Create the alias library. This is currently only used by

ppp (or will be shortly).  Natd can now be updated to use
this library rather than carrying its own version of the code.

Submitted by:	Charles Mott <cmott@srv.net>

1 files changed, 311 insertions, 0 deletions

diff --git a/lib/libalias/alias_irc.c b/lib/libalias/alias_irc.c
new file mode 100644
index 0000000..3657368
--- /dev/null
+++ b/lib/libalias/alias_irc.c
@@ -0,0 +1,311 @@
+/* Alias_irc.c intercepts packages contain IRC CTCP commands, and
+	changes DCC commands to export a port on the aliasing host instead
+	of an aliased host.
+
+    For this routine to work, the DCC command must fit entirely into a
+    single TCP packet.  This will usually happen, but is not
+    guaranteed.
+
+	 The interception is likely to change the length of the packet.
+	 The handling of this is copied more-or-less verbatim from
+	 ftp_alias.c
+
+    This software is placed into the public domain with no restrictions
+    on its distribution.
+
+	 Initial version: Eivind Eklund <perhaps@yes.no> (ee) 97-01-29
+
+         Version 2.1:  May, 1997 (cjm)
+             Very minor changes to conform with
+             local/global/function naming conventions
+             withing the packet alising module.
+*/
+
+/* 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 <limits.h>
+
+#include "alias_local.h"
+
+/* Local defines */
+#define DBprintf(a)
+
+
+void
+AliasHandleIrcOut(struct ip *pip, /* IP packet to examine */
+				 struct alias_link *link,		  /* Which link are we on? */
+				 int maxsize		  /* Maximum size of IP packet including headers */
+				 )
+{       
+    int hlen, tlen, dlen;
+    struct in_addr true_addr;
+    u_short true_port;
+    char *sptr;
+    struct tcphdr *tc;
+	 int i;							  /* Iterator through the source */
+        
+/* 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;
+
+	 /* Return if data length is too short - assume an entire PRIVMSG in each packet. */
+    if (dlen<sizeof(":A!a@n.n PRIVMSG A :aDCC 1 1a")-1)
+        return;
+
+/* Place string pointer at beginning of data */
+    sptr = (char *) pip;  
+    sptr += hlen;
+	 maxsize -= hlen;				  /* We're interested in maximum size of data, not packet */
+
+	 /* Search for a CTCP command [Note 1] */
+	 for(	i=0; i<dlen; i++ ) {
+		 if(sptr[i]=='\001')
+			 goto lFOUND_CTCP;
+	 }
+	 return;					  /* No CTCP commands in  */
+	 /* Handle CTCP commands - the buffer may have to be copied */
+lFOUND_CTCP:
+	 {
+		 char newpacket[65536];	  /* Estimate of maximum packet size :) */
+		 int  copyat = i;			  /* Same */
+		 int  iCopy = 0;			  /* How much data have we written to copy-back string? */
+		 unsigned long org_addr;  /* Original IP address */
+		 unsigned short org_port; /* Original source port address */
+	 lCTCP_START:
+		 if( i >= dlen || iCopy >= sizeof(newpacket) )
+			 goto lPACKET_DONE;
+		 newpacket[iCopy++] = sptr[i++];	/* Copy the CTCP start character */
+		 /* Start of a CTCP */
+		 if( i+4 >= dlen )		  /* Too short for DCC */
+			 goto lBAD_CTCP;
+		 if( sptr[i+0] != 'D' )
+			 goto lBAD_CTCP;
+		 if( sptr[i+1] != 'C' )
+			 goto lBAD_CTCP;
+		 if( sptr[i+2] != 'C' )
+			 goto lBAD_CTCP;
+		 if( sptr[i+3] != ' ' )
+			 goto lBAD_CTCP;
+		 /* We have a DCC command - handle it! */
+		 i+= 4;						  /* Skip "DCC " */
+		 if( iCopy+4 > sizeof(newpacket) )
+			 goto lPACKET_DONE;
