[apple/network_cmds.git] / alias / alias_pptp.c

/*
 * Copyright (c) 2000-2002 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This Original Code and all software distributed under the License are
 * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/*
 * alias_pptp.c
 *
 * Copyright (c) 2000 Whistle Communications, Inc.
 * All rights reserved.
 *
 * Subject to the following obligations and disclaimer of warranty, use and
 * redistribution of this software, in source or object code forms, with or
 * without modifications are expressly permitted by Whistle Communications;
 * provided, however, that:
 * 1. Any and all reproductions of the source or object code must include the
 *    copyright notice above and the following disclaimer of warranties; and
 * 2. No rights are granted, in any manner or form, to use Whistle
 *    Communications, Inc. trademarks, including the mark "WHISTLE
 *    COMMUNICATIONS" on advertising, endorsements, or otherwise except as
 *    such appears in the above copyright notice or in the software.
 *
 * THIS SOFTWARE IS BEING PROVIDED BY WHISTLE COMMUNICATIONS "AS IS", AND
 * TO THE MAXIMUM EXTENT PERMITTED BY LAW, WHISTLE COMMUNICATIONS MAKES NO
 * REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING THIS SOFTWARE,
 * INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT.
 * WHISTLE COMMUNICATIONS DOES NOT WARRANT, GUARANTEE, OR MAKE ANY
 * REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS OF THE USE OF THIS
 * SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, RELIABILITY OR OTHERWISE.
 * IN NO EVENT SHALL WHISTLE COMMUNICATIONS BE LIABLE FOR ANY DAMAGES
 * RESULTING FROM OR ARISING OUT OF ANY USE OF THIS SOFTWARE, INCLUDING
 * WITHOUT LIMITATION, ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
 * PUNITIVE, OR CONSEQUENTIAL DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES, LOSS OF USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF WHISTLE COMMUNICATIONS IS ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * Author: Erik Salander <erik@whistle.com>
 *
 * Based upon:
 * $FreeBSD: src/lib/libalias/alias_pptp.c,v 1.1.2.4 2001/08/01 09:52:27 obrien Exp $
 */

/*
   Alias_pptp.c performs special processing for PPTP sessions under TCP.
   Specifically, watch PPTP control messages and alias the Call ID or the
   Peer's Call ID in the appropriate messages.  Note, PPTP requires
   "de-aliasing" of incoming packets, this is different than any other
   TCP applications that are currently (ie. FTP, IRC and RTSP) aliased.

   For Call IDs encountered for the first time, a PPTP alias link is created.
   The PPTP alias link uses the Call ID in place of the original port number.
   An alias Call ID is created.

   For this routine to work, the PPTP control messages must fit entirely
   into a single TCP packet.  This is typically the case, but is not
   required by the spec.

   Unlike some of the other TCP applications that are aliased (ie. FTP,
   IRC and RTSP), the PPTP control messages that need to be aliased are
   guaranteed to remain the same length.  The aliased Call ID is a fixed
   length field.

   Reference: RFC 2637

   Initial version:  May, 2000 (eds)

*/

/* Includes */
#include <sys/types.h>
#include <netinet/in_systm.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/tcp.h>

#include <stdio.h>

#include "alias_local.h"

/*
 * PPTP definitions
 */

struct grehdr			/* Enhanced GRE header. */
{
    u_int16_t gh_flags;		/* Flags. */
    u_int16_t gh_protocol;	/* Protocol type. */
    u_int16_t gh_length;	/* Payload length. */
    u_int16_t gh_call_id;	/* Call ID. */
    u_int32_t gh_seq_no;	/* Sequence number (optional). */
    u_int32_t gh_ack_no;	/* Acknowledgment number (optional). */
};
typedef struct grehdr		GreHdr;

/* The PPTP protocol ID used in the GRE 'proto' field. */
#define PPTP_GRE_PROTO          0x880b

/* Bits that must be set a certain way in all PPTP/GRE packets. */
#define PPTP_INIT_VALUE		((0x2001 << 16) | PPTP_GRE_PROTO)
#define PPTP_INIT_MASK		0xef7fffff

