1 /* Alias_irc.c intercepts packages contain IRC CTCP commands, and
2 changes DCC commands to export a port on the aliasing host instead
5 For this routine to work, the DCC command must fit entirely into a
6 single TCP packet. This will usually happen, but is not
9 The interception is likely to change the length of the packet.
10 The handling of this is copied more-or-less verbatim from
13 This software is placed into the public domain with no restrictions
16 Initial version: Eivind Eklund <perhaps@yes.no> (ee) 97-01-29
18 Version 2.1: May, 1997 (cjm)
19 Very minor changes to conform with
20 local/global/function naming conventions
21 withing the packet alising module.
30 #include <sys/types.h>
31 #include <netinet/in_systm.h>
32 #include <netinet/in.h>
33 #include <netinet/ip.h>
34 #include <netinet/tcp.h>
37 #include "alias_local.h"
44 AliasHandleIrcOut(struct ip *pip, /* IP packet to examine */
45 struct alias_link *link, /* Which link are we on? */
46 int maxsize /* Maximum size of IP packet including headers */
50 struct in_addr true_addr;
54 int i; /* Iterator through the source */
56 /* Calculate data length of TCP packet */
57 tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2));
58 hlen = (pip->ip_hl + tc->th_off) << 2;
59 tlen = ntohs(pip->ip_len);
62 /* Return if data length is too short - assume an entire PRIVMSG in each packet. */
63 if (dlen<sizeof(":A!a@n.n PRIVMSG A :aDCC 1 1a")-1)
66 /* Place string pointer at beginning of data */
69 maxsize -= hlen; /* We're interested in maximum size of data, not packet */
71 /* Search for a CTCP command [Note 1] */
72 for( i=0; i<dlen; i++ ) {
76 return; /* No CTCP commands in */
77 /* Handle CTCP commands - the buffer may have to be copied */
80 char newpacket[65536]; /* Estimate of maximum packet size :) */
81 int copyat = i; /* Same */
82 int iCopy = 0; /* How much data have we written to copy-back string? */
83 unsigned long org_addr; /* Original IP address */
84 unsigned short org_port; /* Original source port address */
86 if( i >= dlen || iCopy >= sizeof(newpacket) )
88 newpacket[iCopy++] = sptr[i++]; /* Copy the CTCP start character */
90 if( i+4 >= dlen ) /* Too short for DCC */
92 if( sptr[i+0] != 'D' )
94 if( sptr[i+1] != 'C' )
96 if( sptr[i+2] != 'C' )
98 if( sptr[i+3] != ' ' )
100 /* We have a DCC command - handle it! */
101 i+= 4; /* Skip "DCC " */
102 if( iCopy+4 > sizeof(newpacket) )
104 newpacket[iCopy++] = 'D';
105 newpacket[iCopy++] = 'C';
106 newpacket[iCopy++] = 'C';
107 newpacket[iCopy++] = ' ';
109 DBprintf(("Found DCC\n"));
110 /* Skip any extra spaces (should not occur according to
111 protocol, but DCC breaks CTCP protocol anyway */
112 while(sptr[i] == ' ') {
114 DBprintf(("DCC packet terminated in just spaces\n"));
119 DBprintf(("Transferring command...\n"));
120 while(sptr[i] != ' ') {
121 newpacket[iCopy++] = sptr[i];
122 if( ++i >= dlen || iCopy >= sizeof(newpacket) ) {
123 DBprintf(("DCC packet terminated during command\n"));
127 /* Copy _one_ space */
128 if( i+1 < dlen && iCopy < sizeof(newpacket) )
129 newpacket[iCopy++] = sptr[i++];
131 DBprintf(("Done command - removing spaces\n"));
132 /* Skip any extra spaces (should not occur according to
133 protocol, but DCC breaks CTCP protocol anyway */
134 while(sptr[i] == ' ') {
136 DBprintf(("DCC packet terminated in just spaces (post-command)\n"));
141 DBprintf(("Transferring filename...\n"));
142 while(sptr[i] != ' ') {
143 newpacket[iCopy++] = sptr[i];
144 if( ++i >= dlen || iCopy >= sizeof(newpacket) ) {
145 DBprintf(("DCC packet terminated during filename\n"));
149 /* Copy _one_ space */
150 if( i+1 < dlen && iCopy < sizeof(newpacket) )
151 newpacket[iCopy++] = sptr[i++];
153 DBprintf(("Done filename - removing spaces\n"));
154 /* Skip any extra spaces (should not occur according to
155 protocol, but DCC breaks CTCP protocol anyway */
156 while(sptr[i] == ' ') {
158 DBprintf(("DCC packet terminated in just spaces (post-filename)\n"));
163 DBprintf(("Fetching IP address\n"));
164 /* Fetch IP address */
166 while(i<dlen && isdigit(sptr[i])) {
