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- Improved passive mode FTP support by aliasing 229 replies.

Browse Source 
- Stricter checking of PORT/EPRT/227/229 messages format.
- Moved all security checks into one place.
This commit is contained in:
Ruslan Ermilov 2000-06-16 20:36:16 +00:00
parent b106252c19
commit b766604065
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=61735
2 changed files with 672 additions and 622 deletions
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647
lib/libalias/alias_ftp.c
View File

@ -1,28 +1,26 @@
/*
Alias_ftp.c performs special processing for FTP sessions under
TCP. Specifically, when a PORT command from the client side
or PASV/227 reply from the server is sent, it is intercepted
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 PORT/227 must fit entirely
into a single TCP packet. This is typically the case, but exceptions
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 PORT/227 will typically be a different length, and
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.
This version also supports the EPRT command, which is functionally
equivalent to the PORT command, but was designed to support both
IPv4 and IPv6 addresses. See RFC 2428 for specifications.
This software is placed into the public domain with no restrictions
on its distribution.
References: RFC 959, RFC 2428.
Initial version: August, 1996 (cjm)
Version 1.6
@ -32,7 +30,7 @@
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
@ -48,7 +46,7 @@
/* Includes */
#include <ctype.h>
#include <stdio.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in_systm.h>
@ -58,17 +56,25 @@
#include "alias_local.h"
#define FTP_CONTROL_PORT_NUMBER 21
#define MIN_227_REPLY 16
#define MAX_227_REPLY 128
#define FTP_CONTROL_PORT_NUMBER 21
#define MAX_MESSAGE_SIZE 128
static int ParseFtpPortCommand(char *, int, struct ip *, struct alias_link *, int);
static void ParseFtpEprtCommand(char *, int, struct ip *, struct alias_link *, int);
static void NewFtpPortCommand(struct ip *, struct alias_link *, struct in_addr, u_short, int, int);
enum ftp_message_type {
FTP_PORT_COMMAND,
FTP_EPRT_COMMAND,
FTP_227_REPLY,
FTP_229_REPLY,
FTP_UNKNOWN_MESSAGE
};
static int ParseFtp227Reply(char *, int, struct ip *, struct alias_link *, int);
static void NewFtp227Reply(struct ip *, struct alias_link *, struct in_addr, u_short, int);
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(
@ -79,7 +85,8 @@ int maxpacketsize /* The maximum size this packet can grow to (including header
int hlen, tlen, dlen;
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;
@ -87,22 +94,42 @@ int maxpacketsize /* The maximum size this packet can grow to (including header
dlen = tlen - hlen;
/* Place string pointer and beginning of data */
sptr = (char *) pip;
sptr = (char *) pip;
sptr += hlen;
/* When aliasing a client, check for the PORT/EPRT command */
if (ntohs(tc->th_dport) == FTP_CONTROL_PORT_NUMBER) {
/* Parse through string using state diagram method */
if (!ParseFtpPortCommand(sptr, dlen, pip, link, maxpacketsize))
ParseFtpEprtCommand(sptr, dlen, pip, link, maxpacketsize);
} else {
ParseFtp227Reply(sptr, dlen, pip, link, maxpacketsize);
/*
* Check that data length is not too long and previous message was
* properly terminated with CRLF.
