net/ipv4/netfilter/iptable_nat.c

   1 /* (C) 1999-2001 Paul `Rusty' Russell
   2  * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
   3  * (C) 2011 Patrick McHardy <kaber@trash.net>
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License version 2 as
   7  * published by the Free Software Foundation.
   8  */
   9
  10 #include <linux/module.h>
  11 #include <linux/netfilter.h>
  12 #include <linux/netfilter_ipv4.h>
  13 #include <linux/netfilter_ipv4/ip_tables.h>
  14 #include <linux/ip.h>
  15 #include <net/ip.h>
  16
  17 #include <net/netfilter/nf_nat.h>
  18 #include <net/netfilter/nf_nat_core.h>
  19 #include <net/netfilter/nf_nat_l3proto.h>
  20
  21 static const struct xt_table nf_nat_ipv4_table = {
  22         .name           = "nat",
  23         .valid_hooks    = (1 << NF_INET_PRE_ROUTING) |
  24                           (1 << NF_INET_POST_ROUTING) |
  25                           (1 << NF_INET_LOCAL_OUT) |
  26                           (1 << NF_INET_LOCAL_IN),
  27         .me             = THIS_MODULE,
  28         .af             = NFPROTO_IPV4,
  29 };
  30
  31 static unsigned int alloc_null_binding(struct nf_conn *ct, unsigned int hooknum)
  32 {
  33         /* Force range to this IP; let proto decide mapping for
  34          * per-proto parts (hence not IP_NAT_RANGE_PROTO_SPECIFIED).
  35          */
  36         struct nf_nat_range range;
  37
  38         range.flags = 0;
  39         pr_debug("Allocating NULL binding for %p (%pI4)\n", ct,
  40                  HOOK2MANIP(hooknum) == NF_NAT_MANIP_SRC ?
  41                  &ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3.ip :
  42                  &ct->tuplehash[IP_CT_DIR_REPLY].tuple.src.u3.ip);
  43
  44         return nf_nat_setup_info(ct, &range, HOOK2MANIP(hooknum));
  45 }
  46
  47 static unsigned int nf_nat_rule_find(struct sk_buff *skb, unsigned int hooknum,
  48                                      const struct net_device *in,
  49                                      const struct net_device *out,
  50                                      struct nf_conn *ct)
  51 {
  52         struct net *net = nf_ct_net(ct);
  53         unsigned int ret;
  54
  55         ret = ipt_do_table(skb, hooknum, in, out, net->ipv4.nat_table);
  56         if (ret == NF_ACCEPT) {
  57                 if (!nf_nat_initialized(ct, HOOK2MANIP(hooknum)))
  58                         ret = alloc_null_binding(ct, hooknum);
  59         }
  60         return ret;
  61 }
  62
  63 static unsigned int
  64 nf_nat_ipv4_fn(unsigned int hooknum,
  65                struct sk_buff *skb,
  66                const struct net_device *in,
  67                const struct net_device *out,
  68                int (*okfn)(struct sk_buff *))
  69 {
  70         struct nf_conn *ct;
  71         enum ip_conntrack_info ctinfo;
  72         struct nf_conn_nat *nat;
  73         /* maniptype == SRC for postrouting. */
  74         enum nf_nat_manip_type maniptype = HOOK2MANIP(hooknum);
  75
  76         /* We never see fragments: conntrack defrags on pre-routing
  77          * and local-out, and nf_nat_out protects post-routing.
  78          */
  79         NF_CT_ASSERT(!ip_is_fragment(ip_hdr(skb)));
  80
  81         ct = nf_ct_get(skb, &ctinfo);
  82         /* Can't track?  It's not due to stress, or conntrack would
  83          * have dropped it.  Hence it's the user's responsibilty to
  84          * packet filter it out, or implement conntrack/NAT for that
  85          * protocol. 8) --RR
  86          */
  87         if (!ct)
  88                 return NF_ACCEPT;
  89
  90         /* Don't try to NAT if this packet is not conntracked */
  91         if (nf_ct_is_untracked(ct))
  92                 return NF_ACCEPT;
  93
  94         nat = nfct_nat(ct);
  95         if (!nat) {
  96                 /* NAT module was loaded late. */
  97                 if (nf_ct_is_confirmed(ct))
  98                         return NF_ACCEPT;
  99                 nat = nf_ct_ext_add(ct, NF_CT_EXT_NAT, GFP_ATOMIC);
 100                 if (nat == NULL) {
 101                         pr_debug("failed to add NAT extension\n");
 102                         return NF_ACCEPT;
 103                 }
 104         }
 105
 106         switch (ctinfo) {
 107         case IP_CT_RELATED:
 108         case IP_CT_RELATED_REPLY:
 109                 if (ip_hdr(skb)->protocol == IPPROTO_ICMP) {
 110                         if (!nf_nat_icmp_reply_translation(skb, ct, ctinfo,
 111                                                            hooknum))
 112                                 return NF_DROP;
 113                         else
 114                                 return NF_ACCEPT;
 115                 }
 116                 /* Fall thru... (Only ICMPs can be IP_CT_IS_REPLY) */
 117         case IP_CT_NEW:
 118                 /* Seen it before?  This can happen for loopback, retrans,
 119                  * or local packets.
