alias/alias_pptp.c

   1 /*
   2  * Copyright (c) 2000-2002 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
   7  *
   8  * This file contains Original Code and/or Modifications of Original Code
   9  * as defined in and that are subject to the Apple Public Source License
  10  * Version 2.0 (the 'License'). You may not use this file except in
  11  * compliance with the License. Please obtain a copy of the License at
  12  * http://www.opensource.apple.com/apsl/ and read it before using this
  13  * file.
  14  *
  15  * The Original Code and all software distributed under the License are
  16  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  17  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  18  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  20  * Please see the License for the specific language governing rights and
  21  * limitations under the License.
  22  *
  23  * @APPLE_LICENSE_HEADER_END@
  24  */
  25 /*
  26  * alias_pptp.c
  27  *
  28  * Copyright (c) 2000 Whistle Communications, Inc.
  29  * All rights reserved.
  30  *
  31  * Subject to the following obligations and disclaimer of warranty, use and
  32  * redistribution of this software, in source or object code forms, with or
  33  * without modifications are expressly permitted by Whistle Communications;
  34  * provided, however, that:
  35  * 1. Any and all reproductions of the source or object code must include the
  36  *    copyright notice above and the following disclaimer of warranties; and
  37  * 2. No rights are granted, in any manner or form, to use Whistle
  38  *    Communications, Inc. trademarks, including the mark "WHISTLE
  39  *    COMMUNICATIONS" on advertising, endorsements, or otherwise except as
  40  *    such appears in the above copyright notice or in the software.
  41  *
  42  * THIS SOFTWARE IS BEING PROVIDED BY WHISTLE COMMUNICATIONS "AS IS", AND
  43  * TO THE MAXIMUM EXTENT PERMITTED BY LAW, WHISTLE COMMUNICATIONS MAKES NO
  44  * REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING THIS SOFTWARE,
  45  * INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED WARRANTIES OF
  46  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT.
  47  * WHISTLE COMMUNICATIONS DOES NOT WARRANT, GUARANTEE, OR MAKE ANY
  48  * REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS OF THE USE OF THIS
  49  * SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, RELIABILITY OR OTHERWISE.
  50  * IN NO EVENT SHALL WHISTLE COMMUNICATIONS BE LIABLE FOR ANY DAMAGES
  51  * RESULTING FROM OR ARISING OUT OF ANY USE OF THIS SOFTWARE, INCLUDING
  52  * WITHOUT LIMITATION, ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
  53  * PUNITIVE, OR CONSEQUENTIAL DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR
  54  * SERVICES, LOSS OF USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY
  55  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  56  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  57  * THIS SOFTWARE, EVEN IF WHISTLE COMMUNICATIONS IS ADVISED OF THE POSSIBILITY
  58  * OF SUCH DAMAGE.
  59  *
  60  * Author: Erik Salander <erik@whistle.com>
  61  *
  62  * Based upon:
  63  * $FreeBSD: src/lib/libalias/alias_pptp.c,v 1.1.2.4 2001/08/01 09:52:27 obrien Exp $
  64  */
  65
  66 /*
  67    Alias_pptp.c performs special processing for PPTP sessions under TCP.
  68    Specifically, watch PPTP control messages and alias the Call ID or the
  69    Peer's Call ID in the appropriate messages.  Note, PPTP requires
  70    "de-aliasing" of incoming packets, this is different than any other
  71    TCP applications that are currently (ie. FTP, IRC and RTSP) aliased.
  72
  73    For Call IDs encountered for the first time, a PPTP alias link is created.
  74    The PPTP alias link uses the Call ID in place of the original port number.
  75    An alias Call ID is created.
  76
  77    For this routine to work, the PPTP control messages must fit entirely
  78    into a single TCP packet.  This is typically the case, but is not
  79    required by the spec.
  80
  81    Unlike some of the other TCP applications that are aliased (ie. FTP,
  82    IRC and RTSP), the PPTP control messages that need to be aliased are
  83    guaranteed to remain the same length.  The aliased Call ID is a fixed
  84    length field.