*/
if (dlen <= MAX_MESSAGE_SIZE && GetLastLineCrlfTermed(link)) {
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;
}
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 */
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 */
SetLastLineCrlfTermed(link,
(sptr[tlen-2] == '\r') && (sptr[tlen-1] == '\n'));
@ -110,186 +137,177 @@ int maxpacketsize /* The maximum size this packet can grow to (including header
}
static int
ParseFtpPortCommand(
char *sptr,
int dlen,
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) */)
ParseFtpPortCommand(char *sptr, int dlen)
{
struct in_addr true_addr;
u_short true_port;
char ch;
int i, state;
u_long a1, a2, a3, a4;
u_short p1, p2;
u_int32_t addr;
u_short port;
u_int8_t octet;
/* Return if data length is too long or too short */
if (dlen<10 || dlen>80)
/* Format: "PORT A,D,D,R,PO,RT". */
/* Return if data length is too short. */
if (dlen < 18)
return 0;
a1=0; a2=0; a3=0; a4=0; p1=0; p2=0;
state=-4;
for (i=0; i<dlen; i++)
{
addr = port = octet = 0;
state = -4;
for (i = 0; i < dlen; i++) {
ch = sptr[i];
switch (state)
{
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 (isdigit(ch)) {a1=ch-'0'; state++;} break;
case 1 :
if (isdigit(ch)) a1=10*a1+ch-'0'; else state++; break;
case 2 :
if (isdigit(ch)) {a2=ch-'0'; state++;} break;
case 3 :
if (isdigit(ch)) a2=10*a2+ch-'0'; else state++; break;
case 4 :
if (isdigit(ch)) {a3=ch-'0'; state++;} break;
case 5 :
if (isdigit(ch)) a3=10*a3+ch-'0'; else state++; break;
case 6 :
if (isdigit(ch)) {a4=ch-'0'; state++;} break;
case 7 :
if (isdigit(ch)) a4=10*a4+ch-'0'; else state++; break;
case 8 :
if (isdigit(ch)) {p1=ch-'0'; state++;} break;
case 9 :
if (isdigit(ch)) p1=10*p1+ch-'0'; else state++; break;
case 10:
if (isdigit(ch)) {p2=ch-'0'; state++;} break;
case 11:
if (isdigit(ch)) p2=10*p2+ch-'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 == 11 && GetLastLineCrlfTermed(link))
{
true_port = htons((p1<<8) + p2);
true_addr.s_addr = htonl((a1<<24) + (a2<<16) +(a3<<8) + a4);
if ((pip->ip_src.s_addr == true_addr.s_addr) &&
((p1<<8) >= IPPORT_RESERVED))
NewFtpPortCommand(pip, link, true_addr, true_port, maxpacketsize, 0);
if (state == 13) {
true_addr.s_addr = htonl(addr);
true_port = port;
return 1;
}
else
} else
return 0;
}
static void
ParseFtpEprtCommand(
char *sptr,
int dlen,
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) */)
static int
ParseFtpEprtCommand(char *sptr, int dlen)
{
struct in_addr true_addr;
u_short true_port;
char ch, delim;
int i, state;
u_long a1, a2, a3, a4;
u_short pt;
u_int32_t addr;
u_short port;
u_int8_t octet;
/* Return if data length is too long or too short */
if (dlen<10 || dlen>80)
return;
/* Format: "EPRT |1|A.D.D.R|PORT|". */
a1=0; a2=0; a3=0; a4=0; pt=0;
delim='|'; /* XXX gcc -Wuninitialized */
state=-4;
for (i=0; i<dlen; i++)
{
/* 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; break;
case -3: if (ch == 'P') state++; else return; break;
case -2: if (ch == 'R') state++; else return; break;
case -1: if (ch == 'T') state++; else return; break;
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; break;
case 2 :
if (ch==delim) state++; else return; break;
case 3 :
if (isdigit(ch)) {a1=ch-'0'; state++;} else return; break;
case 4 :
if (isdigit(ch)) a1=10*a1+ch-'0';
else if (ch=='.') state++;
else return;
case 0:
if (!isspace(ch)) {
delim = ch;
state++;
}
break;
case 5 :
if (isdigit(ch)) {a2=ch-'0'; state++;} else return; break;
case 6 :
if (isdigit(ch)) a2=10*a2+ch-'0';
else if (ch=='.') state++;
else return;
case 1:
if (ch == '1') /* IPv4 address */
state++;
else
return 0;
break;
case 7:
if (isdigit(ch)) {a3=ch-'0'; state++;} else return; break;
case 8 :
if (isdigit(ch)) a3=10*a3+ch-'0';
else if (ch=='.') state++;
else return;
case 2:
if (ch == delim)
state++;
else
return 0;
break;
case 9 :
if (isdigit(ch)) {a4=ch-'0'; state++;} else return; break;
case 10:
if (isdigit(ch)) a4=10*a4+ch-'0';
else if (ch==delim) state++;
else return;
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)) {pt=ch-'0'; state++;} else return; break;
if (isdigit(ch)) {
port = ch - '0';
state++;
} else
return 0;
break;
case 12:
if (isdigit(ch)) pt=10*pt+ch-'0';
