ppp.c

   1 // L2TPNS PPP Stuff
   2 // $Id: ppp.c,v 1.1 2003-12-16 07:07:39 fred_nerk Exp $
   3
   4 #include <stdio.h>
   5 #include <string.h>
   6 #include <unistd.h>
   7 #include <errno.h>
   8 #include <stdlib.h>
   9 #include "l2tpns.h"
  10 #include "constants.h"
  11 #include "plugin.h"
  12 #include "util.h"
  13
  14 extern char debug;
  15 extern tunnelt *tunnel;
  16 extern sessiont *session;
  17 extern radiust *radius;
  18 extern u16 tapmac[3];
  19 extern int tapfd;
  20 extern char hostname[1000];
  21 extern struct Tstats *_statistics;
  22 extern unsigned long eth_tx;
  23 extern time_t time_now;
  24
  25 // Process PAP messages
  26 void processpap(tunnelidt t, sessionidt s, u8 * p, u16 l)
  27 {
  28         char user[129];
  29         char pass[129];
  30
  31 #ifdef STAT_CALLS
  32         STAT(call_processpap);
  33 #endif
  34         log_hex(5, "PAP", p, l);
  35         if (l < 4)
  36         {
  37                 log(1, 0, s, t, "Short PAP %u bytes", l);
  38                 STAT(tunnel_rx_errors);
  39                 return ;
  40         }
  41         if (*p != 1)
  42         {
  43                 log(1, 0, s, t, "Unexpected PAP code %d\n", *p);
  44                 STAT(tunnel_rx_errors);
  45                 return ;
  46         }
  47         if (ntohs(*(u16 *) (p + 2)) > l)
  48         {
  49                 log(1, 0, s, t, "Length mismatch PAP %d/%d\n", ntohs(*(u16 *) (p + 2)), l);
  50                 STAT(tunnel_rx_errors);
  51                 return ;
  52         }
  53         {
  54                 u8 *b = p;
  55                 b += 4;
  56                 if (*b && *b < sizeof(user))
  57                         memcpy(user, b + 1, *b);
  58                 user[*b] = 0;
  59                 b += 1 + *b;
  60                 if (*b && *b < sizeof(pass))
  61                         memcpy(pass, b + 1, *b);
  62                 pass[*b] = 0;
  63                 log(3, 0, s, t, "PAP login %s/%s\n", user, pass);
  64         }
  65         if (session[s].ip || !session[s].radius)
  66         {
  67                 // respond now, either no RADIUS available or already authenticated
  68                 u8 b[MAXCONTROL];
  69                 u8 id = p[1];
  70                 u8 *p = makeppp(b, 0, 0, t, s, PPPPAP);
  71                 if (session[s].ip)
  72                         *p = 2;              // ACK
  73                 else
  74                         *p = 3;              // cant authorise
  75                 p[1] = id;
  76                 *(u16 *) (p + 2) = htons(5); // length
  77                 p[4] = 0;               // no message
  78                 if (session[s].ip)
  79                 {
  80                     log(3, session[s].ip, s, t, "%d Already an IP allocated: %s (%d)\n", getpid(), inet_toa(htonl(session[s].ip)), session[s].ip);
  81                 }
  82                 else
  83                 {
  84                     log(1, 0, s, t, "No radius session available to authenticate session...\n");
  85                 }
  86                 log(3, 0, s, t, "Fallback response to PAP (%s)\n", (session[s].ip) ? "ACK" : "NAK");
  87                 tunnelsend(b, 5 + (p - b), t); // send it
  88         }
  89         else
  90         {                          // set up RADIUS request
  91                 u8 r = session[s].radius;
  92
  93                 // Run PRE_AUTH plugins
  94                 struct param_pre_auth packet = { &tunnel[t], &session[s], strdup(user), strdup(pass), PPPPAP, 1 };
  95                 run_plugins(PLUGIN_PRE_AUTH, &packet);
  96                 if (!packet.continue_auth)
  97                 {
  98                         log(3, 0, s, t, "A plugin rejected PRE_AUTH\n");
  99                         if (packet.username) free(packet.username);
 100                         if (packet.password) free(packet.password);
 101                         return;
 102                 }
 103
 104                 strncpy(session[s].user, packet.username, sizeof(session[s].user));
 105                 strncpy(radius[r].pass, packet.password, sizeof(radius[r].pass));
 106
 107                 free(packet.username);
 108                 free(packet.password);
 109
 110                 radius[r].id = p[1];
 111                 log(3, 0, s, t, "Sending login for %s/%s to radius\n", user, pass);
 112                 radiussend(r, RADIUSAUTH);
 113         }
 114 }
 115
 116 // Process CHAP messages
