sys/net/libalias/alias_ftp.c

   1 /*-
   2  * Copyright (c) 2001 Charles Mott <cm@linktel.net>
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  24  * SUCH DAMAGE.
  25  */
  26
  27 #include <sys/cdefs.h>
  28 __FBSDID("$FreeBSD: src/sys/netinet/libalias/alias_ftp.c,v 1.29.2.1.2.1 2008/11/25 02:59:29 kensmith Exp $");
  29
  30 /*
  31     Alias_ftp.c performs special processing for FTP sessions under
  32     TCP.  Specifically, when a PORT/EPRT command from the client
  33     side or 227/229 reply from the server is sent, it is intercepted
  34     and modified.  The address is changed to the gateway machine
  35     and an aliasing port is used.
  36
  37     For this routine to work, the message must fit entirely into a
  38     single TCP packet.  This is typically the case, but exceptions
  39     can easily be envisioned under the actual specifications.
  40
  41     Probably the most troubling aspect of the approach taken here is
  42     that the new message will typically be a different length, and
  43     this causes a certain amount of bookkeeping to keep track of the
  44     changes of sequence and acknowledgment numbers, since the client
  45     machine is totally unaware of the modification to the TCP stream.
  46
  47
  48     References: RFC 959, RFC 2428.
  49
  50     Initial version:  August, 1996  (cjm)
  51
  52     Version 1.6
  53          Brian Somers and Martin Renters identified an IP checksum
  54          error for modified IP packets.
  55
  56     Version 1.7:  January 9, 1996 (cjm)
  57          Differential checksum computation for change
  58          in IP packet length.
  59
  60     Version 2.1:  May, 1997 (cjm)
  61          Very minor changes to conform with
  62          local/global/function naming conventions
  63          within the packet aliasing module.
  64
  65     Version 3.1:  May, 2000 (eds)
  66          Add support for passive mode, alias the 227 replies.
  67
  68     See HISTORY file for record of revisions.
  69 */
  70
  71 /* Includes */
  72 #ifdef _KERNEL
  73 #include <sys/param.h>
  74 #include <sys/ctype.h>
  75 #include <sys/systm.h>
  76 #include <sys/kernel.h>
  77 #include <sys/module.h>
  78 #else
  79 #include <errno.h>
  80 #include <sys/types.h>
  81 #include <stdio.h>
  82 #include <string.h>
  83 #endif
  84
  85 #include <netinet/in_systm.h>
  86 #include <netinet/in.h>
  87 #include <netinet/ip.h>
  88 #include <netinet/tcp.h>
  89
  90 #ifdef _KERNEL
  91 #include <netinet/libalias/alias.h>
  92 #include <netinet/libalias/alias_local.h>
  93 #include <netinet/libalias/alias_mod.h>
  94 #else
  95 #include "alias_local.h"
  96 #include "alias_mod.h"
  97 #endif
  98
  99 #define FTP_CONTROL_PORT_NUMBER 21
 100
 101 static void
 102 AliasHandleFtpOut(struct libalias *, struct ip *, struct alias_link *,
 103                   int maxpacketsize);
 104
 105 static int
 106 fingerprint(struct libalias *la, struct ip *pip, struct alias_data *ah)
 107 {
 108
 109         if (ah->dport == NULL || ah->sport == NULL || ah->lnk == NULL ||
 110                 ah->maxpktsize == 0)
 111                 return (-1);
 112         if (ntohs(*ah->dport) == FTP_CONTROL_PORT_NUMBER
 113             || ntohs(*ah->sport) == FTP_CONTROL_PORT_NUMBER)
 114                 return (0);
 115         return (-1);
 116 }
 117
 118 static int
 119 protohandler(struct libalias *la, struct ip *pip, struct alias_data *ah)
 120 {
 121
 122         AliasHandleFtpOut(la, pip, ah->lnk, ah->maxpktsize);
 123         return (0);
 124 }
 125
 126 struct proto_handler handlers[] = {
