1 /* Alias_irc.c intercepts packages contain IRC CTCP commands, and 2 changes DCC commands to export a port on the aliasing host instead 3 of an aliased host. 4 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 7 guaranteed. 8 9 The interception is likely to change the length of the packet. 10 The handling of this is copied more-or-less verbatim from 11 ftp_alias.c 12 13 This software is placed into the public domain with no restrictions 14 on its distribution. 15 16 Initial version: Eivind Eklund <perhaps@yes.no> (ee) 97-01-29 17 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. 22 */ 23 24 /* Includes */ 25 #include <ctype.h> 26 #include <stdio.h> 27 #include <string.h> 28 #include <sys/types.h> 29 #include <netinet/in_systm.h> 30 #include <netinet/in.h> 31 #include <netinet/ip.h> 32 #include <netinet/tcp.h> 33 #include <limits.h> 34 35 #include "alias_local.h" 36 37 /* Local defines */ 38 #define DBprintf(a) 39 40 41 void 42 AliasHandleIrcOut(struct ip *pip, /* IP packet to examine */ 43 struct alias_link *link, /* Which link are we on? */ 44 int maxsize /* Maximum size of IP packet including headers */ 45 ) 46 { 47 int hlen, tlen, dlen; 48 struct in_addr true_addr; 49 u_short true_port; 50 char *sptr; 51 struct tcphdr *tc; 52 int i; /* Iterator through the source */ 53 54 /* Calculate data length of TCP packet */ 55 tc = (struct tcphdr *) ((char *) pip + (pip->ip_hl << 2)); 56 hlen = (pip->ip_hl + tc->th_off) << 2; 57 tlen = ntohs(pip->ip_len); 58 dlen = tlen - hlen; 59 60 /* Return if data length is too short - assume an entire PRIVMSG in each packet. */ 61 if (dlen<sizeof(":A!a@n.n PRIVMSG A :aDCC 1 1a")-1) 62 return; 63 64 /* Place string pointer at beginning of data */ 65 sptr = (char *) pip; 66 sptr += hlen; 67 maxsize -= hlen; /* We're interested in maximum size of data, not packet */ 68 69 /* Search for a CTCP command [Note 1] */ 70 for( i=0; i<dlen; i++ ) { 71 if(sptr[i]=='\001') 72 goto lFOUND_CTCP; 73 } 74 return; /* No CTCP commands in */ 75 /* Handle CTCP commands - the buffer may have to be copied */ 76 lFOUND_CTCP: 77 { 78 char newpacket[65536]; /* Estimate of maximum packet size :) */ 79 int copyat = i; /* Same */ 80 int iCopy = 0; /* How much data have we written to copy-back string? */ 81 unsigned long org_addr; /* Original IP address */ 82 unsigned short org_port; /* Original source port address */ 83 lCTCP_START: 84 if( i >= dlen || iCopy >= sizeof(newpacket) ) 85 goto lPACKET_DONE; 86 newpacket[iCopy++] = sptr[i++]; /* Copy the CTCP start character */ 87 /* Start of a CTCP */ 88 if( i+4 >= dlen ) /* Too short for DCC */ 89 goto lBAD_CTCP; 90 if( sptr[i+0] != 'D' ) 91 goto lBAD_CTCP; 92 if( sptr[i+1] != 'C' ) 93 goto lBAD_CTCP; 94 if( sptr[i+2] != 'C' ) 95 goto lBAD_CTCP; 96 if( sptr[i+3] != ' ' ) 97 goto lBAD_CTCP; 98 /* We have a DCC command - handle it! */ 99 i+= 4; /* Skip "DCC " */ 100 if( iCopy+4 > sizeof(newpacket) ) 101 goto lPACKET_DONE; 102 newpacket[iCopy++] = 'D'; 103 newpacket[iCopy++] = 'C'; 104 newpacket[iCopy++] = 'C'; 105 newpacket[iCopy++] = ' '; 106 107 DBprintf(("Found DCC\n")); 108 /* Skip any extra spaces (should not occur according to 109 protocol, but DCC breaks CTCP protocol anyway */ 110 while(sptr[i] == ' ') { 111 if( ++i >= dlen) { 112 DBprintf(("DCC packet terminated in just spaces\n")); 113 goto lPACKET_DONE; 114 } 115 } 116 117 DBprintf(("Transferring command...