net/ipv4/netfilter/ip_nat_helper_pptp.c

   1 /*
   2  * ip_nat_pptp.c        - Version 3.0
   3  *
   4  * NAT support for PPTP (Point to Point Tunneling Protocol).
   5  * PPTP is a a protocol for creating virtual private networks.
   6  * It is a specification defined by Microsoft and some vendors
   7  * working with Microsoft.  PPTP is built on top of a modified
   8  * version of the Internet Generic Routing Encapsulation Protocol.
   9  * GRE is defined in RFC 1701 and RFC 1702.  Documentation of
  10  * PPTP can be found in RFC 2637
  11  *
  12  * (C) 2000-2005 by Harald Welte <laforge@gnumonks.org>
  13  *
  14  * Development of this code funded by Astaro AG (http://www.astaro.com/)
  15  *
  16  * TODO: - NAT to a unique tuple, not to TCP source port
  17  *         (needs netfilter tuple reservation)
  18  *
  19  * Changes:
  20  *     2002-02-10 - Version 1.3
  21  *       - Use ip_nat_mangle_tcp_packet() because of cloned skb's
  22  *         in local connections (Philip Craig <philipc@snapgear.com>)
  23  *       - add checks for magicCookie and pptp version
  24  *       - make argument list of pptp_{out,in}bound_packet() shorter
  25  *       - move to C99 style initializers
  26  *       - print version number at module loadtime
  27  *     2003-09-22 - Version 1.5
  28  *       - use SNATed tcp sourceport as callid, since we get called before
  29  *         TCP header is mangled (Philip Craig <philipc@snapgear.com>)
  30  *     2004-10-22 - Version 2.0
  31  *       - kernel 2.6.x version
  32  *     2005-06-10 - Version 3.0
  33  *       - kernel >= 2.6.11 version,
  34  *         funded by Oxcoda NetBox Blue (http://www.netboxblue.com/)
  35  *
  36  */
  37
  38 #include <linux/config.h>
  39 #include <linux/module.h>
  40 #include <linux/ip.h>
  41 #include <linux/tcp.h>
  42 #include <net/tcp.h>
  43
  44 #include <linux/netfilter_ipv4/ip_nat.h>
  45 #include <linux/netfilter_ipv4/ip_nat_rule.h>
  46 #include <linux/netfilter_ipv4/ip_nat_helper.h>
  47 #include <linux/netfilter_ipv4/ip_nat_pptp.h>
  48 #include <linux/netfilter_ipv4/ip_conntrack_core.h>
  49 #include <linux/netfilter_ipv4/ip_conntrack_helper.h>
  50 #include <linux/netfilter_ipv4/ip_conntrack_proto_gre.h>
  51 #include <linux/netfilter_ipv4/ip_conntrack_pptp.h>
  52
  53 #define IP_NAT_PPTP_VERSION "3.0"
  54
  55 MODULE_LICENSE("GPL");
  56 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  57 MODULE_DESCRIPTION("Netfilter NAT helper module for PPTP");
  58
  59
  60 #if 0
  61 extern const char *pptp_msg_name[];
  62 #define DEBUGP(format, args...) printk(KERN_DEBUG "%s:%s: " format, __FILE__, \
  63                                        __FUNCTION__, ## args)
  64 #else
  65 #define DEBUGP(format, args...)