  85
  86    Reference: RFC 2637
  87
  88    Initial version:  May, 2000 (eds)
  89
  90 */
  91
  92 /* Includes */
  93 #include <sys/types.h>
  94 #include <netinet/in_systm.h>
  95 #include <netinet/in.h>
  96 #include <netinet/ip.h>
  97 #include <netinet/tcp.h>
  98
  99 #include <stdio.h>
 100
 101 #include "alias_local.h"
 102
 103 /*
 104  * PPTP definitions
 105  */
 106
 107 struct grehdr                   /* Enhanced GRE header. */
 108 {
 109     u_int16_t gh_flags;         /* Flags. */
 110     u_int16_t gh_protocol;      /* Protocol type. */
 111     u_int16_t gh_length;        /* Payload length. */
 112     u_int16_t gh_call_id;       /* Call ID. */
 113     u_int32_t gh_seq_no;        /* Sequence number (optional). */
 114     u_int32_t gh_ack_no;        /* Acknowledgment number (optional). */
 115 };
 116 typedef struct grehdr           GreHdr;
 117
 118 /* The PPTP protocol ID used in the GRE 'proto' field. */
 119 #define PPTP_GRE_PROTO          0x880b
 120
 121 /* Bits that must be set a certain way in all PPTP/GRE packets. */
 122 #define PPTP_INIT_VALUE         ((0x2001 << 16) | PPTP_GRE_PROTO)
 123 #define PPTP_INIT_MASK          0xef7fffff
 124
 125 #define PPTP_MAGIC              0x1a2b3c4d
 126 #define PPTP_CTRL_MSG_TYPE      1
 127
 128 enum {
 129   PPTP_StartCtrlConnRequest = 1,
 130   PPTP_StartCtrlConnReply = 2,
 131   PPTP_StopCtrlConnRequest = 3,
 132   PPTP_StopCtrlConnReply = 4,
 133   PPTP_EchoRequest = 5,
 134   PPTP_EchoReply = 6,
 135   PPTP_OutCallRequest = 7,
 136   PPTP_OutCallReply = 8,
 137   PPTP_InCallRequest = 9,
 138   PPTP_InCallReply = 10,
 139   PPTP_InCallConn = 11,
 140   PPTP_CallClearRequest = 12,
 141   PPTP_CallDiscNotify = 13,
 142   PPTP_WanErrorNotify = 14,
 143   PPTP_SetLinkInfo = 15
 144 };
 145
 146   /* Message structures */
 147   struct pptpMsgHead {
 148     u_int16_t   length;         /* total length */
 149     u_int16_t   msgType;        /* PPTP message type */
 150     u_int32_t   magic;          /* magic cookie */
 151     u_int16_t   type;           /* control message type */
 152     u_int16_t   resv0;          /* reserved */
 153   };
 154   typedef struct pptpMsgHead    *PptpMsgHead;
 155
 156   struct pptpCodes {
 157     u_int8_t    resCode;        /* Result Code */
 158     u_int8_t    errCode;        /* Error Code */
 159   };
 160   typedef struct pptpCodes      *PptpCode;
 161
 162   struct pptpCallIds {
 163     u_int16_t   cid1;           /* Call ID field #1 */
 164     u_int16_t   cid2;           /* Call ID field #2 */
 165   };
 166   typedef struct pptpCallIds    *PptpCallId;
 167
 168 static PptpCallId AliasVerifyPptp(struct ip *, u_int16_t *);
 169
 170
 171 void
 172 AliasHandlePptpOut(struct ip *pip,          /* IP packet to examine/patch */
 173                    struct alias_link *link) /* The PPTP control link */
 174 {
 175     struct alias_link   *pptp_link;
 176     PptpCallId          cptr;
 177     PptpCode            codes;
 178     u_int16_t           ctl_type;           /* control message type */
 179     struct tcphdr       *tc;
 180
 181     /* Verify valid PPTP control message */
 182     if ((cptr = AliasVerifyPptp(pip, &ctl_type)) == NULL)
 183       return;
 184
 185     /* Modify certain PPTP messages */
 186     switch (ctl_type) {
 187     case PPTP_OutCallRequest:
 188     case PPTP_OutCallReply:
 189     case PPTP_InCallRequest:
 190     case PPTP_InCallReply:
 191         /* Establish PPTP link for address and Call ID found in control message. */
 192         pptp_link = AddPptp(GetOriginalAddress(link), GetDestAddress(link),