 127         {
 128           .pri = 80,
 129           .dir = OUT,
 130           .proto = TCP,
 131           .fingerprint = &fingerprint,
 132           .protohandler = &protohandler
 133         },
 134         { EOH }
 135 };
 136
 137 static int
 138 mod_handler(module_t mod, int type, void *data)
 139 {
 140         int error;
 141
 142         switch (type) {
 143         case MOD_LOAD:
 144                 error = 0;
 145                 LibAliasAttachHandlers(handlers);
 146                 break;
 147         case MOD_UNLOAD:
 148                 error = 0;
 149                 LibAliasDetachHandlers(handlers);
 150                 break;
 151         default:
 152                 error = EINVAL;
 153         }
 154         return (error);
 155 }
 156
 157 #ifdef _KERNEL
 158 static
 159 #endif
 160 moduledata_t alias_mod = {
 161        "alias_ftp", mod_handler, NULL
 162 };
 163
 164 #ifdef  _KERNEL
 165 DECLARE_MODULE(alias_ftp, alias_mod, SI_SUB_DRIVERS, SI_ORDER_SECOND);
 166 MODULE_VERSION(alias_ftp, 1);
 167 MODULE_DEPEND(alias_ftp, libalias, 1, 1, 1);
 168 #endif
 169
 170 #define FTP_CONTROL_PORT_NUMBER 21
 171 #define MAX_MESSAGE_SIZE        128
 172
 173 /* FTP protocol flags. */
 174 #define WAIT_CRLF               0x01
 175
 176 enum ftp_message_type {
 177         FTP_PORT_COMMAND,
 178         FTP_EPRT_COMMAND,
 179         FTP_227_REPLY,
 180         FTP_229_REPLY,
 181         FTP_UNKNOWN_MESSAGE
 182 };
 183
 184 static int      ParseFtpPortCommand(struct libalias *la, char *, int);
 185 static int      ParseFtpEprtCommand(struct libalias *la, char *, int);
 186 static int      ParseFtp227Reply(struct libalias *la, char *, int);
 187 static int      ParseFtp229Reply(struct libalias *la, char *, int);
 188 static void     NewFtpMessage(struct libalias *la, struct ip *, struct alias_link *, int, int);
 189
 190 static void
 191 AliasHandleFtpOut(
 192     struct libalias *la,
 193     struct ip *pip,             /* IP packet to examine/patch */
 194     struct alias_link *lnk,     /* The link to go through (aliased port) */
 195     int maxpacketsize           /* The maximum size this packet can grow to
 196         (including headers) */ )
 197 {
 198         int hlen, tlen, dlen, pflags;
 199         char *sptr;
 200         struct tcphdr *tc;
 201         int ftp_message_type;
 202
 203 /* Calculate data length of TCP packet */
 204         tc = (struct tcphdr *)ip_next(pip);
 205         hlen = (pip->ip_hl + tc->th_off) << 2;
 206         tlen = ntohs(pip->ip_len);
 207         dlen = tlen - hlen;
 208
 209 /* Place string pointer and beginning of data */
 210         sptr = (char *)pip;
 211         sptr += hlen;
 212
 213 /*
 214  * Check that data length is not too long and previous message was
 215  * properly terminated with CRLF.
 216  */
 217         pflags = GetProtocolFlags(lnk);
 218         if (dlen <= MAX_MESSAGE_SIZE && !(pflags & WAIT_CRLF)) {
 219                 ftp_message_type = FTP_UNKNOWN_MESSAGE;
 220
 221                 if (ntohs(tc->th_dport) == FTP_CONTROL_PORT_NUMBER) {
 222 /*
 223  * When aliasing a client, check for the PORT/EPRT command.
 224  */
 225                         if (ParseFtpPortCommand(la, sptr, dlen))
 226                                 ftp_message_type = FTP_PORT_COMMAND;
 227                         else if (ParseFtpEprtCommand(la, sptr, dlen))
 228                                 ftp_message_type = FTP_EPRT_COMMAND;
 229                 } else {
 230 /*
 231  * When aliasing a server, check for the 227/229 reply.
