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