#define PPTP_MAGIC		0x1a2b3c4d
#define PPTP_CTRL_MSG_TYPE	1

enum {
  PPTP_StartCtrlConnRequest = 1,
  PPTP_StartCtrlConnReply = 2,
  PPTP_StopCtrlConnRequest = 3,
  PPTP_StopCtrlConnReply = 4,
  PPTP_EchoRequest = 5,
  PPTP_EchoReply = 6,
  PPTP_OutCallRequest = 7,
  PPTP_OutCallReply = 8,
  PPTP_InCallRequest = 9,
  PPTP_InCallReply = 10,
  PPTP_InCallConn = 11,
  PPTP_CallClearRequest = 12,
  PPTP_CallDiscNotify = 13,
  PPTP_WanErrorNotify = 14,
  PPTP_SetLinkInfo = 15
};

  /* Message structures */
  struct pptpMsgHead {
    u_int16_t   length;         /* total length */
    u_int16_t   msgType;        /* PPTP message type */
    u_int32_t   magic;          /* magic cookie */
    u_int16_t   type;           /* control message type */
    u_int16_t   resv0;          /* reserved */
  };
  typedef struct pptpMsgHead    *PptpMsgHead;

  struct pptpCodes {
    u_int8_t    resCode;        /* Result Code */
    u_int8_t    errCode;        /* Error Code */
  };
  typedef struct pptpCodes      *PptpCode;

  struct pptpCallIds {
    u_int16_t   cid1;           /* Call ID field #1 */
    u_int16_t   cid2;           /* Call ID field #2 */
  };
  typedef struct pptpCallIds    *PptpCallId;

static PptpCallId AliasVerifyPptp(struct ip *, u_int16_t *);


void
AliasHandlePptpOut(struct ip *pip,	    /* IP packet to examine/patch */
                   struct alias_link *link) /* The PPTP control link */
{
    struct alias_link   *pptp_link;
    PptpCallId    	cptr;
    PptpCode            codes;
    u_int16_t           ctl_type;           /* control message type */
    struct tcphdr 	*tc;

    /* Verify valid PPTP control message */
    if ((cptr = AliasVerifyPptp(pip, &ctl_type)) == NULL)
      return;

    /* Modify certain PPTP messages */
    switch (ctl_type) {
    case PPTP_OutCallRequest:
    case PPTP_OutCallReply:
    case PPTP_InCallRequest:
    case PPTP_InCallReply:
	/* Establish PPTP link for address and Call ID found in control message. */
	pptp_link = AddPptp(GetOriginalAddress(link), GetDestAddress(link),
			    GetAliasAddress(link), cptr->cid1);
	break;
    case PPTP_CallClearRequest:
    case PPTP_CallDiscNotify:
	/* Find PPTP link for address and Call ID found in control message. */
	pptp_link = FindPptpOutByCallId(GetOriginalAddress(link),
					GetDestAddress(link),
					cptr->cid1);
	break;
    default:
	return;
    }

      if (pptp_link != NULL) {
	int accumulate = cptr->cid1;

	/* alias the Call Id */
	cptr->cid1 = GetAliasPort(pptp_link);

	/* Compute TCP checksum for revised packet */
	tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
	accumulate -= cptr->cid1;
	ADJUST_CHECKSUM(accumulate, tc->th_sum);

	switch (ctl_type) {
	case PPTP_OutCallReply:
	case PPTP_InCallReply:
	    codes = (PptpCode)(cptr + 1);
	    if (codes->resCode == 1)		/* Connection established, */
		SetDestCallId(pptp_link,	/* note the Peer's Call ID. */
			      cptr->cid2);
	    else
		SetExpire(pptp_link, 0);	/* Connection refused. */
	    break;
	case PPTP_CallDiscNotify:		/* Connection closed. */
	    SetExpire(pptp_link, 0);
	    break;
	}
      }
}

void
AliasHandlePptpIn(struct ip *pip,	   /* IP packet to examine/patch */
                  struct alias_link *link) /* The PPTP control link */
{
    struct alias_link   *pptp_link;
    PptpCallId    	cptr;
    u_int16_t     	*pcall_id;
    u_int16_t           ctl_type;           /* control message type */
    struct tcphdr 	*tc;

