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 #define HOOKNAME(hooknum) ((hooknum) == NF_IP_POST_ROUTING ? "POST_ROUTING"  \
  36                            : ((hooknum) == NF_IP_PRE_ROUTING ? "PRE_ROUTING" \
  37                               : ((hooknum) == NF_IP_LOCAL_OUT ? "LOCAL_OUT"  \
  38                                  : ((hooknum) == NF_IP_LOCAL_IN ? "LOCAL_IN"  \
  39                                     : "*ERROR*")))
  40
  41 #ifdef CONFIG_XFRM
  42 static void nat_decode_session(struct sk_buff *skb, struct flowi *fl)
  43 {
  44         struct nf_conn *ct;
  45         struct nf_conntrack_tuple *t;
  46         enum ip_conntrack_info ctinfo;
  47         enum ip_conntrack_dir dir;
  48         unsigned long statusbit;
  49
  50         ct = nf_ct_get(skb, &ctinfo);
  51         if (ct == NULL)
  52                 return;
  53         dir = CTINFO2DIR(ctinfo);
  54         t = &ct->tuplehash[dir].tuple;
  55
  56         if (dir == IP_CT_DIR_ORIGINAL)
  57                 statusbit = IPS_DST_NAT;
  58         else
  59                 statusbit = IPS_SRC_NAT;
  60
  61         if (ct->status & statusbit) {
  62                 fl->fl4_dst = t->dst.u3.ip;
  63                 if (t->dst.protonum == IPPROTO_TCP ||
  64                     t->dst.protonum == IPPROTO_UDP)
  65                         fl->fl_ip_dport = t->dst.u.tcp.port;
  66         }
  67
  68         statusbit ^= IPS_NAT_MASK;
  69
  70         if (ct->status & statusbit) {
  71                 fl->fl4_src = t->src.u3.ip;
  72                 if (t->dst.protonum == IPPROTO_TCP ||
  73                     t->dst.protonum == IPPROTO_UDP)
  74                         fl->fl_ip_sport = t->src.u.tcp.port;
  75         }
  76 }
  77 #endif
  78
  79 static unsigned int
  80 nf_nat_fn(unsigned int hooknum,
  81           struct sk_buff **pskb,
  82           const struct net_device *in,
  83           const struct net_device *out,
  84           int (*okfn)(struct sk_buff *))
  85 {
  86         struct nf_conn *ct;
  87         enum ip_conntrack_info ctinfo;
  88         struct nf_conn_nat *nat;
  89         struct nf_nat_info *info;
  90         /* maniptype == SRC for postrouting. */
  91         enum nf_nat_manip_type maniptype = HOOK2MANIP(hooknum);
  92
  93         /* We never see fragments: conntrack defrags on pre-routing
  94            and local-out, and nf_nat_out protects post-routing. */
  95         NF_CT_ASSERT(!((*pskb)->nh.iph->frag_off
  96                        & htons(IP_MF|IP_OFFSET)));
  97
  98         ct = nf_ct_get(*pskb, &ctinfo);
  99         /* Can't track?  It's not due to stress, or conntrack would
 100            have dropped it.  Hence it's the user's responsibilty to
 101            packet filter it out, or implement conntrack/NAT for that
 102            protocol. 8) --RR */
 103         if (!ct) {
 104                 /* Exception: ICMP redirect to new connection (not in
 105                    hash table yet).  We must not let this through, in
 106                    case we're doing NAT to the same network. */
 107                 if ((*pskb)->nh.iph->protocol == IPPROTO_ICMP) {
 108                         struct icmphdr _hdr, *hp;
 109
 110                         hp = skb_header_pointer(*pskb,
 111                                                 (*pskb)->nh.iph->ihl*4,
 112                                                 sizeof(_hdr), &_hdr);
 113                         if (hp != NULL &&
 114                             hp->type == ICMP_REDIRECT)
 115                                 return NF_DROP;