 117 void processchap(tunnelidt t, sessionidt s, u8 * p, u16 l)
 118 {
 119         u8 r;
 120         u16 len;
 121
 122 #ifdef STAT_CALLS
 123         STAT(call_processchap);
 124 #endif
 125         log_hex(5, "CHAP", p, l);
 126         r = session[s].radius;
 127         if (!r)
 128         {
 129                 log(1, 0, s, t, "Unexpected CHAP message\n");
 130                 STAT(tunnel_rx_errors);
 131                 return;
 132         }
 133         if (*p != 2)
 134         {
 135                 log(1, 0, s, t, "Unexpected CHAP response code %d\n", *p);
 136                 STAT(tunnel_rx_errors);
 137                 return;
 138         }
 139         if (p[1] != radius[r].id)
 140         {
 141                 log(1, 0, s, t, "Wrong CHAP response ID %d (should be %d) (%d)\n", p[1], radius[r].id, r);
 142                 STAT(tunnel_rx_errors);
 143                 return ;
 144         }
 145         len = ntohs(*(u16 *) (p + 2));
 146         if (len > l)
 147         {
 148                 log(1, 0, s, t, "Bad CHAP length %d\n", len);
 149                 STAT(tunnel_rx_errors);
 150                 return ;
 151         }
 152         if (p[4] != 16)
 153         {
 154                 log(1, 0, s, t, "Bad CHAP response length %d\n", p[4]);
 155                 STAT(tunnel_rx_errors);
 156                 return ;
 157         }
 158         if (len - 21 >= sizeof(session[s].user))
 159         {
 160                 log(1, 0, s, t, "CHAP user too long %d\n", len - 21);
 161                 STAT(tunnel_rx_errors);
 162                 return ;
 163         }
 164
 165         // Run PRE_AUTH plugins
 166         {
 167                 struct param_pre_auth packet = { &tunnel[t], &session[s], NULL, NULL, PPPCHAP, 1 };
 168
 169                 packet.username = calloc(len-20, 1);
 170                 packet.password = calloc(16, 1);
 171                 memcpy(packet.username, p + 21, len - 21);
 172                 memcpy(packet.password, p + 5, 16);
 173
 174                 run_plugins(PLUGIN_PRE_AUTH, &packet);
 175                 if (!packet.continue_auth)
 176                 {
 177                         log(3, 0, s, t, "A plugin rejected PRE_AUTH\n");
 178                         if (packet.username) free(packet.username);
 179                         if (packet.password) free(packet.password);
 180                         return;
 181                 }
 182
 183                 strncpy(session[s].user, packet.username, sizeof(session[s].user));
 184                 memcpy(radius[r].pass, packet.password, 16);
 185
 186                 free(packet.username);
 187                 free(packet.password);
 188         }
 189
 190         radius[r].chap = 1;
 191         radiussend(r, RADIUSAUTH);
 192         log(3, 0, s, t, "CHAP login %s\n", session[s].user);
 193 }
 194
 195 char *ppp_lcp_types[] = {
 196         NULL,
 197         "ConfigReq",
 198         "ConfigAck",
 199         "ConfigNak",
 200         "ConfigRej",
 201         "TerminateReq",
 202         "TerminateAck",
 203         "CodeRej",
 204         "ProtocolRej",
 205         "EchoReq",
 206         "EchoReply",
 207         "DiscardRequest",
 208 };
 209
 210 void dumplcp(char *p, int l)
 211 {
 212         signed int x = l - 3;
 213         char *o = (p + 3);
 214
 215         log_hex(5, "PPP LCP Packet", p, l);
 216         log(4, 0, 0, 0, "PPP LCP Packet type %d (%s)\n", *p, ppp_lcp_types[(int)*p]);
 217         log(4, 0, 0, 0, "Length: %d\n", l);
 218         if (*p != ConfigReq && *p != ConfigRej && *p != ConfigAck)
 219                 return;
 220
 221         while (x > 2)
 222         {
 223                 int type = *(u8 *)(o);
 224                 int length = *(u8 *)(o + 1);
 225                 if (length == 0)
 226                 {
 227                         log(4, 0, 0, 0, "       Option length is 0...\n");
 228                         break;
 229                 }
 230                 if (type == 0)
 231                 {
 232                         log(4, 0, 0, 0, "       Option type is 0...\n");
 233                         x -= length;
 234                         o += length;
 235                         continue;
 236                 }
 237                 switch (type)
 238                 {
 239                         case 1: // Maximum-Receive-Unit
 240                                 log(4, 0, 0, 0, "    %s %d\n", lcp_types[type], ntohs(*(u16 *)(o + 2)));
 241                                 break;
