8573e68110
for passive mode data connections (PASV/EPSV -> 227/229). Well, the actual punching happens a bit later, when the aliasing link becomes fully specified. Prodded by: Danny Carroll <dannycarroll@hotmail.com> MFC after: 1 week
584 lines
14 KiB
C
584 lines
14 KiB
C
/*-
|
|
* Copyright (c) 2001 Charles Mott <cm@linktel.net>
|
|
* All rights reserved.
|
|
*
|
|
* Redistribution and use in source and binary forms, with or without
|
|
* modification, are permitted provided that the following conditions
|
|
* are met:
|
|
* 1. Redistributions of source code must retain the above copyright
|
|
* notice, this list of conditions and the following disclaimer.
|
|
* 2. Redistributions in binary form must reproduce the above copyright
|
|
* notice, this list of conditions and the following disclaimer in the
|
|
* documentation and/or other materials provided with the distribution.
|
|
*
|
|
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
|
|
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
|
|
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
* SUCH DAMAGE.
|
|
*/
|
|
|
|
#include <sys/cdefs.h>
|
|
__FBSDID("$FreeBSD$");
|
|
|
|
/*
|
|
Alias_ftp.c performs special processing for FTP sessions under
|
|
TCP. Specifically, when a PORT/EPRT command from the client
|
|
side or 227/229 reply from the server is sent, it is intercepted
|
|
and modified. The address is changed to the gateway machine
|
|
and an aliasing port is used.
|
|
|
|
For this routine to work, the message must fit entirely into a
|
|
single TCP packet. This is typically the case, but exceptions
|
|
can easily be envisioned under the actual specifications.
|
|
|
|
Probably the most troubling aspect of the approach taken here is
|
|
that the new message will typically be a different length, and
|
|
this causes a certain amount of bookkeeping to keep track of the
|
|
changes of sequence and acknowledgment numbers, since the client
|
|
machine is totally unaware of the modification to the TCP stream.
|
|
|
|
|
|
References: RFC 959, RFC 2428.
|
|
|
|
Initial version: August, 1996 (cjm)
|
|
|
|
Version 1.6
|
|
Brian Somers and Martin Renters identified an IP checksum
|
|
error for modified IP packets.
|
|
|
|
Version 1.7: January 9, 1996 (cjm)
|
|
Differential checksum computation for change
|
|
in IP packet length.
|
|
|
|
Version 2.1: May, 1997 (cjm)
|
|
Very minor changes to conform with
|
|
local/global/function naming conventions
|
|
within the packet aliasing module.
|
|
|
|
Version 3.1: May, 2000 (eds)
|
|
Add support for passive mode, alias the 227 replies.
|
|
|
|
See HISTORY file for record of revisions.
|
|
*/
|
|
|
|
/* Includes */
|
|
#include <ctype.h>
|
|
#include <stdio.h>
|
|
#include <string.h>
|
|
#include <sys/types.h>
|
|
#include <netinet/in_systm.h>
|
|
#include <netinet/in.h>
|
|
#include <netinet/ip.h>
|
|
#include <netinet/tcp.h>
|
|
|
|
#include "alias_local.h"
|
|
|
|
#define FTP_CONTROL_PORT_NUMBER 21
|
|
#define MAX_MESSAGE_SIZE 128
|
|
|
|
/* FTP protocol flags. */
|
|
#define WAIT_CRLF 0x01
|
|
|
|
enum ftp_message_type {
|
|
FTP_PORT_COMMAND,
|
|
FTP_EPRT_COMMAND,
|
|
FTP_227_REPLY,
|
|
FTP_229_REPLY,
|
|
FTP_UNKNOWN_MESSAGE
|
|
};
|
|
|
|
static int ParseFtpPortCommand(char *, int);
|
|
static int ParseFtpEprtCommand(char *, int);
|
|
static int ParseFtp227Reply(char *, int);
|
|
static int ParseFtp229Reply(char *, int);
|
|
static void NewFtpMessage(struct ip *, struct alias_link *, int, int);
|
|
|
|
static struct in_addr true_addr; /* in network byte order. */
|
|
static u_short true_port; /* in host byte order. */
|
|
|
|
void
|
|
AliasHandleFtpOut(
|
|
struct ip *pip, /* IP packet to examine/patch */
|
|
struct alias_link *link, /* The link to go through (aliased port) */
|
|
int maxpacketsize /* The maximum size this packet can grow to (including headers) */)
|
|
{
|
|
int hlen, tlen, dlen, pflags;
|
|
char *sptr;
|
|
struct tcphdr *tc;
|
|
int ftp_message_type;
|
|
|
|
/* Calculate data length of TCP packet */
|
|
tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
|
|
hlen = (pip->ip_hl + tc->th_off) << 2;
|
|
tlen = ntohs(pip->ip_len);
|
|
dlen = tlen - hlen;
|
|
|
|
/* Place string pointer and beginning of data */
|
|
sptr = (char *) pip;
|
|
sptr += hlen;
|
|
|
|
/*
|
|
* Check that data length is not too long and previous message was
|
|
* properly terminated with CRLF.
