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)               (*(__be16 *)((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 = 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 = 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 = 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 = 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_expect_find_get(&t);
 105         if (other_exp) {
 106                 ip_conntrack_unexpect_related(other_exp);
 107                 ip_conntrack_expect_put(other_exp);
 108                 DEBUGP("success\n");
 109         } else {
 110                 DEBUGP("not found!\n");
 111         }
 112
 113         /* This must be a fresh one. */
 114         BUG_ON(ct->status & IPS_NAT_DONE_MASK);
 115
 116         /* Change src to where master sends to */
 117         range.flags = IP_NAT_RANGE_MAP_IPS;
 118         range.min_ip = range.max_ip
 119                 = ct->master->tuplehash[!exp->dir].tuple.dst.ip;
 120         if (exp->dir == IP_CT_DIR_ORIGINAL) {
 121                 range.flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
 122                 range.min = range.max = exp->saved_proto;
 123         }
 124         /* hook doesn't matter, but it has to do source manip */
 125         ip_nat_setup_info(ct, &range, NF_IP_POST_ROUTING);
 126
 127         /* For DST manip, map port here to where it's expected. */
 128         range.flags = IP_NAT_RANGE_MAP_IPS;
 129         range.min_ip = range.max_ip
 130                 = ct->master->tuplehash[!exp->dir].tuple.src.ip;
 131         if (exp->dir == IP_CT_DIR_REPLY) {
 132                 range.flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
 133                 range.min = range.max = exp->saved_proto;
 134         }
 135         /* hook doesn't matter, but it has to do destination manip */
 136         ip_nat_setup_info(ct, &range, NF_IP_PRE_ROUTING);
 137 }
 138
 139 /* outbound packets == from PNS to PAC */
 140 static int
 141 pptp_outbound_pkt(struct sk_buff **pskb,
 142                   struct ip_conntrack *ct,
 143                   enum ip_conntrack_info ctinfo,
 144                   struct PptpControlHeader *ctlh,
 145                   union pptp_ctrl_union *pptpReq)
 146
 147 {
 148         struct ip_ct_pptp_master *ct_pptp_info = &ct->help.ct_pptp_info;
 149         struct ip_nat_pptp *nat_pptp_info = &ct->nat.help.nat_pptp_info;
 150         u_int16_t msg;
 151         __be16 new_callid;
 152         unsigned int cid_off;
 153
 154         new_callid = 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 = new_callid;
 173                 break;
 174         case PPTP_IN_CALL_REPLY:
 175                 cid_off = offsetof(union pptp_ctrl_union, icack.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(REQ_CID(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 void
 215 pptp_exp_gre(struct ip_conntrack_expect *expect_orig,
 216              struct ip_conntrack_expect *expect_reply)
 217 {
 218         struct ip_conntrack *ct = expect_orig->master;
 219         struct ip_ct_pptp_master *ct_pptp_info = &ct->help.ct_pptp_info;
 220         struct ip_nat_pptp *nat_pptp_info = &ct->nat.help.nat_pptp_info;
 221
 222         /* save original PAC call ID in nat_info */
 223         nat_pptp_info->pac_call_id = ct_pptp_info->pac_call_id;
 224
 225         /* alter expectation for PNS->PAC direction */
 226         expect_orig->saved_proto.gre.key = ct_pptp_info->pns_call_id;
 227         expect_orig->tuple.src.u.gre.key = nat_pptp_info->pns_call_id;
 228         expect_orig->tuple.dst.u.gre.key = ct_pptp_info->pac_call_id;
 229         expect_orig->dir = IP_CT_DIR_ORIGINAL;
 230
 231         /* alter expectation for PAC->PNS direction */
 232         expect_reply->saved_proto.gre.key = nat_pptp_info->pns_call_id;
 233         expect_reply->tuple.src.u.gre.key = nat_pptp_info->pac_call_id;
 234         expect_reply->tuple.dst.u.gre.key = ct_pptp_info->pns_call_id;
 235         expect_reply->dir = IP_CT_DIR_REPLY;
 236 }
 237
 238 /* inbound packets == from PAC to PNS */
 239 static int
 240 pptp_inbound_pkt(struct sk_buff **pskb,
 241                  struct ip_conntrack *ct,
 242                  enum ip_conntrack_info ctinfo,
 243                  struct PptpControlHeader *ctlh,
 244                  union pptp_ctrl_union *pptpReq)
 245 {
 246         struct ip_nat_pptp *nat_pptp_info = &ct->nat.help.nat_pptp_info;
 247         u_int16_t msg;
 248         __be16 new_pcid;
 249         unsigned int pcid_off;
 250
 251         new_pcid = nat_pptp_info->pns_call_id;
 252
 253         switch (msg = ntohs(ctlh->messageType)) {
 254         case PPTP_OUT_CALL_REPLY:
 255                 pcid_off = offsetof(union pptp_ctrl_union, ocack.peersCallID);
 256                 break;
 257         case PPTP_IN_CALL_CONNECT:
 258                 pcid_off = offsetof(union pptp_ctrl_union, iccon.peersCallID);
 259                 break;
 260         case PPTP_IN_CALL_REQUEST:
 261                 /* only need to nat in case PAC is behind NAT box */
 262                 return NF_ACCEPT;
 263         case PPTP_WAN_ERROR_NOTIFY:
 264                 pcid_off = offsetof(union pptp_ctrl_union, wanerr.peersCallID);
 265                 break;
 266         case PPTP_CALL_DISCONNECT_NOTIFY:
 267                 pcid_off = offsetof(union pptp_ctrl_union, disc.callID);
 268                 break;
 269         case PPTP_SET_LINK_INFO:
 270                 pcid_off = offsetof(union pptp_ctrl_union, setlink.peersCallID);
 271                 break;
 272
 273         default:
 274                 DEBUGP("unknown inbound packet %s\n", (msg <= PPTP_MSG_MAX)?
 275                         pptp_msg_name[msg]:pptp_msg_name[0]);
 276                 /* fall through */
 277
 278         case PPTP_START_SESSION_REQUEST:
 279         case PPTP_START_SESSION_REPLY:
 280         case PPTP_STOP_SESSION_REQUEST:
 281         case PPTP_STOP_SESSION_REPLY:
 282         case PPTP_ECHO_REQUEST:
 283         case PPTP_ECHO_REPLY:
 284                 /* no need to alter packet */
 285                 return NF_ACCEPT;
 286         }
 287
 288         /* only OUT_CALL_REPLY, IN_CALL_CONNECT, IN_CALL_REQUEST,
 289          * WAN_ERROR_NOTIFY, CALL_DISCONNECT_NOTIFY pass down here */
 290
 291         /* mangle packet */
 292         DEBUGP("altering peer call id from 0x%04x to 0x%04x\n",
 293                 ntohs(REQ_CID(pptpReq, pcid_off)), ntohs(new_pcid));
 294
 295         if (ip_nat_mangle_tcp_packet(pskb, ct, ctinfo,
 296                                      pcid_off + sizeof(struct pptp_pkt_hdr) +
 297                                      sizeof(struct PptpControlHeader),
 298                                      sizeof(new_pcid), (char *)&new_pcid,
 299                                      sizeof(new_pcid)) == 0)
 300                 return NF_DROP;
 301         return NF_ACCEPT;
 302 }
 303
 304
 305 extern int __init ip_nat_proto_gre_init(void);
 306 extern void __exit ip_nat_proto_gre_fini(void);
 307
 308 static int __init ip_nat_helper_pptp_init(void)
 309 {
 310         int ret;
 311
 312         DEBUGP("%s: registering NAT helper\n", __FILE__);
 313
 314         ret = ip_nat_proto_gre_init();
 315         if (ret < 0)
 316                 return ret;
 317
 318         BUG_ON(rcu_dereference(ip_nat_pptp_hook_outbound));
 319         rcu_assign_pointer(ip_nat_pptp_hook_outbound, pptp_outbound_pkt);
 320
 321         BUG_ON(rcu_dereference(ip_nat_pptp_hook_inbound));
 322         rcu_assign_pointer(ip_nat_pptp_hook_inbound, pptp_inbound_pkt);
 323
 324         BUG_ON(rcu_dereference(ip_nat_pptp_hook_exp_gre));
 325         rcu_assign_pointer(ip_nat_pptp_hook_exp_gre, pptp_exp_gre);
 326
 327         BUG_ON(rcu_dereference(ip_nat_pptp_hook_expectfn));
 328         rcu_assign_pointer(ip_nat_pptp_hook_expectfn, pptp_nat_expected);
 329
 330         printk("ip_nat_pptp version %s loaded\n", IP_NAT_PPTP_VERSION);
 331         return 0;
 332 }
 333
 334 static void __exit ip_nat_helper_pptp_fini(void)
 335 {
 336         DEBUGP("cleanup_module\n" );
 337
 338         rcu_assign_pointer(ip_nat_pptp_hook_expectfn, NULL);
 339         rcu_assign_pointer(ip_nat_pptp_hook_exp_gre, NULL);
 340         rcu_assign_pointer(ip_nat_pptp_hook_inbound, NULL);
 341         rcu_assign_pointer(ip_nat_pptp_hook_outbound, NULL);
 342         synchronize_rcu();
 343
 344         ip_nat_proto_gre_fini();
 345
 346         printk("ip_nat_pptp version %s unloaded\n", IP_NAT_PPTP_VERSION);
 347 }
 348
 349 module_init(ip_nat_helper_pptp_init);
 350 module_exit(ip_nat_helper_pptp_fini);