 184                 = { IP_NAT_RANGE_MAP_IPS, ip, ip, { 0 }, { 0 } };
 185
 186         pr_debug("Allocating NULL binding for %p (%u.%u.%u.%u)\n",
 187                  ct, NIPQUAD(ip));
 188         return nf_nat_setup_info(ct, &range, HOOK2MANIP(hooknum));
 189 }
 190
 191 int nf_nat_rule_find(struct sk_buff *skb,
 192                      unsigned int hooknum,
 193                      const struct net_device *in,
 194                      const struct net_device *out,
 195                      struct nf_conn *ct)
 196 {
 197         int ret;
 198
 199         ret = ipt_do_table(skb, hooknum, in, out, nat_table);
 200
 201         if (ret == NF_ACCEPT) {
 202                 if (!nf_nat_initialized(ct, HOOK2MANIP(hooknum)))
 203                         /* NUL mapping */
 204                         ret = alloc_null_binding(ct, hooknum);
 205         }
 206         return ret;
 207 }
 208
 209 static struct xt_target ipt_snat_reg __read_mostly = {
 210         .name           = "SNAT",
 211         .target         = ipt_snat_target,
 212         .targetsize     = sizeof(struct nf_nat_multi_range_compat),
 213         .table          = "nat",
 214         .hooks          = 1 << NF_INET_POST_ROUTING,
 215         .checkentry     = ipt_snat_checkentry,
 216         .family         = AF_INET,
 217 };
 218
 219 static struct xt_target ipt_dnat_reg __read_mostly = {
 220         .name           = "DNAT",
 221         .target         = ipt_dnat_target,
 222         .targetsize     = sizeof(struct nf_nat_multi_range_compat),
 223         .table          = "nat",
 224         .hooks          = (1 << NF_INET_PRE_ROUTING) | (1 << NF_INET_LOCAL_OUT),
 225         .checkentry     = ipt_dnat_checkentry,
 226         .family         = AF_INET,
 227 };
 228
 229 int __init nf_nat_rule_init(void)
 230 {
 231         int ret;
 232
 233         nat_table = ipt_register_table(&init_net, &__nat_table,
 234                                        &nat_initial_table.repl);
 235         if (IS_ERR(nat_table))
 236                 return PTR_ERR(nat_table);
 237         ret = xt_register_target(&ipt_snat_reg);
 238         if (ret != 0)
 239                 goto unregister_table;
 240
 241         ret = xt_register_target(&ipt_dnat_reg);
 242         if (ret != 0)
 243                 goto unregister_snat;
 244
 245         return ret;
 246
 247  unregister_snat:
 248         xt_unregister_target(&ipt_snat_reg);
 249  unregister_table:
 250         ipt_unregister_table(nat_table);
 251
 252         return ret;
 253 }
 254
 255 void nf_nat_rule_cleanup(void)
 256 {
 257         xt_unregister_target(&ipt_dnat_reg);
 258         xt_unregister_target(&ipt_snat_reg);
 259         ipt_unregister_table(nat_table);
 260 }