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 #define REQ_CID(req, off)               (*(u_int16_t *)((char *)(req) + (off)))
  56
  57 MODULE_LICENSE("GPL");
  58 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  59 MODULE_DESCRIPTION("Netfilter NAT helper module for PPTP");
  60
  61
  62 #if 0
  63 extern const char *pptp_msg_name[];
  64 #define DEBUGP(format, args...) printk(KERN_DEBUG "%s:%s: " format, __FILE__, \
  65                                        __FUNCTION__, ## args)
  66 #else
  67 #define DEBUGP(format, args...)
  68 #endif
  69
  70 static void pptp_nat_expected(struct ip_conntrack *ct,
  71                               struct ip_conntrack_expect *exp)
  72 {
  73         struct ip_conntrack *master = ct->master;
  74         struct ip_conntrack_expect *other_exp;
  75         struct ip_conntrack_tuple t;
  76         struct ip_ct_pptp_master *ct_pptp_info;
  77         struct ip_nat_pptp *nat_pptp_info;
  78         struct ip_nat_range range;
  79
  80         ct_pptp_info = &master->help.ct_pptp_info;
  81         nat_pptp_info = &master->nat.help.nat_pptp_info;
  82
  83         /* And here goes the grand finale of corrosion... */
  84
  85         if (exp->dir == IP_CT_DIR_ORIGINAL) {
  86                 DEBUGP("we are PNS->PAC\n");
  87                 /* therefore, build tuple for PAC->PNS */
  88                 t.src.ip = master->tuplehash[IP_CT_DIR_REPLY].tuple.src.ip;
  89                 t.src.u.gre.key = htons(master->help.ct_pptp_info.pac_call_id);
  90                 t.dst.ip = master->tuplehash[IP_CT_DIR_REPLY].tuple.dst.ip;
  91                 t.dst.u.gre.key = htons(master->help.ct_pptp_info.pns_call_id);
  92                 t.dst.protonum = IPPROTO_GRE;
  93         } else {
  94                 DEBUGP("we are PAC->PNS\n");
  95                 /* build tuple for PNS->PAC */
  96                 t.src.ip = master->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.ip;
  97                 t.src.u.gre.key =
  98                         htons(master->nat.help.nat_pptp_info.pns_call_id);
  99                 t.dst.ip = master->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.ip;
 100                 t.dst.u.gre.key =
 101                         htons(master->nat.help.nat_pptp_info.pac_call_id);
 102                 t.dst.protonum = IPPROTO_GRE;
 103         }
 104
 105         DEBUGP("trying to unexpect other dir: ");
 106         DUMP_TUPLE(&t);
 107         other_exp = ip_conntrack_expect_find(&t);
 108         if (other_exp) {
 109                 ip_conntrack_unexpect_related(other_exp);
 110                 ip_conntrack_expect_put(other_exp);
 111                 DEBUGP("success\n");
 112         } else {
 113                 DEBUGP("not found!\n");
 114         }
 115
 116         /* This must be a fresh one. */
 117         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
 118
 119         /* Change src to where master sends to */
 120         range.flags = IP_NAT_RANGE_MAP_IPS;
 121         range.min_ip = range.max_ip
 122                 = ct->master->tuplehash[!exp->dir].tuple.dst.ip;
 123         if (exp->dir == IP_CT_DIR_ORIGINAL) {
 124                 range.flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
 125                 range.min = range.max = exp->saved_proto;
 126         }
 127         /* hook doesn't matter, but it has to do source manip */
 128         ip_nat_setup_info(ct, &range, NF_IP_POST_ROUTING);
 129
 130         /* For DST manip, map port here to where it's expected. */
 131         range.flags = IP_NAT_RANGE_MAP_IPS;
 132         range.min_ip = range.max_ip
 133                 = ct->master->tuplehash[!exp->dir].tuple.src.ip;
 134         if (exp->dir == IP_CT_DIR_REPLY) {
 135                 range.flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
 136                 range.min = range.max = exp->saved_proto;
 137         }
 138         /* hook doesn't matter, but it has to do destination manip */
 139         ip_nat_setup_info(ct, &range, NF_IP_PRE_ROUTING);
 140 }
 141
 142 /* outbound packets == from PNS to PAC */
 143 static int
 144 pptp_outbound_pkt(struct sk_buff **pskb,
 145                   struct ip_conntrack *ct,
 146                   enum ip_conntrack_info ctinfo,
 147                   struct PptpControlHeader *ctlh,
