1/*
2 Alias_ftp.c performs special processing for FTP sessions under
3 TCP. Specifically, when a PORT command from the client side
4 is sent, it is intercepted and modified. The address is changed
5 to the gateway machine and an aliasing port is used.
6
7 For this routine to work, the PORT command must fit entirely
8 into a single TCP packet. This is typically the case, but exceptions
9 can easily be envisioned under the actual specifications.
10
11 Probably the most troubling aspect of the approach taken here is
12 that the new PORT command will typically be a different length, and
13 this causes a certain amount of bookkeeping to keep track of the
14 changes of sequence and acknowledgment numbers, since the client
15 machine is totally unaware of the modification to the TCP stream.
16
17
18 This software is placed into the public domain with no restrictions
19 on its distribution.
20
21 Initial version: August, 1996 (cjm)
22
23 Version 1.6
24 Brian Somers and Martin Renters identified an IP checksum
25 error for modified IP packets.
26
27 Version 1.7: January 9, 1996 (cjm)
28 Differental checksum computation for change
29 in IP packet length.
30
31 Version 2.1: May, 1997 (cjm)
32 Very minor changes to conform with
33 local/global/function naming conventions
34 withing the packet alising module.
35
36 See HISTORY file for record of revisions.
37
38 $FreeBSD: head/sys/netinet/libalias/alias_ftp.c 50597 1999-08-29 23:17:04Z billf $
39*/
40
41/* Includes */
42#include <ctype.h>
43#include <stdio.h>
44#include <string.h>
45#include <sys/types.h>
46#include <netinet/in_systm.h>
47#include <netinet/in.h>
48#include <netinet/ip.h>
49#include <netinet/tcp.h>
50
51#include "alias_local.h"
52
53static void NewFtpPortCommand(struct ip *, struct alias_link *, struct in_addr, u_short, int);
54
55
56
57void
58AliasHandleFtpOut(
59struct ip *pip, /* IP packet to examine/patch */
60struct alias_link *link, /* The link to go through (aliased port) */
61int maxpacketsize /* The maximum size this packet can grow to (including headers) */)
62{
63 int hlen, tlen, dlen;
64 struct in_addr true_addr;
65 u_short true_port;
66 char *sptr;
67 struct tcphdr *tc;
68
69/* Calculate data length of TCP packet */
70 tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
71 hlen = (pip->ip_hl + tc->th_off) << 2;
72 tlen = ntohs(pip->ip_len);
73 dlen = tlen - hlen;
74
75/* Return is data length is too long or too short */
76 if (dlen<10 || dlen>80)
77 return;
78
79/* Place string pointer and beginning of data */
80 sptr = (char *) pip;
81 sptr += hlen;
82
83/* Parse through string using state diagram method */
84 {
85 char ch, zero;
86 int i, state;
87 u_long a1, a2, a3, a4;
88 u_short p1, p2;
89
90 a1=0; a2=0; a3=0; a4=0; p1=0; p2=0;
91 zero = '0';
92 state=-4;
93 for (i=0; i<dlen; i++)
94 {
95 ch = sptr[i];
96 switch (state)
97 {
98 case -4: if (ch == 'P') state=-3; else return; break;
99 case -3: if (ch == 'O') state=-2; else return; break;
100 case -2: if (ch == 'R') state=-1; else return; break;
101 case -1: if (ch == 'T') state= 0; else return; break;
102
103 case 0 :
104 if (isdigit(ch)) {a1=ch-zero; state=1 ;} break;
105 case 1 :
106 if (isdigit(ch)) a1=10*a1+ch-zero; else state=2 ; break;
107 case 2 :
108 if (isdigit(ch)) {a2=ch-zero; state=3 ;} break;
109 case 3 :
110 if (isdigit(ch)) a2=10*a2+ch-zero; else state=4 ; break;
111 case 4 :
112 if (isdigit(ch)) {a3=ch-zero; state=5 ;} break;
113 case 5 :
114 if (isdigit(ch)) a3=10*a3+ch-zero; else state=6 ; break;
115 case 6 :
116 if (isdigit(ch)) {a4=ch-zero; state=7 ;} break;
117 case 7 :
118 if (isdigit(ch)) a4=10*a4+ch-zero; else state=8 ; break;
119 case 8 :
120 if (isdigit(ch)) {p1=ch-zero; state=9 ;} break;
121 case 9 :
122 if (isdigit(ch)) p1=10*p1+ch-zero; else state=10; break;
123 case 10:
124 if (isdigit(ch)) {p2=ch-zero; state=11;} break;
125 case 11:
126 if (isdigit(ch)) p2=10*p2+ch-zero; break;
127 }
128 }
129
130 if (state == 11)
131 {
132 true_port = htons((p1<<8) + p2);
133 true_addr.s_addr = htonl((a1<<24) + (a2<<16) +(a3<<8) + a4);
134 NewFtpPortCommand(pip, link, true_addr, true_port, maxpacketsize);
135 }
136 }
137}
138
139static void
140NewFtpPortCommand(struct ip *pip,
141 struct alias_link *link,
142 struct in_addr true_addr,
143 u_short true_port,
144 int maxpacketsize)
145{
146 struct alias_link *ftp_link;
147
148/* Establish link to address and port found in PORT command */
149 ftp_link = FindUdpTcpOut(true_addr, GetDestAddress(link),
150 true_port, 0, IPPROTO_TCP);
151
152 if (ftp_link != NULL)

--- 21 unchanged lines hidden (view full) ---

174 int a1, a2, a3, a4, p1, p2;
175 struct in_addr alias_address;
176
177/* Decompose alias address into quad format */
178 alias_address = GetAliasAddress(link);
179 ptr = (u_char *) &alias_address.s_addr;
180 a1 = *ptr++; a2=*ptr++; a3=*ptr++; a4=*ptr;
181
182/* Decompose alias port into pair format */
183 alias_port = GetAliasPort(ftp_link);
184 ptr = (char *) &alias_port;
185 p1 = *ptr++; p2=*ptr;
186
187/* Generate command string */
188 sprintf(stemp, "PORT %d,%d,%d,%d,%d,%d\r\n",
189 a1,a2,a3,a4,p1,p2);
190
191/* Save string length for IP header modification */
192 slen = strlen(stemp);
193
194/* Copy into IP packet */
195 sptr = (char *) pip; sptr += hlen;
196 strncpy(sptr, stemp, maxpacketsize-hlen);
197 }

--- 34 unchanged lines hidden ---