 116                 }
 117                 return NF_ACCEPT;
 118         }
 119
 120         /* Don't try to NAT if this packet is not conntracked */
 121         if (ct == &nf_conntrack_untracked)
 122                 return NF_ACCEPT;
 123
 124         nat = nfct_nat(ct);
 125         if (!nat)
 126                 return NF_ACCEPT;
 127
 128         switch (ctinfo) {
 129         case IP_CT_RELATED:
 130         case IP_CT_RELATED+IP_CT_IS_REPLY:
 131                 if ((*pskb)->nh.iph->protocol == IPPROTO_ICMP) {
 132                         if (!nf_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 = &nat->info;
 141
 142                 /* Seen it before?  This can happen for loopback, retrans,
 143                    or local packets.. */
 144                 if (!nf_nat_initialized(ct, maniptype)) {
 145                         unsigned int ret;
 146
 147                         if (unlikely(nf_ct_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 = nf_nat_rule_find(pskb, hooknum, in, out,
 156                                                        ct, info);
 157
 158                         if (ret != NF_ACCEPT) {
 159                                 return ret;
 160                         }
 161                 } else
 162                         DEBUGP("Already setup manip %s for ct %p\n",
 163                                maniptype == IP_NAT_MANIP_SRC ? "SRC" : "DST",
 164                                ct);
 165                 break;
 166
 167         default:
 168                 /* ESTABLISHED */
 169                 NF_CT_ASSERT(ctinfo == IP_CT_ESTABLISHED ||
 170                              ctinfo == (IP_CT_ESTABLISHED+IP_CT_IS_REPLY));
 171                 info = &nat->info;
 172         }
 173
 174         NF_CT_ASSERT(info);
 175         return nf_nat_packet(ct, ctinfo, hooknum, pskb);
 176 }
 177
 178 static unsigned int
 179 nf_nat_in(unsigned int hooknum,
 180           struct sk_buff **pskb,
 181           const struct net_device *in,
 182           const struct net_device *out,
 183           int (*okfn)(struct sk_buff *))
 184 {
 185         unsigned int ret;
 186         __be32 daddr = (*pskb)->nh.iph->daddr;
 187
 188         ret = nf_nat_fn(hooknum, pskb, in, out, okfn);
 189         if (ret != NF_DROP && ret != NF_STOLEN &&
 190             daddr != (*pskb)->nh.iph->daddr) {
 191                 dst_release((*pskb)->dst);
 192                 (*pskb)->dst = NULL;
 193         }
 194         return ret;
 195 }
 196
 197 static unsigned int
 198 nf_nat_out(unsigned int hooknum,
 199            struct sk_buff **pskb,
 200            const struct net_device *in,
 201            const struct net_device *out,
 202            int (*okfn)(struct sk_buff *))
 203 {
 204 #ifdef CONFIG_XFRM
 205         struct nf_conn *ct;
 206         enum ip_conntrack_info ctinfo;
 207 #endif
 208         unsigned int ret;
 209
 210         /* root is playing with raw sockets. */
 211         if ((*pskb)->len < sizeof(struct iphdr) ||
 212             (*pskb)->nh.iph->ihl * 4 < sizeof(struct iphdr))
 213                 return NF_ACCEPT;
 214
 215         ret = nf_nat_fn(hooknum, pskb, in, out, okfn);
 216 #ifdef CONFIG_XFRM
 217         if (ret != NF_DROP && ret != NF_STOLEN &&
 218             (ct = nf_ct_get(*pskb, &ctinfo)) != NULL) {
 219                 enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 220
 221                 if (ct->tuplehash[dir].tuple.src.u3.ip !=
 222                     ct->tuplehash[!dir].tuple.dst.u3.ip
 223                     || ct->tuplehash[dir].tuple.src.u.all !=
