net/ipv4/netfilter/nf_nat_standalone.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 #include <linux/types.h>
   9 #include <linux/icmp.h>
  10 #include <linux/ip.h>
  11 #include <linux/netfilter.h>
  12 #include <linux/netfilter_ipv4.h>
  13 #include <linux/module.h>
  14 #include <linux/skbuff.h>
  15 #include <linux/proc_fs.h>
  16 #include <net/ip.h>
  17 #include <net/checksum.h>
  18 #include <linux/spinlock.h>
  19
  20 #include <net/netfilter/nf_conntrack.h>
  21 #include <net/netfilter/nf_conntrack_core.h>
  22 #include <net/netfilter/nf_nat.h>
  23 #include <net/netfilter/nf_nat_rule.h>
  24 #include <net/netfilter/nf_nat_protocol.h>
  25 #include <net/netfilter/nf_nat_core.h>
  26 #include <net/netfilter/nf_nat_helper.h>
  27 #include <linux/netfilter_ipv4/ip_tables.h>
  28
  29 #if 0
  30 #define DEBUGP printk
  31 #else
  32 #define DEBUGP(format, args...)
  33 #endif
  34
  35 #ifdef CONFIG_XFRM
  36 static void nat_decode_session(struct sk_buff *skb, struct flowi *fl)
  37 {
  38         struct nf_conn *ct;
  39         struct nf_conntrack_tuple *t;
  40         enum ip_conntrack_info ctinfo;
  41         enum ip_conntrack_dir dir;
  42         unsigned long statusbit;
  43
  44         ct = nf_ct_get(skb, &ctinfo);
  45         if (ct == NULL)
  46                 return;
  47         dir = CTINFO2DIR(ctinfo);
  48         t = &ct->tuplehash[dir].tuple;
  49
  50         if (dir == IP_CT_DIR_ORIGINAL)
  51                 statusbit = IPS_DST_NAT;
  52         else
  53                 statusbit = IPS_SRC_NAT;
  54
  55         if (ct->status & statusbit) {
  56                 fl->fl4_dst = t->dst.u3.ip;
  57                 if (t->dst.protonum == IPPROTO_TCP ||
  58                     t->dst.protonum == IPPROTO_UDP)
  59                         fl->fl_ip_dport = t->dst.u.tcp.port;
  60         }
  61
  62         statusbit ^= IPS_NAT_MASK;
  63
  64         if (ct->status & statusbit) {
  65                 fl->fl4_src = t->src.u3.ip;
  66                 if (t->dst.protonum == IPPROTO_TCP ||
  67                     t->dst.protonum == IPPROTO_UDP)
  68                         fl->fl_ip_sport = t->src.u.tcp.port;
  69         }
  70 }
  71 #endif
  72
  73 static unsigned int
  74 nf_nat_fn(unsigned int hooknum,
  75           struct sk_buff **pskb,
  76           const struct net_device *in,
  77           const struct net_device *out,
  78           int (*okfn)(struct sk_buff *))
  79 {
  80         struct nf_conn *ct;
  81         enum ip_conntrack_info ctinfo;
  82         struct nf_conn_nat *nat;
  83         struct nf_nat_info *info;
  84         /* maniptype == SRC for postrouting. */
  85         enum nf_nat_manip_type maniptype = HOOK2MANIP(hooknum);
  86
  87         /* We never see fragments: conntrack defrags on pre-routing
  88            and local-out, and nf_nat_out protects post-routing. */
  89         NF_CT_ASSERT(!((*pskb)->nh.iph->frag_off
  90                        & htons(IP_MF|IP_OFFSET)));
  91
  92         ct = nf_ct_get(*pskb, &ctinfo);
  93         /* Can't track?  It's not due to stress, or conntrack would
  94            have dropped it.  Hence it's the user's responsibilty to
  95            packet filter it out, or implement conntrack/NAT for that
  96            protocol. 8) --RR */
  97         if (!ct) {
  98                 /* Exception: ICMP redirect to new connection (not in
  99                    hash table yet).  We must not let this through, in
 100                    case we're doing NAT to the same network. */
 101                 if ((*pskb)->nh.iph->protocol == IPPROTO_ICMP) {
 102                         struct icmphdr _hdr, *hp;
 103
 104                         hp = skb_header_pointer(*pskb,
 105                                                 (*pskb)->nh.iph->ihl*4,
 106                                                 sizeof(_hdr), &_hdr);
 107                         if (hp != NULL &&
