net/ipv4/netfilter/ip_nat_standalone.c

   1 /* This file contains all the functions required for the standalone
   2    ip_nat module.
   3
   4    These are not required by the compatibility layer.
   5 */
   6
   7 /* (C) 1999-2001 Paul `Rusty' Russell
   8  * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
   9  *
  10  * This program is free software; you can redistribute it and/or modify
  11  * it under the terms of the GNU General Public License version 2 as
  12  * published by the Free Software Foundation.
  13  */
  14
  15 /*
  16  * 23 Apr 2001: Harald Welte <laforge@gnumonks.org>
  17  *      - new API and handling of conntrack/nat helpers
  18  *      - now capable of multiple expectations for one master
  19  * */
  20
  21 #include <linux/types.h>
  22 #include <linux/icmp.h>
  23 #include <linux/ip.h>
  24 #include <linux/netfilter.h>
  25 #include <linux/netfilter_ipv4.h>
  26 #include <linux/module.h>
  27 #include <linux/skbuff.h>
  28 #include <linux/proc_fs.h>
  29 #include <net/ip.h>
  30 #include <net/checksum.h>
  31 #include <linux/spinlock.h>
  32
  33 #include <linux/netfilter_ipv4/ip_nat.h>
  34 #include <linux/netfilter_ipv4/ip_nat_rule.h>
  35 #include <linux/netfilter_ipv4/ip_nat_protocol.h>
  36 #include <linux/netfilter_ipv4/ip_nat_core.h>
  37 #include <linux/netfilter_ipv4/ip_nat_helper.h>
  38 #include <linux/netfilter_ipv4/ip_tables.h>
  39 #include <linux/netfilter_ipv4/ip_conntrack_core.h>
  40
  41 #if 0
  42 #define DEBUGP printk
  43 #else
  44 #define DEBUGP(format, args...)
  45 #endif
  46
  47 #ifdef CONFIG_XFRM
  48 static void nat_decode_session(struct sk_buff *skb, struct flowi *fl)
  49 {
  50         struct ip_conntrack *ct;
  51         struct ip_conntrack_tuple *t;
  52         enum ip_conntrack_info ctinfo;
  53         enum ip_conntrack_dir dir;
  54         unsigned long statusbit;
  55
  56         ct = ip_conntrack_get(skb, &ctinfo);
  57         if (ct == NULL)
  58                 return;
  59         dir = CTINFO2DIR(ctinfo);
  60         t = &ct->tuplehash[dir].tuple;
  61
  62         if (dir == IP_CT_DIR_ORIGINAL)
  63                 statusbit = IPS_DST_NAT;
  64         else
  65                 statusbit = IPS_SRC_NAT;
  66
  67         if (ct->status & statusbit) {
  68                 fl->fl4_dst = t->dst.ip;
  69                 if (t->dst.protonum == IPPROTO_TCP ||
  70                     t->dst.protonum == IPPROTO_UDP)
  71                         fl->fl_ip_dport = t->dst.u.tcp.port;
  72         }
  73
  74         statusbit ^= IPS_NAT_MASK;
  75
  76         if (ct->status & statusbit) {
  77                 fl->fl4_src = t->src.ip;
  78                 if (t->dst.protonum == IPPROTO_TCP ||
  79                     t->dst.protonum == IPPROTO_UDP)
  80                         fl->fl_ip_sport = t->src.u.tcp.port;
  81         }
  82 }
  83 #endif
  84
  85 static unsigned int
  86 ip_nat_fn(unsigned int hooknum,
  87           struct sk_buff **pskb,
  88           const struct net_device *in,
  89           const struct net_device *out,
  90           int (*okfn)(struct sk_buff *))
  91 {
  92         struct ip_conntrack *ct;
  93         enum ip_conntrack_info ctinfo;
  94         struct ip_nat_info *info;
  95         /* maniptype == SRC for postrouting. */
  96         enum ip_nat_manip_type maniptype = HOOK2MANIP(hooknum);
  97
  98         /* We never see fragments: conntrack defrags on pre-routing
  99            and local-out, and ip_nat_out protects post-routing. */
 100         IP_NF_ASSERT(!(ip_hdr(*pskb)->frag_off
 101                        & htons(IP_MF|IP_OFFSET)));
 102
 103         ct = ip_conntrack_get(*pskb, &ctinfo);
 104         /* Can't track?  It's not due to stress, or conntrack would
