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 * $FreeBSD$ 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 <ctype.h> 69 #include <stdio.h> 70 #include <string.h> 71 #include <sys/types.h> 72 #include <netinet/in_systm.h> 73 #include <netinet/in.h> 74 #include <netinet/ip.h> 75 #include <netinet/tcp.h> 76 77 #include "alias_local.h" 78 79 /* 80 * PPTP definitions 81 */ 82 83 struct grehdr /* Enhanced GRE header. */ 84 { 85 u_char gh_recursion:3, /* Recursion control. */ 86 gh_ssr_flag:1, /* Strict source route present. */ 87 gh_seq_no_flag:1, /* Sequence number present. */ 88 gh_key_flag:1, /* Key present. */ 89 gh_rt_flag:1, /* Routing present. */ 90 gh_cksum_flag:1; /* Checksum present. */ 91 u_char gh_version:3, /* GRE version. */ 92 gh_flags:4, /* Flags. */ 93 gh_ack_no_flag:1; /* Acknowledgment sequence number present. */ 94 u_short gh_protocol; /* Protocol type. */ 95 u_short gh_length; /* Payload length. */ 96 u_short gh_call_id; /* Call ID. */ 97 u_int32_t gh_seq_no; /* Sequence number (optional). */ 98 u_int32_t gh_ack_no; /* Acknowledgment number (optional). */ 99 }; 100 101 /* The PPTP protocol ID used in the GRE 'proto' field. */ 102 #define PPTP_GRE_PROTO 0x880b 103 104 /* Bits that must be set a certain way in all PPTP/GRE packets. */ 105 #define PPTP_INIT_VALUE ((0x2001 << 16) | PPTP_GRE_PROTO) 106 #define PPTP_INIT_MASK 0xef7fffff 107 108 #define PPTP_MAGIC 0x1a2b3c4d 109 #define PPTP_CTRL_MSG_TYPE 1 110 111 enum { 112 PPTP_StartCtrlConnRequest = 1, 113 PPTP_StartCtrlConnReply = 2, 114 PPTP_StopCtrlConnRequest = 3, 115 PPTP_StopCtrlConnReply = 4, 116 PPTP_EchoRequest = 5, 117 PPTP_EchoReply = 6, 118 PPTP_OutCallRequest = 7, 119 PPTP_OutCallReply = 8, 120 PPTP_InCallRequest = 9, 121 PPTP_InCallReply = 10, 122 PPTP_InCallConn = 11, 123 PPTP_CallClearRequest = 12, 124 PPTP_CallDiscNotify = 13, 125 PPTP_WanErrorNotify = 14, 126 PPTP_SetLinkInfo = 15, 127 }; 128 129 /* Message structures */ 130 struct pptpMsgHead { 131 u_int16_t length; /* total length */ 132 u_int16_t msgType; /* PPTP message type */ 133 u_int32_t magic; /* magic cookie */ 134 u_int16_t type; /* control message type */ 135 u_int16_t resv0; /* reserved */ 136 }; 137 typedef struct pptpMsgHead *PptpMsgHead; 138 139 struct pptpCallIds { 140 u_int16_t cid1; /* Call ID field #1 */ 141 u_int16_t cid2; /* Call ID field #2 */ 142 }; 143 typedef struct pptpCallIds *PptpCallId; 144 145 static PptpCallId AliasVerifyPptp(struct ip *, u_int16_t *); 146 147 int 148 PptpGetCallID(struct ip *pip, 149 u_short *call_id) 150 { 151 struct grehdr *gr; 152 153 gr = (struct grehdr *)((char *)pip + (pip->ip_hl << 2)); 154 155 /* Check GRE header bits. */ 156 if ((ntohl(*((u_int32_t *)gr)) & PPTP_INIT_MASK) == PPTP_INIT_VALUE) { 157 *call_id = gr->gh_call_id; 158 return 1; 159 } else 160 return 0; 161 }; 162 163 void PptpSetCallID(struct ip *pip, u_short call_id) 164 { 165 struct grehdr *gr; 166 167 gr = (struct grehdr *)((char *)pip + (pip->ip_hl << 2)); 168 gr->gh_call_id = call_id; 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 u_int16_t ctl_type; /* control message type */ 178 