  66 #endif
  67
  68 static void pptp_nat_expected(struct ip_conntrack *ct,
  69                               struct ip_conntrack_expect *exp)
  70 {
  71         struct ip_conntrack *master = ct->master;
  72         struct ip_conntrack_expect *other_exp;
  73         struct ip_conntrack_tuple t;
  74         struct ip_ct_pptp_master *ct_pptp_info;
  75         struct ip_nat_pptp *nat_pptp_info;
  76         struct ip_nat_range range;
  77
  78         ct_pptp_info = &master->help.ct_pptp_info;
  79         nat_pptp_info = &master->nat.help.nat_pptp_info;
  80
  81         /* And here goes the grand finale of corrosion... */
  82
  83         if (exp->dir == IP_CT_DIR_ORIGINAL) {
  84                 DEBUGP("we are PNS->PAC\n");
  85                 /* therefore, build tuple for PAC->PNS */
  86                 t.src.ip = master->tuplehash[IP_CT_DIR_REPLY].tuple.src.ip;
  87                 t.src.u.gre.key = htons(master->help.ct_pptp_info.pac_call_id);
  88                 t.dst.ip = master->tuplehash[IP_CT_DIR_REPLY].tuple.dst.ip;
  89                 t.dst.u.gre.key = htons(master->help.ct_pptp_info.pns_call_id);
  90                 t.dst.protonum = IPPROTO_GRE;
  91         } else {
  92                 DEBUGP("we are PAC->PNS\n");
  93                 /* build tuple for PNS->PAC */
  94                 t.src.ip = master->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.ip;
  95                 t.src.u.gre.key =
  96                         htons(master->nat.help.nat_pptp_info.pns_call_id);
  97                 t.dst.ip = master->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.ip;
  98                 t.dst.u.gre.key =
  99                         htons(master->nat.help.nat_pptp_info.pac_call_id);
 100                 t.dst.protonum = IPPROTO_GRE;
 101         }
 102
 103         DEBUGP("trying to unexpect other dir: ");
 104         DUMP_TUPLE(&t);
 105         other_exp = ip_conntrack_expect_find(&t);
 106         if (other_exp) {
 107                 ip_conntrack_unexpect_related(other_exp);
 108                 ip_conntrack_expect_put(other_exp);
 109                 DEBUGP("success\n");
 110         } else {
 111                 DEBUGP("not found!\n");
 112         }
 113
 114         /* This must be a fresh one. */
 115         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
 116
 117         /* Change src to where master sends to */
 118         range.flags = IP_NAT_RANGE_MAP_IPS;
 119         range.min_ip = range.max_ip
 120                 = ct->master->tuplehash[!exp->dir].tuple.dst.ip;
 121         if (exp->dir == IP_CT_DIR_ORIGINAL) {
 122                 range.flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
 123                 range.min = range.max = exp->saved_proto;
 124         }
 125         /* hook doesn't matter, but it has to do source manip */
 126         ip_nat_setup_info(ct, &range, NF_IP_POST_ROUTING);
 127
 128         /* For DST manip, map port here to where it's expected. */
 129         range.flags = IP_NAT_RANGE_MAP_IPS;
 130         range.min_ip = range.max_ip
 131                 = ct->master->tuplehash[!exp->dir].tuple.src.ip;
 132         if (exp->dir == IP_CT_DIR_REPLY) {
 133                 range.flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
 134                 range.min = range.max = exp->saved_proto;
 135         }
 136         /* hook doesn't matter, but it has to do destination manip */
 137         ip_nat_setup_info(ct, &range, NF_IP_PRE_ROUTING);
 138 }
 139
 140 /* outbound packets == from PNS to PAC */
 141 static int
 142 pptp_outbound_pkt(struct sk_buff **pskb,
 143                   struct ip_conntrack *ct,
 144                   enum ip_conntrack_info ctinfo,
 145                   struct PptpControlHeader *ctlh,
 146                   union pptp_ctrl_union *pptpReq)
 147
 148 {
 149         struct ip_ct_pptp_master *ct_pptp_info = &ct->help.ct_pptp_info;
 150         struct ip_nat_pptp *nat_pptp_info = &ct->nat.help.nat_pptp_info;
 151         u_int16_t msg, new_callid;
 152         unsigned int cid_off;
 153
 154         new_callid = htons(ct_pptp_info->pns_call_id);
 155
 156         switch (msg = ntohs(ctlh->messageType)) {
 157                 case PPTP_OUT_CALL_REQUEST:
 158                         cid_off = offsetof(union pptp_ctrl_union, ocreq.callID);
 159                         /* FIXME: ideally we would want to reserve a call ID
 160                          * here.  current netfilter NAT core is not able to do
 161                          * this :( For now we use TCP source port. This breaks
 162                          * multiple calls within one control session */
 163
 164                         /* save original call ID in nat_info */
 165                         nat_pptp_info->pns_call_id = ct_pptp_info->pns_call_id;
 166
 167                         /* don't use tcph->source since we are at a DSTmanip
 168                          * hook (e.g. PREROUTING) and pkt is not mangled yet */
 169                         new_callid = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u.tcp.port;
 170
 171                         /* save new call ID in ct info */
 172                         ct_pptp_info->pns_call_id = ntohs(new_callid);
 173                         break;
 174                 case PPTP_IN_CALL_REPLY:
 175                         cid_off = offsetof(union pptp_ctrl_union, icreq.callID);
 176                         break;
 177                 case PPTP_CALL_CLEAR_REQUEST:
 178                         cid_off = offsetof(union pptp_ctrl_union, clrreq.callID);
 179                         break;
 180                 default:
 181                         DEBUGP("unknown outbound packet 0x%04x:%s\n", msg,
 182                               (msg <= PPTP_MSG_MAX)?