else if (ch==delim) state++;
else return;
if (isdigit(ch))
port = 10 * port + ch - '0';
else if (ch == delim)
state++;
else
return 0;
break;
}
}
if (state == 13 && GetLastLineCrlfTermed(link))
{
true_port = htons(pt);
true_addr.s_addr = htonl((a1<<24) + (a2<<16) +(a3<<8) + a4);
if ((pip->ip_src.s_addr == true_addr.s_addr) &&
(pt >= IPPORT_RESERVED))
NewFtpPortCommand(pip, link, true_addr, true_port, maxpacketsize, 1);
}
if (state == 13) {
true_addr.s_addr = htonl(addr);
true_port = port;
return 1;
} else
return 0;
}
static int
ParseFtp227Reply(char *sptr,
int dlen,
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) */
ParseFtp227Reply(char *sptr, int dlen)
{
struct in_addr true_addr;
u_short true_port;
char ch;
int i, state;
u_long a1, a2, a3, a4;
u_short p1, p2;
u_int32_t addr;
u_short port;
u_int8_t octet;
/* Format: "227 Entering Passive Mode (A,D,D,R,PO,RT)" */
/* Return if wrong size, in case more packet types added later */
if (dlen<MIN_227_REPLY || dlen>MAX_227_REPLY)
return 0;
/* Return if data length is too short. */
if (dlen < 17)
return 0;
a1=0; a2=0; a3=0; a4=0; p1=0; p2=0;
state=-3;
for (i=0; i<dlen; i++)
{
addr = port = octet = 0;
state = -3;
for (i = 0; i < dlen; i++) {
ch = sptr[i];
switch (state)
{
@ -297,59 +315,135 @@ ParseFtp227Reply(char *sptr,
case -2: if (ch == '2') state++; else return 0; break;
case -1: if (ch == '7') state++; else return 0; break;
case 0 :
if (isdigit(ch)) {a1=ch-'0'; state++;} break;
case 1 :
if (isdigit(ch)) a1=10*a1+ch-'0'; else state++; break;
case 2 :
if (isdigit(ch)) {a2=ch-'0'; state++;} break;
case 3 :
if (isdigit(ch)) a2=10*a2+ch-'0'; else state++; break;
case 4 :
if (isdigit(ch)) {a3=ch-'0'; state++;} break;
case 5 :
if (isdigit(ch)) a3=10*a3+ch-'0'; else state++; break;
case 6 :
if (isdigit(ch)) {a4=ch-'0'; state++;} break;
case 7 :
if (isdigit(ch)) a4=10*a4+ch-'0'; else state++; break;
case 8 :
if (isdigit(ch)) {p1=ch-'0'; state++;} break;
case 9 :
if (isdigit(ch)) p1=10*p1+ch-'0'; else state++; break;
case 10:
if (isdigit(ch)) {p2=ch-'0'; state++;} break;
case 11:
if (isdigit(ch)) p2=10*p2+ch-'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 == 11 && GetLastLineCrlfTermed(link))
{
true_port = htons((p1<<8) + p2);
true_addr.s_addr = htonl((a1<<24) + (a2<<16) +(a3<<8) + a4);
if ((pip->ip_src.s_addr == true_addr.s_addr) &&
((p1<<8) >= IPPORT_RESERVED))
NewFtp227Reply(pip, link, true_addr, true_port, maxpacketsize);
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;
}
}
else
if (state == 7) {
true_port = port;
return 1;
} else
return 0;
}
static void
NewFtpPortCommand(struct ip *pip,
struct alias_link *link,
struct in_addr true_addr,
u_short true_port,
int maxpacketsize,
int is_eprt)
{
NewFtpMessage(struct ip *pip,
struct alias_link *link,
int maxpacketsize,
int ftp_message_type)
{
struct alias_link *ftp_link;
/* Establish link to address and port found in PORT command */
/* Security checks. */
if (ftp_message_type != FTP_229_REPLY &&
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),
true_port, 0, IPPROTO_TCP);
htons(true_port), 0, IPPROTO_TCP);
if (ftp_link != NULL)
{
@ -357,8 +451,11 @@ NewFtpPortCommand(struct ip *pip,
struct tcphdr *tc;
#ifndef NO_FW_PUNCH
/* Punch hole in firewall */
PunchFWHole(ftp_link);
if (ftp_message_type == FTP_PORT_COMMAND ||
ftp_message_type == FTP_EPRT_COMMAND) {
/* Punch hole in firewall */
PunchFWHole(ftp_link);
}
#endif
/* Calculate data length of TCP packet */
@ -367,15 +464,15 @@ NewFtpPortCommand(struct ip *pip,
tlen = ntohs(pip->ip_len);
dlen = tlen - hlen;
/* Create new PORT command */
/* Create new FTP message. */
{
char stemp[80];
char stemp[MAX_MESSAGE_SIZE + 1];
char *sptr;
u_short alias_port;
u_char *ptr;
int a1, a2, a3, a4, p1, p2;
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;
@ -383,24 +480,41 @@ NewFtpPortCommand(struct ip *pip,
alias_port = GetAliasPort(ftp_link);
if (is_eprt) {
/* Generate EPRT command string */
sprintf(stemp, "EPRT |1|%d.%d.%d.%d|%d|\r\n",
a1,a2,a3,a4,ntohs(alias_port));
} else {
/* Decompose alias port into pair format */
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;
/* Generate PORT command string */
