net/ipv4/netfilter/ip_nat_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 1
  61 #include "ip_conntrack_pptp_priv.h"
  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
  77         ct_pptp_info = &master->help.ct_pptp_info;
  78         nat_pptp_info = &master->nat.help.nat_pptp_info;
  79
  80         /* And here goes the grand finale of corrosion... */
  81
  82         if (exp->dir == IP_CT_DIR_ORIGINAL) {
  83                 DEBUGP("we are PNS->PAC\n");
  84                 /* therefore, build tuple for PAC->PNS */
  85                 t.src.ip = master->tuplehash[IP_CT_DIR_REPLY].tuple.src.ip;
  86                 t.src.u.gre.key = htons(master->help.ct_pptp_info.pac_call_id);
  87                 t.dst.ip = master->tuplehash[IP_CT_DIR_REPLY].tuple.dst.ip;
  88                 t.dst.u.gre.key = htons(master->help.ct_pptp_info.pns_call_id);
  89                 t.dst.protonum = IPPROTO_GRE;
  90         } else {
  91                 DEBUGP("we are PAC->PNS\n");
  92                 /* build tuple for PNS->PAC */
  93                 t.src.ip = master->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.ip;
  94                 t.src.u.gre.key =
  95                         htons(master->nat.help.nat_pptp_info.pns_call_id);
  96                 t.dst.ip = master->tuplehash[IP_CT_DIR_ORIGINAL].tuple.dst.ip;
  97                 t.dst.u.gre.key =
  98                         htons(master->nat.help.nat_pptp_info.pac_call_id);
  99                 t.dst.protonum = IPPROTO_GRE;
 100         }
 101
 102         DEBUGP("trying to unexpect other dir: ");
 103         DUMP_TUPLE(&t);
 104         other_exp = __ip_conntrack_exp_find(&t);
 105         if (other_exp) {
 106                 ip_conntrack_unexpect_related(other_exp);
 107                 DEBUGP("success\n");
 108         } else {
 109                 DEBUGP("not found!\n");
 110         }
 111
 112         ip_nat_follow_master(ct, exp);
 113 }
 114
 115 /* outbound packets == from PNS to PAC */
 116 static int
 117 pptp_outbound_pkt(struct sk_buff **pskb,
 118                   struct ip_conntrack *ct,
 119                   enum ip_conntrack_info ctinfo,
 120                   struct PptpControlHeader *ctlh,
 121                   union pptp_ctrl_union *pptpReq)
 122
 123 {
 124         struct ip_ct_pptp_master *ct_pptp_info = &ct->help.ct_pptp_info;
 125         struct ip_nat_pptp *nat_pptp_info = &ct->nat.help.nat_pptp_info;
 126
 127         u_int16_t msg, *cid = NULL, new_callid;
 128
 129         new_callid = htons(ct_pptp_info->pns_call_id);
 130
 131         switch (msg = ntohs(ctlh->messageType)) {
 132                 case PPTP_OUT_CALL_REQUEST:
 133                         cid = &pptpReq->ocreq.callID;
 134                         /* FIXME: ideally we would want to reserve a call ID
 135                          * here.  current netfilter NAT core is not able to do
 136                          * this :( For now we use TCP source port. This breaks
 137                          * multiple calls within one control session */
 138
 139                         /* save original call ID in nat_info */
 140                         nat_pptp_info->pns_call_id = ct_pptp_info->pns_call_id;
 141
 142                         /* don't use tcph->source since we are at a DSTmanip
 143                          * hook (e.g. PREROUTING) and pkt is not mangled yet */
 144                         new_callid = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u.tcp.port;
 145
 146                         /* save new call ID in ct info */
 147                         ct_pptp_info->pns_call_id = ntohs(new_callid);
 148                         break;
 149                 case PPTP_IN_CALL_REPLY:
 150                         cid = &pptpReq->icreq.callID;
 151                         break;
 152                 case PPTP_CALL_CLEAR_REQUEST:
 153                         cid = &pptpReq->clrreq.callID;
 154                         break;
 155                 default:
 156                         DEBUGP("unknown outbound packet 0x%04x:%s\n", msg,
 157                               (msg <= PPTP_MSG_MAX)? strMName[msg]:strMName[0]);
 158                         /* fall through */
 159
 160                 case PPTP_SET_LINK_INFO:
 161                         /* only need to NAT in case PAC is behind NAT box */
 162                 case PPTP_START_SESSION_REQUEST:
 163                 case PPTP_START_SESSION_REPLY:
 164                 case PPTP_STOP_SESSION_REQUEST:
 165                 case PPTP_STOP_SESSION_REPLY:
 166                 case PPTP_ECHO_REQUEST:
 167                 case PPTP_ECHO_REPLY:
 168                         /* no need to alter packet */
 169                         return NF_ACCEPT;
 170         }
 171
 172         /* only OUT_CALL_REQUEST, IN_CALL_REPLY, CALL_CLEAR_REQUEST pass
 173          * down to here */
 174
 175         IP_NF_ASSERT(cid);
 176
 177         DEBUGP("altering call id from 0x%04x to 0x%04x\n",
 178                 ntohs(*cid), ntohs(new_callid));
 179
 180         /* mangle packet */
 181         if (ip_nat_mangle_tcp_packet(pskb, ct, ctinfo,
 182                 (void *)cid - ((void *)ctlh - sizeof(struct pptp_pkt_hdr)),
 183                                         sizeof(new_callid),
 184                                         (char *)&new_callid,
 185                                         sizeof(new_callid)) == 0)
 186                 return NF_DROP;
 187
 188         return NF_ACCEPT;
 189 }
 190
 191 static int
 192 pptp_exp_gre(struct ip_conntrack_expect *expect_orig,
 193              struct ip_conntrack_expect *expect_reply)
 194 {
 195         struct ip_ct_pptp_master *ct_pptp_info =
 196                                 &expect_orig->master->help.ct_pptp_info;
 197         struct ip_nat_pptp *nat_pptp_info =
 198                                 &expect_orig->master->nat.help.nat_pptp_info;
 199
 200         struct ip_conntrack *ct = expect_orig->master;
 201
 202         struct ip_conntrack_tuple inv_t;
 203         struct ip_conntrack_tuple *orig_t, *reply_t;
 204
 205         /* save original PAC call ID in nat_info */
 206         nat_pptp_info->pac_call_id = ct_pptp_info->pac_call_id;
 207
 208         /* alter expectation */
 209         orig_t = &ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple;
 210         reply_t = &ct->tuplehash[IP_CT_DIR_REPLY].tuple;
 211
 212         /* alter expectation for PNS->PAC direction */
 213         invert_tuplepr(&inv_t, &expect_orig->tuple);
 214         expect_orig->saved_proto.gre.key = htons(nat_pptp_info->pac_call_id);
 215         expect_orig->tuple.src.u.gre.key = htons(nat_pptp_info->pns_call_id);
 216         expect_orig->tuple.dst.u.gre.key = htons(ct_pptp_info->pac_call_id);
 217         inv_t.src.ip = reply_t->src.ip;
 218         inv_t.dst.ip = reply_t->dst.ip;
 219         inv_t.src.u.gre.key = htons(nat_pptp_info->pac_call_id);
 220         inv_t.dst.u.gre.key = htons(ct_pptp_info->pns_call_id);
 221
 222         if (!ip_conntrack_expect_related(expect_orig)) {
 223                 DEBUGP("successfully registered expect\n");
 224         } else {
 225                 DEBUGP("can't expect_related(expect_orig)\n");
 226                 ip_conntrack_expect_free(expect_orig);
 227                 return 1;
 228         }
 229
 230         /* alter expectation for PAC->PNS direction */
 231         invert_tuplepr(&inv_t, &expect_reply->tuple);
 232         expect_reply->saved_proto.gre.key = htons(nat_pptp_info->pns_call_id);
 233         expect_reply->tuple.src.u.gre.key = htons(nat_pptp_info->pac_call_id);
 234         expect_reply->tuple.dst.u.gre.key = htons(ct_pptp_info->pns_call_id);
 235         inv_t.src.ip = orig_t->src.ip;
 236         inv_t.dst.ip = orig_t->dst.ip;
 237         inv_t.src.u.gre.key = htons(nat_pptp_info->pns_call_id);
 238         inv_t.dst.u.gre.key = htons(ct_pptp_info->pac_call_id);
 239
 240         if (!ip_conntrack_expect_related(expect_reply)) {
 241                 DEBUGP("successfully registered expect\n");
 242         } else {
 243                 DEBUGP("can't expect_related(expect_reply)\n");
 244                 ip_conntrack_unexpect_related(expect_orig);
 245                 ip_conntrack_expect_free(expect_reply);
 246                 return 1;
 247         }
 248
 249         if (ip_ct_gre_keymap_add(ct, &expect_reply->tuple, 0) < 0) {
 250                 DEBUGP("can't register original keymap\n");
 251                 ip_conntrack_unexpect_related(expect_orig);
 252                 ip_conntrack_unexpect_related(expect_reply);
 253                 return 1;
 254         }
 255
 256         if (ip_ct_gre_keymap_add(ct, &inv_t, 1) < 0) {
 257                 DEBUGP("can't register reply keymap\n");
 258                 ip_conntrack_unexpect_related(expect_orig);
 259                 ip_conntrack_unexpect_related(expect_reply);
 260                 ip_ct_gre_keymap_destroy(ct);
 261                 return 1;
 262         }
 263
 264         return 0;
 265 }
 266
 267 /* inbound packets == from PAC to PNS */
 268 static int
 269 pptp_inbound_pkt(struct sk_buff **pskb,
 270                  struct ip_conntrack *ct,