 105            have dropped it.  Hence it's the user's responsibilty to
 106            packet filter it out, or implement conntrack/NAT for that
 107            protocol. 8) --RR */
 108         if (!ct) {
 109                 /* Exception: ICMP redirect to new connection (not in
 110                    hash table yet).  We must not let this through, in
 111                    case we're doing NAT to the same network. */
 112                 if (ip_hdr(*pskb)->protocol == IPPROTO_ICMP) {
 113                         struct icmphdr _hdr, *hp;
 114
 115                         hp = skb_header_pointer(*pskb, ip_hdrlen(*pskb),
 116                                                 sizeof(_hdr), &_hdr);
 117                         if (hp != NULL &&
 118                             hp->type == ICMP_REDIRECT)
 119                                 return NF_DROP;
 120                 }
 121                 return NF_ACCEPT;
 122         }
 123
 124         /* Don't try to NAT if this packet is not conntracked */
 125         if (ct == &ip_conntrack_untracked)
 126                 return NF_ACCEPT;
 127
 128         switch (ctinfo) {
 129         case IP_CT_RELATED:
 130         case IP_CT_RELATED+IP_CT_IS_REPLY:
 131                 if (ip_hdr(*pskb)->protocol == IPPROTO_ICMP) {
 132                         if (!ip_nat_icmp_reply_translation(ct, ctinfo,
 133                                                            hooknum, pskb))
 134                                 return NF_DROP;
 135                         else
 136                                 return NF_ACCEPT;
 137                 }
 138                 /* Fall thru... (Only ICMPs can be IP_CT_IS_REPLY) */
 139         case IP_CT_NEW:
 140                 info = &ct->nat.info;
 141
 142                 /* Seen it before?  This can happen for loopback, retrans,
 143                    or local packets.. */
 144                 if (!ip_nat_initialized(ct, maniptype)) {
 145                         unsigned int ret;
 146
 147                         if (unlikely(is_confirmed(ct)))
 148                                 /* NAT module was loaded late */
 149                                 ret = alloc_null_binding_confirmed(ct, info,
 150                                                                    hooknum);
 151                         else if (hooknum == NF_IP_LOCAL_IN)
 152                                 /* LOCAL_IN hook doesn't have a chain!  */
 153                                 ret = alloc_null_binding(ct, info, hooknum);
 154                         else
 155                                 ret = ip_nat_rule_find(pskb, hooknum,
 156                                                        in, out, ct,
 157                                                        info);
 158
 159                         if (ret != NF_ACCEPT) {
 160                                 return ret;
 161                         }
 162                 } else
 163                         DEBUGP("Already setup manip %s for ct %p\n",
 164                                maniptype == IP_NAT_MANIP_SRC ? "SRC" : "DST",
 165                                ct);
 166                 break;
 167
 168         default:
 169                 /* ESTABLISHED */
 170                 IP_NF_ASSERT(ctinfo == IP_CT_ESTABLISHED
 171                              || ctinfo == (IP_CT_ESTABLISHED+IP_CT_IS_REPLY));
 172                 info = &ct->nat.info;
 173         }
 174
 175         IP_NF_ASSERT(info);
 176         return ip_nat_packet(ct, ctinfo, hooknum, pskb);
 177 }
 178
 179 static unsigned int
 180 ip_nat_in(unsigned int hooknum,
 181           struct sk_buff **pskb,
 182           const struct net_device *in,
 183           const struct net_device *out,
 184           int (*okfn)(struct sk_buff *))
 185 {