|
|
*/
|
|
pflags = GetProtocolFlags(link);
|
|
if (dlen <= MAX_MESSAGE_SIZE && !(pflags & WAIT_CRLF)) {
|
|
ftp_message_type = FTP_UNKNOWN_MESSAGE;
|
|
|
|
if (ntohs(tc->th_dport) == FTP_CONTROL_PORT_NUMBER) {
|
|
/*
|
|
* When aliasing a client, check for the PORT/EPRT command.
|
|
*/
|
|
if (ParseFtpPortCommand(sptr, dlen))
|
|
ftp_message_type = FTP_PORT_COMMAND;
|
|
else if (ParseFtpEprtCommand(sptr, dlen))
|
|
ftp_message_type = FTP_EPRT_COMMAND;
|
|
} else {
|
|
/*
|
|
* When aliasing a server, check for the 227/229 reply.
|
|
*/
|
|
if (ParseFtp227Reply(sptr, dlen))
|
|
ftp_message_type = FTP_227_REPLY;
|
|
else if (ParseFtp229Reply(sptr, dlen)) {
|
|
ftp_message_type = FTP_229_REPLY;
|
|
true_addr.s_addr = pip->ip_src.s_addr;
|
|
}
|
|
}
|
|
|
|
if (ftp_message_type != FTP_UNKNOWN_MESSAGE)
|
|
NewFtpMessage(pip, link, maxpacketsize, ftp_message_type);
|
|
}
|
|
|
|
/* Track the msgs which are CRLF term'd for PORT/PASV FW breach */
|
|
|
|
if (dlen) { /* only if there's data */
|
|
sptr = (char *) pip; /* start over at beginning */
|
|
tlen = ntohs(pip->ip_len); /* recalc tlen, pkt may have grown */
|
|
if (sptr[tlen-2] == '\r' && sptr[tlen-1] == '\n')
|
|
pflags &= ~WAIT_CRLF;
|
|
else
|
|
pflags |= WAIT_CRLF;
|
|
SetProtocolFlags(link, pflags);
|
|
}
|
|
}
|
|
|
|
static int
|
|
ParseFtpPortCommand(char *sptr, int dlen)
|
|
{
|
|
char ch;
|
|
int i, state;
|
|
u_int32_t addr;
|
|
u_short port;
|
|
u_int8_t octet;
|
|
|
|
/* Format: "PORT A,D,D,R,PO,RT". */
|
|
|
|
/* Return if data length is too short. */
|
|
if (dlen < 18)
|
|
return 0;
|
|
|
|
addr = port = octet = 0;
|
|
state = -4;
|
|
for (i = 0; i < dlen; i++) {
|
|
ch = sptr[i];
|
|
switch (state) {
|
|
case -4: if (ch == 'P') state++; else return 0; break;
|
|
case -3: if (ch == 'O') state++; else return 0; break;
|
|
case -2: if (ch == 'R') state++; else return 0; break;
|
|
case -1: if (ch == 'T') state++; else return 0; break;
|
|
|
|
case 0:
|
|
if (isspace(ch))
|
|
break;
|
|
else
|
|
state++;
|
|
case 1: case 3: case 5: case 7: case 9: case 11:
|
|
if (isdigit(ch)) {
|
|
octet = ch - '0';
|
|
state++;
|
|
} else
|
|
return 0;
|
|
break;
|
|
case 2: case 4: case 6: case 8:
|
|
if (isdigit(ch))
|
|
octet = 10 * octet + ch - '0';
|
|
else if (ch == ',') {
|
|
addr = (addr << 8) + octet;
|
|
state++;
|
|
} else
|
|
return 0;
|
|
break;
|
|
case 10: case 12:
|
|
if (isdigit(ch))
|
|
octet = 10 * octet + ch - '0';
|
|
else if (ch == ',' || state == 12) {
|
|
port = (port << 8) + octet;
|
|
state++;
|
|
} else
|
|
return 0;
