CVE-2006-3324 arbitary file overwrite

CVE-2006-3324
The Automatic Downloading option in the id3 Quake 3 Engine and the
Icculus Quake 3 Engine (ioquake3) before revision 804 allows remote
attackers to overwrite arbitrary files in the quake3 directory
(fs_homepath cvar) via a long string of filenames, as contained in the
neededpaks buffer.

Luigi Auriemma q3cfilevar

from Thilo Schulz in ioquake3
svn 804 git 813a6ecdc3b8572796a8a85b260b03e1c3d87ef4

- Fix bug that allows a malicious server to write and overwrite any
  files in the quake3 directory.  Reported by Luigi Auriemma.
- Moved directory traversal check to a more proper location.
- Added a few sanity checks for checksum/pakname storage to fix a crash
  that can occur under certain circumstances.

codemp/qcommon/files_pc.cpp

@@ -2356,15 +2356,16 @@ we are not interested in a download string format, we want something human-reada
 qboolean FS_ComparePaks( char *neededpaks, int len, qboolean dlstring ) {
 	searchpath_t	*sp;
 	qboolean havepak, badchecksum;
+	char *origpos = neededpaks;
 	int i;
 
-	if ( !fs_numServerReferencedPaks ) {
+	if (!fs_numServerReferencedPaks)
 		return qfalse; // Server didn't send any pack information along
-	}
 
 	*neededpaks = 0;
 
-	for ( i = 0 ; i < fs_numServerReferencedPaks ; i++ ) {
+	for ( i = 0 ; i < fs_numServerReferencedPaks ; i++ )
+	{
 		// Ok, see if we have this pak file
 		badchecksum = qfalse;
 		havepak = qfalse;
@@ -2374,6 +2375,13 @@ qboolean FS_ComparePaks( char *neededpaks, int len, qboolean dlstring ) {
 			continue;
 		}
 
+		// Make sure the server cannot make us write to non-quake3 directories.
+		if(FS_CheckDirTraversal(fs_serverReferencedPakNames[i]))
+		{
+			Com_Printf("WARNING: Invalid download name %s\n", fs_serverReferencedPakNames[i]);
+			continue;
+		}
+
 		for ( sp = fs_searchpaths ; sp ; sp = sp->next ) {
 			if ( sp->pack && sp->pack->checksum == fs_serverReferencedPaks[i] ) {
 				havepak = qtrue; // This is it!
@@ -2386,6 +2394,12 @@ qboolean FS_ComparePaks( char *neededpaks, int len, qboolean dlstring ) {
 			
 			if (dlstring)
 			{
+				// We need this to make sure we won't hit the end of the buffer or the server could
+				// overwrite non-pk3 files on clients by writing so much crap into neededpaks that
+				// Q_strcat cuts off the .pk3 extension.
+
+				origpos += strlen(origpos);
+
 				// Remote name
 				Q_strcat( neededpaks, len, "@");
 				Q_strcat( neededpaks, len, fs_serverReferencedPakNames[i] );
@@ -2404,6 +2418,14 @@ qboolean FS_ComparePaks( char *neededpaks, int len, qboolean dlstring ) {
 					Q_strcat( neededpaks, len, fs_serverReferencedPakNames[i] );
 					Q_strcat( neededpaks, len, ".pk3" );
 				}
+
+				// Find out whether it might have overflowed the buffer and don't add this file to the
+				// list if that is the case.
+				if(strlen(origpos) + (origpos - neededpaks) >= len - 1)
+				{
+					*origpos = '\0';
+					break;
+				}
 			}
 			else
 			{
@@ -2962,7 +2984,7 @@ checksums to see if any pk3 files need to be auto-downloaded.
 =====================
 */
 void FS_PureServerSetReferencedPaks( const char *pakSums, const char *pakNames ) {
-	int		i, c, d;
+	int		i, c, d = 0;
 
 	Cmd_TokenizeString( pakSums );
 
@@ -2971,30 +2993,35 @@ void FS_PureServerSetReferencedPaks( const char *pakSums, const char *pakNames )
 		c = MAX_SEARCH_PATHS;
 	}
 
-	fs_numServerReferencedPaks = c;
-
 	for ( i = 0 ; i < c ; i++ ) {
 		fs_serverReferencedPaks[i] = atoi( Cmd_Argv( i ) );
 	}
 
-	for ( i = 0 ; i < c ; i++ ) {
+	for (i = 0 ; i < ARRAY_LEN(fs_serverReferencedPakNames); i++)
-		if (fs_serverReferencedPakNames[i]) {
+	{
+		if (fs_serverReferencedPakNames[i])
 			Z_Free(fs_serverReferencedPakNames[i]);
-		}
 		fs_serverReferencedPakNames[i] = NULL;
 	}
+
 	if ( pakNames && *pakNames ) {
 		Cmd_TokenizeString( pakNames );
 
 		d = Cmd_Argc();
-		if ( d > MAX_SEARCH_PATHS ) {
+
-			d = MAX_SEARCH_PATHS;
+		if(d > c)
-		}
+			d = c;
 
 		for ( i = 0 ; i < d ; i++ ) {
 			fs_serverReferencedPakNames[i] = CopyString( Cmd_Argv( i ) );
 		}
 	}
+
+	// ensure that there are as many checksums as there are pak names.
+	if(d < c)
+		c = d;
+
+	fs_numServerReferencedPaks = c;
 }
 
 /*