+		 newpacket[iCopy++] = 'D';
+		 newpacket[iCopy++] = 'C';
+		 newpacket[iCopy++] = 'C';
+		 newpacket[iCopy++] = ' ';
+
+		 DBprintf(("Found DCC\n"));
+		 /* Skip any extra spaces (should not occur according to
+          protocol, but DCC breaks CTCP protocol anyway */
+		 while(sptr[i] == ' ') {
+			 if( ++i >= dlen) {
+				 DBprintf(("DCC packet terminated in just spaces\n"));
+				 goto lPACKET_DONE;
+			 }
+		 }
+
+		 DBprintf(("Transferring command...\n"));
+		 while(sptr[i] != ' ') {
+			 newpacket[iCopy++] = sptr[i];
+			 if( ++i >= dlen || iCopy >= sizeof(newpacket) ) {
+				 DBprintf(("DCC packet terminated during command\n"));
+				 goto lPACKET_DONE;
+			 }
+		 }
+		 /* Copy _one_ space */
+		 if( i+1 < dlen && iCopy < sizeof(newpacket) )
+			 newpacket[iCopy++] = sptr[i++];
+
+		 DBprintf(("Done command - removing spaces\n"));
+		 /* Skip any extra spaces (should not occur according to
+          protocol, but DCC breaks CTCP protocol anyway */
+		 while(sptr[i] == ' ') {
+			 if( ++i >= dlen ) {
+				 DBprintf(("DCC packet terminated in just spaces (post-command)\n"));
+				 goto lPACKET_DONE;
+			 }
+		 }
+
+		 DBprintf(("Transferring filename...\n"));
+		 while(sptr[i] != ' ') {
+			 newpacket[iCopy++] = sptr[i];
+			 if( ++i >= dlen || iCopy >= sizeof(newpacket) ) {
+				 DBprintf(("DCC packet terminated during filename\n"));
+				 goto lPACKET_DONE;
+			 }
+		 }
+		 /* Copy _one_ space */
+		 if( i+1 < dlen && iCopy < sizeof(newpacket) )
+			 newpacket[iCopy++] = sptr[i++];
+
+		 DBprintf(("Done filename - removing spaces\n"));
+		 /* Skip any extra spaces (should not occur according to
+          protocol, but DCC breaks CTCP protocol anyway */
+		 while(sptr[i] == ' ') {
+			 if( ++i >= dlen ) {
+				 DBprintf(("DCC packet terminated in just spaces (post-filename)\n"));
+				 goto lPACKET_DONE;
+			 }
+		 }
+
+		 DBprintf(("Fetching IP address\n"));
+		 /* Fetch IP address */
+		 org_addr = 0;
+		 while(i<dlen && isdigit(sptr[i])) {
+			 if( org_addr > ULONG_MAX/10UL )	{ /* Terminate on overflow */
+				 DBprintf(("DCC Address overflow (org_addr == 0x%08lx, next char %c\n", org_addr, sptr[i]));
+				 goto lBAD_CTCP;
+			 }
+			 org_addr *= 10;
+			 org_addr += sptr[i++]-'0';
+		 }
+		 DBprintf(("Skipping space\n"));
+		 if( i+1 >= dlen || sptr[i] != ' ' ) {
+			 DBprintf(("Overflow (%d >= %d) or bad character (%02x) terminating IP address\n", i+1, dlen, sptr[i]));
+			 goto lBAD_CTCP;
+		 }
+		 /* Skip any extra spaces (should not occur according to
+          protocol, but DCC breaks CTCP protocol anyway, so we might
+          as well play it safe */
+		 while(sptr[i] == ' ') {
+			 if( ++i >= dlen ) {
+				 DBprintf(("Packet failure - space overflow.\n"));
+				 goto lPACKET_DONE;
+			 }
+		 }
+		 DBprintf(("Fetching port number\n"));
+		 /* Fetch source port */
+		 org_port = 0;
+		 while(i<dlen && isdigit(sptr[i])) {
+			 if( org_port > 6554 )	{ /* Terminate on overflow (65536/10 rounded up*/
+				 DBprintf(("DCC: port number overflow\n"));
+				 goto lBAD_CTCP;
+			 }
+			 org_port *= 10;
+			 org_port += sptr[i++]-'0';
+		 }
+		 /* Skip illegal addresses (or early termination) */
+		 if( i >= dlen || (sptr[i] != '\001' && sptr[i] != ' ') ) {
+			 DBprintf(("Bad port termination\n"));
+			 goto lBAD_CTCP;
+		 }
+		 DBprintf(("Got IP %lu and port %u\n", org_addr, (unsigned)org_port));
+
