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 <[email protected]> 37 */ 38 39 #include <sys/cdefs.h> 40 __FBSDID("$FreeBSD$"); 41 42 /* 43 Alias_pptp.c performs special processing for PPTP sessions under TCP. 44 Specifically, watch PPTP control messages and alias the Call ID or the 45 Peer's Call ID in the appropriate messages. Note, PPTP requires 46 "de-aliasing" of incoming packets, this is different than any other 47 TCP applications that are currently (ie. FTP, IRC and RTSP) aliased. 48 49 For Call IDs encountered for the first time, a PPTP alias link is created. 50 The PPTP alias link uses the Call ID in place of the original port number. 51 An alias Call ID is created. 52 53 For this routine to work, the PPTP control messages must fit entirely 54 into a single TCP packet. This is typically the case, but is not 55 required by the spec. 56 57 Unlike some of the other TCP applications that are aliased (ie. FTP, 58 IRC and RTSP), the PPTP control messages that need to be aliased are 59 guaranteed to remain the same length. The aliased Call ID is a fixed 60 length field. 61 62 Reference: RFC 2637 63 64 Initial version: May, 2000 (eds) 65 66 */ 67 68 /* Includes */ 69 #ifdef _KERNEL 70 #include <sys/param.h> 71 #else 72 #include <sys/types.h> 73 #include <stdio.h> 74 #endif 75 76 #include <netinet/in_systm.h> 77 #include <netinet/in.h> 78 #include <netinet/ip.h> 79 #include <netinet/tcp.h> 80 81 #ifdef _KERNEL 82 #include <netinet/libalias/alias_local.h> 83 #else 84 #include "alias_local.h" 85 #endif 86 87 /* 88 * PPTP definitions 89 */ 90 91 struct grehdr { /* Enhanced GRE header. */ 92 u_int16_t gh_flags; /* Flags. */ 93 u_int16_t gh_protocol; /* Protocol type. */ 94 u_int16_t gh_length; /* Payload length. */ 95 u_int16_t gh_call_id; /* Call ID. */ 96 u_int32_t gh_seq_no; /* Sequence number (optional). */ 97 u_int32_t gh_ack_no; /* Acknowledgment number 98 * (optional). */ 99 }; 100 typedef struct grehdr GreHdr; 101 102 /* The PPTP protocol ID used in the GRE 'proto' field. */ 103 #define PPTP_GRE_PROTO 0x880b 104 105 /* Bits that must be set a certain way in all PPTP/GRE packets. */ 106 #define PPTP_INIT_VALUE ((0x2001 << 16) | PPTP_GRE_PROTO) 107 #define PPTP_INIT_MASK 0xef7fffff 108 109 #define PPTP_MAGIC 0x1a2b3c4d 110 #define PPTP_CTRL_MSG_TYPE 1 111 112 enum { 113 PPTP_StartCtrlConnRequest = 1, 114 PPTP_StartCtrlConnReply = 2, 115 PPTP_StopCtrlConnRequest = 3, 116 PPTP_StopCtrlConnReply = 4, 117 PPTP_EchoRequest = 5, 118 PPTP_EchoReply = 6, 119 PPTP_OutCallRequest = 7, 120 PPTP_OutCallReply = 8, 121 PPTP_InCallRequest = 9, 122 PPTP_InCallReply = 10, 123 PPTP_InCallConn = 11, 124 PPTP_CallClearRequest = 12, 125 PPTP_CallDiscNotify = 13, 126 PPTP_WanErrorNotify = 14, 127 PPTP_SetLinkInfo = 15 128 }; 129 130 /* Message structures */ 131 struct pptpMsgHead { 132 u_int16_t length; /* total length */ 133 u_int16_t msgType;/* PPTP message type */ 134 u_int32_t magic; /* magic cookie */ 135 u_int16_t type; /* control message type */ 136 u_int16_t resv0; /* reserved */ 137 }; 138 typedef struct pptpMsgHead *PptpMsgHead; 139 140 struct pptpCodes { 141 u_int8_t resCode;/* Result Code */ 142 u_int8_t errCode;/* Error Code */ 143 }; 144 typedef struct