 193                             GetAliasAddress(link), cptr->cid1);
 194         break;
 195     case PPTP_CallClearRequest:
 196     case PPTP_CallDiscNotify:
 197         /* Find PPTP link for address and Call ID found in control message. */
 198         pptp_link = FindPptpOutByCallId(GetOriginalAddress(link),
 199                                         GetDestAddress(link),
 200                                         cptr->cid1);
 201         break;
 202     default:
 203         return;
 204     }
 205
 206       if (pptp_link != NULL) {
 207         int accumulate = cptr->cid1;
 208
 209         /* alias the Call Id */
 210         cptr->cid1 = GetAliasPort(pptp_link);
 211
 212         /* Compute TCP checksum for revised packet */
 213         tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
 214         accumulate -= cptr->cid1;
 215         ADJUST_CHECKSUM(accumulate, tc->th_sum);
 216
 217         switch (ctl_type) {
 218         case PPTP_OutCallReply:
 219         case PPTP_InCallReply:
 220             codes = (PptpCode)(cptr + 1);
 221             if (codes->resCode == 1)            /* Connection established, */
 222                 SetDestCallId(pptp_link,        /* note the Peer's Call ID. */
 223                               cptr->cid2);
 224             else
 225                 SetExpire(pptp_link, 0);        /* Connection refused. */
 226             break;
 227         case PPTP_CallDiscNotify:               /* Connection closed. */
 228             SetExpire(pptp_link, 0);
 229             break;
 230         }
 231       }
 232 }
 233
 234 void
 235 AliasHandlePptpIn(struct ip *pip,          /* IP packet to examine/patch */
 236                   struct alias_link *link) /* The PPTP control link */
 237 {
 238     struct alias_link   *pptp_link;
 239     PptpCallId          cptr;
 240     u_int16_t           *pcall_id;
 241     u_int16_t           ctl_type;           /* control message type */
 242     struct tcphdr       *tc;
 243
 244     /* Verify valid PPTP control message */
 245     if ((cptr = AliasVerifyPptp(pip, &ctl_type)) == NULL)
 246       return;
 247
 248     /* Modify certain PPTP messages */
 249     switch (ctl_type)
 250     {
 251     case PPTP_InCallConn:
 252     case PPTP_WanErrorNotify:
 253     case PPTP_SetLinkInfo:
 254       pcall_id = &cptr->cid1;
 255       break;
 256     case PPTP_OutCallReply:
 257     case PPTP_InCallReply:
 258       pcall_id = &cptr->cid2;
 259       break;
 260     case PPTP_CallDiscNotify:                   /* Connection closed. */
 261       pptp_link = FindPptpInByCallId(GetDestAddress(link),
 262                                      GetAliasAddress(link),
 263                                      cptr->cid1);
 264       if (pptp_link != NULL)
 265             SetExpire(pptp_link, 0);
 266       return;
 267     default:
 268       return;
 269     }
 270
 271     /* Find PPTP link for address and Call ID found in PPTP Control Msg */
 272     pptp_link = FindPptpInByPeerCallId(GetDestAddress(link),
 273                                        GetAliasAddress(link),
 274                                        *pcall_id);
 275
 276     if (pptp_link != NULL) {
 277       int accumulate = *pcall_id;
 278
 279       /* De-alias the Peer's Call Id. */
 280       *pcall_id = GetOriginalPort(pptp_link);
 281
 282       /* Compute TCP checksum for modified packet */
 283       tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
 284       accumulate -= *pcall_id;
 285       ADJUST_CHECKSUM(accumulate, tc->th_sum);
 286