    /* Verify valid PPTP control message */
    if ((cptr = AliasVerifyPptp(pip, &ctl_type)) == NULL)
      return;

    /* Modify certain PPTP messages */
    switch (ctl_type)
    {
    case PPTP_InCallConn:
    case PPTP_WanErrorNotify:
    case PPTP_SetLinkInfo:
      pcall_id = &cptr->cid1;
      break;
    case PPTP_OutCallReply:
    case PPTP_InCallReply:
      pcall_id = &cptr->cid2;
      break;
    case PPTP_CallDiscNotify:			/* Connection closed. */
      pptp_link = FindPptpInByCallId(GetDestAddress(link),
				     GetAliasAddress(link),
				     cptr->cid1);
      if (pptp_link != NULL)
	    SetExpire(pptp_link, 0);
      return;
    default:
      return;
    }

    /* Find PPTP link for address and Call ID found in PPTP Control Msg */
    pptp_link = FindPptpInByPeerCallId(GetDestAddress(link),
				       GetAliasAddress(link),
				       *pcall_id);

    if (pptp_link != NULL) {
      int accumulate = *pcall_id;

      /* De-alias the Peer's Call Id. */
      *pcall_id = GetOriginalPort(pptp_link);

      /* Compute TCP checksum for modified packet */
      tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
      accumulate -= *pcall_id;
      ADJUST_CHECKSUM(accumulate, tc->th_sum);

      if (ctl_type == PPTP_OutCallReply || ctl_type == PPTP_InCallReply) {
	    PptpCode codes = (PptpCode)(cptr + 1);

	    if (codes->resCode == 1)		/* Connection established, */
		SetDestCallId(pptp_link,	/* note the Call ID. */
			      cptr->cid1);
	    else
		SetExpire(pptp_link, 0);	/* Connection refused. */
      }
    }
}

static PptpCallId
AliasVerifyPptp(struct ip *pip, u_int16_t *ptype) /* IP packet to examine/patch */
{
    int           	hlen, tlen, dlen;
    PptpMsgHead   	hptr;
    struct tcphdr 	*tc;

    /* Calculate some lengths */
    tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
    hlen = (pip->ip_hl + tc->th_off) << 2;
    tlen = ntohs(pip->ip_len);
    dlen = tlen - hlen;

    /* Verify data length */
    if (dlen < (sizeof(struct pptpMsgHead) + sizeof(struct pptpCallIds)))
      return(NULL);

    /* Move up to PPTP message header */
    hptr = (PptpMsgHead)(((char *) pip) + hlen);

    /* Return the control message type */
    *ptype = ntohs(hptr->type);

    /* Verify PPTP Control Message */
    if ((ntohs(hptr->msgType) != PPTP_CTRL_MSG_TYPE) ||
        (ntohl(hptr->magic) != PPTP_MAGIC))
      return(NULL);

    /* Verify data length. */
    if ((*ptype == PPTP_OutCallReply || *ptype == PPTP_InCallReply) &&
	(dlen < sizeof(struct pptpMsgHead) + sizeof(struct pptpCallIds) +
		sizeof(struct pptpCodes)))
	return (NULL);
    else
	return (PptpCallId)(hptr + 1);
}


int
AliasHandlePptpGreOut(struct ip *pip)
{
    GreHdr		*gr;
    struct alias_link	*link;

    gr = (GreHdr *)((char *)pip + (pip->ip_hl << 2));

    /* Check GRE header bits. */
    if ((ntohl(*((u_int32_t *)gr)) & PPTP_INIT_MASK) != PPTP_INIT_VALUE)
	return (-1);

    link = FindPptpOutByPeerCallId(pip->ip_src, pip->ip_dst, gr->gh_call_id);
    if (link != NULL) {
	struct in_addr alias_addr = GetAliasAddress(link);

	/* Change source IP address. */
	DifferentialChecksum(&pip->ip_sum,
			     (u_short *)&alias_addr,
			     (u_short *)&pip->ip_src,
			     2);
	pip->ip_src = alias_addr;
    }

    return (0);
}


int
AliasHandlePptpGreIn(struct ip *pip)
{
    GreHdr		*gr;
    struct alias_link	*link;

    gr = (GreHdr *)((char *)pip + (pip->ip_hl << 2));