 242                         case 3: // Authentication-Protocol
 243                                 {
 244                                         int proto = ntohs(*(u16 *)(o + 2));
 245                                         log(4, 0, 0, 0, "    %s %s\n", lcp_types[type],
 246                                                         proto == 0xC223 ? "CHAP" : "PAP");
 247                                         break;
 248                                 }
 249                         case 5: // Magic-Number
 250                                 {
 251                                         u32 magicno = ntohl(*(u32 *)(o + 2));
 252                                         log(4, 0, 0, 0, "    %s %x\n", lcp_types[type], magicno);
 253                                         break;
 254                                 }
 255                         case 4: // Quality-Protocol
 256                                 {
 257                                         u32 qp = ntohl(*(u32 *)(o + 2));
 258                                         log(4, 0, 0, 0, "    %s %x\n", lcp_types[type], qp);
 259                                         break;
 260                                 }
 261                         case 7: // Protocol-Field-Compression
 262                                 {
 263                                         u32 pfc = ntohl(*(u32 *)(o + 2));
 264                                         log(4, 0, 0, 0, "    %s %x\n", lcp_types[type], pfc);
 265                                         break;
 266                                 }
 267                         case 8: // Address-And-Control-Field-Compression
 268                                 {
 269                                         u32 afc = ntohl(*(u32 *)(o + 2));
 270                                         log(4, 0, 0, 0, "    %s %x\n", lcp_types[type], afc);
 271                                         break;
 272                                 }
 273                         default:
 274                                 log(2, 0, 0, 0, "    Unknown PPP LCP Option type %d\n", type);
 275                                 break;
 276                 }
 277                 x -= length;
 278                 o += length;
 279         }
 280 }
 281
 282 // Process LCP messages
 283 void processlcp(tunnelidt t, sessionidt s, u8 * p, u16 l)
 284 {
 285         u8 b[MAXCONTROL];
 286         u8 *q = NULL;
 287
 288 #ifdef STAT_CALLS
 289         STAT(call_processlcp);
 290 #endif
 291         log_hex(5, "LCP", p, l);
 292         if (l < 4)
 293         {
 294                 log(1, session[s].ip, s, t, "Short LCP %d bytes", l);
 295                 STAT(tunnel_rx_errors);
 296                 return ;
 297         }
 298         if (*p == ConfigAck)
 299         {
 300                 log(3, session[s].ip, s, t, "LCP: Discarding ConfigAck\n");
 301         }
 302         else if (*p == ConfigReq)
 303         {
 304                 signed int x = l - 1;
 305                 char *o = (p + 1);
 306
 307                 log(3, session[s].ip, s, t, "LCP: ConfigReq (%d bytes)...\n", l);
 308
 309                 while (x > 2)
 310                 {
 311                         int type = *(u8 *)(o);
 312                         int length = *(u8 *)(o + 1);
 313                         if (length == 0 || type == 0) break;
 314                         switch (type)
 315                         {
 316                                 case 1: // Maximum-Receive-Unit
 317                                         session[s].mru = ntohs(*(u16 *)(o + 2));
 318                                         break;
 319                                 case 3: // Authentication-Protocol
 320                                         {
 321                                                 int proto = ntohs(*(u16 *)(o + 2));
 322                                                 if (proto == 0xC223)
 323                                                 {
 324                                                         log(2, session[s].ip, s, t, "    Remote end is trying to do CHAP. Rejecting it.\n");
 325
 326                                                         if (!q)
 327                                                         {
 328                                                                 q = makeppp(b, p, l, t, s, PPPLCP);
 329                                                                 *q++ = ConfigNak;
 330                                                         }