 183                               pptp_msg_name[msg]:pptp_msg_name[0]);
 184                         /* fall through */
 185
 186                 case PPTP_SET_LINK_INFO:
 187                         /* only need to NAT in case PAC is behind NAT box */
 188                 case PPTP_START_SESSION_REQUEST:
 189                 case PPTP_START_SESSION_REPLY:
 190                 case PPTP_STOP_SESSION_REQUEST:
 191                 case PPTP_STOP_SESSION_REPLY:
 192                 case PPTP_ECHO_REQUEST:
 193                 case PPTP_ECHO_REPLY:
 194                         /* no need to alter packet */
 195                         return NF_ACCEPT;
 196         }
 197
 198         /* only OUT_CALL_REQUEST, IN_CALL_REPLY, CALL_CLEAR_REQUEST pass
 199          * down to here */
 200         DEBUGP("altering call id from 0x%04x to 0x%04x\n",
 201                 ntohs(*(u_int16_t *)pptpReq + cid_off), ntohs(new_callid));
 202
 203         /* mangle packet */
 204         if (ip_nat_mangle_tcp_packet(pskb, ct, ctinfo,
 205                                      cid_off + sizeof(struct pptp_pkt_hdr) +
 206                                      sizeof(struct PptpControlHeader),
 207                                      sizeof(new_callid), (char *)&new_callid,
 208                                      sizeof(new_callid)) == 0)
 209                 return NF_DROP;
 210
 211         return NF_ACCEPT;
 212 }
 213
 214 static int
 215 pptp_exp_gre(struct ip_conntrack_expect *expect_orig,
 216              struct ip_conntrack_expect *expect_reply)
 217 {
 218         struct ip_ct_pptp_master *ct_pptp_info =
 219                                 &expect_orig->master->help.ct_pptp_info;
 220         struct ip_nat_pptp *nat_pptp_info =
 221                                 &expect_orig->master->nat.help.nat_pptp_info;
 222
 223         struct ip_conntrack *ct = expect_orig->master;
 224
 225         struct ip_conntrack_tuple inv_t;
 226         struct ip_conntrack_tuple *orig_t, *reply_t;
 227
 228         /* save original PAC call ID in nat_info */
 229         nat_pptp_info->pac_call_id = ct_pptp_info->pac_call_id;
 230
 231         /* alter expectation */
 232         orig_t = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
 233         reply_t = &ct->tuplehash[IP_CT_DIR_REPLY].tuple;
 234
 235         /* alter expectation for PNS->PAC direction */
 236         invert_tuplepr(&inv_t, &expect_orig->tuple);
 237         expect_orig->saved_proto.gre.key = htons(ct_pptp_info->pns_call_id);
 238         expect_orig->tuple.src.u.gre.key = htons(nat_pptp_info->pns_call_id);
 239         expect_orig->tuple.dst.u.gre.key = htons(ct_pptp_info->pac_call_id);
 240         expect_orig->dir = IP_CT_DIR_ORIGINAL;
 241         inv_t.src.ip = reply_t->src.ip;
 242         inv_t.dst.ip = reply_t->dst.ip;
 243         inv_t.src.u.gre.key = htons(nat_pptp_info->pac_call_id);
 244         inv_t.dst.u.gre.key = htons(ct_pptp_info->pns_call_id);
 245
 246         if (!ip_conntrack_expect_related(expect_orig)) {
 247                 DEBUGP("successfully registered expect\n");
 248         } else {
 249                 DEBUGP("can't expect_related(expect_orig)\n");
 250                 return 1;
 251         }
 252
 253         /* alter expectation for PAC->PNS direction */