    /* Check GRE header bits. */
    if ((ntohl(*((u_int32_t *)gr)) & PPTP_INIT_MASK) != PPTP_INIT_VALUE)
	return (-1);

    link = FindPptpInByPeerCallId(pip->ip_src, pip->ip_dst, gr->gh_call_id);
    if (link != NULL) {
	struct in_addr src_addr = GetOriginalAddress(link);

	/* De-alias the Peer's Call Id. */
	gr->gh_call_id = GetOriginalPort(link);

	/* Restore original IP address. */
	DifferentialChecksum(&pip->ip_sum,
			     (u_short *)&src_addr,
			     (u_short *)&pip->ip_dst,
			     2);
	pip->ip_dst = src_addr;
    }

    return (0);
}
Commit	Line	Data
7ba0088d A	1	/*
	2	* Copyright (c) 2000-2002 Apple Computer, Inc. All rights reserved.
	3	*
	4	* @APPLE_LICENSE_HEADER_START@
	5	*
a2c93a76 A	6	* The contents of this file constitute Original Code as defined in and
	7	* are subject to the Apple Public Source License Version 1.1 (the
	8	* "License"). You may not use this file except in compliance with the
	9	* License. Please obtain a copy of the License at
	10	* http://www.apple.com/publicsource and read it before using this file.
7ba0088d	11	*
a2c93a76 A	12	* This Original Code and all software distributed under the License are
a2c93a76 A	13	* distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
7ba0088d A	14	* EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
7ba0088d A	15	* INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
a2c93a76 A	16	* FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT. Please see the
	17	* License for the specific language governing rights and limitations
	18	* under the License.
7ba0088d A	19	*
	20	* @APPLE_LICENSE_HEADER_END@
	21	*/
	22	/*
	23	* alias_pptp.c
	24	*
	25	* Copyright (c) 2000 Whistle Communications, Inc.
	26	* All rights reserved.
	27	*
	28	* Subject to the following obligations and disclaimer of warranty, use and
	29	* redistribution of this software, in source or object code forms, with or
	30	* without modifications are expressly permitted by Whistle Communications;
	31	* provided, however, that:
	32	* 1. Any and all reproductions of the source or object code must include the
	33	* copyright notice above and the following disclaimer of warranties; and
	34	* 2. No rights are granted, in any manner or form, to use Whistle
	35	* Communications, Inc. trademarks, including the mark "WHISTLE
	36	* COMMUNICATIONS" on advertising, endorsements, or otherwise except as
	37	* such appears in the above copyright notice or in the software.
	38	*
	39	* THIS SOFTWARE IS BEING PROVIDED BY WHISTLE COMMUNICATIONS "AS IS", AND
	40	* TO THE MAXIMUM EXTENT PERMITTED BY LAW, WHISTLE COMMUNICATIONS MAKES NO
	41	* REPRESENTATIONS OR WARRANTIES, EXPRESS OR IMPLIED, REGARDING THIS SOFTWARE,
	42	* INCLUDING WITHOUT LIMITATION, ANY AND ALL IMPLIED WARRANTIES OF
	43	* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT.
	44	* WHISTLE COMMUNICATIONS DOES NOT WARRANT, GUARANTEE, OR MAKE ANY
	45	* REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS OF THE USE OF THIS
	46	* SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, RELIABILITY OR OTHERWISE.
	47	* IN NO EVENT SHALL WHISTLE COMMUNICATIONS BE LIABLE FOR ANY DAMAGES
	48	* RESULTING FROM OR ARISING OUT OF ANY USE OF THIS SOFTWARE, INCLUDING
	49	* WITHOUT LIMITATION, ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