 287       if (ctl_type == PPTP_OutCallReply || ctl_type == PPTP_InCallReply) {
 288             PptpCode codes = (PptpCode)(cptr + 1);
 289
 290             if (codes->resCode == 1)            /* Connection established, */
 291                 SetDestCallId(pptp_link,        /* note the Call ID. */
 292                               cptr->cid1);
 293             else
 294                 SetExpire(pptp_link, 0);        /* Connection refused. */
 295       }
 296     }
 297 }
 298
 299 static PptpCallId
 300 AliasVerifyPptp(struct ip *pip, u_int16_t *ptype) /* IP packet to examine/patch */
 301 {
 302     int                 hlen, tlen, dlen;
 303     PptpMsgHead         hptr;
 304     struct tcphdr       *tc;
 305
 306     /* Calculate some lengths */
 307     tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
 308     hlen = (pip->ip_hl + tc->th_off) << 2;
 309     tlen = ntohs(pip->ip_len);
 310     dlen = tlen - hlen;
 311
 312     /* Verify data length */
 313     if (dlen < (sizeof(struct pptpMsgHead) + sizeof(struct pptpCallIds)))
 314       return(NULL);
 315
 316     /* Move up to PPTP message header */
 317     hptr = (PptpMsgHead)(((char *) pip) + hlen);
 318
 319     /* Return the control message type */
 320     *ptype = ntohs(hptr->type);
 321
 322     /* Verify PPTP Control Message */
 323     if ((ntohs(hptr->msgType) != PPTP_CTRL_MSG_TYPE) ||
 324         (ntohl(hptr->magic) != PPTP_MAGIC))
 325       return(NULL);
 326
 327     /* Verify data length. */
 328     if ((*ptype == PPTP_OutCallReply || *ptype == PPTP_InCallReply) &&
 329         (dlen < sizeof(struct pptpMsgHead) + sizeof(struct pptpCallIds) +
 330                 sizeof(struct pptpCodes)))
 331         return (NULL);
 332     else
 333         return (PptpCallId)(hptr + 1);
 334 }
 335
 336
 337 int
 338 AliasHandlePptpGreOut(struct ip *pip)
 339 {
 340     GreHdr              *gr;
 341     struct alias_link   *link;
 342
 343     gr = (GreHdr *)((char *)pip + (pip->ip_hl << 2));
 344
 345     /* Check GRE header bits. */
 346     if ((ntohl(*((u_int32_t *)gr)) & PPTP_INIT_MASK) != PPTP_INIT_VALUE)
 347         return (-1);
 348
 349     link = FindPptpOutByPeerCallId(pip->ip_src, pip->ip_dst, gr->gh_call_id);
 350     if (link != NULL) {
 351         struct in_addr alias_addr = GetAliasAddress(link);
 352
 353         /* Change source IP address. */
 354         DifferentialChecksum(&pip->ip_sum,
 355                              (u_short *)&alias_addr,
 356                              (u_short *)&pip->ip_src,
 357                              2);
 358         pip->ip_src = alias_addr;
 359     }
 360
 361     return (0);
 362 }
 363
 364
 365 int
 366 AliasHandlePptpGreIn(struct ip *pip)
 367 {
 368     GreHdr              *gr;
 369     struct alias_link   *link;
 370
 371     gr = (GreHdr *)((char *)pip + (pip->ip_hl << 2));
 372
 373     /* Check GRE header bits. */
 374     if ((ntohl(*((u_int32_t *)gr)) & PPTP_INIT_MASK) != PPTP_INIT_VALUE)
 375         return (-1);
 376
 377     link = FindPptpInByPeerCallId(pip->ip_src, pip->ip_dst, gr->gh_call_id);
 378     if (link != NULL) {
 379         struct in_addr src_addr = GetOriginalAddress(link);
 380
 381         /* De-alias the Peer's Call Id. */
 382         gr->gh_call_id = GetOriginalPort(link);
 383
 384         /* Restore original IP address. */
 385         DifferentialChecksum(&pip->ip_sum,
 386                              (u_short *)&src_addr,
 387                              (u_short *)&pip->ip_dst,
 388                              2);
 389         pip->ip_dst = src_addr;
 390     }
 391
 392     return (0);
 393 }