 148                   union pptp_ctrl_union *pptpReq)
 149
 150 {
 151         struct ip_ct_pptp_master *ct_pptp_info = &ct->help.ct_pptp_info;
 152         struct ip_nat_pptp *nat_pptp_info = &ct->nat.help.nat_pptp_info;
 153         u_int16_t msg, new_callid;
 154         unsigned int cid_off;
 155
 156         new_callid = htons(ct_pptp_info->pns_call_id);
 157
 158         switch (msg = ntohs(ctlh->messageType)) {
 159                 case PPTP_OUT_CALL_REQUEST:
 160                         cid_off = offsetof(union pptp_ctrl_union, ocreq.callID);
 161                         /* FIXME: ideally we would want to reserve a call ID
 162                          * here.  current netfilter NAT core is not able to do
 163                          * this :( For now we use TCP source port. This breaks
 164                          * multiple calls within one control session */
 165
 166                         /* save original call ID in nat_info */
 167                         nat_pptp_info->pns_call_id = ct_pptp_info->pns_call_id;
 168
 169                         /* don't use tcph->source since we are at a DSTmanip
 170                          * hook (e.g. PREROUTING) and pkt is not mangled yet */
 171                         new_callid = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u.tcp.port;
 172
 173                         /* save new call ID in ct info */
 174                         ct_pptp_info->pns_call_id = ntohs(new_callid);
 175                         break;
 176                 case PPTP_IN_CALL_REPLY:
 177                         cid_off = offsetof(union pptp_ctrl_union, icreq.callID);
 178                         break;
 179                 case PPTP_CALL_CLEAR_REQUEST:
 180                         cid_off = offsetof(union pptp_ctrl_union, clrreq.callID);
 181                         break;
 182                 default:
 183                         DEBUGP("unknown outbound packet 0x%04x:%s\n", msg,
 184                               (msg <= PPTP_MSG_MAX)?
 185                               pptp_msg_name[msg]:pptp_msg_name[0]);
 186                         /* fall through */
 187
 188                 case PPTP_SET_LINK_INFO:
 189                         /* only need to NAT in case PAC is behind NAT box */
 190                 case PPTP_START_SESSION_REQUEST:
 191                 case PPTP_START_SESSION_REPLY:
 192                 case PPTP_STOP_SESSION_REQUEST:
 193                 case PPTP_STOP_SESSION_REPLY:
 194                 case PPTP_ECHO_REQUEST:
 195                 case PPTP_ECHO_REPLY:
 196                         /* no need to alter packet */
 197                         return NF_ACCEPT;
 198         }
 199
 200         /* only OUT_CALL_REQUEST, IN_CALL_REPLY, CALL_CLEAR_REQUEST pass
 201          * down to here */
 202         DEBUGP("altering call id from 0x%04x to 0x%04x\n",
 203                 ntohs(REQ_CID(pptpReq, cid_off)), ntohs(new_callid));
 204
 205         /* mangle packet */
 206         if (ip_nat_mangle_tcp_packet(pskb, ct, ctinfo,
 207                                      cid_off + sizeof(struct pptp_pkt_hdr) +
 208                                      sizeof(struct PptpControlHeader),
 209                                      sizeof(new_callid), (char *)&new_callid,
 210                                      sizeof(new_callid)) == 0)
 211                 return NF_DROP;
 212
 213         return NF_ACCEPT;
 214 }
 215
 216 static int
 217 pptp_exp_gre(struct ip_conntrack_expect *expect_orig,
 218              struct ip_conntrack_expect *expect_reply)
 219 {
 220         struct ip_ct_pptp_master *ct_pptp_info =
 221                                 &expect_orig->master->help.ct_pptp_info;
 222         struct ip_nat_pptp *nat_pptp_info =
 223                                 &expect_orig->master->nat.help.nat_pptp_info;
 224
 225         struct ip_conntrack *ct = expect_orig->master;
 226
 227         struct ip_conntrack_tuple inv_t;
 228         struct ip_conntrack_tuple *orig_t, *reply_t;
 229
 230         /* save original PAC call ID in nat_info */
 231         nat_pptp_info->pac_call_id = ct_pptp_info->pac_call_id;
 232
 233         /* alter expectation */
 234         orig_t = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