	50	* PUNITIVE, OR CONSEQUENTIAL DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR
	51	* SERVICES, LOSS OF USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY
	52	* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	53	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
	54	* THIS SOFTWARE, EVEN IF WHISTLE COMMUNICATIONS IS ADVISED OF THE POSSIBILITY
	55	* OF SUCH DAMAGE.
	56	*
	57	* Author: Erik Salander <erik@whistle.com>
	58	*
	59	* Based upon:
	60	* $FreeBSD: src/lib/libalias/alias_pptp.c,v 1.1.2.4 2001/08/01 09:52:27 obrien Exp $
	61	*/
	62
	63	/*
	64	Alias_pptp.c performs special processing for PPTP sessions under TCP.
	65	Specifically, watch PPTP control messages and alias the Call ID or the
	66	Peer's Call ID in the appropriate messages. Note, PPTP requires
	67	"de-aliasing" of incoming packets, this is different than any other
	68	TCP applications that are currently (ie. FTP, IRC and RTSP) aliased.
	69
	70	For Call IDs encountered for the first time, a PPTP alias link is created.
	71	The PPTP alias link uses the Call ID in place of the original port number.
	72	An alias Call ID is created.
	73
	74	For this routine to work, the PPTP control messages must fit entirely
	75	into a single TCP packet. This is typically the case, but is not
	76	required by the spec.
	77
	78	Unlike some of the other TCP applications that are aliased (ie. FTP,
	79	IRC and RTSP), the PPTP control messages that need to be aliased are
	80	guaranteed to remain the same length. The aliased Call ID is a fixed
	81	length field.
	82
83	Reference: RFC 2637
84
85	Initial version: May, 2000 (eds)
86
87	*/
88
89	/* Includes */
90	#include <sys/types.h>
91	#include <netinet/in_systm.h>
92	#include <netinet/in.h>
93	#include <netinet/ip.h>
94	#include <netinet/tcp.h>
95
96	#include <stdio.h>
97
98	#include "alias_local.h"
99
100	/*
101	* PPTP definitions
102	*/
103
104	struct grehdr /* Enhanced GRE header. */
105	{
106	u_int16_t gh_flags; /* Flags. */
107	u_int16_t gh_protocol; /* Protocol type. */
108	u_int16_t gh_length; /* Payload length. */
109	u_int16_t gh_call_id; /* Call ID. */
110	u_int32_t gh_seq_no; /* Sequence number (optional). */
111	u_int32_t gh_ack_no; /* Acknowledgment number (optional). */
112	};
113	typedef struct grehdr GreHdr;
114
115	/* The PPTP protocol ID used in the GRE 'proto' field. */
116	#define PPTP_GRE_PROTO 0x880b
117
118	/* Bits that must be set a certain way in all PPTP/GRE packets. */
119	#define PPTP_INIT_VALUE ((0x2001 << 16) \| PPTP_GRE_PROTO)
120	#define PPTP_INIT_MASK 0xef7fffff
121
122	#define PPTP_MAGIC 0x1a2b3c4d
123	#define PPTP_CTRL_MSG_TYPE 1
124
125	enum {
126	PPTP_StartCtrlConnRequest = 1,
127	PPTP_StartCtrlConnReply = 2,
128	PPTP_StopCtrlConnRequest = 3,
129	PPTP_StopCtrlConnReply = 4,
130	PPTP_EchoRequest = 5,
131	PPTP_EchoReply = 6,
132	PPTP_OutCallRequest = 7,
133	PPTP_OutCallReply = 8,
134	PPTP_InCallRequest = 9,
135	PPTP_InCallReply = 10,
136	PPTP_InCallConn = 11,
137	PPTP_CallClearRequest = 12,
138	PPTP_CallDiscNotify = 13,
139	PPTP_WanErrorNotify = 14,
140	PPTP_SetLinkInfo = 15
141	};
142
143	/* Message structures */
144	struct pptpMsgHead {
145	u_int16_t length; /* total length */
146	u_int16_t msgType; /* PPTP message type */
147	u_int32_t magic; /* magic cookie */
148	u_int16_t type; /* control message type */
149	u_int16_t resv0; /* reserved */