 186         unsigned int ret;
 187         __be32 daddr = ip_hdr(*pskb)->daddr;
 188
 189         ret = ip_nat_fn(hooknum, pskb, in, out, okfn);
 190         if (ret != NF_DROP && ret != NF_STOLEN
 191             && daddr != ip_hdr(*pskb)->daddr) {
 192                 dst_release((*pskb)->dst);
 193                 (*pskb)->dst = NULL;
 194         }
 195         return ret;
 196 }
 197
 198 static unsigned int
 199 ip_nat_out(unsigned int hooknum,
 200            struct sk_buff **pskb,
 201            const struct net_device *in,
 202            const struct net_device *out,
 203            int (*okfn)(struct sk_buff *))
 204 {
 205 #ifdef CONFIG_XFRM
 206         struct ip_conntrack *ct;
 207         enum ip_conntrack_info ctinfo;
 208 #endif
 209         unsigned int ret;
 210
 211         /* root is playing with raw sockets. */
 212         if ((*pskb)->len < sizeof(struct iphdr)
 213             || ip_hdrlen(*pskb) < sizeof(struct iphdr))
 214                 return NF_ACCEPT;
 215
 216         ret = ip_nat_fn(hooknum, pskb, in, out, okfn);
 217 #ifdef CONFIG_XFRM
 218         if (ret != NF_DROP && ret != NF_STOLEN
 219             && (ct = ip_conntrack_get(*pskb, &ctinfo)) != NULL) {
 220                 enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 221
 222                 if (ct->tuplehash[dir].tuple.src.ip !=
 223                     ct->tuplehash[!dir].tuple.dst.ip
 224                     || ct->tuplehash[dir].tuple.src.u.all !=
 225                        ct->tuplehash[!dir].tuple.dst.u.all
 226                     )
 227                         return ip_xfrm_me_harder(pskb) == 0 ? ret : NF_DROP;
 228         }
 229 #endif
 230         return ret;
 231 }
 232
 233 static unsigned int
 234 ip_nat_local_fn(unsigned int hooknum,
 235                 struct sk_buff **pskb,
 236                 const struct net_device *in,
 237                 const struct net_device *out,
 238                 int (*okfn)(struct sk_buff *))
 239 {
 240         struct ip_conntrack *ct;
 241         enum ip_conntrack_info ctinfo;
 242         unsigned int ret;
 243
 244         /* root is playing with raw sockets. */
 245         if ((*pskb)->len < sizeof(struct iphdr)
 246             || ip_hdrlen(*pskb) < sizeof(struct iphdr))
 247                 return NF_ACCEPT;
 248
 249         ret = ip_nat_fn(hooknum, pskb, in, out, okfn);
 250         if (ret != NF_DROP && ret != NF_STOLEN
 251             && (ct = ip_conntrack_get(*pskb, &ctinfo)) != NULL) {
 252                 enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 253
 254                 if (ct->tuplehash[dir].tuple.dst.ip !=
 255                     ct->tuplehash[!dir].tuple.src.ip) {
 256                         if (ip_route_me_harder(pskb, RTN_UNSPEC))
 257                                 ret = NF_DROP;
 258                 }
 259 #ifdef CONFIG_XFRM
 260                 else if (ct->tuplehash[dir].tuple.dst.u.all !=
 261                          ct->tuplehash[!dir].tuple.src.u.all)
 262                         if (ip_xfrm_me_harder(pskb))
 263                                 ret = NF_DROP;
 264 #endif
 265
 266         }
 267         return ret;
 268 }
 269
 270 static unsigned int
 271 ip_nat_adjust(unsigned int hooknum,
 272               struct sk_buff **pskb,
 273               const struct net_device *in,
 274               const struct net_device *out,
 275               int (*okfn)(struct sk_buff *))
 276 {
 277         struct ip_conntrack *ct;
 278         enum ip_conntrack_info ctinfo;
 279
 280         ct = ip_conntrack_get(*pskb, &ctinfo);
 281         if (ct && test_bit(IPS_SEQ_ADJUST_BIT, &ct->status)) {
 282                 DEBUGP("ip_nat_standalone: adjusting sequence number\n");
 283                 if (!ip_nat_seq_adjust(pskb, ct, ctinfo))