sprintf(stemp, "PORT %d,%d,%d,%d,%d,%d\r\n",
a1,a2,a3,a4,p1,p2);
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 into IP packet */
/* Copy modified buffer into IP packet. */
sptr = (char *) pip; sptr += hlen;
strncpy(sptr, stemp, maxpacketsize-hlen);
}
@ -434,96 +548,7 @@ NewFtpPortCommand(struct ip *pip,
{
#ifdef DEBUG
fprintf(stderr,
"PacketAlias/HandleFtpOut, PORT: Cannot allocate FTP data port\n");
#endif
}
}
static void
NewFtp227Reply(struct ip *pip,
struct alias_link *link,
struct in_addr true_addr,
u_short true_port,
int maxpacketsize)
{
struct alias_link *ftp_link;
/* Establish link to address and port found in 227 reply */
ftp_link = FindUdpTcpOut(true_addr, GetDestAddress(link),
true_port, 0, IPPROTO_TCP);
if (ftp_link != NULL)
{
int slen, hlen, tlen, dlen;
struct tcphdr *tc;
/* 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 227 reply */
{
char stemp[MAX_227_REPLY+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;
/* Decompose alias port into pair format */
alias_port = GetAliasPort(ftp_link);
ptr = (char *) &alias_port;
p1 = *ptr++; p2=*ptr;
/* Generate command string */
sprintf(stemp, "227 Entering Passive Mode (%d,%d,%d,%d,%d,%d)\r\n",
a1,a2,a3,a4,p1,p2);
/* 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, 227: Cannot allocate FTP data port\n");
"PacketAlias/HandleFtpOut: Cannot allocate FTP data port\n");
#endif
}
}

647
sys/netinet/libalias/alias_ftp.c
View File

@ -1,28 +1,26 @@
/*
Alias_ftp.c performs special processing for FTP sessions under
TCP. Specifically, when a PORT command from the client side
or PASV/227 reply from the server is sent, it is intercepted
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 PORT/227 must fit entirely
into a single TCP packet. This is typically the case, but exceptions
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 PORT/227 will typically be a different length, and
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.
This version also supports the EPRT command, which is functionally
equivalent to the PORT command, but was designed to support both
IPv4 and IPv6 addresses. See RFC 2428 for specifications.
This software is placed into the public domain with no restrictions
on its distribution.
References: RFC 959, RFC 2428.
Initial version: August, 1996 (cjm)
Version 1.6
@ -32,7 +30,7 @@
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
@ -48,7 +46,7 @@
/* Includes */
#include <ctype.h>
#include <stdio.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in_systm.h>
@ -58,17 +56,25 @@
#include "alias_local.h"
#define FTP_CONTROL_PORT_NUMBER 21
#define MIN_227_REPLY 16
#define MAX_227_REPLY 128
#define FTP_CONTROL_PORT_NUMBER 21
#define MAX_MESSAGE_SIZE 128
static int ParseFtpPortCommand(char *, int, struct ip *, struct alias_link *, int);
static void ParseFtpEprtCommand(char *, int, struct ip *, struct alias_link *, int);
static void NewFtpPortCommand(struct ip *, struct alias_link *, struct in_addr, u_short, int, int);
enum ftp_message_type {
FTP_PORT_COMMAND,
FTP_EPRT_COMMAND,
FTP_227_REPLY,
FTP_229_REPLY,
FTP_UNKNOWN_MESSAGE
};
static int ParseFtp227Reply(char *, int, struct ip *, struct alias_link *, int);
static void NewFtp227Reply(struct ip *, struct alias_link *, struct in_addr, u_short, int);
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(
@ -79,7 +85,8 @@ int maxpacketsize /* The maximum size this packet can grow to (including header
int hlen, tlen, dlen;
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;
@ -87,22 +94,42 @@ int maxpacketsize /* The maximum size this packet can grow to (including header
dlen = tlen - hlen;
/* Place string pointer and beginning of data */
sptr = (char *) pip;
sptr = (char *) pip;
sptr += hlen;
/* When aliasing a client, check for the PORT/EPRT command */
if (ntohs(tc->th_dport) == FTP_CONTROL_PORT_NUMBER) {
/* Parse through string using state diagram method */
if (!ParseFtpPortCommand(sptr, dlen, pip, link, maxpacketsize))
ParseFtpEprtCommand(sptr, dlen, pip, link, maxpacketsize);
} else {
ParseFtp227Reply(sptr, dlen, pip, link, maxpacketsize);
/*
* Check that data length is not too long and previous message was
* properly terminated with CRLF.