150	};
151	typedef struct pptpMsgHead *PptpMsgHead;
152
153	struct pptpCodes {
154	u_int8_t resCode; /* Result Code */
155	u_int8_t errCode; /* Error Code */
156	};
157	typedef struct pptpCodes *PptpCode;
158
159	struct pptpCallIds {
160	u_int16_t cid1; /* Call ID field #1 */
161	u_int16_t cid2; /* Call ID field #2 */
162	};
163	typedef struct pptpCallIds *PptpCallId;
164
165	static PptpCallId AliasVerifyPptp(struct ip , u_int16_t );
166
167
168	void
169	AliasHandlePptpOut(struct ip pip, / IP packet to examine/patch */
170	struct alias_link link) / The PPTP control link */
171	{
172	struct alias_link *pptp_link;
173	PptpCallId cptr;
174	PptpCode codes;
175	u_int16_t ctl_type; /* control message type */
176	struct tcphdr *tc;
177
178	/* Verify valid PPTP control message */
179	if ((cptr = AliasVerifyPptp(pip, &ctl_type)) == NULL)
180	return;
181
182	/* Modify certain PPTP messages */
183	switch (ctl_type) {
184	case PPTP_OutCallRequest:
185	case PPTP_OutCallReply:
186	case PPTP_InCallRequest:
187	case PPTP_InCallReply:
188	/* Establish PPTP link for address and Call ID found in control message. */
189	pptp_link = AddPptp(GetOriginalAddress(link), GetDestAddress(link),
190	GetAliasAddress(link), cptr->cid1);
191	break;
192	case PPTP_CallClearRequest:
193	case PPTP_CallDiscNotify:
194	/* Find PPTP link for address and Call ID found in control message. */
195	pptp_link = FindPptpOutByCallId(GetOriginalAddress(link),
196	GetDestAddress(link),
197	cptr->cid1);
198	break;
199	default:
200	return;
201	}
202
203	if (pptp_link != NULL) {
204	int accumulate = cptr->cid1;
205
206	/* alias the Call Id */
207	cptr->cid1 = GetAliasPort(pptp_link);
208
209	/* Compute TCP checksum for revised packet */
210	tc = (struct tcphdr ) ((char ) pip + (pip->ip_hl << 2));
211	accumulate -= cptr->cid1;
212	ADJUST_CHECKSUM(accumulate, tc->th_sum);
213
214	switch (ctl_type) {
215	case PPTP_OutCallReply:
216	case PPTP_InCallReply:
217	codes = (PptpCode)(cptr + 1);
218	if (codes->resCode == 1) /* Connection established, */
219	SetDestCallId(pptp_link, /* note the Peer's Call ID. */
220	cptr->cid2);
221	else
222	SetExpire(pptp_link, 0); /* Connection refused. */
223	break;
224	case PPTP_CallDiscNotify: /* Connection closed. */
225	SetExpire(pptp_link, 0);
226	break;
227	}
228	}
229	}
230
231	void
232	AliasHandlePptpIn(struct ip pip, / IP packet to examine/patch */
233	struct alias_link link) / The PPTP control link */
234	{
235	struct alias_link *pptp_link;
236	PptpCallId cptr;
237	u_int16_t *pcall_id;
238	u_int16_t ctl_type; /* control message type */
239	struct tcphdr *tc;
240
241	/* Verify valid PPTP control message */
242	if ((cptr = AliasVerifyPptp(pip, &ctl_type)) == NULL)
243	return;
244
245	/* Modify certain PPTP messages */
246	switch (ctl_type)
247	{
248	case PPTP_InCallConn:
249	case PPTP_WanErrorNotify:
250	case PPTP_SetLinkInfo:
251	pcall_id = &cptr->cid1;
252	break;
253	case PPTP_OutCallReply:
254	case PPTP_InCallReply:
255	pcall_id = &cptr->cid2;
256	break;
257	case PPTP_CallDiscNotify: /* Connection closed. */
258	pptp_link = FindPptpInByCallId(GetDestAddress(link),
259	GetAliasAddress(link),
260	cptr->cid1);
261	if (pptp_link != NULL)
262	SetExpire(pptp_link, 0);
263	return;
264	default:
265	return;
266	}
267
268	/* Find PPTP link for address and Call ID found in PPTP Control Msg */