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (state == 13) {
|
|
true_addr.s_addr = htonl(addr);
|
|
true_port = port;
|
|
return 1;
|
|
} else
|
|
return 0;
|
|
}
|
|
|
|
static int
|
|
ParseFtpEprtCommand(char *sptr, int dlen)
|
|
{
|
|
char ch, delim;
|
|
int i, state;
|
|
u_int32_t addr;
|
|
u_short port;
|
|
u_int8_t octet;
|
|
|
|
/* Format: "EPRT |1|A.D.D.R|PORT|". */
|
|
|
|
/* Return if data length is too short. */
|
|
if (dlen < 18)
|
|
return 0;
|
|
|
|
addr = port = octet = 0;
|
|
delim = '|'; /* XXX gcc -Wuninitialized */
|
|
state = -4;
|
|
for (i = 0; i < dlen; i++) {
|
|
ch = sptr[i];
|
|
switch (state)
|
|
{
|
|
case -4: if (ch == 'E') state++; else return 0; break;
|
|
case -3: if (ch == 'P') state++; else return 0; break;
|
|
case -2: if (ch == 'R') state++; else return 0; break;
|
|
case -1: if (ch == 'T') state++; else return 0; break;
|
|
|
|
case 0:
|
|
if (!isspace(ch)) {
|
|
delim = ch;
|
|
state++;
|
|
}
|
|
break;
|
|
case 1:
|
|
if (ch == '1') /* IPv4 address */
|
|
state++;
|
|
else
|
|
return 0;
|
|
break;
|
|
case 2:
|
|
if (ch == delim)
|
|
state++;
|
|
else
|
|
return 0;
|
|
break;
|
|
case 3: case 5: case 7: case 9:
|
|
if (isdigit(ch)) {
|
|
octet = ch - '0';
|
|
state++;
|
|
} else
|
|
return 0;
|
|
break;
|
|
case 4: case 6: case 8: case 10:
|
|
if (isdigit(ch))
|
|
octet = 10 * octet + ch - '0';
|
|
else if (ch == '.' || state == 10) {
|
|
addr = (addr << 8) + octet;
|
|
state++;
|
|
} else
|
|
return 0;
|
|
break;
|
|
case 11:
|
|
if (isdigit(ch)) {
|
|
port = ch - '0';
|
|
state++;
|
|
} else
|
|
return 0;
|
|
break;
|
|
case 12:
|
|
if (isdigit(ch))
|
|
port = 10 * port + ch - '0';
|
|
else if (ch == delim)
|
|
state++;
|
|
else
|
|
return 0;
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (state == 13) {
|
|
true_addr.s_addr = htonl(addr);
|
|
true_port = port;
|
|
return 1;
|
|
} else
|
|
return 0;
|
|
}
|
|
|
|
static int
|
|
ParseFtp227Reply(char *sptr, int dlen)
|
|
{
|
|
char ch;
|
|
int i, state;
|
|
u_int32_t addr;
|
|
u_short port;
|
|
u_int8_t octet;
|
|
|
|
/* Format: "227 Entering Passive Mode (A,D,D,R,PO,RT)" */
|
|
|
|
/* Return if data length is too short. */
|
|
if (dlen < 17)
|
|
return 0;
|
|
|
|
addr = port = octet = 0;
|
|
|
|
state = -3;
|
|
for (i = 0; i < dlen; i++) {
|
|
ch = sptr[i];
|
|
switch (state)
|
|
{
|
|
case -3: if (ch == '2') state++; else return 0; break;
|
|
case -2: if (ch == '2') state++; else return 0; break;
|
|
case -1: if (ch == '7') state++; else return 0; break;
|
|
|
|
case 0:
|
|
if (ch == '(')
|
|
state++;
|
