NOLOCKWS, version 0.9 beta, June 1997

A program to modify msgina.dll in order to inactivate the Lock Workstation button in the Windows NT Security (Ctrl-Alt-Del) dialog.

Copyright (C) 1997 by

This program is free software under the GNU General Public License. See the file LICENSE for details. The latest version of NOLOCKWS can be found at http://wwwthep.physik.uni-mainz.de/~frink/nt.html.

Contents

1. Introduction
2. Legal stuff
3. Concept
4. Usage
5. Implemented and tested platforms
6. Files
7. Feedback/possible improvements

1. Introduction

Especially for large PC pools in universities or schools it is very annoying when users lock their NT workstations, leave, and forget to come back. Subsequent users have the choice of resetting the PC or calling an administrator who can unlock the workstation. While lots of Windows NT settings can be changed through the registry, disabling the Lock Workstation button in the Windows NT Security (Ctrl-Alt-Del) dialog seems to be forgotten.

Some time ago, I suggested a method how to overcome this: load msgina.dll from the \winnt\system32 directory with a resource editor (which come with most C++ compilers for Windows) and modify the window style attributes of the Lock Workstation button in dialog #1650 (this is the Windows NT Security dialog).

However, this is cumbersome, dangerous (a corrupt msgina.dll may prevent the system from booting properly), and not everybody has a resource compiler to hand. Therefore I decided to write a program that automates this task. This is the first BETA version intended for a broader testing than I can do.

2. Legal stuff

For short, the main aspects of the GNU General Public License are in my personal interpretation which may not be 100% accurate (I am a physicist, not a lawyer):

• Everybody (private or commercial users) can use this program freely. However, there is now warranty of any kind, since this is free software. Use it at your own risk!
• Everybody may copy and distribute it, as long as you include the copyright notice, a disclaimer of warranty, the GNU License, and the source code (or make it freely available).
• You may modify the program or use parts of it in own programs, as long as you distribute it under this license as well (included, but not limited to making the source code available). Further include appropriate copyright notices and take responsibility for ALL bugs in this modified version.

3. Concept

Let me briefly explain how the program works. Source code is included, so you may examine it on your own and modify it under the restrictions of the GNU General Public License.

The Windows NT Security dialog with the Lock Workstation button is contained in %systemroot%\system32\msgina.dll. NOLOCKWS scans this file for the text on the button. For the English version, this is Lock &Workstation in Unicode (16 bit), the '&' in front of the 'W' denotes the accelerator key Alt-W. Located 22 bytes ahead of this string, one finds the button's 32 bit window attributes. By default, these are 0x50010001L (least significant bit may be zero) . To disable the button, the WS_DISABLED flag (0x08000000L) has to be set, i.e. the window attributes have to be modified to 0x58010001L (alternatively it would be possible to hide the button by clearing the WS_VISIBLE 0x10000000L flag). The modified file cannot immediately replace the original one, since it is in use. Therefore, the original file has to be renamed to something else, afterwards the modified file can be saved as msgina.dll. The changes become active at the next reboot.

4. Usage

Again: This program is still in BETA state and is distributed WITHOUT ANY WARRANTY. Before you use this program, make a backup of all your important data, create an Emergency Repair Disk (with RDISK /S), and have your three NT Setup disks and the CD to hand, since it is possible that an unexpected failure may leave your system in an unusable state (although I have not experienced any problems yet).