 331                                                         memcpy(q, o, length);
 332                                                         *(u16 *)(q += 2) = htons(0xC023); // NAK -> Use PAP instead
 333                                                         q += length;
 334                                                 }
 335                                                 break;
 336                                         }
 337                                 case 5: // Magic-Number
 338                                         {
 339 //                                              u32 magicno = ntohl(*(u32 *)(o + 2));
 340                                                 break;
 341                                         }
 342                                 case 4: // Quality-Protocol
 343                                         {
 344 //                                              u32 qp = ntohl(*(u32 *)(o + 2));
 345                                                 break;
 346                                         }
 347                                 case 7: // Protocol-Field-Compression
 348                                         {
 349 //                                              u32 pfc = ntohl(*(u32 *)(o + 2));
 350                                                 break;
 351                                         }
 352                                 case 8: // Address-And-Control-Field-Compression
 353                                         {
 354 //                                              u32 afc = ntohl(*(u32 *)(o + 2));
 355                                                 break;
 356                                         }
 357                                 default:
 358                                         log(2, session[s].ip, s, t, "    Unknown PPP LCP Option type %d\n", type);
 359                                         break;
 360                         }
 361                         x -= length;
 362                         o += length;
 363                 }
 364
 365                 if (!q)
 366                 {
 367                         // Send back a ConfigAck
 368                         log(3, session[s].ip, s, t, "ConfigReq accepted, sending as Ack\n");
 369                         q = makeppp(b, p, l, t, s, PPPLCP);
 370                         *q = ConfigAck;
 371                         tunnelsend(b, l + (q - b), t);
 372                 }
 373                 else
 374                 {
 375                         // Already built a ConfigNak... send it
 376                         log(3, session[s].ip, s, t, "Sending ConfigNak\n");
 377                         tunnelsend(b, l + (q - b), t);
 378
 379                         log(3, session[s].ip, s, t, "Sending ConfigReq, requesting PAP login\n");
 380                         q = makeppp(b, NULL, 0, t, s, PPPLCP);
 381                         *q++ = ConfigReq;
 382                         *(u8 *)(q++) = 3;
 383                         *(u8 *)(q++) = 4;
 384                         *(u16 *)(q += 2) = htons(0xC023);
 385                         tunnelsend(b, l + (q - b), t);
 386                 }
 387         }
 388         else if (*p == ConfigNak)
 389         {
 390                 log(1, session[s].ip, s, t, "Remote end sent a ConfigNak. Ignoring\n");
 391                 dumplcp(p, l);
 392                 return ;
 393         }
 394         else if (*p == TerminateReq)
 395         {
 396                 *p = TerminateAck;     // close
 397                 q = makeppp(b, p, l, t, s, PPPLCP);
 398                 log(3, session[s].ip, s, t, "LCP: Received TerminateReq. Sending TerminateAck\n");
 399                 sessionshutdown(s, "Remote end closed connection.");
 400                 tunnelsend(b, l + (q - b), t); // send it
 401         }
 402         else if (*p == TerminateReq)
 403         {
 404                 sessionshutdown(s, "Remote end closed connection.");
 405         }
 406         else if (*p == EchoReq)
 407         {
 408                 *p = EchoReply;      // reply
 409                 *(u32 *) (p + 4) = htonl(session[s].magic); // our magic number
 410                 q = makeppp(b, p, l, t, s, PPPLCP);
 411                 log(3, session[s].ip, s, t, "LCP: Received EchoReq. Sending EchoReply\n");
 412                 tunnelsend(b, l + (q - b), t); // send it
 413         }
 414         else if (*p == EchoReply)
 415         {
 416                 // Ignore it, last_packet time is set earlier than this.