 224                        ct->tuplehash[!dir].tuple.dst.u.all
 225                     )
 226                         return ip_xfrm_me_harder(pskb) == 0 ? ret : NF_DROP;
 227         }
 228 #endif
 229         return ret;
 230 }
 231
 232 static unsigned int
 233 nf_nat_local_fn(unsigned int hooknum,
 234                 struct sk_buff **pskb,
 235                 const struct net_device *in,
 236                 const struct net_device *out,
 237                 int (*okfn)(struct sk_buff *))
 238 {
 239         struct nf_conn *ct;
 240         enum ip_conntrack_info ctinfo;
 241         unsigned int ret;
 242
 243         /* root is playing with raw sockets. */
 244         if ((*pskb)->len < sizeof(struct iphdr) ||
 245             (*pskb)->nh.iph->ihl * 4 < sizeof(struct iphdr))
 246                 return NF_ACCEPT;
 247
 248         ret = nf_nat_fn(hooknum, pskb, in, out, okfn);
 249         if (ret != NF_DROP && ret != NF_STOLEN &&
 250             (ct = nf_ct_get(*pskb, &ctinfo)) != NULL) {
 251                 enum ip_conntrack_dir dir = CTINFO2DIR(ctinfo);
 252
 253                 if (ct->tuplehash[dir].tuple.dst.u3.ip !=
 254                     ct->tuplehash[!dir].tuple.src.u3.ip
 255 #ifdef CONFIG_XFRM
 256                     || ct->tuplehash[dir].tuple.dst.u.all !=
 257                        ct->tuplehash[!dir].tuple.src.u.all
 258 #endif
 259                     )
 260                         if (ip_route_me_harder(pskb, RTN_UNSPEC))
 261                                 ret = NF_DROP;
 262         }
 263         return ret;
 264 }
 265
 266 static unsigned int
 267 nf_nat_adjust(unsigned int hooknum,
 268               struct sk_buff **pskb,
 269               const struct net_device *in,
 270               const struct net_device *out,
 271               int (*okfn)(struct sk_buff *))
 272 {
 273         struct nf_conn *ct;
 274         enum ip_conntrack_info ctinfo;
 275
 276         ct = nf_ct_get(*pskb, &ctinfo);
 277         if (ct && test_bit(IPS_SEQ_ADJUST_BIT, &ct->status)) {
 278                 DEBUGP("nf_nat_standalone: adjusting sequence number\n");
 279                 if (!nf_nat_seq_adjust(pskb, ct, ctinfo))
 280                         return NF_DROP;
 281         }
 282         return NF_ACCEPT;
 283 }
 284
 285 /* We must be after connection tracking and before packet filtering. */
 286
 287 static struct nf_hook_ops nf_nat_ops[] = {
 288         /* Before packet filtering, change destination */
 289         {
 290                 .hook           = nf_nat_in,
 291                 .owner          = THIS_MODULE,
 292                 .pf             = PF_INET,
 293                 .hooknum        = NF_IP_PRE_ROUTING,
 294                 .priority       = NF_IP_PRI_NAT_DST,
 295         },
 296         /* After packet filtering, change source */
 297         {
 298                 .hook           = nf_nat_out,
 299                 .owner          = THIS_MODULE,
 300                 .pf             = PF_INET,
 301                 .hooknum        = NF_IP_POST_ROUTING,
 302                 .priority       = NF_IP_PRI_NAT_SRC,
 303         },
 304         /* After conntrack, adjust sequence number */
 305         {
 306                 .hook           = nf_nat_adjust,
 307                 .owner          = THIS_MODULE,
 308                 .pf             = PF_INET,
 309                 .hooknum        = NF_IP_POST_ROUTING,
 310                 .priority       = NF_IP_PRI_NAT_SEQ_ADJUST,
 311         },
 312         /* Before packet filtering, change destination */