269	pptp_link = FindPptpInByPeerCallId(GetDestAddress(link),
270	GetAliasAddress(link),
271	*pcall_id);
272
273	if (pptp_link != NULL) {
274	int accumulate = *pcall_id;
275
276	/* De-alias the Peer's Call Id. */
277	*pcall_id = GetOriginalPort(pptp_link);
278
279	/* Compute TCP checksum for modified packet */
280	tc = (struct tcphdr ) ((char ) pip + (pip->ip_hl << 2));
281	accumulate -= *pcall_id;
282	ADJUST_CHECKSUM(accumulate, tc->th_sum);
283
284	if (ctl_type == PPTP_OutCallReply \|\| ctl_type == PPTP_InCallReply) {
285	PptpCode codes = (PptpCode)(cptr + 1);
286
287	if (codes->resCode == 1) /* Connection established, */
288	SetDestCallId(pptp_link, /* note the Call ID. */
289	cptr->cid1);
290	else
291	SetExpire(pptp_link, 0); /* Connection refused. */
292	}
293	}
294	}
295
296	static PptpCallId
297	AliasVerifyPptp(struct ip pip, u_int16_t ptype) /* IP packet to examine/patch */
298	{
299	int hlen, tlen, dlen;
300	PptpMsgHead hptr;
301	struct tcphdr *tc;
302
303	/* Calculate some lengths */
304	tc = (struct tcphdr ) ((char ) pip + (pip->ip_hl << 2));
305	hlen = (pip->ip_hl + tc->th_off) << 2;
306	tlen = ntohs(pip->ip_len);
307	dlen = tlen - hlen;
308
309	/* Verify data length */
310	if (dlen < (sizeof(struct pptpMsgHead) + sizeof(struct pptpCallIds)))
311	return(NULL);
312
313	/* Move up to PPTP message header */
314	hptr = (PptpMsgHead)(((char *) pip) + hlen);
315
316	/* Return the control message type */
317	*ptype = ntohs(hptr->type);
318
319	/* Verify PPTP Control Message */
320	if ((ntohs(hptr->msgType) != PPTP_CTRL_MSG_TYPE) \|\|
321	(ntohl(hptr->magic) != PPTP_MAGIC))
322	return(NULL);
323
324	/* Verify data length. */
325	if ((ptype == PPTP_OutCallReply \|\| ptype == PPTP_InCallReply) &&
326	(dlen < sizeof(struct pptpMsgHead) + sizeof(struct pptpCallIds) +
327	sizeof(struct pptpCodes)))
328	return (NULL);
329	else
330	return (PptpCallId)(hptr + 1);
331	}
332
333
334	int
335	AliasHandlePptpGreOut(struct ip *pip)
336	{
337	GreHdr *gr;
338	struct alias_link *link;
339
340	gr = (GreHdr )((char )pip + (pip->ip_hl << 2));
341
342	/* Check GRE header bits. */
343	if ((ntohl(((u_int32_t )gr)) & PPTP_INIT_MASK) != PPTP_INIT_VALUE)
344	return (-1);
345
346	link = FindPptpOutByPeerCallId(pip->ip_src, pip->ip_dst, gr->gh_call_id);
347	if (link != NULL) {
348	struct in_addr alias_addr = GetAliasAddress(link);
349
350	/* Change source IP address. */
351	DifferentialChecksum(&pip->ip_sum,
352	(u_short *)&alias_addr,
353	(u_short *)&pip->ip_src,
354	2);
355	pip->ip_src = alias_addr;
356	}
357
358	return (0);
359	}
360
361
362	int
363	AliasHandlePptpGreIn(struct ip *pip)
364	{
365	GreHdr *gr;
366	struct alias_link *link;
367
368	gr = (GreHdr )((char )pip + (pip->ip_hl << 2));
369
370	/* Check GRE header bits. */
371	if ((ntohl(((u_int32_t )gr)) & PPTP_INIT_MASK) != PPTP_INIT_VALUE)
372	return (-1);
373
374	link = FindPptpInByPeerCallId(pip->ip_src, pip->ip_dst, gr->gh_call_id);
375	if (link != NULL) {
376	struct in_addr src_addr = GetOriginalAddress(link);
377
378	/* De-alias the Peer's Call Id. */
379	gr->gh_call_id = GetOriginalPort(link);
380
381	/* Restore original IP address. */
382	DifferentialChecksum(&pip->ip_sum,
383	(u_short *)&src_addr,
384	(u_short *)&pip->ip_dst,
385	2);
386	pip->ip_dst = src_addr;
387	}
388
389	return (0);
390	}