+		 /* We've got the address and port - now alias it */
+		 {
+			 struct alias_link *dcc_link;
+			 struct in_addr destaddr;
+			 
+
+			 true_port = htons(org_port);
+			 true_addr.s_addr = htonl(org_addr);
+			 destaddr.s_addr = 0;
+
+			 /* Steal the FTP_DATA_PORT - it doesn't really matter, and this
+				 would probably allow it through at least _some_
+				 firewalls. */
+			 dcc_link = FindUdpTcpOut (true_addr,
+											destaddr,
+										   true_port,
+											0, IPPROTO_TCP);
+			 DBprintf(("Got a DCC link\n"));
+			 if ( dcc_link ) {
+				 struct in_addr alias_address;	/* Address from aliasing */
+				 u_short alias_port;	/* Port given by aliasing */
+
+				 alias_address = GetAliasAddress(link);
+				 iCopy += snprintf(&newpacket[iCopy],
+										 sizeof(newpacket)-iCopy, 
+										 "%lu ", htonl(alias_address.s_addr));
+				 if( iCopy >= sizeof(newpacket) ) { /* Truncated/fit exactly - bad news */
+					 DBprintf(("DCC constructed packet overflow.\n"));
+					 goto lBAD_CTCP;
+				 }
+				 alias_port = GetAliasPort(dcc_link);
+				 iCopy += snprintf(&newpacket[iCopy],
+										 sizeof(newpacket)-iCopy, 
+										 "%u", htons(alias_port) );
+				 /* Done - truncated cases will be taken care of by lBAD_CTCP */
+				 DBprintf(("Aliased IP %lu and port %u\n", alias_address.s_addr, (unsigned)alias_port));
+			 }
+		 }
+		 /* An uninteresting CTCP - state entered right after '\001' has
+          been pushed.  Also used to copy the rest of a DCC, after IP
+          address and port has been handled */
+	 lBAD_CTCP:
+		 for(; i<dlen && iCopy<sizeof(newpacket); i++,iCopy++) {
+			 newpacket[iCopy] = sptr[i]; /* Copy CTCP unchanged */
+			 if(sptr[i] == '\001') {
+				 goto lNORMAL_TEXT;
+			 }
+		 }
+		 goto lPACKET_DONE;
+		 /* Normal text */
+	 lNORMAL_TEXT:
+		 for(; i<dlen && iCopy<sizeof(newpacket); i++,iCopy++) {
+			 newpacket[iCopy] = sptr[i]; /* Copy CTCP unchanged */
+			 if(sptr[i] == '\001') {
+				 goto lCTCP_START;
+			 }
+		 }
+		 /* Handle the end of a packet */
+	 lPACKET_DONE:
+		 iCopy = iCopy > maxsize-copyat ? maxsize-copyat : iCopy;
+		 memcpy(sptr+copyat, newpacket, iCopy);
+
+/* Save information regarding modified seq and ack numbers */
+        {
+            int delta;
+
+            SetAckModified(link);
+            delta = GetDeltaSeqOut(pip, link);
+            AddSeq(pip, link, delta+copyat+iCopy-dlen);
+        }
+
+		  /* Revise IP header */
+        {
+			  u_short new_len;
+			  
+			  new_len = htons(hlen + iCopy + copyat);
+			  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);
+		  return;
+	 }
+}
+
+/* Notes:
+	[Note 1]
+	The initial search will most often fail; it could be replaced with a 32-bit specific search.
+	Such a search would be done for 32-bit unsigned value V:
+	V ^= 0x01010101;				  (Search is for null bytes)
+	if( ((V-0x01010101)^V) & 0x80808080 ) {
+     (found a null bytes which was a 01 byte)
+	}
+   To assert that the processor is 32-bits, do
+   extern int ircdccar[32];        (32 bits)
+   extern int ircdccar[CHAR_BIT*sizeof(unsigned int)];
+   which will generate a type-error on all but 32-bit machines.
+
+	[Note 2] This routine really ought to be replaced with one that
+	creates a transparent proxy on the aliasing host, to allow arbitary
+	changes in the TCP stream.  This should not be too difficult given
+	this base;  I (ee) will try to do this some time later.
+	*/