 232  */
 233                         if (ParseFtp227Reply(la, sptr, dlen))
 234                                 ftp_message_type = FTP_227_REPLY;
 235                         else if (ParseFtp229Reply(la, sptr, dlen)) {
 236                                 ftp_message_type = FTP_229_REPLY;
 237                                 la->true_addr.s_addr = pip->ip_src.s_addr;
 238                         }
 239                 }
 240
 241                 if (ftp_message_type != FTP_UNKNOWN_MESSAGE)
 242                         NewFtpMessage(la, pip, lnk, maxpacketsize, ftp_message_type);
 243         }
 244 /* Track the msgs which are CRLF term'd for PORT/PASV FW breach */
 245
 246         if (dlen) {             /* only if there's data */
 247                 sptr = (char *)pip;     /* start over at beginning */
 248                 tlen = ntohs(pip->ip_len);      /* recalc tlen, pkt may
 249                                                  * have grown */
 250                 if (sptr[tlen - 2] == '\r' && sptr[tlen - 1] == '\n')
 251                         pflags &= ~WAIT_CRLF;
 252                 else
 253                         pflags |= WAIT_CRLF;
 254                 SetProtocolFlags(lnk, pflags);
 255         }
 256 }
 257
 258 static int
 259 ParseFtpPortCommand(struct libalias *la, char *sptr, int dlen)
 260 {
 261         char ch;
 262         int i, state;
 263         u_int32_t addr;
 264         u_short port;
 265         u_int8_t octet;
 266
 267         /* Format: "PORT A,D,D,R,PO,RT". */
 268
 269         /* Return if data length is too short. */
 270         if (dlen < 18)
 271                 return (0);
 272
 273         if (strncasecmp("PORT ", sptr, 5))
 274                 return (0);
 275
 276         addr = port = octet = 0;
 277         state = 0;
 278         for (i = 5; i < dlen; i++) {
 279                 ch = sptr[i];
 280                 switch (state) {
 281                 case 0:
 282                         if (isspace(ch))
 283                                 break;
 284                         else
 285                                 state++;
 286                 case 1:
 287                 case 3:
 288                 case 5:
 289                 case 7:
 290                 case 9:
 291                 case 11:
 292                         if (isdigit(ch)) {
 293                                 octet = ch - '0';
 294                                 state++;
 295                         } else
 296                                 return (0);
 297                         break;
 298                 case 2:
 299                 case 4:
 300                 case 6:
 301                 case 8:
 302                         if (isdigit(ch))
 303                                 octet = 10 * octet + ch - '0';
 304                         else if (ch == ',') {
 305                                 addr = (addr << 8) + octet;
 306                                 state++;
 307                         } else
 308                                 return (0);
 309                         break;
 310                 case 10:
 311                 case 12:
 312                         if (isdigit(ch))
 313                                 octet = 10 * octet + ch - '0';
 314                         else if (ch == ',' || state == 12) {
 315                                 port = (port << 8) + octet;
 316                                 state++;
 317                         } else
 318                                 return (0);
 319                         break;
 320                 }
 321         }
 322
 323         if (state == 13) {
 324                 la->true_addr.s_addr = htonl(addr);
 325                 la->true_port = port;
 326                 return (1);
 327         } else
 328                 return (0);
 329 }
 330
 331 static int
 332 ParseFtpEprtCommand(struct libalias *la, char *sptr, int dlen)
 333 {
 334         char ch, delim;
 335         int i, state;
 336         u_int32_t addr;
 337         u_short port;
 338         u_int8_t octet;
 339
 340         /* Format: "EPRT |1|A.D.D.R|PORT|". */
 341
 342         /* Return if data length is too short. */
 343         if (dlen < 18)
 344                 return (0);
 345
 346         if (strncasecmp("EPRT ", sptr, 5))
 347                 return (0);
 348
 349         addr = port = octet = 0;
 350         delim = '|';            /* XXX gcc -Wuninitialized */
 351         state = 0;
 352         for (i = 5; i < dlen; i++) {
 353                 ch = sptr[i];
 354                 switch (state) {
 355                 case 0:
 356                         if (!isspace(ch)) {
 357                                 delim = ch;
 358                                 state++;
 359                         }
 360                         break;
 361                 case 1:
 362                         if (ch == '1')  /* IPv4 address */
 363                                 state++;
 364                         else
 365                                 return (0);
 366                         break;
 367                 case 2:
 368                         if (ch == delim)
 369                                 state++;
 370                         else
 371                                 return (0);
 372                         break;
 373                 case 3:
 374                 case 5:
 375                 case 7:
 376                 case 9:
 377                         if (isdigit(ch)) {
 378                                 octet = ch - '0';
 379                                 state++;
 380                         } else
 381                                 return (0);
 382                         break;
 383                 case 4:
 384                 case 6:
 385                 case 8:
 386                 case 10:
 387                         if (isdigit(ch))