*/
if (dlen <= MAX_MESSAGE_SIZE && GetLastLineCrlfTermed(link)) {
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;
}
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 */
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 */
SetLastLineCrlfTermed(link,
(sptr[tlen-2] == '\r') && (sptr[tlen-1] == '\n'));
@ -110,186 +137,177 @@ int maxpacketsize /* The maximum size this packet can grow to (including header
}
static int
ParseFtpPortCommand(
char *sptr,
int dlen,
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) */)
ParseFtpPortCommand(char *sptr, int dlen)
{
struct in_addr true_addr;
u_short true_port;
char ch;
int i, state;
u_long a1, a2, a3, a4;
u_short p1, p2;
u_int32_t addr;
u_short port;
u_int8_t octet;
/* Return if data length is too long or too short */
if (dlen<10 || dlen>80)
/* Format: "PORT A,D,D,R,PO,RT". */
/* Return if data length is too short. */
if (dlen < 18)
return 0;
a1=0; a2=0; a3=0; a4=0; p1=0; p2=0;
state=-4;
for (i=0; i<dlen; i++)
{
addr = port = octet = 0;
state = -4;
for (i = 0; i < dlen; i++) {
ch = sptr[i];
switch (state)
{
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 (isdigit(ch)) {a1=ch-'0'; state++;} break;
case 1 :
if (isdigit(ch)) a1=10*a1+ch-'0'; else state++; break;
case 2 :
if (isdigit(ch)) {a2=ch-'0'; state++;} break;
case 3 :
if (isdigit(ch)) a2=10*a2+ch-'0'; else state++; break;
case 4 :
if (isdigit(ch)) {a3=ch-'0'; state++;} break;
case 5 :
if (isdigit(ch)) a3=10*a3+ch-'0'; else state++; break;
case 6 :
if (isdigit(ch)) {a4=ch-'0'; state++;} break;
case 7 :
if (isdigit(ch)) a4=10*a4+ch-'0'; else state++; break;
case 8 :
if (isdigit(ch)) {p1=ch-'0'; state++;} break;
case 9 :
if (isdigit(ch)) p1=10*p1+ch-'0'; else state++; break;
case 10:
if (isdigit(ch)) {p2=ch-'0'; state++;} break;
case 11:
if (isdigit(ch)) p2=10*p2+ch-'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 == 11 && GetLastLineCrlfTermed(link))
{
true_port = htons((p1<<8) + p2);
true_addr.s_addr = htonl((a1<<24) + (a2<<16) +(a3<<8) + a4);
if ((pip->ip_src.s_addr == true_addr.s_addr) &&
((p1<<8) >= IPPORT_RESERVED))
NewFtpPortCommand(pip, link, true_addr, true_port, maxpacketsize, 0);
if (state == 13) {
true_addr.s_addr = htonl(addr);
true_port = port;
return 1;
}
else
} else
return 0;
}
static void
ParseFtpEprtCommand(
char *sptr,
int dlen,
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) */)
static int
ParseFtpEprtCommand(char *sptr, int dlen)
{
struct in_addr true_addr;
u_short true_port;
char ch, delim;
int i, state;
u_long a1, a2, a3, a4;
u_short pt;
u_int32_t addr;
u_short port;
u_int8_t octet;
/* Return if data length is too long or too short */
if (dlen<10 || dlen>80)
return;
/* Format: "EPRT |1|A.D.D.R|PORT|". */
a1=0; a2=0; a3=0; a4=0; pt=0;
delim='|'; /* XXX gcc -Wuninitialized */
state=-4;
for (i=0; i<dlen; i++)
{
/* 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; break;
case -3: if (ch == 'P') state++; else return; break;
case -2: if (ch == 'R') state++; else return; break;
case -1: if (ch == 'T') state++; else return; break;
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; break;
case 2 :
if (ch==delim) state++; else return; break;
case 3 :
if (isdigit(ch)) {a1=ch-'0'; state++;} else return; break;
case 4 :
