2 * Copyright (c) 2001 Charles Mott <cm@linktel.net>
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
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.
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
26 * $FreeBSD: src/lib/libalias/alias_ftp.c,v 1.5.2.7 2001/12/06 09:00:26 ru Exp $
30 Alias_ftp.c performs special processing for FTP sessions under
31 TCP. Specifically, when a PORT/EPRT command from the client
32 side or 227/229 reply from the server is sent, it is intercepted
33 and modified. The address is changed to the gateway machine
34 and an aliasing port is used.
36 For this routine to work, the message must fit entirely into a
37 single TCP packet. This is typically the case, but exceptions
38 can easily be envisioned under the actual specifications.
40 Probably the most troubling aspect of the approach taken here is
41 that the new message will typically be a different length, and
42 this causes a certain amount of bookkeeping to keep track of the
43 changes of sequence and acknowledgment numbers, since the client
44 machine is totally unaware of the modification to the TCP stream.
47 References: RFC 959, RFC 2428.
49 Initial version: August, 1996 (cjm)
52 Brian Somers and Martin Renters identified an IP checksum
53 error for modified IP packets.
55 Version 1.7: January 9, 1996 (cjm)
56 Differential checksum computation for change
59 Version 2.1: May, 1997 (cjm)
60 Very minor changes to conform with
61 local/global/function naming conventions
62 within the packet aliasing module.
64 Version 3.1: May, 2000 (eds)
65 Add support for passive mode, alias the 227 replies.
67 See HISTORY file for record of revisions.
74 #include <sys/types.h>
75 #include <netinet/in_systm.h>
76 #include <netinet/in.h>
77 #include <netinet/ip.h>
78 #include <netinet/tcp.h>
80 #include "alias_local.h"
82 #define FTP_CONTROL_PORT_NUMBER 21
83 #define MAX_MESSAGE_SIZE 128
85 enum ftp_message_type {
93 static int ParseFtpPortCommand(char *, int);
94 static int ParseFtpEprtCommand(char *, int);
95 static int ParseFtp227Reply(char *, int);
96 static int ParseFtp229Reply(char *, int);
97 static void NewFtpMessage(struct ip *, struct alias_link *, int, int);
99 static struct in_addr true_addr; /* in network byte order. */
100 static u_short true_port; /* in host byte order. */
104 struct ip *pip, /* IP packet to examine/patch */
105 struct alias_link *link, /* The link to go through (aliased port) */
106 int maxpacketsize /* The maximum size this packet can grow to (including headers) */)
108 int hlen, tlen, dlen;
111 int ftp_message_type;
113 /* Calculate data length of TCP packet */
114 tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
115 hlen = (pip->ip_hl + tc->th_off) << 2;
116 tlen = ntohs(pip->ip_len);
119 /* Place string pointer and beginning of data */
124 * Check that data length is not too long and previous message was
125 * properly terminated with CRLF.
127 if (dlen <= MAX_MESSAGE_SIZE && GetLastLineCrlfTermed(link)) {
128 ftp_message_type = FTP_UNKNOWN_MESSAGE;
130 if (ntohs(tc->th_dport) == FTP_CONTROL_PORT_NUMBER) {
132 * When aliasing a client, check for the PORT/EPRT command.
134 if (ParseFtpPortCommand(sptr, dlen))
135 ftp_message_type = FTP_PORT_COMMAND;
136 else if (ParseFtpEprtCommand(sptr, dlen))
137 ftp_message_type = FTP_EPRT_COMMAND;
140 * When aliasing a server, check for the 227/229 reply.
142 if (ParseFtp227Reply(sptr, dlen))
143 ftp_message_type = FTP_227_REPLY;
144 else if (ParseFtp229Reply(sptr, dlen)) {
145 ftp_message_type = FTP_229_REPLY;
146 true_addr.s_addr = pip->ip_src.s_addr;
150 if (ftp_message_type != FTP_UNKNOWN_MESSAGE)
151 NewFtpMessage(pip, link, maxpacketsize, ftp_message_type);
154 /* Track the msgs which are CRLF term'd for PORT/PASV FW breach */
156 if (dlen) { /* only if there's data */
157 sptr = (char *) pip; /* start over at beginning */
158 tlen = ntohs(pip->ip_len); /* recalc tlen, pkt may have grown */
159 SetLastLineCrlfTermed(link,
160 (sptr[tlen-2] == '\r') && (sptr[tlen-1] == '\n'));
165 ParseFtpPortCommand(char *sptr, int dlen)
173 /* Format: "PORT A,D,D,R,PO,RT". */
175 /* Return if data length is too short. */
179 addr = port = octet = 0;
181 for (i = 0; i < dlen; i++) {
184 case -4: if (ch == 'P') state++; else return 0; break;
185 case -3: if (ch == 'O') state++; else return 0; break;
186 case -2: if (ch == 'R') state++; else return 0; break;
187 case -1: if (ch == 'T') state++; else return 0; break;
194 case 1: case 3: case 5: case 7: case 9: case 11:
201 case 2: case 4: case 6: case 8:
203 octet = 10 * octet + ch - '0';