 108                             hp->type == ICMP_REDIRECT)
 109                                 return NF_DROP;
 110                 }
 111                 return NF_ACCEPT;
 112         }
 113
 114         /* Don't try to NAT if this packet is not conntracked */
 115         if (ct == &nf_conntrack_untracked)
 116                 return NF_ACCEPT;
 117
 118         nat = nfct_nat(ct);
 119         if (!nat)
 120                 return NF_ACCEPT;
 121
 122         switch (ctinfo) {
 123         case IP_CT_RELATED:
 124         case IP_CT_RELATED+IP_CT_IS_REPLY:
 125                 if ((*pskb)->nh.iph->protocol == IPPROTO_ICMP) {
 126                         if (!nf_nat_icmp_reply_translation(ct, ctinfo,
 127                                                            hooknum, pskb))
 128                                 return NF_DROP;
 129                         else
 130                                 return NF_ACCEPT;
 131                 }
 132                 /* Fall thru... (Only ICMPs can be IP_CT_IS_REPLY) */
 133         case IP_CT_NEW:
 134                 info = &nat->info;
 135
 136                 /* Seen it before?  This can happen for loopback, retrans,
 137                    or local packets.. */
 138                 if (!nf_nat_initialized(ct, maniptype)) {
 139                         unsigned int ret;
 140
 141                         if (unlikely(nf_ct_is_confirmed(ct)))
 142                                 /* NAT module was loaded late */
 143                                 ret = alloc_null_binding_confirmed(ct, info,
 144                                                                    hooknum);
 145                         else if (hooknum == NF_IP_LOCAL_IN)
 146                                 /* LOCAL_IN hook doesn't have a chain!  */
 147                                 ret = alloc_null_binding(ct, info, hooknum);
 148                         else
 149                                 ret = nf_nat_rule_find(pskb, hooknum, in, out,
 150                                                        ct, info);
 151
 152                         if (ret != NF_ACCEPT) {
 153                                 return ret;
 154                         }
 155                 } else
 156                         DEBUGP("Already setup manip %s for ct %p\n",
 157                                maniptype == IP_NAT_MANIP_SRC ? "SRC" : "DST",
 158                                ct);
 159                 break;
 160
 161         default:
 162                 /* ESTABLISHED */
 163                 NF_CT_ASSERT(ctinfo == IP_CT_ESTABLISHED ||
 164                              ctinfo == (IP_CT_ESTABLISHED+IP_CT_IS_REPLY));
 165                 info = &nat->info;
 166         }
 167
 168         NF_CT_ASSERT(info);
 169         return nf_nat_packet(ct, ctinfo, hooknum, pskb);
 170 }
 171
 172 static unsigned int
 173 nf_nat_in(unsigned int hooknum,
 174           struct sk_buff **pskb,
 175           const struct net_device *in,
 176           const struct net_device *out,
 177           int (*okfn)(struct sk_buff *))
 178 {
 179         unsigned int ret;
 180         __be32 daddr = (*pskb)->nh.iph->daddr;
 181
 182         ret = nf_nat_fn(hooknum, pskb, in, out, okfn);
 183         if (ret != NF_DROP && ret != NF_STOLEN &&
 184             daddr != (*pskb)->nh.iph->daddr) {
 185                 dst_release((*pskb)->dst);
 186                 (*pskb)->dst = NULL;
 187         }
 188         return ret;
 189 }
 190
 191 static unsigned int
 192 nf_nat_out(unsigned int hooknum,
 193            struct sk_buff **pskb,
 194            const struct net_device *in,
 195            const struct net_device *out,
 196            int (*okfn)(struct sk_buff *))
 197 {
 198 #ifdef CONFIG_XFRM
 199         struct nf_conn *ct;
 200         enum ip_conntrack_info ctinfo;
 201 #endif
 202         unsigned int ret;
 203