|
break;
|
|
case 1: case 3: case 5: case 7: case 9: case 11:
|
|
if (isdigit(ch)) {
|
|
octet = ch - '0';
|
|
state++;
|
|
} else
|
|
return 0;
|
|
break;
|
|
case 2: case 4: case 6: case 8:
|
|
if (isdigit(ch))
|
|
octet = 10 * octet + ch - '0';
|
|
else if (ch == ',') {
|
|
addr = (addr << 8) + octet;
|
|
state++;
|
|
} else
|
|
return 0;
|
|
break;
|
|
case 10: case 12:
|
|
if (isdigit(ch))
|
|
octet = 10 * octet + ch - '0';
|
|
else if (ch == ',' || (state == 12 && ch == ')')) {
|
|
port = (port << 8) + octet;
|
|
state++;
|
|
} else
|
|
return 0;
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (state == 13) {
|
|
true_port = port;
|
|
true_addr.s_addr = htonl(addr);
|
|
return 1;
|
|
} else
|
|
return 0;
|
|
}
|
|
|
|
static int
|
|
ParseFtp229Reply(char *sptr, int dlen)
|
|
{
|
|
char ch, delim;
|
|
int i, state;
|
|
u_short port;
|
|
|
|
/* Format: "229 Entering Extended Passive Mode (|||PORT|)" */
|
|
|
|
/* Return if data length is too short. */
|
|
if (dlen < 11)
|
|
return 0;
|
|
|
|
port = 0;
|
|
delim = '|'; /* XXX gcc -Wuninitialized */
|
|
|
|
state = -3;
|
|
for (i = 0; i < dlen; i++) {
|
|
ch = sptr[i];
|
|
switch (state)
|
|
{
|
|
case -3: if (ch == '2') state++; else return 0; break;
|
|
case -2: if (ch == '2') state++; else return 0; break;
|
|
case -1: if (ch == '9') state++; else return 0; break;
|
|
|
|
case 0:
|
|
if (ch == '(')
|
|
state++;
|
|
break;
|
|
case 1:
|
|
delim = ch;
|
|
state++;
|
|
break;
|
|
case 2: case 3:
|
|
if (ch == delim)
|
|
state++;
|
|
else
|
|
return 0;
|
|
break;
|
|
case 4:
|
|
if (isdigit(ch)) {
|
|
port = ch - '0';
|
|
state++;
|
|
} else
|
|
return 0;
|
|
break;
|
|
case 5:
|
|
if (isdigit(ch))
|
|
port = 10 * port + ch - '0';
|
|
else if (ch == delim)
|
|
state++;
|
|
else
|
|
return 0;
|
|
break;
|
|
case 6:
|
|
if (ch == ')')
|
|
state++;
|
|
else
|
|
return 0;
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (state == 7) {
|
|
true_port = port;
|
|
return 1;
|
|
} else
|
|
return 0;
|
|
}
|
|
|
|
static void
|
|
NewFtpMessage(struct ip *pip,
|
|
struct alias_link *link,
|
|
int maxpacketsize,
|
|
int ftp_message_type)
|
|
{
|
|
struct alias_link *ftp_link;
|
|
|
|
/* Security checks. */
|
|
if (pip->ip_src.s_addr != true_addr.s_addr)
|
|
return;
|
|
|
|
if (true_port < IPPORT_RESERVED)
|
|
return;
|
|
|
|
/* Establish link to address and port found in FTP control message. */
|
|
ftp_link = FindUdpTcpOut(true_addr, GetDestAddress(link),
|
|
htons(true_port), 0, IPPROTO_TCP, 1);
|
|
|
|
if (ftp_link != NULL)
|
|
{
|
|
int slen, hlen, tlen, dlen;