 417         }
 418         else
 419         {
 420                 log(1, session[s].ip, s, t, "Unexpected LCP code %d\n", *p);
 421                 STAT(tunnel_rx_errors);
 422                 return ;
 423         }
 424 }
 425
 426 // Process IPCP messages
 427 void processipcp(tunnelidt t, sessionidt s, u8 * p, u16 l)
 428 {
 429 #ifdef STAT_CALLS
 430         STAT(call_processipcp);
 431 #endif
 432         log_hex(5, "IPCP", p, l);
 433         if (l < 5)
 434         {
 435                 log(1, 0, s, t, "Short IPCP %d bytes", l);
 436                 STAT(tunnel_rx_errors);
 437                 return ;
 438         }
 439         if (*p == ConfigAck)
 440         {                          // happy with our IPCP
 441                 u8 r = session[s].radius;
 442                 if ((!r || radius[r].state == RADIUSIPCP) && !session[s].walled_garden)
 443                         if (!r)
 444                                 r = radiusnew(s);
 445                         if (r)
 446                                 radiussend(r, RADIUSSTART); // send radius start, having got IPCP at last
 447                 return ;                 // done
 448         }
 449         if (*p != ConfigReq)
 450         {
 451                 log(1, 0, s, t, "Unexpected IPCP code %d\n", *p);
 452                 STAT(tunnel_rx_errors);
 453                 return ;
 454         }
 455         if (ntohs(*(u16 *) (p + 2)) > l)
 456         {
 457                 log(1, 0, s, t, "Length mismatch IPCP %d/%d\n", ntohs(*(u16 *) (p + 2)), l);
 458                 STAT(tunnel_rx_errors);
 459                 return ;
 460         }
 461         if (!session[s].ip)
 462         {
 463                 log(3, 0, s, t, "Waiting on radius reply\n");
 464                 return ;                   // have to wait on RADIUS eply
 465         }
 466         // form a config reply quoting the IP in the session
 467         {
 468                 u8 b[MAXCONTROL];
 469                 u8 *i,
 470                 *q;
 471
 472                 q = p + 4;
 473                 i = p + l;
 474                 while (q < i && q[1])
 475                 {
 476                         if (*q != 0x81 && *q != 0x83 && *q != 3)
 477                                 break;
 478                         q += q[1];
 479                 }
 480                 if (q < i)
 481                 {                       // reject
 482                         u16 n = 4;
 483                         i = p + l;
 484                         q = makeppp(b, p, l, t, s, PPPIPCP);
 485                         *q = ConfigRej;
 486                         p += 4;
 487                         while (p < i && p[1])
 488                         {
 489                                 if (*p != 0x81 && *p != 0x83 && *p != 3)
 490                                 {
 491                                         log(2, 0, s, t, "IPCP reject %d\n", *p);
 492                                         memcpy(q + n, p, p[1]);
 493                                         n += p[1];
 494                                 }
 495                                 p += p[1];
 496                         }
 497                         *(u16 *) (q + 2) = htons(n);
 498                         tunnelsend(b, n + (q - b), t); // send it
 499                 }
 500                 else
 501                 {
 502                         *p = ConfigAck;
 503                         i = findppp(p, 0x81); // Primary DNS address
 504                         if (i)
 505                         {
 506                                 if (*(u32 *) (i + 2) != htonl(session[s].dns1))
 507                                 {
 508                                         *(u32 *) (i + 2) = htonl(session[s].dns1);
 509                                         *p = ConfigNak;
 510                                 }
 511                         }