 120                  */
 121                 if (!nf_nat_initialized(ct, maniptype)) {
 122                         unsigned int ret;
 123
 124                         ret = nf_nat_rule_find(skb, hooknum, in, out, ct);
 125                         if (ret != NF_ACCEPT)
 126                                 return ret;
 127                 } else {
 128                         pr_debug("Already setup manip %s for ct %p\n",
 129                                  maniptype == NF_NAT_MANIP_SRC ? "SRC" : "DST",
 130                                  ct);
 131                         if (nf_nat_oif_changed(hooknum, ctinfo, nat, out))
 132                                 goto oif_changed;
 133                 }
 134                 break;
 135
 136         default:
 137                 /* ESTABLISHED */
 138                 NF_CT_ASSERT(ctinfo == IP_CT_ESTABLISHED ||
 139                              ctinfo == IP_CT_ESTABLISHED_REPLY);
 140                 if (nf_nat_oif_changed(hooknum, ctinfo, nat, out))
 141                         goto oif_changed;
 142         }
 143
 144         return nf_nat_packet(ct, ctinfo, hooknum, skb);
 145
 146 oif_changed:
 147         nf_ct_kill_acct(ct, ctinfo, skb);
 148         return NF_DROP;
 149 }
 150
 151 static unsigned int
 152 nf_nat_ipv4_in(unsigned int hooknum,
 153                struct sk_buff *skb,
 154                const struct net_device *in,
 155                const struct net_device *out,
 156                int (*okfn)(struct sk_buff *))
 157 {
 158         unsigned int ret;
 159         __be32 daddr = ip_hdr(skb)->daddr;
 160
 161         ret = nf_nat_ipv4_fn(hooknum, skb, in, out, okfn);
 162         if (ret != NF_DROP && ret != NF_STOLEN &&
 163             daddr != ip_hdr(skb)->daddr)
 164                 skb_dst_drop(skb);
 165
 166         return ret;
 167 }
 168
 169 static unsigned int
 170 nf_nat_ipv4_out(unsigned int hooknum,
 171                 struct sk_buff *skb,
 172                 const struct net_device *in,
 173                 const struct net_device *out,
 174                 int (*okfn)(struct sk_buff *))
 175 {
 176 #ifdef CONFIG_XFRM
 177         const struct nf_conn *ct;
 178         enum ip_conntrack_info ctinfo;
 179         int err;
 180 #endif
 181         unsigned int ret;
 182
 183         /* root is playing with raw sockets. */
 184         if (skb->len < sizeof(struct iphdr) ||
 185             ip_hdrlen(skb) < sizeof(struct iphdr))
 186                 return NF_ACCEPT;
 187
 188         ret = nf_nat_ipv4_fn(hooknum, skb, in, out, okfn);
 189 #ifdef CONFIG_XFRM
 190         if (ret != NF_DROP && ret != NF_STOLEN &&
 191             !(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
 192             (ct = nf_ct_get(skb, &ctinfo)) != NULL) {
 193                 enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 194
 195                 if ((ct->tuplehash[dir].tuple.src.u3.ip !=
 196                      ct->tuplehash[!dir].tuple.dst.u3.ip) ||
 197                     (ct->tuplehash[dir].tuple.dst.protonum != IPPROTO_ICMP &&
 198                      ct->tuplehash[dir].tuple.src.u.all !=
 199                      ct->tuplehash[!dir].tuple.dst.u.all)) {
 200                         err = nf_xfrm_me_harder(skb, AF_INET);
 201                         if (err < 0)
 202                                 ret = NF_DROP_ERR(err);
 203                 }
 204         }
 205 #endif
 206         return ret;
 207 }
 208
 209 static unsigned int
 210 nf_nat_ipv4_local_fn(unsigned int hooknum,
 211                      struct sk_buff *skb,
 212                      const struct net_device *in,
 213                      const struct net_device *out,
 214                      int (*okfn)(struct sk_buff *))
 215 {
 216         const struct nf_conn *ct;
 217         enum ip_conntrack_info ctinfo;
 218         unsigned int ret;
 219         int err;
 220
 221         /* root is playing with raw sockets. */
 222         if (skb->len < sizeof(struct iphdr) ||
 223             ip_hdrlen(skb) < sizeof(struct iphdr))
 224                 return NF_ACCEPT;
 225
 226         ret = nf_nat_ipv4_fn(hooknum, skb, in, out, okfn);