 271                  enum ip_conntrack_info ctinfo,
 272                  struct PptpControlHeader *ctlh,
 273                  union pptp_ctrl_union *pptpReq)
 274 {
 275         struct ip_nat_pptp *nat_pptp_info = &ct->nat.help.nat_pptp_info;
 276         u_int16_t msg, new_cid = 0, new_pcid, *pcid = NULL, *cid = NULL;
 277
 278         int ret = NF_ACCEPT, rv;
 279
 280         new_pcid = htons(nat_pptp_info->pns_call_id);
 281
 282         switch (msg = ntohs(ctlh->messageType)) {
 283         case PPTP_OUT_CALL_REPLY:
 284                 pcid = &pptpReq->ocack.peersCallID;
 285                 cid = &pptpReq->ocack.callID;
 286                 break;
 287         case PPTP_IN_CALL_CONNECT:
 288                 pcid = &pptpReq->iccon.peersCallID;
 289                 break;
 290         case PPTP_IN_CALL_REQUEST:
 291                 /* only need to nat in case PAC is behind NAT box */
 292                 break;
 293         case PPTP_WAN_ERROR_NOTIFY:
 294                 pcid = &pptpReq->wanerr.peersCallID;
 295                 break;
 296         case PPTP_CALL_DISCONNECT_NOTIFY:
 297                 pcid = &pptpReq->disc.callID;
 298                 break;
 299
 300         default:
 301                 DEBUGP("unknown inbound packet %s\n",
 302                         (msg <= PPTP_MSG_MAX)? strMName[msg]:strMName[0]);
 303                 /* fall through */
 304
 305         case PPTP_START_SESSION_REQUEST:
 306         case PPTP_START_SESSION_REPLY:
 307         case PPTP_STOP_SESSION_REQUEST:
 308         case PPTP_STOP_SESSION_REPLY:
 309         case PPTP_ECHO_REQUEST:
 310         case PPTP_ECHO_REPLY:
 311                 /* no need to alter packet */
 312                 return NF_ACCEPT;
 313         }
 314
 315         /* only OUT_CALL_REPLY, IN_CALL_CONNECT, IN_CALL_REQUEST,
 316          * WAN_ERROR_NOTIFY, CALL_DISCONNECT_NOTIFY pass down here */
 317
 318         /* mangle packet */
 319         IP_NF_ASSERT(pcid);
 320         DEBUGP("altering peer call id from 0x%04x to 0x%04x\n",
 321                 ntohs(*pcid), ntohs(new_pcid));
 322
 323         rv = ip_nat_mangle_tcp_packet(pskb, ct, ctinfo,
 324                                       (void *)pcid - ((void *)ctlh - sizeof(struct pptp_pkt_hdr)),
 325                                       sizeof(new_pcid), (char *)&new_pcid,
 326                                       sizeof(new_pcid));
 327         if (rv != NF_ACCEPT)
 328                 return rv;
 329
 330         if (new_cid) {
 331                 IP_NF_ASSERT(cid);
 332                 DEBUGP("altering call id from 0x%04x to 0x%04x\n",
 333                         ntohs(*cid), ntohs(new_cid));
 334                 rv = ip_nat_mangle_tcp_packet(pskb, ct, ctinfo,
 335                                               (void *)cid - ((void *)ctlh - sizeof(struct pptp_pkt_hdr)),
 336                                               sizeof(new_cid),
 337                                               (char *)&new_cid,
 338                                               sizeof(new_cid));
 339                 if (rv != NF_ACCEPT)
 340                         return rv;
 341         }
 342
 343         /* check for earlier return value of 'switch' above */
 344         if (ret != NF_ACCEPT)
 345                 return ret;
 346
 347         /* great, at least we don't need to resize packets */
 348         return NF_ACCEPT;
 349 }
 350
 351
 352 static int __init init(void)
 353 {
 354         DEBUGP("%s: registering NAT helper\n", __FILE__);
 355
 356         BUG_ON(ip_nat_pptp_hook_outbound);
 357         ip_nat_pptp_hook_outbound = &pptp_outbound_pkt;
 358
 359         BUG_ON(ip_nat_pptp_hook_inbound);
 360         ip_nat_pptp_hook_inbound = &pptp_inbound_pkt;
 361
 362         BUG_ON(ip_nat_pptp_hook_exp_gre);
 363         ip_nat_pptp_hook_exp_gre = &pptp_exp_gre;
 364
 365         BUG_ON(ip_nat_pptp_hook_expectfn);
 366         ip_nat_pptp_hook_expectfn = &pptp_nat_expected;
 367
 368         printk("ip_nat_pptp version %s loaded\n", IP_NAT_PPTP_VERSION);
 369         return 0;
 370 }
 371
 372 static void __exit fini(void)
 373 {
 374         DEBUGP("cleanup_module\n" );
 375
 376         ip_nat_pptp_hook_expectfn = NULL;
 377         ip_nat_pptp_hook_exp_gre = NULL;
 378         ip_nat_pptp_hook_inbound = NULL;
 379         ip_nat_pptp_hook_outbound = NULL;
 380
 381         /* Make sure noone calls it, meanwhile */
 382         synchronize_net();
 383
 384         printk("ip_nat_pptp version %s unloaded\n", IP_NAT_PPTP_VERSION);
 385 }
 386
 387 module_init(init);
 388 module_exit(fini);