\n")); 118 while(sptr[i] != ' ') { 119 newpacket[iCopy++] = sptr[i]; 120 if( ++i >= dlen || iCopy >= sizeof(newpacket) ) { 121 DBprintf(("DCC packet terminated during command\n")); 122 goto lPACKET_DONE; 123 } 124 } 125 /* Copy _one_ space */ 126 if( i+1 < dlen && iCopy < sizeof(newpacket) ) 127 newpacket[iCopy++] = sptr[i++]; 128 129 DBprintf(("Done command - removing spaces\n")); 130 /* Skip any extra spaces (should not occur according to 131 protocol, but DCC breaks CTCP protocol anyway */ 132 while(sptr[i] == ' ') { 133 if( ++i >= dlen ) { 134 DBprintf(("DCC packet terminated in just spaces (post-command)\n")); 135 goto lPACKET_DONE; 136 } 137 } 138 139 DBprintf(("Transferring filename...\n")); 140 while(sptr[i] != ' ') { 141 newpacket[iCopy++] = sptr[i]; 142 if( ++i >= dlen || iCopy >= sizeof(newpacket) ) { 143 DBprintf(("DCC packet terminated during filename\n")); 144 goto lPACKET_DONE; 145 } 146 } 147 /* Copy _one_ space */ 148 if( i+1 < dlen && iCopy < sizeof(newpacket) ) 149 newpacket[iCopy++] = sptr[i++]; 150 151 DBprintf(("Done filename - removing spaces\n")); 152 /* Skip any extra spaces (should not occur according to 153 protocol, but DCC breaks CTCP protocol anyway */ 154 while(sptr[i] == ' ') { 155 if( ++i >= dlen ) { 156 DBprintf(("DCC packet terminated in just spaces (post-filename)\n")); 157 goto lPACKET_DONE; 158 } 159 } 160 161 DBprintf(("Fetching IP address\n")); 162 /* Fetch IP address */ 163 org_addr = 0; 164 while(i<dlen && isdigit(sptr[i])) { 165 if( org_addr > ULONG_MAX/10UL ) { /* Terminate on overflow */ 166 DBprintf(("DCC Address overflow (org_addr == 0x%08lx, next char %c\n", org_addr, sptr[i])); 167 goto lBAD_CTCP; 168 } 169 org_addr *= 10; 170 org_addr += sptr[i++]-'0'; 171 } 172 DBprintf(("Skipping space\n")); 173 if( i+1 >= dlen || sptr[i] != ' ' ) { 174 DBprintf(("Overflow (%d >= %d) or bad character (%02x) terminating IP address\n", i+1, dlen, sptr[i])); 175 goto lBAD_CTCP; 176 } 177 /* Skip any extra spaces (should not occur according to 178 protocol, but DCC breaks CTCP protocol anyway, so we might 179 as well play it safe */ 180 while(sptr[i] == ' ') { 181 if( ++i >= dlen ) { 182 DBprintf(("Packet failure - space overflow.\n")); 183 goto lPACKET_DONE; 184 } 185 } 186 DBprintf(("Fetching port number\n")); 187 /* Fetch source port */ 188 org_port = 0; 189 while(i<dlen && isdigit(sptr[i])) { 190 if( org_port > 6554 ) { /* Terminate on overflow (65536/10 rounded up*/ 191 DBprintf(("DCC: port number overflow\n")); 192 goto lBAD_CTCP; 193 } 194 org_port *= 10; 195 org_port += sptr[i++]-'0'; 196 } 197 /* Skip illegal addresses (or early termination) */ 198 if( i >= dlen || (sptr[i] != '\001' && sptr[i] != ' ') ) { 199 DBprintf(("Bad port termination\n")); 200 goto lBAD_CTCP; 201 } 202 DBprintf(("Got IP %lu and port %u\n", org_addr, (unsigned)org_port)); 203 204 /* We've got the address and port - now alias it */ 205 { 206 struct alias_link *dcc_link; 207 struct in_addr destaddr; 208 209 210 true_port = htons(org_port); 211 true_addr.s_addr = htonl(org_addr); 212 destaddr.s_addr = 0; 213 214 /* Steal the FTP_DATA_PORT - it doesn't really