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, ip_hdrlen(*pskb),
 105                                                 sizeof(_hdr), &_hdr);
 106                         if (hp != NULL &&
 107                             hp->type == ICMP_REDIRECT)
 108                                 return NF_DROP;
 109                 }
 110                 return NF_ACCEPT;
 111         }
 112
 113         /* Don't try to NAT if this packet is not conntracked */
 114         if (ct == &nf_conntrack_untracked)
 115                 return NF_ACCEPT;
 116
 117         nat = nfct_nat(ct);
 118         if (!nat)
 119                 return NF_ACCEPT;
 120
 121         switch (ctinfo) {
 122         case IP_CT_RELATED:
 123         case IP_CT_RELATED+IP_CT_IS_REPLY:
 124                 if ((*pskb)->nh.iph->protocol == IPPROTO_ICMP) {
 125                         if (!nf_nat_icmp_reply_translation(ct, ctinfo,
 126                                                            hooknum, pskb))
 127                                 return NF_DROP;
 128                         else
 129                                 return NF_ACCEPT;
 130                 }
 131                 /* Fall thru... (Only ICMPs can be IP_CT_IS_REPLY) */
 132         case IP_CT_NEW:
 133                 info = &nat->info;
 134
 135                 /* Seen it before?  This can happen for loopback, retrans,
 136                    or local packets.. */
 137                 if (!nf_nat_initialized(ct, maniptype)) {
 138                         unsigned int ret;
 139
 140                         if (unlikely(nf_ct_is_confirmed(ct)))
 141                                 /* NAT module was loaded late */
 142                                 ret = alloc_null_binding_confirmed(ct, info,
 143                                                                    hooknum);
 144                         else if (hooknum == NF_IP_LOCAL_IN)
 145                                 /* LOCAL_IN hook doesn't have a chain!  */
 146                                 ret = alloc_null_binding(ct, info, hooknum);
 147                         else
 148                                 ret = nf_nat_rule_find(pskb, hooknum, in, out,
 149                                                        ct, info);
 150
 151                         if (ret != NF_ACCEPT) {
 152                                 return ret;
 153                         }
 154                 } else
 155                         DEBUGP("Already setup manip %s for ct %p\n",
 156                                maniptype == IP_NAT_MANIP_SRC ? "SRC" : "DST",
 157                                ct);
 158                 break;
 159
 160         default:
 161                 /* ESTABLISHED */
 162                 NF_CT_ASSERT(ctinfo == IP_CT_ESTABLISHED ||
 163                              ctinfo == (IP_CT_ESTABLISHED+IP_CT_IS_REPLY));
 164                 info = &nat->info;
 165         }
 166
 167         NF_CT_ASSERT(info);
 168         return nf_nat_packet(ct, ctinfo, hooknum, pskb);
 169 }
 170
 171 static unsigned int
 172 nf_nat_in(unsigned int hooknum,
 173           struct sk_buff **pskb,
 174           const struct net_device *in,
 175           const struct net_device *out,
 176           int (*okfn)(struct sk_buff *))
 177 {
 178         unsigned int ret;
 179         __be32 daddr = (*pskb)->nh.iph->daddr;
 180
 181         ret = nf_nat_fn(hooknum, pskb, in, out, okfn);
 182         if (ret != NF_DROP && ret != NF_STOLEN &&
 183             daddr != (*pskb)->nh.iph->daddr) {
 184                 dst_release((*pskb)->dst);
 185                 (*pskb)->dst = NULL;
 186         }
 187         return ret;
 188 }
 189
 190 static unsigned int
 191 nf_nat_out(unsigned int hooknum,
 192            struct sk_buff **pskb,
 193            const struct net_device *in,
 194            const struct net_device *out,
 195            int (*okfn)(struct sk_buff *))
 196 {
 197 #ifdef CONFIG_XFRM
 198         struct nf_conn *ct;
 199         enum ip_conntrack_info ctinfo;