 512                         i = findppp(p, 0x83); // Secondary DNS address (TBA, is it)
 513                         if (i)
 514                         {
 515                                 if (*(u32 *) (i + 2) != htonl(session[s].dns2))
 516                                 {
 517                                         *(u32 *) (i + 2) = htonl(session[s].dns2);
 518                                         *p = ConfigNak;
 519                                 }
 520                         }
 521                         i = findppp(p, 3);   // IP address
 522                         if (!i || i[1] != 6)
 523                         {
 524                                 log(1, 0, s, t, "No IP in IPCP request\n");
 525                                 STAT(tunnel_rx_errors);
 526                                 return ;
 527                         }
 528                         if (*(u32 *) (i + 2) != htonl(session[s].ip))
 529                         {
 530                                 *(u32 *) (i + 2) = htonl(session[s].ip);
 531                                 *p = ConfigNak;
 532                         }
 533                         q = makeppp(b, p, l, t, s, PPPIPCP);
 534                         tunnelsend(b, l + (q - b), t); // send it
 535                 }
 536         }
 537 }
 538
 539 // process IP packet received
 540 void processipin(tunnelidt t, sessionidt s, u8 * p, u16 l)
 541 {
 542 #ifdef STAT_CALLS
 543         STAT(call_processipin);
 544 #endif
 545         log_hex(5, "IP", p, l);
 546
 547         if (l > MAXETHER)
 548         {
 549                 log(1, *(u32 *)(p + 12), s, t, "IP packet too long %d\n", l);
 550                 STAT(tunnel_rx_errors);
 551                 return ;
 552         }
 553
 554         session[s].cin += l;
 555         session[s].pin++;
 556         eth_tx += l;
 557
 558         // Add on the tun header
 559         p -= 4;
 560         *(u32 *)p = htonl(0x00000800);
 561         l += 4;
 562
 563         // Plugin hook
 564         {
 565                 struct param_packet_rx packet = { &tunnel[t], &session[s], p, l };
 566                 run_plugins(PLUGIN_PACKET_TX, &packet);
 567         }
 568
 569         // send to ethernet
 570         if (write(tapfd, p, l) < 0)
 571         {
 572                 STAT(tap_tx_errors);
 573                 log(0, 0, s, t, "Error writing %d bytes to TAP device: %s (tapfd=%d, p=%p)\n",
 574                         l, strerror(errno), tapfd, p);
 575         }
 576
 577         if (session[s].snoop)
 578         {
 579                 // Snooping this session, send it to ASIO
 580                 snoop_send_packet(p, l);
 581         }
 582         STAT(tap_tx_packets);
 583         INC_STAT(tap_tx_bytes, l);
 584 }
 585
 586 // Process LCP messages
 587 void processccp(tunnelidt t, sessionidt s, u8 * p, u16 l)
 588 {
 589 #ifdef STAT_CALLS
 590         STAT(call_processccp);
 591 #endif
 592         log_hex(5, "CCP", p, l);
 593         if (l < 2 || (*p != ConfigReq && *p != TerminateReq))
 594         {
 595                 log(1, 0, s, t, "Unexpecetd CCP request code %d\n", *p);
 596                 STAT(tunnel_rx_errors);
 597                 return ;
 598         }
 599         // reject
 600         {
 601                 u8 b[MAXCONTROL];
 602                 u8 *q;
 603                 if (*p == ConfigReq)
 604                 {
 605                         if (l < 6)
 606                         {
 607                                 *p = ConfigAck;         // accept no compression
 608                         }
 609                         else
 610                         {
 611                                 *p = ConfigRej;        // reject
 612                         }
 613                 }
 614                 else
 615                         *p = TerminateAck;     // close