 284                         return NF_DROP;
 285         }
 286         return NF_ACCEPT;
 287 }
 288
 289 /* We must be after connection tracking and before packet filtering. */
 290
 291 static struct nf_hook_ops ip_nat_ops[] = {
 292         /* Before packet filtering, change destination */
 293         {
 294                 .hook           = ip_nat_in,
 295                 .owner          = THIS_MODULE,
 296                 .pf             = PF_INET,
 297                 .hooknum        = NF_IP_PRE_ROUTING,
 298                 .priority       = NF_IP_PRI_NAT_DST,
 299         },
 300         /* After packet filtering, change source */
 301         {
 302                 .hook           = ip_nat_out,
 303                 .owner          = THIS_MODULE,
 304                 .pf             = PF_INET,
 305                 .hooknum        = NF_IP_POST_ROUTING,
 306                 .priority       = NF_IP_PRI_NAT_SRC,
 307         },
 308         /* After conntrack, adjust sequence number */
 309         {
 310                 .hook           = ip_nat_adjust,
 311                 .owner          = THIS_MODULE,
 312                 .pf             = PF_INET,
 313                 .hooknum        = NF_IP_POST_ROUTING,
 314                 .priority       = NF_IP_PRI_NAT_SEQ_ADJUST,
 315         },
 316         /* Before packet filtering, change destination */
 317         {
 318                 .hook           = ip_nat_local_fn,
 319                 .owner          = THIS_MODULE,
 320                 .pf             = PF_INET,
 321                 .hooknum        = NF_IP_LOCAL_OUT,
 322                 .priority       = NF_IP_PRI_NAT_DST,
 323         },
 324         /* After packet filtering, change source */
 325         {
 326                 .hook           = ip_nat_fn,
 327                 .owner          = THIS_MODULE,
 328                 .pf             = PF_INET,
 329                 .hooknum        = NF_IP_LOCAL_IN,
 330                 .priority       = NF_IP_PRI_NAT_SRC,
 331         },
 332         /* After conntrack, adjust sequence number */
 333         {
 334                 .hook           = ip_nat_adjust,
 335                 .owner          = THIS_MODULE,
 336                 .pf             = PF_INET,
 337                 .hooknum        = NF_IP_LOCAL_IN,
 338                 .priority       = NF_IP_PRI_NAT_SEQ_ADJUST,
 339         },
 340 };
 341
 342 static int __init ip_nat_standalone_init(void)
 343 {
 344         int ret = 0;
 345
 346         need_conntrack();
 347
 348 #ifdef CONFIG_XFRM
 349         BUG_ON(ip_nat_decode_session != NULL);
 350         ip_nat_decode_session = nat_decode_session;
 351 #endif
 352         ret = ip_nat_rule_init();
 353         if (ret < 0) {
 354                 printk("ip_nat_init: can't setup rules.\n");
 355                 goto cleanup_decode_session;
 356         }
 357         ret = nf_register_hooks(ip_nat_ops, ARRAY_SIZE(ip_nat_ops));
 358         if (ret < 0) {
 359                 printk("ip_nat_init: can't register hooks.\n");
 360                 goto cleanup_rule_init;
 361         }
 362         return ret;
 363
 364  cleanup_rule_init:
 365         ip_nat_rule_cleanup();
 366  cleanup_decode_session:
 367 #ifdef CONFIG_XFRM
 368         ip_nat_decode_session = NULL;
 369         synchronize_net();
 370 #endif
 371         return ret;
 372 }
 373
 374 static void __exit ip_nat_standalone_fini(void)
 375 {
 376         nf_unregister_hooks(ip_nat_ops, ARRAY_SIZE(ip_nat_ops));
 377         ip_nat_rule_cleanup();
 378 #ifdef CONFIG_XFRM
 379         ip_nat_decode_session = NULL;
 380         synchronize_net();
 381 #endif
 382 }
 383
 384 module_init(ip_nat_standalone_init);
 385 module_exit(ip_nat_standalone_fini);
 386
 387 MODULE_LICENSE("GPL");