if (isdigit(ch)) a1=10*a1+ch-'0';
else if (ch=='.') state++;
else return;
case 0:
if (!isspace(ch)) {
delim = ch;
state++;
}
break;
case 5 :
if (isdigit(ch)) {a2=ch-'0'; state++;} else return; break;
case 6 :
if (isdigit(ch)) a2=10*a2+ch-'0';
else if (ch=='.') state++;
else return;
case 1:
if (ch == '1') /* IPv4 address */
state++;
else
return 0;
break;
case 7:
if (isdigit(ch)) {a3=ch-'0'; state++;} else return; break;
case 8 :
if (isdigit(ch)) a3=10*a3+ch-'0';
else if (ch=='.') state++;
else return;
case 2:
if (ch == delim)
state++;
else
return 0;
break;
case 9 :
if (isdigit(ch)) {a4=ch-'0'; state++;} else return; break;
case 10:
if (isdigit(ch)) a4=10*a4+ch-'0';
else if (ch==delim) state++;
else return;
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)) {pt=ch-'0'; state++;} else return; break;
if (isdigit(ch)) {
port = ch - '0';
state++;
} else
return 0;
break;
case 12:
if (isdigit(ch)) pt=10*pt+ch-'0';
else if (ch==delim) state++;
else return;
if (isdigit(ch))
port = 10 * port + ch - '0';
else if (ch == delim)
state++;
else
return 0;
break;
}
}
if (state == 13 && GetLastLineCrlfTermed(link))
{
true_port = htons(pt);
true_addr.s_addr = htonl((a1<<24) + (a2<<16) +(a3<<8) + a4);
if ((pip->ip_src.s_addr == true_addr.s_addr) &&
(pt >= IPPORT_RESERVED))
NewFtpPortCommand(pip, link, true_addr, true_port, maxpacketsize, 1);
}
if (state == 13) {
true_addr.s_addr = htonl(addr);
true_port = port;
return 1;
} else
return 0;
}
static int
ParseFtp227Reply(char *sptr,
int dlen,
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) */
ParseFtp227Reply(char *sptr, int dlen)
{
struct in_addr true_addr;
u_short true_port;
char ch;
int i, state;
u_long a1, a2, a3, a4;
u_short p1, p2;
u_int32_t addr;
u_short port;
u_int8_t octet;
/* Format: "227 Entering Passive Mode (A,D,D,R,PO,RT)" */
/* Return if wrong size, in case more packet types added later */
if (dlen<MIN_227_REPLY || dlen>MAX_227_REPLY)
return 0;
/* Return if data length is too short. */
if (dlen < 17)
return 0;
a1=0; a2=0; a3=0; a4=0; p1=0; p2=0;
state=-3;
for (i=0; i<dlen; i++)
{
addr = port = octet = 0;
state = -3;
for (i = 0; i < dlen; i++) {
ch = sptr[i];
switch (state)
{
@ -297,59 +315,135 @@ ParseFtp227Reply(char *sptr,
case -2: if (ch == '2') state++; else return 0; break;
case -1: if (ch == '7') state++; else return 0; break;
case 0 :
if (isdigit(ch)) {a1=ch-'0'; state++;} break;
case 1 :
if (isdigit(ch)) a1=10*a1+ch-'0'; else state++; break;
case 2 :
if (isdigit(ch)) {a2=ch-'0'; state++;} break;
case 3 :
if (isdigit(ch)) a2=10*a2+ch-'0'; else state++; break;
case 4 :
if (isdigit(ch)) {a3=ch-'0'; state++;} break;
case 5 :
if (isdigit(ch)) a3=10*a3+ch-'0'; else state++; break;
case 6 :
if (isdigit(ch)) {a4=ch-'0'; state++;} break;
case 7 :
if (isdigit(ch)) a4=10*a4+ch-'0'; else state++; break;
case 8 :
if (isdigit(ch)) {p1=ch-'0'; state++;} break;
case 9 :
if (isdigit(ch)) p1=10*p1+ch-'0'; else state++; break;
case 10:
if (isdigit(ch)) {p2=ch-'0'; state++;} break;
case 11:
if (isdigit(ch)) p2=10*p2+ch-'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 == 11 && GetLastLineCrlfTermed(link))
{
true_port = htons((p1<<8) + p2);
true_addr.s_addr = htonl((a1<<24) + (a2<<16) +(a3<<8) + a4);