167 if( org_addr > ULONG_MAX/10UL ) { /* Terminate on overflow */
168 DBprintf(("DCC Address overflow (org_addr == 0x%08lx, next char %c\n", org_addr, sptr[i]));
172 org_addr += sptr[i++]-'0';
174 DBprintf(("Skipping space\n"));
175 if( i+1 >= dlen || sptr[i] != ' ' ) {
176 DBprintf(("Overflow (%d >= %d) or bad character (%02x) terminating IP address\n", i+1, dlen, sptr[i]));
179 /* Skip any extra spaces (should not occur according to
180 protocol, but DCC breaks CTCP protocol anyway, so we might
181 as well play it safe */
182 while(sptr[i] == ' ') {
184 DBprintf(("Packet failure - space overflow.\n"));
188 DBprintf(("Fetching port number\n"));
189 /* Fetch source port */
191 while(i<dlen && isdigit(sptr[i])) {
192 if( org_port > 6554 ) { /* Terminate on overflow (65536/10 rounded up*/
193 DBprintf(("DCC: port number overflow\n"));
197 org_port += sptr[i++]-'0';
199 /* Skip illegal addresses (or early termination) */
200 if( i >= dlen || (sptr[i] != '\001' && sptr[i] != ' ') ) {
201 DBprintf(("Bad port termination\n"));
204 DBprintf(("Got IP %lu and port %u\n", org_addr, (unsigned)org_port));
206 /* We've got the address and port - now alias it */
208 struct alias_link *dcc_link;
209 struct in_addr destaddr;
212 true_port = htons(org_port);
213 true_addr.s_addr = htonl(org_addr);
216 /* Steal the FTP_DATA_PORT - it doesn't really matter, and this
217 would probably allow it through at least _some_
219 dcc_link = FindUdpTcpOut (true_addr,
223 DBprintf(("Got a DCC link\n"));
225 struct in_addr alias_address; /* Address from aliasing */
226 u_short alias_port; /* Port given by aliasing */
229 /* Generate firewall hole as appropriate */
230 PunchFWHole(dcc_link);
233 alias_address = GetAliasAddress(link);
234 iCopy += snprintf(&newpacket[iCopy],
235 sizeof(newpacket)-iCopy,
236 "%lu ", (u_long)htonl(alias_address.s_addr));
237 if( iCopy >= sizeof(newpacket) ) { /* Truncated/fit exactly - bad news */
238 DBprintf(("DCC constructed packet overflow.\n"));
241 alias_port = GetAliasPort(dcc_link);
242 iCopy += snprintf(&newpacket[iCopy],
243 sizeof(newpacket)-iCopy,
244 "%u", htons(alias_port) );
245 /* Done - truncated cases will be taken care of by lBAD_CTCP */
246 DBprintf(("Aliased IP %lu and port %u\n", alias_address.s_addr, (unsigned)alias_port));
249 /* An uninteresting CTCP - state entered right after '\001' has
250 been pushed. Also used to copy the rest of a DCC, after IP
251 address and port has been handled */
253 for(; i<dlen && iCopy<sizeof(newpacket); i++,iCopy++) {
254 newpacket[iCopy] = sptr[i]; /* Copy CTCP unchanged */
255 if(sptr[i] == '\001') {
262 for(; i<dlen && iCopy<sizeof(newpacket); i++,iCopy++) {
263 newpacket[iCopy] = sptr[i]; /* Copy CTCP unchanged */
264 if(sptr[i] == '\001') {
268 /* Handle the end of a packet */
270 iCopy = iCopy > maxsize-copyat ? maxsize-copyat : iCopy;
271 memcpy(sptr+copyat, newpacket, iCopy);
273 /* Save information regarding modified seq and ack numbers */
277 SetAckModified(link);
278 delta = GetDeltaSeqOut(pip, link);
279 AddSeq(pip, link, delta+copyat+iCopy-dlen);
282 /* Revise IP header */
286 new_len = htons(hlen + iCopy + copyat);
287 DifferentialChecksum(&pip->ip_sum,
291 pip->ip_len = new_len;
294 /* Compute TCP checksum for revised packet */
296 tc->th_sum = TcpChecksum(pip);
303 The initial search will most often fail; it could be replaced with a 32-bit specific search.
304 Such a search would be done for 32-bit unsigned value V:
305 V ^= 0x01010101; (Search is for null bytes)
306 if( ((V-0x01010101)^V) & 0x80808080 ) {
307 (found a null bytes which was a 01 byte)
309 To assert that the processor is 32-bits, do
310 extern int ircdccar[32]; (32 bits)
311 extern int ircdccar[CHAR_BIT*sizeof(unsigned int)];
312 which will generate a type-error on all but 32-bit machines.
314 [Note 2] This routine really ought to be replaced with one that
315 creates a transparent proxy on the aliasing host, to allow arbitary
316 changes in the TCP stream. This should not be too difficult given
317 this base; I (ee) will try to do this some time later.