 235         reply_t = &ct->tuplehash[IP_CT_DIR_REPLY].tuple;
 236
 237         /* alter expectation for PNS->PAC direction */
 238         invert_tuplepr(&inv_t, &expect_orig->tuple);
 239         expect_orig->saved_proto.gre.key = htons(ct_pptp_info->pns_call_id);
 240         expect_orig->tuple.src.u.gre.key = htons(nat_pptp_info->pns_call_id);
 241         expect_orig->tuple.dst.u.gre.key = htons(ct_pptp_info->pac_call_id);
 242         expect_orig->dir = IP_CT_DIR_ORIGINAL;
 243         inv_t.src.ip = reply_t->src.ip;
 244         inv_t.dst.ip = reply_t->dst.ip;
 245         inv_t.src.u.gre.key = htons(nat_pptp_info->pac_call_id);
 246         inv_t.dst.u.gre.key = htons(ct_pptp_info->pns_call_id);
 247
 248         if (!ip_conntrack_expect_related(expect_orig)) {
 249                 DEBUGP("successfully registered expect\n");
 250         } else {
 251                 DEBUGP("can't expect_related(expect_orig)\n");
 252                 return 1;
 253         }
 254
 255         /* alter expectation for PAC->PNS direction */
 256         invert_tuplepr(&inv_t, &expect_reply->tuple);
 257         expect_reply->saved_proto.gre.key = htons(nat_pptp_info->pns_call_id);
 258         expect_reply->tuple.src.u.gre.key = htons(nat_pptp_info->pac_call_id);
 259         expect_reply->tuple.dst.u.gre.key = htons(ct_pptp_info->pns_call_id);
 260         expect_reply->dir = IP_CT_DIR_REPLY;
 261         inv_t.src.ip = orig_t->src.ip;
 262         inv_t.dst.ip = orig_t->dst.ip;
 263         inv_t.src.u.gre.key = htons(nat_pptp_info->pns_call_id);
 264         inv_t.dst.u.gre.key = htons(ct_pptp_info->pac_call_id);
 265
 266         if (!ip_conntrack_expect_related(expect_reply)) {
 267                 DEBUGP("successfully registered expect\n");
 268         } else {
 269                 DEBUGP("can't expect_related(expect_reply)\n");
 270                 ip_conntrack_unexpect_related(expect_orig);
 271                 return 1;
 272         }
 273
 274         if (ip_ct_gre_keymap_add(ct, &expect_reply->tuple, 0) < 0) {
 275                 DEBUGP("can't register original keymap\n");
 276                 ip_conntrack_unexpect_related(expect_orig);
 277                 ip_conntrack_unexpect_related(expect_reply);
 278                 return 1;
 279         }
 280
 281         if (ip_ct_gre_keymap_add(ct, &inv_t, 1) < 0) {
 282                 DEBUGP("can't register reply keymap\n");
 283                 ip_conntrack_unexpect_related(expect_orig);
 284                 ip_conntrack_unexpect_related(expect_reply);
 285                 ip_ct_gre_keymap_destroy(ct);
 286                 return 1;
 287         }
 288
 289         return 0;
 290 }
 291
 292 /* inbound packets == from PAC to PNS */
 293 static int
 294 pptp_inbound_pkt(struct sk_buff **pskb,
 295                  struct ip_conntrack *ct,
 296                  enum ip_conntrack_info ctinfo,
 297                  struct PptpControlHeader *ctlh,
 298                  union pptp_ctrl_union *pptpReq)
 299 {
 300         struct ip_nat_pptp *nat_pptp_info = &ct->nat.help.nat_pptp_info;
 301         u_int16_t msg, new_cid = 0, new_pcid;
 302         unsigned int pcid_off, cid_off = 0;
 303
 304         new_pcid = htons(nat_pptp_info->pns_call_id);
 305
 306         switch (msg = ntohs(ctlh->messageType)) {
 307         case PPTP_OUT_CALL_REPLY:
 308                 pcid_off = offsetof(union pptp_ctrl_union, ocack.peersCallID);
 309                 cid_off = offsetof(union pptp_ctrl_union, ocack.callID);
 310                 break;
 311         case PPTP_IN_CALL_CONNECT:
 312                 pcid_off = offsetof(union pptp_ctrl_union, iccon.peersCallID);
 313                 break;
 314         case PPTP_IN_CALL_REQUEST:
 315                 /* only need to nat in case PAC is behind NAT box */
 316                 return NF_ACCEPT;
 317         case PPTP_WAN_ERROR_NOTIFY:
 318                 pcid_off = offsetof(union pptp_ctrl_union, wanerr.peersCallID);
 319                 break;
 320         case PPTP_CALL_DISCONNECT_NOTIFY:
 321                 pcid_off = offsetof(union pptp_ctrl_union, disc.callID);
 322                 break;
 323         case PPTP_SET_LINK_INFO:
 324                 pcid_off = offsetof(union pptp_ctrl_union, setlink.peersCallID);
 325                 break;
 326
 327         default:
 328                 DEBUGP("unknown inbound packet %s\n", (msg <= PPTP_MSG_MAX)?
 329                         pptp_msg_name[msg]:pptp_msg_name[0]);
 330                 /* fall through */
 331
 332         case PPTP_START_SESSION_REQUEST:
 333         case PPTP_START_SESSION_REPLY:
 334         case PPTP_STOP_SESSION_REQUEST:
 335         case PPTP_STOP_SESSION_REPLY:
 336         case PPTP_ECHO_REQUEST:
 337         case PPTP_ECHO_REPLY:
 338                 /* no need to alter packet */
 339                 return NF_ACCEPT;
 340         }
 341
 342         /* only OUT_CALL_REPLY, IN_CALL_CONNECT, IN_CALL_REQUEST,
 343          * WAN_ERROR_NOTIFY, CALL_DISCONNECT_NOTIFY pass down here */
 344
 345         /* mangle packet */
 346         DEBUGP("altering peer call id from 0x%04x to 0x%04x\n",
 347                 ntohs(REQ_CID(pptpReq, pcid_off)), ntohs(new_pcid));
 348
 349         if (ip_nat_mangle_tcp_packet(pskb, ct, ctinfo,
 350                                      pcid_off + sizeof(struct pptp_pkt_hdr) +
 351                                      sizeof(struct PptpControlHeader),
 352                                      sizeof(new_pcid), (char *)&new_pcid,
 353                                      sizeof(new_pcid)) == 0)
 354                 return NF_DROP;
 355
 356         if (new_cid) {
 357                 DEBUGP("altering call id from 0x%04x to 0x%04x\n",
 358                         ntohs(REQ_CID(pptpReq, cid_off)), ntohs(new_cid));
 359                 if (ip_nat_mangle_tcp_packet(pskb, ct, ctinfo,
 360                                              cid_off + sizeof(struct pptp_pkt_hdr) +
 361                                              sizeof(struct PptpControlHeader),
 362                                              sizeof(new_cid), (char *)&new_cid,
 363                                              sizeof(new_cid)) == 0)
 364                         return NF_DROP;
 365         }
 366         return NF_ACCEPT;
 367 }
 368
 369
 370 extern int __init ip_nat_proto_gre_init(void);
 371 extern void __exit ip_nat_proto_gre_fini(void);
 372
 373 static int __init ip_nat_helper_pptp_init(void)
 374 {
 375         int ret;
 376
 377         DEBUGP("%s: registering NAT helper\n", __FILE__);
 378
 379         ret = ip_nat_proto_gre_init();
 380         if (ret < 0)
 381                 return ret;
 382
 383         BUG_ON(ip_nat_pptp_hook_outbound);
 384         ip_nat_pptp_hook_outbound = &pptp_outbound_pkt;
 385
 386         BUG_ON(ip_nat_pptp_hook_inbound);
 387         ip_nat_pptp_hook_inbound = &pptp_inbound_pkt;
 388
 389         BUG_ON(ip_nat_pptp_hook_exp_gre);
 390         ip_nat_pptp_hook_exp_gre = &pptp_exp_gre;
 391
 392         BUG_ON(ip_nat_pptp_hook_expectfn);
 393         ip_nat_pptp_hook_expectfn = &pptp_nat_expected;
 394
 395         printk("ip_nat_pptp version %s loaded\n", IP_NAT_PPTP_VERSION);
 396         return 0;
 397 }
 398
 399 static void __exit ip_nat_helper_pptp_fini(void)
 400 {
 401         DEBUGP("cleanup_module\n" );
 402
 403         ip_nat_pptp_hook_expectfn = NULL;
 404         ip_nat_pptp_hook_exp_gre = NULL;
 405         ip_nat_pptp_hook_inbound = NULL;
 406         ip_nat_pptp_hook_outbound = NULL;
 407
 408         ip_nat_proto_gre_fini();
 409         /* Make sure noone calls it, meanwhile */
 410         synchronize_net();
 411
 412         printk("ip_nat_pptp version %s unloaded\n", IP_NAT_PPTP_VERSION);
 413 }
 414
 415 module_init(ip_nat_helper_pptp_init);
 416 module_exit(ip_nat_helper_pptp_fini);