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