 313         {
 314                 .hook           = nf_nat_local_fn,
 315                 .owner          = THIS_MODULE,
 316                 .pf             = PF_INET,
 317                 .hooknum        = NF_IP_LOCAL_OUT,
 318                 .priority       = NF_IP_PRI_NAT_DST,
 319         },
 320         /* After packet filtering, change source */
 321         {
 322                 .hook           = nf_nat_fn,
 323                 .owner          = THIS_MODULE,
 324                 .pf             = PF_INET,
 325                 .hooknum        = NF_IP_LOCAL_IN,
 326                 .priority       = NF_IP_PRI_NAT_SRC,
 327         },
 328         /* After conntrack, adjust sequence number */
 329         {
 330                 .hook           = nf_nat_adjust,
 331                 .owner          = THIS_MODULE,
 332                 .pf             = PF_INET,
 333                 .hooknum        = NF_IP_LOCAL_IN,
 334                 .priority       = NF_IP_PRI_NAT_SEQ_ADJUST,
 335         },
 336 };
 337
 338 static int __init nf_nat_standalone_init(void)
 339 {
 340         int size, ret = 0;
 341
 342         need_conntrack();
 343
 344         size = ALIGN(sizeof(struct nf_conn), __alignof__(struct nf_conn_nat)) +
 345                sizeof(struct nf_conn_nat);
 346         ret = nf_conntrack_register_cache(NF_CT_F_NAT, "nf_nat:base", size);
 347         if (ret < 0) {
 348                 printk(KERN_ERR "nf_nat_init: Unable to create slab cache\n");
 349                 return ret;
 350         }
 351
 352         size = ALIGN(size, __alignof__(struct nf_conn_help)) +
 353                sizeof(struct nf_conn_help);
 354         ret = nf_conntrack_register_cache(NF_CT_F_NAT|NF_CT_F_HELP,
 355                                           "nf_nat:help", size);
 356         if (ret < 0) {
 357                 printk(KERN_ERR "nf_nat_init: Unable to create slab cache\n");
 358                 goto cleanup_register_cache;
 359         }
 360 #ifdef CONFIG_XFRM
 361         BUG_ON(ip_nat_decode_session != NULL);
 362         ip_nat_decode_session = nat_decode_session;
 363 #endif
 364         ret = nf_nat_rule_init();
 365         if (ret < 0) {
 366                 printk("nf_nat_init: can't setup rules.\n");
 367                 goto cleanup_decode_session;
 368         }
 369         ret = nf_register_hooks(nf_nat_ops, ARRAY_SIZE(nf_nat_ops));
 370         if (ret < 0) {
 371                 printk("nf_nat_init: can't register hooks.\n");
 372                 goto cleanup_rule_init;
 373         }
 374         nf_nat_module_is_loaded = 1;
 375         return ret;
 376
 377  cleanup_rule_init:
 378         nf_nat_rule_cleanup();
 379  cleanup_decode_session:
 380 #ifdef CONFIG_XFRM
 381         ip_nat_decode_session = NULL;
 382         synchronize_net();
 383 #endif
 384         nf_conntrack_unregister_cache(NF_CT_F_NAT|NF_CT_F_HELP);
 385  cleanup_register_cache:
 386         nf_conntrack_unregister_cache(NF_CT_F_NAT);
 387         return ret;
 388 }
 389
 390 static void __exit nf_nat_standalone_fini(void)
 391 {
 392         nf_unregister_hooks(nf_nat_ops, ARRAY_SIZE(nf_nat_ops));
 393         nf_nat_rule_cleanup();
 394         nf_nat_module_is_loaded = 0;
 395 #ifdef CONFIG_XFRM
 396         ip_nat_decode_session = NULL;
 397         synchronize_net();
 398 #endif
 399         /* Conntrack caches are unregistered in nf_conntrack_cleanup */
 400 }
 401
 402 module_init(nf_nat_standalone_init);
 403 module_exit(nf_nat_standalone_fini);
 404
 405 MODULE_LICENSE("GPL");
 406 MODULE_ALIAS("ip_nat");