 200 #endif
 201         unsigned int ret;
 202
 203         /* root is playing with raw sockets. */
 204         if ((*pskb)->len < sizeof(struct iphdr) ||
 205             ip_hdrlen(*pskb) < sizeof(struct iphdr))
 206                 return NF_ACCEPT;
 207
 208         ret = nf_nat_fn(hooknum, pskb, in, out, okfn);
 209 #ifdef CONFIG_XFRM
 210         if (ret != NF_DROP && ret != NF_STOLEN &&
 211             (ct = nf_ct_get(*pskb, &ctinfo)) != NULL) {
 212                 enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 213
 214                 if (ct->tuplehash[dir].tuple.src.u3.ip !=
 215                     ct->tuplehash[!dir].tuple.dst.u3.ip
 216                     || ct->tuplehash[dir].tuple.src.u.all !=
 217                        ct->tuplehash[!dir].tuple.dst.u.all
 218                     )
 219                         return ip_xfrm_me_harder(pskb) == 0 ? ret : NF_DROP;
 220         }
 221 #endif
 222         return ret;
 223 }
 224
 225 static unsigned int
 226 nf_nat_local_fn(unsigned int hooknum,
 227                 struct sk_buff **pskb,
 228                 const struct net_device *in,
 229                 const struct net_device *out,
 230                 int (*okfn)(struct sk_buff *))
 231 {
 232         struct nf_conn *ct;
 233         enum ip_conntrack_info ctinfo;
 234         unsigned int ret;
 235
 236         /* root is playing with raw sockets. */
 237         if ((*pskb)->len < sizeof(struct iphdr) ||
 238             ip_hdrlen(*pskb) < sizeof(struct iphdr))
 239                 return NF_ACCEPT;
 240
 241         ret = nf_nat_fn(hooknum, pskb, in, out, okfn);
 242         if (ret != NF_DROP && ret != NF_STOLEN &&
 243             (ct = nf_ct_get(*pskb, &ctinfo)) != NULL) {
 244                 enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 245
 246                 if (ct->tuplehash[dir].tuple.dst.u3.ip !=
 247                     ct->tuplehash[!dir].tuple.src.u3.ip) {
 248                         if (ip_route_me_harder(pskb, RTN_UNSPEC))
 249                                 ret = NF_DROP;
 250                 }
 251 #ifdef CONFIG_XFRM
 252                 else if (ct->tuplehash[dir].tuple.dst.u.all !=
 253                          ct->tuplehash[!dir].tuple.src.u.all)
 254                         if (ip_xfrm_me_harder(pskb))
 255                                 ret = NF_DROP;
 256 #endif
 257         }
 258         return ret;
 259 }
 260
 261 static unsigned int
 262 nf_nat_adjust(unsigned int hooknum,
 263               struct sk_buff **pskb,
 264               const struct net_device *in,
 265               const struct net_device *out,
 266               int (*okfn)(struct sk_buff *))
 267 {
 268         struct nf_conn *ct;
 269         enum ip_conntrack_info ctinfo;
 270
 271         ct = nf_ct_get(*pskb, &ctinfo);
 272         if (ct && test_bit(IPS_SEQ_ADJUST_BIT, &ct->status)) {
 273                 DEBUGP("nf_nat_standalone: adjusting sequence number\n");
 274                 if (!nf_nat_seq_adjust(pskb, ct, ctinfo))
 275                         return NF_DROP;
 276         }
 277         return NF_ACCEPT;
 278 }
 279
 280 /* We must be after connection tracking and before packet filtering. */
 281
 282 static struct nf_hook_ops nf_nat_ops[] = {
 283         /* Before packet filtering, change destination */
 284         {
 285                 .hook           = nf_nat_in,
 286                 .owner          = THIS_MODULE,
 287                 .pf             = PF_INET,
 288                 .hooknum        = NF_IP_PRE_ROUTING,
 289                 .priority       = NF_IP_PRI_NAT_DST,
 290         },
 291         /* After packet filtering, change source */
 292         {
 293                 .hook           = nf_nat_out,
 294                 .owner          = THIS_MODULE,
 295                 .pf             = PF_INET,
 296                 .hooknum        = NF_IP_POST_ROUTING,
 297                 .priority       = NF_IP_PRI_NAT_SRC,
 298         },