Using this program is simple:

• Log on as a user with administrative privileges (not necessarily the Administrator account, but the program explicitly checks if you are a member of the Administrators group). You must have permissions to modify files in the %systemroot%\system32 directory (usually Full Control is granted by default at least to the Adminstrators group).
• Close all running applications, to avoid loss of data if something goes wrong. You have to reboot later anyhow.
• Invoke the program from the Command Prompt. Command switches are not supported. You have to answer three questions (you can interrupt the program at any time with Ctrl-C or Ctrl-Break):
  1. Where is msgina.dll located?
     NOLOCKWS suggests the %systemroot%\system32 directory (%systemroot% is expanded to e.g. c:\winnt). You should accept it and press Enter.
  2. Type in exactly the text on your Lock Workstation button (this text depends on your language). You must pay attention to upper/lower case letters. In front of the accelerator key (the letter that is underlined), type an &-character.
     If you have an US/English version of Windows NT, accept the proposed Lock &Workstation. Otherwise press Ctrl-Alt-Del to look up the equivalent in your language at the Windows NT Security dialog.
  3. Do you want to (a)llow or (d)isallow workstation locking?
     Answer with 'd' (this is the default) if you run this program for the first time. You can undo the changes later if you choose an 'a' here, but you must have rebooted before!
• NOLOCKWS will now make the desired changes to msgina.dll and then ask you if you want to reboot Windows NT. This is necessary to activate the changes and must be done before you run NOLOCKWS again.

On successful completion, NOLOCKWS will have created a backup of the unmodified msgina.dll called msgina.bak in the same directory. If this file already exists (when you run the program for the second time), NOLOCKWS will prompt you to rename (with File Manager/Explorer, then choose retry) or delete it.

Desaster recovery, if something went wrong (I hope this never happens, these are just some ideas, untested because it has not been necessary yet):

• Boot from the three NT Setup disks and repair the files (especially msgina.dll). If you have any Service Packs installed, many files may appear to be corrupt because the checksums do not match anymore.
• If interactive logins fail, but network access is still possible, it may be possible to map ADMIN$ and replace msgina.dll with the original one from the distribution CD.
• Install a new copy of NT in a different directory on your hard disk if you have enough free disk space. Leave the current file system intact during installation (no formatting). Then replace msgina.dll in the original %systemroot%\system32 directory.

5. Implemented and tested platforms

As a proper GPL program, NOLOCKWS comes with source code. Therefore it should be easy to compile it on any NT platform. Adjust the /machine: qualifier in the .mak makefile. Link with your C runtime library, kernel32.lib, user32.lib and advapi32.lib. I have compiled it for Intel x86 with Microsoft Visual C++ 4.2 (Cygnus' gcc for GNU-Win32 lacks <conio.h>), and for DEC Alpha with VC++ 4.1, both under NT 4.0. You should have received both binary versions. They should run under NT 3.5/3.51 as well.

Since NOLOCKWS simply scans msgina.dll for a text sequence and modifies a byte near this sequence where it expects the window attributes for the Lock workstation button, it relies heavily on an unchanged resource format. I do not want to rule out problems with 64 bit versions of NT 5.0 (announced e.g. for axp).

NOLOCKWS runs fine on NT 4.0 Server and Workstation U.S. (x86) and NT 4.0 WS U.S. (axp). I have successfully modified msgina.dlls from NT 3.51 x86 and axp, which indicated an identical resource format.

To do: More tests, especially on international versions (I need the text in your local language. Please help me, see section 7)

This program does not run on Windows 95! (Why should it?)

6. Files

7. Feedback/possible improvements

If you have any suggestions, ideas for improvements, problems or anything else concerning the program or the documentation, send an e-mail to Alexander.Frink@Uni-Mainz.DE or snailmail to Alexander Frink, Hermann Schauss Str. 8, D-65232 Taunusstein, Germany.

A short list of possible improvements I have collected:

• automatic detection of common languages:
  - How to do this programmatically?
  - What is the Lock &Workstation equivalent string in other languages?
• react better/faster on Ctrl-C/Ctrl-Break (program sometimes continues until a _getch()) (rewrite gets() with _getch()?)
• search for information on the Win32 resource format to eliminate the heuristics and put it on a well-founded basis (MSDN CDs)
• discuss advantages and disadvantages of the alternative way to install the modified msgina.dll via the HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\ Winlogon\GinaDLL registry setting