struct tcphdr *tc; 179 180 /* Verify valid PPTP control message */ 181 if ((cptr = AliasVerifyPptp(pip, &ctl_type)) == NULL) 182 return; 183 184 /* Modify certain PPTP messages */ 185 switch (ctl_type) { 186 case PPTP_OutCallRequest: 187 case PPTP_OutCallReply: 188 case PPTP_InCallRequest: 189 case PPTP_InCallReply: 190 case PPTP_CallClearRequest: 191 case PPTP_CallDiscNotify: 192 193 /* Establish PPTP link for address and Call ID found in PPTP Control Msg */ 194 pptp_link = FindPptpOut(GetOriginalAddress(link), GetDestAddress(link), 195 cptr->cid1); 196 197 if (pptp_link != NULL) { 198 int accumulate = cptr->cid1; 199 200 /* alias the Call Id */ 201 cptr->cid1 = GetAliasPort(pptp_link); 202 203 /* Compute TCP checksum for revised packet */ 204 tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2)); 205 accumulate -= cptr->cid1; 206 ADJUST_CHECKSUM(accumulate, tc->th_sum); 207 } 208 break; 209 default: 210 return; 211 } 212 } 213 214 void 215 AliasHandlePptpIn(struct ip *pip, /* IP packet to examine/patch */ 216 struct alias_link *link) /* The PPTP control link */ 217 { 218 struct alias_link *pptp_link; 219 PptpCallId cptr; 220 u_int16_t *pcall_id; 221 u_int16_t ctl_type; /* control message type */ 222 struct tcphdr *tc; 223 224 /* Verify valid PPTP control message */ 225 if ((cptr = AliasVerifyPptp(pip, &ctl_type)) == NULL) 226 return; 227 228 /* Modify certain PPTP messages */ 229 switch (ctl_type) 230 { 231 case PPTP_InCallConn: 232 case PPTP_WanErrorNotify: 233 case PPTP_SetLinkInfo: 234 pcall_id = &cptr->cid1; 235 break; 236 case PPTP_OutCallReply: 237 case PPTP_InCallReply: 238 pcall_id = &cptr->cid2; 239 break; 240 default: 241 return; 242 } 243 244 /* Find PPTP link for address and Call ID found in PPTP Control Msg */ 245 pptp_link = FindPptpIn(GetDestAddress(link), GetAliasAddress(link), 246 *pcall_id); 247 248 if (pptp_link != NULL) { 249 int accumulate = *pcall_id; 250 251 /* alias the Call Id */ 252 *pcall_id = GetOriginalPort(pptp_link); 253 254 /* Compute TCP checksum for modified packet */ 255 tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2)); 256 accumulate -= *pcall_id; 257 ADJUST_CHECKSUM(accumulate, tc->th_sum); 258 } 259 } 260 261 PptpCallId 262 AliasVerifyPptp(struct ip *pip, u_int16_t *ptype) /* IP packet to examine/patch */ 263 { 264 int hlen, tlen, dlen; 265 PptpMsgHead hptr; 266 struct tcphdr *tc; 267 268 /* Calculate some lengths */ 269 tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2)); 270 hlen = (pip->ip_hl + tc->th_off) << 2; 271 tlen = ntohs(pip->ip_len); 272 dlen = tlen - hlen; 273 274 /* Verify data length */ 275 if (dlen < (sizeof(struct pptpMsgHead) + sizeof(struct pptpCallIds))) 276 return(NULL); 277 278 /* Move up to PPTP message header */ 279 hptr = (PptpMsgHead)(((char *) pip) + hlen); 280 281 /* Return the control message type */ 282 *ptype = ntohs(hptr->type); 283 284 /* Verify PPTP Control Message */ 285 if ((ntohs(hptr->msgType) != PPTP_CTRL_MSG_TYPE) || 286 (ntohl(hptr->magic) != PPTP_MAGIC)) 287 return(NULL); 288 else 289 return((PptpCallId)(((char *)hptr) + sizeof(struct pptpMsgHead))); 290 } 291