 299         /* After conntrack, adjust sequence number */
 300         {
 301                 .hook           = nf_nat_adjust,
 302                 .owner          = THIS_MODULE,
 303                 .pf             = PF_INET,
 304                 .hooknum        = NF_IP_POST_ROUTING,
 305                 .priority       = NF_IP_PRI_NAT_SEQ_ADJUST,
 306         },
 307         /* Before packet filtering, change destination */
 308         {
 309                 .hook           = nf_nat_local_fn,
 310                 .owner          = THIS_MODULE,
 311                 .pf             = PF_INET,
 312                 .hooknum        = NF_IP_LOCAL_OUT,
 313                 .priority       = NF_IP_PRI_NAT_DST,
 314         },
 315         /* After packet filtering, change source */
 316         {
 317                 .hook           = nf_nat_fn,
 318                 .owner          = THIS_MODULE,
 319                 .pf             = PF_INET,
 320                 .hooknum        = NF_IP_LOCAL_IN,
 321                 .priority       = NF_IP_PRI_NAT_SRC,
 322         },
 323         /* After conntrack, adjust sequence number */
 324         {
 325                 .hook           = nf_nat_adjust,
 326                 .owner          = THIS_MODULE,
 327                 .pf             = PF_INET,
 328                 .hooknum        = NF_IP_LOCAL_IN,
 329                 .priority       = NF_IP_PRI_NAT_SEQ_ADJUST,
 330         },
 331 };
 332
 333 static int __init nf_nat_standalone_init(void)
 334 {
 335         int size, ret = 0;
 336
 337         need_conntrack();
 338
 339         size = ALIGN(sizeof(struct nf_conn), __alignof__(struct nf_conn_nat)) +
 340                sizeof(struct nf_conn_nat);
 341         ret = nf_conntrack_register_cache(NF_CT_F_NAT, "nf_nat:base", size);
 342         if (ret < 0) {
 343                 printk(KERN_ERR "nf_nat_init: Unable to create slab cache\n");
 344                 return ret;
 345         }
 346
 347         size = ALIGN(size, __alignof__(struct nf_conn_help)) +
 348                sizeof(struct nf_conn_help);
 349         ret = nf_conntrack_register_cache(NF_CT_F_NAT|NF_CT_F_HELP,
 350                                           "nf_nat:help", size);
 351         if (ret < 0) {
 352                 printk(KERN_ERR "nf_nat_init: Unable to create slab cache\n");
 353                 goto cleanup_register_cache;
 354         }
 355 #ifdef CONFIG_XFRM
 356         BUG_ON(ip_nat_decode_session != NULL);
 357         ip_nat_decode_session = nat_decode_session;
 358 #endif
 359         ret = nf_nat_rule_init();
 360         if (ret < 0) {
 361                 printk("nf_nat_init: can't setup rules.\n");
 362                 goto cleanup_decode_session;
 363         }
 364         ret = nf_register_hooks(nf_nat_ops, ARRAY_SIZE(nf_nat_ops));
 365         if (ret < 0) {
 366                 printk("nf_nat_init: can't register hooks.\n");
 367                 goto cleanup_rule_init;
 368         }
 369         nf_nat_module_is_loaded = 1;
 370         return ret;
 371
 372  cleanup_rule_init:
 373         nf_nat_rule_cleanup();
 374  cleanup_decode_session:
 375 #ifdef CONFIG_XFRM
 376         ip_nat_decode_session = NULL;
 377         synchronize_net();
 378 #endif
 379         nf_conntrack_unregister_cache(NF_CT_F_NAT|NF_CT_F_HELP);
 380  cleanup_register_cache:
 381         nf_conntrack_unregister_cache(NF_CT_F_NAT);
 382         return ret;
 383 }
 384
 385 static void __exit nf_nat_standalone_fini(void)
 386 {
 387         nf_unregister_hooks(nf_nat_ops, ARRAY_SIZE(nf_nat_ops));
 388         nf_nat_rule_cleanup();
 389         nf_nat_module_is_loaded = 0;
 390 #ifdef CONFIG_XFRM
 391         ip_nat_decode_session = NULL;
 392         synchronize_net();
 393 #endif
 394         /* Conntrack caches are unregistered in nf_conntrack_cleanup */
 395 }
 396
 397 module_init(nf_nat_standalone_init);
 398 module_exit(nf_nat_standalone_fini);
 399
 400 MODULE_LICENSE("GPL");
 401 MODULE_ALIAS("ip_nat");