matter, and this 215 would probably allow it through at least _some_ 216 firewalls. */ 217 dcc_link = FindUdpTcpOut (true_addr, 218 destaddr, 219 true_port, 220 0, IPPROTO_TCP); 221 DBprintf(("Got a DCC link\n")); 222 if ( dcc_link ) { 223 struct in_addr alias_address; /* Address from aliasing */ 224 u_short alias_port; /* Port given by aliasing */ 225 226 #ifndef NO_FW_PUNCH 227 /* Generate firewall hole as appropriate */ 228 PunchFWHole(dcc_link); 229 #endif 230 231 alias_address = GetAliasAddress(link); 232 iCopy += snprintf(&newpacket[iCopy], 233 sizeof(newpacket)-iCopy, 234 "%lu ", (u_long)htonl(alias_address.s_addr)); 235 if( iCopy >= sizeof(newpacket) ) { /* Truncated/fit exactly - bad news */ 236 DBprintf(("DCC constructed packet overflow.\n")); 237 goto lBAD_CTCP; 238 } 239 alias_port = GetAliasPort(dcc_link); 240 iCopy += snprintf(&newpacket[iCopy], 241 sizeof(newpacket)-iCopy, 242 "%u", htons(alias_port) ); 243 /* Done - truncated cases will be taken care of by lBAD_CTCP */ 244 DBprintf(("Aliased IP %lu and port %u\n", alias_address.s_addr, (unsigned)alias_port)); 245 } 246 } 247 /* An uninteresting CTCP - state entered right after '\001' has 248 been pushed. Also used to copy the rest of a DCC, after IP 249 address and port has been handled */ 250 lBAD_CTCP: 251 for(; i<dlen && iCopy<sizeof(newpacket); i++,iCopy++) { 252 newpacket[iCopy] = sptr[i]; /* Copy CTCP unchanged */ 253 if(sptr[i] == '\001') { 254 goto lNORMAL_TEXT; 255 } 256 } 257 goto lPACKET_DONE; 258 /* Normal text */ 259 lNORMAL_TEXT: 260 for(; i<dlen && iCopy<sizeof(newpacket); i++,iCopy++) { 261 newpacket[iCopy] = sptr[i]; /* Copy CTCP unchanged */ 262 if(sptr[i] == '\001') { 263 goto lCTCP_START; 264 } 265 } 266 /* Handle the end of a packet */ 267 lPACKET_DONE: 268 iCopy = iCopy > maxsize-copyat ? maxsize-copyat : iCopy; 269 memcpy(sptr+copyat, newpacket, iCopy); 270 271 /* Save information regarding modified seq and ack numbers */ 272 { 273 int delta; 274 275 SetAckModified(link); 276 delta = GetDeltaSeqOut(pip, link); 277 AddSeq(pip, link, delta+copyat+iCopy-dlen); 278 } 279 280 /* Revise IP header */ 281 { 282 u_short new_len; 283 284 new_len = htons(hlen + iCopy + copyat); 285 DifferentialChecksum(&pip->ip_sum, 286 &new_len, 287 &pip->ip_len, 288 1); 289 pip->ip_len = new_len; 290 } 291 292 /* Compute TCP checksum for revised packet */ 293 tc->th_sum = 0; 294 tc->th_sum = TcpChecksum(pip); 295 return; 296 } 297 } 298 299 /* Notes: 300 [Note 1] 301 The initial search will most often fail; it could be replaced with a 32-bit specific search. 302 Such a search would be done for 32-bit unsigned value V: 303 V ^= 0x01010101; (Search is for null bytes) 304 if( ((V-0x01010101)^V) & 0x80808080 ) { 305 (found a null bytes which was a 01 byte) 306 } 307 To assert that the processor is 32-bits, do 308 extern int ircdccar[32]; (32 bits) 309 extern int ircdccar[CHAR_BIT*sizeof(unsigned int)]; 310 which will generate a type-error on all but 32-bit machines. 311 312 [Note 2] This routine really ought to be replaced with one that 313 creates a transparent proxy on the aliasing host, to allow arbitary 314 changes in the TCP stream. This should not be too difficult given 315 this base; I (ee) will try to do this some time later. 316 */ 317