204 else if (ch == ',') {
205 addr = (addr << 8) + octet;
212 octet = 10 * octet + ch - '0';
213 else if (ch == ',' || state == 12) {
214 port = (port << 8) + octet;
223 true_addr.s_addr = htonl(addr);
231 ParseFtpEprtCommand(char *sptr, int dlen)
239 /* Format: "EPRT |1|A.D.D.R|PORT|". */
241 /* Return if data length is too short. */
245 addr = port = octet = 0;
246 delim = '|'; /* XXX gcc -Wuninitialized */
248 for (i = 0; i < dlen; i++) {
252 case -4: if (ch == 'E') state++; else return 0; break;
253 case -3: if (ch == 'P') state++; else return 0; break;
254 case -2: if (ch == 'R') state++; else return 0; break;
255 case -1: if (ch == 'T') state++; else return 0; break;
264 if (ch == '1') /* IPv4 address */
275 case 3: case 5: case 7: case 9:
282 case 4: case 6: case 8: case 10:
284 octet = 10 * octet + ch - '0';
285 else if (ch == '.' || state == 10) {
286 addr = (addr << 8) + octet;
300 port = 10 * port + ch - '0';
301 else if (ch == delim)
310 true_addr.s_addr = htonl(addr);
318 ParseFtp227Reply(char *sptr, int dlen)
326 /* Format: "227 Entering Passive Mode (A,D,D,R,PO,RT)" */
328 /* Return if data length is too short. */
332 addr = port = octet = 0;
335 for (i = 0; i < dlen; i++) {
339 case -3: if (ch == '2') state++; else return 0; break;
340 case -2: if (ch == '2') state++; else return 0; break;
341 case -1: if (ch == '7') state++; else return 0; break;
347 case 1: case 3: case 5: case 7: case 9: case 11:
354 case 2: case 4: case 6: case 8:
356 octet = 10 * octet + ch - '0';
357 else if (ch == ',') {
358 addr = (addr << 8) + octet;
365 octet = 10 * octet + ch - '0';
366 else if (ch == ',' || (state == 12 && ch == ')')) {
367 port = (port << 8) + octet;
377 true_addr.s_addr = htonl(addr);
384 ParseFtp229Reply(char *sptr, int dlen)
390 /* Format: "229 Entering Extended Passive Mode (|||PORT|)" */
392 /* Return if data length is too short. */
397 delim = '|'; /* XXX gcc -Wuninitialized */
400 for (i = 0; i < dlen; i++) {
404 case -3: if (ch == '2') state++; else return 0; break;
405 case -2: if (ch == '2') state++; else return 0; break;
406 case -1: if (ch == '9') state++; else return 0; break;
431 port = 10 * port + ch - '0';
432 else if (ch == delim)
454 NewFtpMessage(struct ip *pip,
455 struct alias_link *link,
457 int ftp_message_type)
459 struct alias_link *ftp_link;
461 /* Security checks. */
462 if (pip->ip_src.s_addr != true_addr.s_addr)
465 if (true_port < IPPORT_RESERVED)
468 /* Establish link to address and port found in FTP control message. */
469 ftp_link = FindUdpTcpOut(true_addr, GetDestAddress(link),
470 htons(true_port), 0, IPPROTO_TCP, 1);
472 if (ftp_link != NULL)
474 int slen, hlen, tlen, dlen;
478 /* Punch hole in firewall */
479 PunchFWHole(ftp_link);
482 /* Calculate data length of TCP packet */
483 tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
484 hlen = (pip->ip_hl + tc->th_off) << 2;
485 tlen = ntohs(pip->ip_len);
488 /* Create new FTP message. */
490 char stemp[MAX_MESSAGE_SIZE + 1];
494 int a1, a2, a3, a4, p1, p2;
495 struct in_addr alias_address;
497 /* Decompose alias address into quad format */
498 alias_address = GetAliasAddress(link);
499 ptr = (u_char *) &alias_address.s_addr;
500 a1 = *ptr++; a2=*ptr++; a3=*ptr++; a4=*ptr;
502 alias_port = GetAliasPort(ftp_link);
504 switch (ftp_message_type)
506 case FTP_PORT_COMMAND:
508 /* Decompose alias port into pair format. */
509 ptr = (char *) &alias_port;
510 p1 = *ptr++; p2=*ptr;
512 if (ftp_message_type == FTP_PORT_COMMAND) {
513 /* Generate PORT command string. */
514 sprintf(stemp, "PORT %d,%d,%d,%d,%d,%d\r\n",
517 /* Generate 227 reply string. */
519 "227 Entering Passive Mode (%d,%d,%d,%d,%d,%d)\r\n",
523 case FTP_EPRT_COMMAND:
524 /* Generate EPRT command string. */
525 sprintf(stemp, "EPRT |1|%d.%d.%d.%d|%d|\r\n",
526 a1,a2,a3,a4,ntohs(alias_port));
529 /* Generate 229 reply string. */
530 sprintf(stemp, "229 Entering Extended Passive Mode (|||%d|)\r\n",
535 /* Save string length for IP header modification */
536 slen = strlen(stemp);
538 /* Copy modified buffer into IP packet. */
539 sptr = (char *) pip; sptr += hlen;
540 strncpy(sptr, stemp, maxpacketsize-hlen);
543 /* Save information regarding modified seq and ack numbers */
547 SetAckModified(link);
548 delta = GetDeltaSeqOut(pip, link);
549 AddSeq(pip, link, delta+slen-dlen);
552 /* Revise IP header */
556 new_len = htons(hlen + slen);
557 DifferentialChecksum(&pip->ip_sum,
561 pip->ip_len = new_len;
564 /* Compute TCP checksum for revised packet */
566 tc->th_sum = TcpChecksum(pip);
572 "PacketAlias/HandleFtpOut: Cannot allocate FTP data port\n");