 388                                 octet = 10 * octet + ch - '0';
 389                         else if (ch == '.' || state == 10) {
 390                                 addr = (addr << 8) + octet;
 391                                 state++;
 392                         } else
 393                                 return (0);
 394                         break;
 395                 case 11:
 396                         if (isdigit(ch)) {
 397                                 port = ch - '0';
 398                                 state++;
 399                         } else
 400                                 return (0);
 401                         break;
 402                 case 12:
 403                         if (isdigit(ch))
 404                                 port = 10 * port + ch - '0';
 405                         else if (ch == delim)
 406                                 state++;
 407                         else
 408                                 return (0);
 409                         break;
 410                 }
 411         }
 412
 413         if (state == 13) {
 414                 la->true_addr.s_addr = htonl(addr);
 415                 la->true_port = port;
 416                 return (1);
 417         } else
 418                 return (0);
 419 }
 420
 421 static int
 422 ParseFtp227Reply(struct libalias *la, char *sptr, int dlen)
 423 {
 424         char ch;
 425         int i, state;
 426         u_int32_t addr;
 427         u_short port;
 428         u_int8_t octet;
 429
 430         /* Format: "227 Entering Passive Mode (A,D,D,R,PO,RT)" */
 431
 432         /* Return if data length is too short. */
 433         if (dlen < 17)
 434                 return (0);
 435
 436         if (strncmp("227 ", sptr, 4))
 437                 return (0);
 438
 439         addr = port = octet = 0;
 440
 441         state = 0;
 442         for (i = 4; i < dlen; i++) {
 443                 ch = sptr[i];
 444                 switch (state) {
 445                 case 0:
 446                         if (ch == '(')
 447                                 state++;
 448                         break;
 449                 case 1:
 450                 case 3:
 451                 case 5:
 452                 case 7:
 453                 case 9:
 454                 case 11:
 455                         if (isdigit(ch)) {
 456                                 octet = ch - '0';
 457                                 state++;
 458                         } else
 459                                 return (0);
 460                         break;
 461                 case 2:
 462                 case 4:
 463                 case 6:
 464                 case 8:
 465                         if (isdigit(ch))
 466                                 octet = 10 * octet + ch - '0';
 467                         else if (ch == ',') {
 468                                 addr = (addr << 8) + octet;
 469                                 state++;
 470                         } else
 471                                 return (0);
 472                         break;
 473                 case 10:
 474                 case 12:
 475                         if (isdigit(ch))
 476                                 octet = 10 * octet + ch - '0';
 477                         else if (ch == ',' || (state == 12 && ch == ')')) {
 478                                 port = (port << 8) + octet;
 479                                 state++;
 480                         } else
 481                                 return (0);
 482                         break;
 483                 }
 484         }
 485
 486         if (state == 13) {
 487                 la->true_port = port;
 488                 la->true_addr.s_addr = htonl(addr);
 489                 return (1);
 490         } else
 491                 return (0);
 492 }
 493
 494 static int
 495 ParseFtp229Reply(struct libalias *la, char *sptr, int dlen)
 496 {
 497         char ch, delim;
 498         int i, state;
 499         u_short port;
 500
 501         /* Format: "229 Entering Extended Passive Mode (|||PORT|)" */
 502
 503         /* Return if data length is too short. */
 504         if (dlen < 11)
 505                 return (0);
 506
 507         if (strncmp("229 ", sptr, 4))
 508                 return (0);
 509
 510         port = 0;
 511         delim = '|';            /* XXX gcc -Wuninitialized */
 512
 513         state = 0;
 514         for (i = 4; i < dlen; i++) {
 515                 ch = sptr[i];
 516                 switch (state) {
 517                 case 0:
 518                         if (ch == '(')
 519                                 state++;
 520                         break;
 521                 case 1:
 522                         delim = ch;
 523                         state++;
 524                         break;
 525                 case 2:
 526                 case 3:
 527                         if (ch == delim)
 528                                 state++;
 529                         else
 530                                 return (0);
 531                         break;
 532                 case 4:
 533                         if (isdigit(ch)) {
 534                                 port = ch - '0';
 535                                 state++;
 536                         } else
 537                                 return (0);
 538                         break;
 539                 case 5:
 540                         if (isdigit(ch))
 541                                 port = 10 * port + ch - '0';
 542                         else if (ch == delim)
 543                                 state++;
 544                         else
 545                                 return (0);
 546                         break;
 547                 case 6:
 548                         if (ch == ')')
 549                                 state++;
 550                         else
 551                                 return (0);
 552                         break;
 553                 }
 554         }
 555
 556         if (state == 7) {
 557                 la->true_port = port;
 558                 return (1);
 559         } else
 560                 return (0);
 561 }
 562
 563 static void
 564 NewFtpMessage(struct libalias *la, struct ip *pip,
 565     struct alias_link *lnk,
 566     int maxpacketsize,
 567     int ftp_message_type)
 568 {
 569         struct alias_link *ftp_lnk;
 570
 571 /* Security checks. */
 572         if (pip->ip_src.s_addr != la->true_addr.s_addr)
 573                 return;
 574
 575         if (la->true_port < IPPORT_RESERVED)
 576                 return;
 577
 578 /* Establish link to address and port found in FTP control message. */
 579         ftp_lnk = FindUdpTcpOut(la, la->true_addr, GetDestAddress(lnk),
 580             htons(la->true_port), 0, IPPROTO_TCP, 1);
 581
 582         if (ftp_lnk != NULL) {
 583                 int slen, hlen, tlen, dlen;
 584                 struct tcphdr *tc;
 585
 586 #ifndef NO_FW_PUNCH
 587                 /* Punch hole in firewall */
 588                 PunchFWHole(ftp_lnk);
 589 #endif
 590
 591 /* Calculate data length of TCP packet */
 592                 tc = (struct tcphdr *)ip_next(pip);
 593                 hlen = (pip->ip_hl + tc->th_off) << 2;
 594                 tlen = ntohs(pip->ip_len);
 595                 dlen = tlen - hlen;
 596
 597 /* Create new FTP message. */
 598                 {
 599                         char stemp[MAX_MESSAGE_SIZE + 1];
 600                         char *sptr;
 601                         u_short alias_port;
 602                         u_char *ptr;
 603                         int a1, a2, a3, a4, p1, p2;
 604                         struct in_addr alias_address;
 605
 606 /* Decompose alias address into quad format */
 607                         alias_address = GetAliasAddress(lnk);
 608                         ptr = (u_char *) & alias_address.s_addr;
 609                         a1 = *ptr++;
 610                         a2 = *ptr++;
 611                         a3 = *ptr++;
 612                         a4 = *ptr;
 613
 614                         alias_port = GetAliasPort(ftp_lnk);
 615
 616 /* Prepare new command */
 617                         switch (ftp_message_type) {
 618                         case FTP_PORT_COMMAND:
 619                         case FTP_227_REPLY:
 620                                 /* Decompose alias port into pair format. */
 621                                 ptr = (char *)&alias_port;
 622                                 p1 = *ptr++;
 623                                 p2 = *ptr;
 624
 625                                 if (ftp_message_type == FTP_PORT_COMMAND) {
 626                                         /* Generate PORT command string. */
 627                                         sprintf(stemp, "PORT %d,%d,%d,%d,%d,%d\r\n",
 628                                             a1, a2, a3, a4, p1, p2);
 629                                 } else {
 630                                         /* Generate 227 reply string. */
 631                                         sprintf(stemp,
 632                                             "227 Entering Passive Mode (%d,%d,%d,%d,%d,%d)\r\n",
 633                                             a1, a2, a3, a4, p1, p2);
 634                                 }
 635                                 break;
 636                         case FTP_EPRT_COMMAND:
 637                                 /* Generate EPRT command string. */
 638                                 sprintf(stemp, "EPRT |1|%d.%d.%d.%d|%d|\r\n",
 639                                     a1, a2, a3, a4, ntohs(alias_port));
 640                                 break;
 641                         case FTP_229_REPLY:
 642                                 /* Generate 229 reply string. */
 643                                 sprintf(stemp, "229 Entering Extended Passive Mode (|||%d|)\r\n",
 644                                     ntohs(alias_port));
 645                                 break;
 646                         }
 647
 648 /* Save string length for IP header modification */
 649                         slen = strlen(stemp);
 650
 651 /* Copy modified buffer into IP packet. */
 652                         sptr = (char *)pip;
 653                         sptr += hlen;
 654                         strncpy(sptr, stemp, maxpacketsize - hlen);
 655                 }
 656
 657 /* Save information regarding modified seq and ack numbers */
 658                 {
 659                         int delta;
 660
 661                         SetAckModified(lnk);
 662                         delta = GetDeltaSeqOut(pip, lnk);
 663                         AddSeq(pip, lnk, delta + slen - dlen);
 664                 }
 665
 666 /* Revise IP header */
 667                 {
 668                         u_short new_len;
 669
 670                         new_len = htons(hlen + slen);
 671                         DifferentialChecksum(&pip->ip_sum,
 672                             &new_len,
 673                             &pip->ip_len,
 674                             1);
 675                         pip->ip_len = new_len;
 676                 }
 677
 678 /* Compute TCP checksum for revised packet */
 679                 tc->th_sum = 0;
 680 #ifdef _KERNEL
 681                 tc->th_x2 = 1;
 682 #else
 683                 tc->th_sum = TcpChecksum(pip);
 684 #endif
 685         } else {
 686 #ifdef LIBALIAS_DEBUG
 687                 fprintf(stderr,
 688                     "PacketAlias/HandleFtpOut: Cannot allocate FTP data port\n");
 689 #endif
 690         }
 691 }