pptpCodes *PptpCode; 145 146 struct pptpCallIds { 147 u_int16_t cid1; /* Call ID field #1 */ 148 u_int16_t cid2; /* Call ID field #2 */ 149 }; 150 typedef struct pptpCallIds *PptpCallId; 151 152 static PptpCallId AliasVerifyPptp(struct ip *, u_int16_t *); 153 154 155 void 156 AliasHandlePptpOut(struct libalias *la, 157 struct ip *pip, /* IP packet to examine/patch */ 158 struct alias_link *lnk) 159 { /* The PPTP control link */ 160 struct alias_link *pptp_lnk; 161 PptpCallId cptr; 162 PptpCode codes; 163 u_int16_t ctl_type; /* control message type */ 164 struct tcphdr *tc; 165 166 /* Verify valid PPTP control message */ 167 if ((cptr = AliasVerifyPptp(pip, &ctl_type)) == NULL) 168 return; 169 170 /* Modify certain PPTP messages */ 171 switch (ctl_type) { 172 case PPTP_OutCallRequest: 173 case PPTP_OutCallReply: 174 case PPTP_InCallRequest: 175 case PPTP_InCallReply: 176 /* 177 * Establish PPTP link for address and Call ID found in 178 * control message. 179 */ 180 pptp_lnk = AddPptp(la, GetOriginalAddress(lnk), GetDestAddress(lnk), 181 GetAliasAddress(lnk), cptr->cid1); 182 break; 183 case PPTP_CallClearRequest: 184 case PPTP_CallDiscNotify: 185 /* 186 * Find PPTP link for address and Call ID found in control 187 * message. 188 */ 189 pptp_lnk = FindPptpOutByCallId(la, GetOriginalAddress(lnk), 190 GetDestAddress(lnk), 191 cptr->cid1); 192 break; 193 default: 194 return; 195 } 196 197 if (pptp_lnk != NULL) { 198 int accumulate = cptr->cid1; 199 200 /* alias the Call Id */ 201 cptr->cid1 = GetAliasPort(pptp_lnk); 202 203 /* Compute TCP checksum for revised packet */ 204 tc = (struct tcphdr *)ip_next(pip); 205 accumulate -= cptr->cid1; 206 ADJUST_CHECKSUM(accumulate, tc->th_sum); 207 208 switch (ctl_type) { 209 case PPTP_OutCallReply: 210 case PPTP_InCallReply: 211 codes = (PptpCode) (cptr + 1); 212 if (codes->resCode == 1) /* Connection 213 * established, */ 214 SetDestCallId(pptp_lnk, /* note the Peer's Call 215 * ID. */ 216 cptr->cid2); 217 else 218 SetExpire(pptp_lnk, 0); /* Connection refused. */ 219 break; 220 case PPTP_CallDiscNotify: /* Connection closed. */ 221 SetExpire(pptp_lnk, 0); 222 break; 223 } 224 } 225 } 226 227 void 228 AliasHandlePptpIn(struct libalias *la, 229 struct ip *pip, /* IP packet to examine/patch */ 230 struct alias_link *lnk) 231 { /* The PPTP control link */ 232 struct alias_link *pptp_lnk; 233 PptpCallId cptr; 234 u_int16_t *pcall_id; 235 u_int16_t ctl_type; /* control message type */ 236 struct tcphdr *tc; 237 238 /* Verify valid PPTP control message */ 239 if ((cptr = AliasVerifyPptp(pip, &ctl_type)) == NULL) 240 return; 241 242 /* Modify certain PPTP messages */ 243 switch (ctl_type) { 244 case PPTP_InCallConn: 245 case PPTP_WanErrorNotify: 246 case PPTP_SetLinkInfo: 247 pcall_id = &cptr->cid1; 248 break; 249 case PPTP_OutCallReply: 250 case PPTP_InCallReply: 251 pcall_id = &cptr->cid2; 252 break; 253 case PPTP_CallDiscNotify: /* Connection closed. */ 254 pptp_lnk = FindPptpInByCallId(la, GetDestAddress(lnk), 255 GetAliasAddress(lnk), 256 cptr->cid1); 257 if (pptp_lnk != NULL) 258 SetExpire(pptp_lnk, 0); 259 return; 260 default: 261 return; 262 } 263 264 /* Find PPTP link for address and Call ID found in PPTP Control Msg */ 265 pptp_lnk = FindPptpInByPeerCallId(la, GetDestAddress(lnk), 266 GetAliasAddress(lnk), 267 *pcall_id); 268 269 if (pptp_lnk != NULL) { 270 int accumulate = *pcall_id; 271 272 /* De-alias the Peer's Call Id. */ 273 *pcall_id = GetOriginalPort(pptp_lnk); 274 275 /* Compute TCP checksum for modified packet */ 276 tc = (struct tcphdr *)ip_next(pip); 277 accumulate -= *pcall_id; 278 ADJUST_CHECKSUM(accumulate, tc->th_sum); 279 280 if (ctl_type == PPTP_OutCallReply || ctl_type == PPTP_InCallReply) { 281 PptpCode codes = (PptpCode) (cptr + 1); 282 283 if (codes->resCode == 1) /* Connection 284 * established, */ 285 SetDestCallId(pptp_lnk, /* note the Call ID. */ 286 cptr->cid1); 287 else 288 SetExpire(pptp_lnk, 0); /* Connection refused. */ 289 } 290 } 291 } 292 293 static PptpCallId 294 AliasVerifyPptp(struct ip *pip, u_int16_t * ptype) 295 { /* IP packet to examine/patch */ 296 int hlen, tlen, dlen; 297 PptpMsgHead hptr; 298 struct tcphdr *tc; 299 300 /* Calculate some lengths */ 301 tc = (struct tcphdr *)ip_next(pip); 302 hlen = (pip->ip_hl + tc->th_off) << 2; 303 tlen = ntohs(pip->ip_len); 304 dlen = tlen - hlen; 305 306 /* Verify data length */ 307 if (dlen < (int)(sizeof(struct pptpMsgHead) + sizeof(struct pptpCallIds))) 308 return (NULL); 309 310 /* Move up to PPTP message header */ 311 hptr = (PptpMsgHead) tcp_next(tc); 312 313 /* Return the control message type */ 314 *ptype = ntohs(hptr->type); 315 316 /* Verify PPTP Control Message */ 317 if ((ntohs(hptr->msgType) != PPTP_CTRL_MSG_TYPE) || 318 (ntohl(hptr->magic) != PPTP_MAGIC)) 319 return (NULL); 320 321 /* Verify data length. */ 322 if ((*ptype == PPTP_OutCallReply || *ptype == PPTP_InCallReply) && 323 (dlen < (int)(sizeof(struct pptpMsgHead) + sizeof(struct pptpCallIds) + 324 sizeof(struct pptpCodes)))) 325 return (NULL); 326 else 327 return (PptpCallId) (hptr + 1); 328 } 329 330 331 int 332 AliasHandlePptpGreOut(struct libalias *la, struct ip *pip) 333 { 334 GreHdr *gr; 335 struct alias_link *lnk; 336 337 gr = (GreHdr *) ip_next(pip); 338 339 /* Check GRE header bits. */ 340 if ((ntohl(*((u_int32_t *) gr)) & PPTP_INIT_MASK) != PPTP_INIT_VALUE) 341 return (-1); 342 343 lnk = FindPptpOutByPeerCallId(la, pip->ip_src, pip->ip_dst, gr->gh_call_id); 344 if (lnk != NULL) { 345 struct in_addr alias_addr = GetAliasAddress(lnk); 346 347 /* Change source IP address. */ 348 DifferentialChecksum(&pip->ip_sum, 349 &alias_addr, &pip->ip_src, 2); 350 pip->ip_src = alias_addr; 351 } 352 return (0); 353 } 354 355 356 int 357 AliasHandlePptpGreIn(struct libalias *la, struct ip *pip) 358 { 359 GreHdr *gr; 360 struct alias_link *lnk; 361 362 gr = (GreHdr *) ip_next(pip); 363 364 /* Check GRE header bits. */ 365 if ((ntohl(*((u_int32_t *) gr)) & PPTP_INIT_MASK) != PPTP_INIT_VALUE) 366 return (-1); 367 368 lnk = FindPptpInByPeerCallId(la, pip->ip_src, pip->ip_dst, gr->gh_call_id); 369 if (lnk != NULL) { 370 struct in_addr src_addr = GetOriginalAddress(lnk); 371 372 /* De-alias the Peer's Call Id. */ 373 gr->gh_call_id = GetOriginalPort(lnk); 374 375 /* Restore original IP address. */ 376 DifferentialChecksum(&pip->ip_sum, 377 &src_addr, &pip->ip_dst, 2); 378 pip->ip_dst = src_addr; 379 } 380 return (0); 381 } 382