|
|
struct tcphdr *tc;
|
|
|
|
#ifndef NO_FW_PUNCH
|
|
/* Punch hole in firewall */
|
|
PunchFWHole(ftp_link);
|
|
#endif
|
|
|
|
/* Calculate data length of TCP packet */
|
|
tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
|
|
hlen = (pip->ip_hl + tc->th_off) << 2;
|
|
tlen = ntohs(pip->ip_len);
|
|
dlen = tlen - hlen;
|
|
|
|
/* Create new FTP message. */
|
|
{
|
|
char stemp[MAX_MESSAGE_SIZE + 1];
|
|
char *sptr;
|
|
u_short alias_port;
|
|
u_char *ptr;
|
|
int a1, a2, a3, a4, p1, p2;
|
|
struct in_addr alias_address;
|
|
|
|
/* Decompose alias address into quad format */
|
|
alias_address = GetAliasAddress(link);
|
|
ptr = (u_char *) &alias_address.s_addr;
|
|
a1 = *ptr++; a2=*ptr++; a3=*ptr++; a4=*ptr;
|
|
|
|
alias_port = GetAliasPort(ftp_link);
|
|
|
|
switch (ftp_message_type)
|
|
{
|
|
case FTP_PORT_COMMAND:
|
|
case FTP_227_REPLY:
|
|
/* Decompose alias port into pair format. */
|
|
ptr = (char *) &alias_port;
|
|
p1 = *ptr++; p2=*ptr;
|
|
|
|
if (ftp_message_type == FTP_PORT_COMMAND) {
|
|
/* Generate PORT command string. */
|
|
sprintf(stemp, "PORT %d,%d,%d,%d,%d,%d\r\n",
|
|
a1,a2,a3,a4,p1,p2);
|
|
} else {
|
|
/* Generate 227 reply string. */
|
|
sprintf(stemp,
|
|
"227 Entering Passive Mode (%d,%d,%d,%d,%d,%d)\r\n",
|
|
a1,a2,a3,a4,p1,p2);
|
|
}
|
|
break;
|
|
case FTP_EPRT_COMMAND:
|
|
/* Generate EPRT command string. */
|
|
sprintf(stemp, "EPRT |1|%d.%d.%d.%d|%d|\r\n",
|
|
a1,a2,a3,a4,ntohs(alias_port));
|
|
break;
|
|
case FTP_229_REPLY:
|
|
/* Generate 229 reply string. */
|
|
sprintf(stemp, "229 Entering Extended Passive Mode (|||%d|)\r\n",
|
|
ntohs(alias_port));
|
|
break;
|
|
}
|
|
|
|
/* Save string length for IP header modification */
|
|
slen = strlen(stemp);
|
|
|
|
/* Copy modified buffer into IP packet. */
|
|
sptr = (char *) pip; sptr += hlen;
|
|
strncpy(sptr, stemp, maxpacketsize-hlen);
|
|
}
|
|
|
|
/* Save information regarding modified seq and ack numbers */
|
|
{
|
|
int delta;
|
|
|
|
SetAckModified(link);
|
|
delta = GetDeltaSeqOut(pip, link);
|
|
AddSeq(pip, link, delta+slen-dlen);
|
|
}
|
|
|
|
/* Revise IP header */
|
|
{
|
|
u_short new_len;
|
|
|
|
new_len = htons(hlen + slen);
|
|
DifferentialChecksum(&pip->ip_sum,
|
|
&new_len,
|
|
&pip->ip_len,
|
|
1);
|
|
pip->ip_len = new_len;
|
|
}
|
|
|
|
/* Compute TCP checksum for revised packet */
|
|
tc->th_sum = 0;
|
|
tc->th_sum = TcpChecksum(pip);
|
|
}
|
|
else
|
|
{
|
|
#ifdef DEBUG
|
|
fprintf(stderr,
|
|
"PacketAlias/HandleFtpOut: Cannot allocate FTP data port\n");
|
|
#endif
|
|
}
|
|
}
|