 254         invert_tuplepr(&inv_t, &expect_reply->tuple);
 255         expect_reply->saved_proto.gre.key = htons(nat_pptp_info->pns_call_id);
 256         expect_reply->tuple.src.u.gre.key = htons(nat_pptp_info->pac_call_id);
 257         expect_reply->tuple.dst.u.gre.key = htons(ct_pptp_info->pns_call_id);
 258         expect_reply->dir = IP_CT_DIR_REPLY;
 259         inv_t.src.ip = orig_t->src.ip;
 260         inv_t.dst.ip = orig_t->dst.ip;
 261         inv_t.src.u.gre.key = htons(nat_pptp_info->pns_call_id);
 262         inv_t.dst.u.gre.key = htons(ct_pptp_info->pac_call_id);
 263
 264         if (!ip_conntrack_expect_related(expect_reply)) {
 265                 DEBUGP("successfully registered expect\n");
 266         } else {
 267                 DEBUGP("can't expect_related(expect_reply)\n");
 268                 ip_conntrack_unexpect_related(expect_orig);
 269                 return 1;
 270         }
 271
 272         if (ip_ct_gre_keymap_add(ct, &expect_reply->tuple, 0) < 0) {
 273                 DEBUGP("can't register original keymap\n");
 274                 ip_conntrack_unexpect_related(expect_orig);
 275                 ip_conntrack_unexpect_related(expect_reply);
 276                 return 1;
 277         }
 278
 279         if (ip_ct_gre_keymap_add(ct, &inv_t, 1) < 0) {
 280                 DEBUGP("can't register reply keymap\n");
 281                 ip_conntrack_unexpect_related(expect_orig);
 282                 ip_conntrack_unexpect_related(expect_reply);
 283                 ip_ct_gre_keymap_destroy(ct);
 284                 return 1;
 285         }
 286
 287         return 0;
 288 }
 289
 290 /* inbound packets == from PAC to PNS */
 291 static int
 292 pptp_inbound_pkt(struct sk_buff **pskb,
 293                  struct ip_conntrack *ct,
 294                  enum ip_conntrack_info ctinfo,
 295                  struct PptpControlHeader *ctlh,
 296                  union pptp_ctrl_union *pptpReq)
 297 {
 298         struct ip_nat_pptp *nat_pptp_info = &ct->nat.help.nat_pptp_info;
 299         u_int16_t msg, new_cid = 0, new_pcid;
 300         unsigned int pcid_off, cid_off = 0;
 301
 302         new_pcid = htons(nat_pptp_info->pns_call_id);
 303
 304         switch (msg = ntohs(ctlh->messageType)) {
 305         case PPTP_OUT_CALL_REPLY:
 306                 pcid_off = offsetof(union pptp_ctrl_union, ocack.peersCallID);
 307                 cid_off = offsetof(union pptp_ctrl_union, ocack.callID);
 308                 break;
 309         case PPTP_IN_CALL_CONNECT:
 310                 pcid_off = offsetof(union pptp_ctrl_union, iccon.peersCallID);
 311                 break;
 312         case PPTP_IN_CALL_REQUEST:
 313                 /* only need to nat in case PAC is behind NAT box */
 314                 return NF_ACCEPT;
 315         case PPTP_WAN_ERROR_NOTIFY:
 316                 pcid_off = offsetof(union pptp_ctrl_union, wanerr.peersCallID);
 317                 break;
 318         case PPTP_CALL_DISCONNECT_NOTIFY:
 319                 pcid_off = offsetof(union pptp_ctrl_union, disc.callID);
 320                 break;
 321         case PPTP_SET_LINK_INFO:
 322                 pcid_off = offsetof(union pptp_ctrl_union, setlink.peersCallID);
 323                 break;
 324
 325         default:
 326                 DEBUGP("unknown inbound packet %s\n", (msg <= PPTP_MSG_MAX)?
 327                         pptp_msg_name[msg]:pptp_msg_name[0]);
 328                 /* fall through */
 329
 330         case PPTP_START_SESSION_REQUEST:
 331         case PPTP_START_SESSION_REPLY:
 332         case PPTP_STOP_SESSION_REQUEST:
 333         case PPTP_STOP_SESSION_REPLY:
 334         case PPTP_ECHO_REQUEST:
 335         case PPTP_ECHO_REPLY:
 336                 /* no need to alter packet */
 337                 return NF_ACCEPT;
 338         }
 339
 340         /* only OUT_CALL_REPLY, IN_CALL_CONNECT, IN_CALL_REQUEST,
 341          * WAN_ERROR_NOTIFY, CALL_DISCONNECT_NOTIFY pass down here */
 342
 343         /* mangle packet */
 344         DEBUGP("altering peer call id from 0x%04x to 0x%04x\n",
 345                 ntohs(*(u_int16_t *)pptpReq + pcid_off), ntohs(new_pcid));
 346
 347         if (ip_nat_mangle_tcp_packet(pskb, ct, ctinfo,
 348                                      pcid_off + sizeof(struct pptp_pkt_hdr) +
 349                                      sizeof(struct PptpControlHeader),
 350                                      sizeof(new_pcid), (char *)&new_pcid,
 351                                      sizeof(new_pcid)) == 0)
 352                 return NF_DROP;
 353
 354         if (new_cid) {
 355                 DEBUGP("altering call id from 0x%04x to 0x%04x\n",
 356                         ntohs(*(u_int16_t *)pptpReq + cid_off), ntohs(new_cid));
 357                 if (ip_nat_mangle_tcp_packet(pskb, ct, ctinfo,
 358                                              cid_off + sizeof(struct pptp_pkt_hdr) +
 359                                              sizeof(struct PptpControlHeader),
 360                                              sizeof(new_cid), (char *)&new_cid,
 361                                              sizeof(new_cid)) == 0)
 362                         return NF_DROP;
 363         }
 364         return NF_ACCEPT;
 365 }
 366
 367
 368 extern int __init ip_nat_proto_gre_init(void);
 369 extern void __exit ip_nat_proto_gre_fini(void);
 370
 371 static int __init init(void)
 372 {
 373         int ret;
 374
 375         DEBUGP("%s: registering NAT helper\n", __FILE__);
 376
 377         ret = ip_nat_proto_gre_init();
 378         if (ret < 0)
 379                 return ret;
 380
 381         BUG_ON(ip_nat_pptp_hook_outbound);
 382         ip_nat_pptp_hook_outbound = &pptp_outbound_pkt;
 383
 384         BUG_ON(ip_nat_pptp_hook_inbound);
 385         ip_nat_pptp_hook_inbound = &pptp_inbound_pkt;
 386
 387         BUG_ON(ip_nat_pptp_hook_exp_gre);
 388         ip_nat_pptp_hook_exp_gre = &pptp_exp_gre;
 389
 390         BUG_ON(ip_nat_pptp_hook_expectfn);
 391         ip_nat_pptp_hook_expectfn = &pptp_nat_expected;
 392
 393         printk("ip_nat_pptp version %s loaded\n", IP_NAT_PPTP_VERSION);
 394         return 0;
 395 }
 396
 397 static void __exit fini(void)
 398 {
 399         DEBUGP("cleanup_module\n" );
 400
 401         ip_nat_pptp_hook_expectfn = NULL;
 402         ip_nat_pptp_hook_exp_gre = NULL;
 403         ip_nat_pptp_hook_inbound = NULL;
 404         ip_nat_pptp_hook_outbound = NULL;
 405
 406         ip_nat_proto_gre_fini();
 407         /* Make sure noone calls it, meanwhile */
 408         synchronize_net();
 409
 410         printk("ip_nat_pptp version %s unloaded\n", IP_NAT_PPTP_VERSION);
 411 }
 412
 413 module_init(init);
 414 module_exit(fini);