 204         /* root is playing with raw sockets. */
 205         if ((*pskb)->len < sizeof(struct iphdr) ||
 206             (*pskb)->nh.iph->ihl * 4 < sizeof(struct iphdr))
 207                 return NF_ACCEPT;
 208
 209         ret = nf_nat_fn(hooknum, pskb, in, out, okfn);
 210 #ifdef CONFIG_XFRM
 211         if (ret != NF_DROP && ret != NF_STOLEN &&
 212             (ct = nf_ct_get(*pskb, &ctinfo)) != NULL) {
 213                 enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 214
 215                 if (ct->tuplehash[dir].tuple.src.u3.ip !=
 216                     ct->tuplehash[!dir].tuple.dst.u3.ip
 217                     || ct->tuplehash[dir].tuple.src.u.all !=
 218                        ct->tuplehash[!dir].tuple.dst.u.all
 219                     )
 220                         return ip_xfrm_me_harder(pskb) == 0 ? ret : NF_DROP;
 221         }
 222 #endif
 223         return ret;
 224 }
 225
 226 static unsigned int
 227 nf_nat_local_fn(unsigned int hooknum,
 228                 struct sk_buff **pskb,
 229                 const struct net_device *in,
 230                 const struct net_device *out,
 231                 int (*okfn)(struct sk_buff *))
 232 {
 233         struct nf_conn *ct;
 234         enum ip_conntrack_info ctinfo;
 235         unsigned int ret;
 236
 237         /* root is playing with raw sockets. */
 238         if ((*pskb)->len < sizeof(struct iphdr) ||
 239             (*pskb)->nh.iph->ihl * 4 < sizeof(struct iphdr))
 240                 return NF_ACCEPT;
 241
 242         ret = nf_nat_fn(hooknum, pskb, in, out, okfn);
 243         if (ret != NF_DROP && ret != NF_STOLEN &&
 244             (ct = nf_ct_get(*pskb, &ctinfo)) != NULL) {
 245                 enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 246
 247                 if (ct->tuplehash[dir].tuple.dst.u3.ip !=
 248                     ct->tuplehash[!dir].tuple.src.u3.ip
 249 #ifdef CONFIG_XFRM
 250                     || ct->tuplehash[dir].tuple.dst.u.all !=
 251                        ct->tuplehash[!dir].tuple.src.u.all
 252 #endif
 253                     )
 254                         if (ip_route_me_harder(pskb, RTN_UNSPEC))
 255                                 ret = NF_DROP;
 256         }
 257         return ret;
 258 }
 259
 260 static unsigned int
 261 nf_nat_adjust(unsigned int hooknum,
 262               struct sk_buff **pskb,
 263               const struct net_device *in,
 264               const struct net_device *out,
 265               int (*okfn)(struct sk_buff *))
 266 {
 267         struct nf_conn *ct;
 268         enum ip_conntrack_info ctinfo;
 269
 270         ct = nf_ct_get(*pskb, &ctinfo);
 271         if (ct && test_bit(IPS_SEQ_ADJUST_BIT, &ct->status)) {
 272                 DEBUGP("nf_nat_standalone: adjusting sequence number\n");
 273                 if (!nf_nat_seq_adjust(pskb, ct, ctinfo))
 274                         return NF_DROP;
 275         }
 276         return NF_ACCEPT;
 277 }
 278
 279 /* We must be after connection tracking and before packet filtering. */
 280
 281 static struct nf_hook_ops nf_nat_ops[] = {
 282         /* Before packet filtering, change destination */
 283         {
 284                 .hook           = nf_nat_in,
 285                 .owner          = THIS_MODULE,
 286                 .pf             = PF_INET,
 287                 .hooknum        = NF_IP_PRE_ROUTING,
 288                 .priority       = NF_IP_PRI_NAT_DST,
 289         },
 290         /* After packet filtering, change source */
 291         {
 292                 .hook           = nf_nat_out,
 293                 .owner          = THIS_MODULE,
 294                 .pf             = PF_INET,
 295                 .hooknum        = NF_IP_POST_ROUTING,
 296                 .priority       = NF_IP_PRI_NAT_SRC,
 297         },
 298         /* After conntrack, adjust sequence number */
 299         {