 616                 q = makeppp(b, p, l, t, s, PPPCCP);
 617                 tunnelsend(b, l + (q - b), t); // send it
 618         }
 619 }
 620
 621 // send a CHAP PP packet
 622 void sendchap(tunnelidt t, sessionidt s)
 623 {
 624         u8 b[MAXCONTROL];
 625         u8 r = session[s].radius;
 626         u8 *q;
 627 #ifdef STAT_CALLS
 628         STAT(call_sendchap);
 629 #endif
 630         if (!r)
 631         {
 632                 log(1, 0, s, t, "No RADIUS to send challenge\n");
 633                 STAT(tunnel_tx_errors);
 634                 return ;
 635         }
 636         log(1, 0, s, t, "Send CHAP challenge\n");
 637         {                            // new challenge
 638                 int n;
 639                 for (n = 0; n < 15; n++)
 640                         radius[r].auth[n] = rand();
 641         }
 642         radius[r].chap = 1;          // CHAP not PAP
 643         radius[r].id++;
 644         if (radius[r].state != RADIUSCHAP)
 645                 radius[r].try = 0;
 646         radius[r].state = RADIUSCHAP;
 647         radius[r].retry = backoff(radius[r].try++);
 648         if (radius[r].try > 5)
 649         {
 650                 sessionshutdown(s, "Timeout CHAP");
 651                 STAT(tunnel_tx_errors);
 652                 return ;
 653         }
 654         q = makeppp(b, 0, 0, t, s, PPPCHAP);
 655         *q = 1;                      // challenhe
 656         q[1] = radius[r].id;         // ID
 657         q[4] = 16;                   // length
 658         memcpy(q + 5, radius[r].auth, 16); // challenge
 659         strcpy(q + 21, hostname);    // our name
 660         *(u16 *) (q + 2) = htons(strlen(hostname) + 21); // length
 661         tunnelsend(b, strlen(hostname) + 21 + (q - b), t); // send it
 662 }
 663
 664 // fill in a L2TP message with a PPP frame,
 665 // copies existing PPP message and changes magic number if seen
 666 // returns start of PPP frame
 667 u8 *makeppp(u8 * b, u8 * p, int l, tunnelidt t, sessionidt s, u16 mtype)
 668 {
 669         *(u16 *) (b + 0) = htons(0x0002); // L2TP with no options
 670         *(u16 *) (b + 2) = htons(tunnel[t].far); // tunnel
 671         *(u16 *) (b + 4) = htons(session[s].far); // session
 672         b += 6;
 673         if (mtype != PPPLCP && !(session[s].flags & SESSIONACFC))
 674         {
 675                 *(u16 *) b = htons(0xFF03); // HDLC header
 676                 b += 2;
 677         }
 678         if (mtype < 0x100 && session[s].flags & SESSIONPFC)
 679                 *b++ = mtype;
 680         else
 681         {
 682                 *(u16 *) b = htons(mtype);
 683                 b += 2;
 684         }
 685         if (p && l)
 686                 memcpy(b, p, l);
 687         return b;
 688 }
 689
 690 // find a PPP option, returns point to option, or 0 if not found
 691 u8 *findppp(u8 * b, u8 mtype)
 692 {
 693         u16 l = ntohs(*(u16 *) (b + 2));
 694         if (l < 4)
 695                 return 0;
 696         b += 4;
 697         l -= 4;
 698         while (l)
 699         {
 700                 if (l < b[1] || !b[1])
 701                         return 0;            // faulty
 702                 if (*b == mtype)
 703                         return b;
 704                 l -= b[1];
 705                 b += b[1];
 706         }
 707         return 0;
 708 }
 709
 710 // Send initial LCP ConfigReq
 711 void initlcp(tunnelidt t, sessionidt s)
 712 {
 713         char b[500] = {0}, *q;
 714
 715         q = makeppp(b, NULL, 0, t, s, PPPLCP);
 716         log(4, 0, s, t, "Sending LCP ConfigReq for PAP\n");
 717         *q = ConfigReq;
 718         *(u8 *)(q + 1) = (time_now % 255) + 1; // ID
 719         *(u16 *)(q + 2) = htons(8); // Length
 720         *(u8 *)(q + 4) = 3;
 721         *(u8 *)(q + 5) = 4;
 722         *(u16 *)(q + 6) = htons(0xC023); // PAP
 723         tunnelsend(b, 12 + 8, t);
 724 }
 725