if ((pip->ip_src.s_addr == true_addr.s_addr) &&
((p1<<8) >= IPPORT_RESERVED))
NewFtp227Reply(pip, link, true_addr, true_port, maxpacketsize);
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;
}
}
else
if (state == 7) {
true_port = port;
return 1;
} else
return 0;
}
static void
NewFtpPortCommand(struct ip *pip,
struct alias_link *link,
struct in_addr true_addr,
u_short true_port,
int maxpacketsize,
int is_eprt)
{
NewFtpMessage(struct ip *pip,
struct alias_link *link,
int maxpacketsize,
int ftp_message_type)
{
struct alias_link *ftp_link;
/* Establish link to address and port found in PORT command */
/* Security checks. */
if (ftp_message_type != FTP_229_REPLY &&
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),
true_port, 0, IPPROTO_TCP);
htons(true_port), 0, IPPROTO_TCP);
if (ftp_link != NULL)
{
@ -357,8 +451,11 @@ NewFtpPortCommand(struct ip *pip,
struct tcphdr *tc;
#ifndef NO_FW_PUNCH
/* Punch hole in firewall */
PunchFWHole(ftp_link);
if (ftp_message_type == FTP_PORT_COMMAND ||
ftp_message_type == FTP_EPRT_COMMAND) {
/* Punch hole in firewall */
PunchFWHole(ftp_link);
}
#endif
/* Calculate data length of TCP packet */
@ -367,15 +464,15 @@ NewFtpPortCommand(struct ip *pip,
tlen = ntohs(pip->ip_len);
dlen = tlen - hlen;
/* Create new PORT command */
/* Create new FTP message. */
{
char stemp[80];
char stemp[MAX_MESSAGE_SIZE + 1];
char *sptr;
u_short alias_port;
u_char *ptr;
int a1, a2, a3, a4, p1, p2;
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;
@ -383,24 +480,41 @@ NewFtpPortCommand(struct ip *pip,
alias_port = GetAliasPort(ftp_link);
if (is_eprt) {
/* Generate EPRT command string */
sprintf(stemp, "EPRT |1|%d.%d.%d.%d|%d|\r\n",
a1,a2,a3,a4,ntohs(alias_port));
} else {
/* Decompose alias port into pair format */
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;
/* Generate PORT command string */
sprintf(stemp, "PORT %d,%d,%d,%d,%d,%d\r\n",
a1,a2,a3,a4,p1,p2);
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 into IP packet */
/* Copy modified buffer into IP packet. */
sptr = (char *) pip; sptr += hlen;
strncpy(sptr, stemp, maxpacketsize-hlen);
}
@ -434,96 +548,7 @@ NewFtpPortCommand(struct ip *pip,
{
#ifdef DEBUG
fprintf(stderr,
"PacketAlias/HandleFtpOut, PORT: Cannot allocate FTP data port\n");
#endif
}
}
static void
NewFtp227Reply(struct ip *pip,
struct alias_link *link,
struct in_addr true_addr,
u_short true_port,
int maxpacketsize)
{
struct alias_link *ftp_link;
/* Establish link to address and port found in 227 reply */
ftp_link = FindUdpTcpOut(true_addr, GetDestAddress(link),
true_port, 0, IPPROTO_TCP);
if (ftp_link != NULL)
{
int slen, hlen, tlen, dlen;
struct tcphdr *tc;
/* 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 227 reply */
{
char stemp[MAX_227_REPLY+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;
/* Decompose alias port into pair format */
alias_port = GetAliasPort(ftp_link);
ptr = (char *) &alias_port;
p1 = *ptr++; p2=*ptr;
/* Generate command string */
sprintf(stemp, "227 Entering Passive Mode (%d,%d,%d,%d,%d,%d)\r\n",
a1,a2,a3,a4,p1,p2);
/* 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, 227: Cannot allocate FTP data port\n");
"PacketAlias/HandleFtpOut: Cannot allocate FTP data port\n");
#endif
}
}