 227         if (ret != NF_DROP && ret != NF_STOLEN &&
 228             (ct = nf_ct_get(skb, &ctinfo)) != NULL) {
 229                 enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 230
 231                 if (ct->tuplehash[dir].tuple.dst.u3.ip !=
 232                     ct->tuplehash[!dir].tuple.src.u3.ip) {
 233                         err = ip_route_me_harder(skb, RTN_UNSPEC);
 234                         if (err < 0)
 235                                 ret = NF_DROP_ERR(err);
 236                 }
 237 #ifdef CONFIG_XFRM
 238                 else if (!(IPCB(skb)->flags & IPSKB_XFRM_TRANSFORMED) &&
 239                          ct->tuplehash[dir].tuple.dst.protonum != IPPROTO_ICMP &&
 240                          ct->tuplehash[dir].tuple.dst.u.all !=
 241                          ct->tuplehash[!dir].tuple.src.u.all) {
 242                         err = nf_xfrm_me_harder(skb, AF_INET);
 243                         if (err < 0)
 244                                 ret = NF_DROP_ERR(err);
 245                 }
 246 #endif
 247         }
 248         return ret;
 249 }
 250
 251 static struct nf_hook_ops nf_nat_ipv4_ops[] __read_mostly = {
 252         /* Before packet filtering, change destination */
 253         {
 254                 .hook           = nf_nat_ipv4_in,
 255                 .owner          = THIS_MODULE,
 256                 .pf             = NFPROTO_IPV4,
 257                 .hooknum        = NF_INET_PRE_ROUTING,
 258                 .priority       = NF_IP_PRI_NAT_DST,
 259         },
 260         /* After packet filtering, change source */
 261         {
 262                 .hook           = nf_nat_ipv4_out,
 263                 .owner          = THIS_MODULE,
 264                 .pf             = NFPROTO_IPV4,
 265                 .hooknum        = NF_INET_POST_ROUTING,
 266                 .priority       = NF_IP_PRI_NAT_SRC,
 267         },
 268         /* Before packet filtering, change destination */
 269         {
 270                 .hook           = nf_nat_ipv4_local_fn,
 271                 .owner          = THIS_MODULE,
 272                 .pf             = NFPROTO_IPV4,
 273                 .hooknum        = NF_INET_LOCAL_OUT,
 274                 .priority       = NF_IP_PRI_NAT_DST,
 275         },
 276         /* After packet filtering, change source */
 277         {
 278                 .hook           = nf_nat_ipv4_fn,
 279                 .owner          = THIS_MODULE,
 280                 .pf             = NFPROTO_IPV4,
 281                 .hooknum        = NF_INET_LOCAL_IN,
 282                 .priority       = NF_IP_PRI_NAT_SRC,
 283         },
 284 };
 285
 286 static int __net_init iptable_nat_net_init(struct net *net)
 287 {
 288         struct ipt_replace *repl;
 289
 290         repl = ipt_alloc_initial_table(&nf_nat_ipv4_table);
 291         if (repl == NULL)
 292                 return -ENOMEM;
 293         net->ipv4.nat_table = ipt_register_table(net, &nf_nat_ipv4_table, repl);
 294         kfree(repl);
 295         return PTR_RET(net->ipv4.nat_table);
 296 }
 297
 298 static void __net_exit iptable_nat_net_exit(struct net *net)
 299 {
 300         ipt_unregister_table(net, net->ipv4.nat_table);
 301 }
 302
 303 static struct pernet_operations iptable_nat_net_ops = {
 304         .init   = iptable_nat_net_init,
 305         .exit   = iptable_nat_net_exit,
 306 };
 307
 308 static int __init iptable_nat_init(void)
 309 {
 310         int err;
 311
 312         err = register_pernet_subsys(&iptable_nat_net_ops);
 313         if (err < 0)
 314                 goto err1;
 315
 316         err = nf_register_hooks(nf_nat_ipv4_ops, ARRAY_SIZE(nf_nat_ipv4_ops));
 317         if (err < 0)
 318                 goto err2;
 319         return 0;
 320
 321 err2:
 322         unregister_pernet_subsys(&iptable_nat_net_ops);
 323 err1:
 324         return err;
 325 }
 326
 327 static void __exit iptable_nat_exit(void)
 328 {
 329         nf_unregister_hooks(nf_nat_ipv4_ops, ARRAY_SIZE(nf_nat_ipv4_ops));
 330         unregister_pernet_subsys(&iptable_nat_net_ops);
 331 }
 332
 333 module_init(iptable_nat_init);
 334 module_exit(iptable_nat_exit);
 335
 336 MODULE_LICENSE("GPL");