 300                 .hook           = nf_nat_adjust,
 301                 .owner          = THIS_MODULE,
 302                 .pf             = PF_INET,
 303                 .hooknum        = NF_IP_POST_ROUTING,
 304                 .priority       = NF_IP_PRI_NAT_SEQ_ADJUST,
 305         },
 306         /* Before packet filtering, change destination */
 307         {
 308                 .hook           = nf_nat_local_fn,
 309                 .owner          = THIS_MODULE,
 310                 .pf             = PF_INET,
 311                 .hooknum        = NF_IP_LOCAL_OUT,
 312                 .priority       = NF_IP_PRI_NAT_DST,
 313         },
 314         /* After packet filtering, change source */
 315         {
 316                 .hook           = nf_nat_fn,
 317                 .owner          = THIS_MODULE,
 318                 .pf             = PF_INET,
 319                 .hooknum        = NF_IP_LOCAL_IN,
 320                 .priority       = NF_IP_PRI_NAT_SRC,
 321         },
 322         /* After conntrack, adjust sequence number */
 323         {
 324                 .hook           = nf_nat_adjust,
 325                 .owner          = THIS_MODULE,
 326                 .pf             = PF_INET,
 327                 .hooknum        = NF_IP_LOCAL_IN,
 328                 .priority       = NF_IP_PRI_NAT_SEQ_ADJUST,
 329         },
 330 };
 331
 332 static int __init nf_nat_standalone_init(void)
 333 {
 334         int size, ret = 0;
 335
 336         need_conntrack();
 337
 338         size = ALIGN(sizeof(struct nf_conn), __alignof__(struct nf_conn_nat)) +
 339                sizeof(struct nf_conn_nat);
 340         ret = nf_conntrack_register_cache(NF_CT_F_NAT, "nf_nat:base", size);
 341         if (ret < 0) {
 342                 printk(KERN_ERR "nf_nat_init: Unable to create slab cache\n");
 343                 return ret;
 344         }
 345
 346         size = ALIGN(size, __alignof__(struct nf_conn_help)) +
 347                sizeof(struct nf_conn_help);
 348         ret = nf_conntrack_register_cache(NF_CT_F_NAT|NF_CT_F_HELP,
 349                                           "nf_nat:help", size);
 350         if (ret < 0) {
 351                 printk(KERN_ERR "nf_nat_init: Unable to create slab cache\n");
 352                 goto cleanup_register_cache;
 353         }
 354 #ifdef CONFIG_XFRM
 355         BUG_ON(ip_nat_decode_session != NULL);
 356         ip_nat_decode_session = nat_decode_session;
 357 #endif
 358         ret = nf_nat_rule_init();
 359         if (ret < 0) {
 360                 printk("nf_nat_init: can't setup rules.\n");
 361                 goto cleanup_decode_session;
 362         }
 363         ret = nf_register_hooks(nf_nat_ops, ARRAY_SIZE(nf_nat_ops));
 364         if (ret < 0) {
 365                 printk("nf_nat_init: can't register hooks.\n");
 366                 goto cleanup_rule_init;
 367         }
 368         nf_nat_module_is_loaded = 1;
 369         return ret;
 370
 371  cleanup_rule_init:
 372         nf_nat_rule_cleanup();
 373  cleanup_decode_session:
 374 #ifdef CONFIG_XFRM
 375         ip_nat_decode_session = NULL;
 376         synchronize_net();
 377 #endif
 378         nf_conntrack_unregister_cache(NF_CT_F_NAT|NF_CT_F_HELP);
 379  cleanup_register_cache:
 380         nf_conntrack_unregister_cache(NF_CT_F_NAT);
 381         return ret;
 382 }
 383
 384 static void __exit nf_nat_standalone_fini(void)
 385 {
 386         nf_unregister_hooks(nf_nat_ops, ARRAY_SIZE(nf_nat_ops));
 387         nf_nat_rule_cleanup();
 388         nf_nat_module_is_loaded = 0;
 389 #ifdef CONFIG_XFRM
 390         ip_nat_decode_session = NULL;
 391         synchronize_net();
 392 #endif
 393         /* Conntrack caches are unregistered in nf_conntrack_cleanup */
 394 }
 395
 396 module_init(nf_nat_standalone_init);
 397 module_exit(nf_nat_standalone_fini);
 398
 399 MODULE_LICENSE("GPL");
 400 MODULE_ALIAS("ip_nat");