Dr Sly's Technical Ramblings

A quick look into the DOS exe header and relocation table

nospam@example.com (Sylvester Rac) — Sun, 12 Nov 2023 08:51:00 +0000

Continuing from where we left off, let's examine USNF.EXE in a hex editor, to get a better understanding of the file structure. The file command identifies the executable as MS-DOS executable. Loading into a hex editor:

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Reverse Engineering with DOSBox debug build

nospam@example.com (Sylvester Rac) — Sat, 04 Nov 2023 23:43:00 +0000

DosBox comes with it's own built-in debugger, which can be useful when reversing old DOS games.

This feature needs to be enabled at build time (--enable-debug or --enable-debug=heavy), so either download the special binary or build it from source. I went through the build process in a previous post: https://blog.aupcgroup.com/index.php?/archives/32-Hacking-a-DOS-32-bit-protected-mode-game-from-1997.html

This gives a nice view with registers, dissassembly and memory views:

This VOGONS thread has a quick summary on the DosBox built-in debugger: https://www.vogons.org/viewtopic.php?t=3944

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Hacking a DOS 32 bit protected mode game from 1997

nospam@example.com (Sylvester Rac) — Fri, 03 Nov 2023 11:41:00 +0000

It's been a long time since I've looked at X86 assembly, and I thought it might be fun to reverse engineer a game I enjoyed playing when I was much younger - US Navy Fighters.

Hacking tools

IDA (Interactive Dissassembler) - download IDA 8.3 from https://hex-rays.com/ida-free/ (free for personal use). I'm using the linux version. To install chmod +xx the installer and accept the license agreement. Choose the install location, I chose idafree-8.3 in my home folder.

chmod +x idafree83_linux.run
./idafree-8.3/ida64

Debugger - USNF is a DOS game and won't run on linux natively, however it runs perfectly fine through DOS-Box. The good news is DOS-Box is available as a special debug build, with an integrated debugger. This allows us to set breakpoints, peek at memory locations, etc, and should very helpful in analysing the game. To get the debug build we'll need to build DOS-Box from source. Download the source code from https://www.dosbox.com. There is some information on the build process on VOGONS.

Download the file: dosbox-0.74-3.tar.gz, and run the build. Install autotools if it's missing. Also, note the SDL 1.2 and curses dependencies:

sudo apt install autoconf autotools-dev automake
sudo apt install libsdl1.2-dev libncurses-dev
tar xvf dosbox-0.74-3.tar.gz
cd dosbox-0.74-3/
./autogen.sh
./configure --enable-debug=heavy
make
sudo make install

By default, the binary is installed into /usr/local/bin. I renamed my binary to dosbox-debug to distinguish it from the standard version:

sudo mv /usr/local/bin/dosbox /usr/local/bin/dosbox-debug

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Installing printer drivers for cm215fw

nospam@example.com (Sylvester Rac) — Tue, 07 Feb 2023 23:45:00 +0000

A google search quickly reveals foo2hbpl2 is the correct driver, but no real clear instructions on how to install it on a debian system.

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Setting up a cyber lab

nospam@example.com (Sylvester Rac) — Sat, 26 Dec 2020 11:54:00 +0000

It is a good idea to be careful when deploying an unknown virtual machine created by someone else. We should not allow it access to the Internet or our local network. In this article I will describe the steps I take to achieve this.

Virtualisation

My virtualisation platform of choice is VirtualBox - it is simple to set up, easy to use, and open source. VirtualBox supports importing machines using the Open Virtualization Format (OVF). VirtualBox offers an 'Internal Network' which is completely isolated from the host network environment. We shall connect any unknown virtual machines to this internal network.

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Plans for the year ahead - 2021

nospam@example.com (Sylvester Rac) — Sat, 26 Dec 2020 10:16:00 +0000

No can argue it's been an easy year, for now let's think about our plans for the year to come.

I have set some simple goals for 2021:

Become more active on the Stack Exchange network
Learn as much as possible about cyber security
Finish my PC emulator and release it to the public
Increase the frequency of my blog posts

Resize an NTFS partition using Linux

nospam@example.com (Sylvester Rac) — Wed, 16 Sep 2020 11:49:00 +0000

Today I spent some time resizing an existing ntfs partition, in order to make space for an LFS build.

Here's the existing partition structure:

# fdisk -l -u /dev/sdb
Disk /dev/sdb: 465.8 GiB, 500106780160 bytes, 976771055 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xa7cea7ce

Device     Boot     Start       End   Sectors   Size Id Type
/dev/sdb1  *      2048    206847    204800   100M  7 HPFS/NTFS/exFAT
/dev/sdb2       206848 976766975 976560128 465.7G  7 HPFS/NTFS/exFAT

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Mount a Bochs disk image

nospam@example.com (Sylvester Rac) — Sat, 18 Apr 2020 04:58:00 +0000

We can mount a bochs disk image from Linx with the following command:

sudo mount -t msdos -o loop,offset=32256 disk.img /mnt/bochs/

The offset of 32256 is correct if the image was created with the Bochs Disk Image Creator, but how can the offset be calculated?

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How to share a directory over a network using NFS

nospam@example.com (Sylvester Rac) — Sun, 14 Oct 2018 10:36:00 +0000

NFS or Network File System is a quick and easy way to share files between Linux hosts on a network. Client machines are able to mount specific directories on a server machine and access the files as if they are on the client's local filesystem.

Configuring an NFS share is as easy as installing a package and editing a config file. For the steps below I'm using a Debian client and a Ubuntu based server.

Configuring the server

Begin by installing the nfs-kernel-server package if it isn't already installed:

sudo apt-get install nfs-kernel-server

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Fix broken Alt-Tab behaviour in Gnome 3

nospam@example.com (Sylvester Rac) — Sun, 31 Dec 2017 03:50:00 +0000

The Gnome 3 default behaviour for Alt-Tab switching displays applications across all virtual desktops and groups together multiple instances of the same application.

If you find this annoying, the list of applications can be limited to the current virtual desktop, using the command:

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Utility to patch VirtualBox .vdi files

nospam@example.com (Sylvester Rac) — Wed, 28 Dec 2016 13:52:00 +0000

I wrote a utility to write content directly to .vdi files.

Bitbucket repo: https://bitbucket.org/DrSly/patch_vdi/

Ubuntu - restart wifi connection without rebooting

nospam@example.com (Sylvester Rac) — Sat, 16 Jul 2016 10:50:00 +0000

Restarting a wifi connection without rebooting

I have a Mythbuntu box who's only connection to the outside world is through a wi-fi connection. It can be frustrating when the connection drops out at a critical time - during an upgrade to the next LTS release for instance. Here are some things to try to reset the connection.

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Backup your web server with rsync, mysqldump and tar

nospam@example.com (Sylvester Rac) — Wed, 11 May 2016 03:27:00 +0000

In this article I will demonstrate one way to backup up a Debian based web server, together with MySQL databases.

The concepts shown here should easily adapt to work on most Linux distributions.

The tools we will use include rsync, mysqldump and tar.

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Building Ogre3D with Microsoft Visual C++ 14.0 (Visual Studio Community 2015)

nospam@example.com (Sylvester Rac) — Thu, 03 Dec 2015 10:46:00 +0000

Today we will build Ogre3D graphics rendering engine (http://www.ogre3d.org/) using Microsoft Visual C++ 14.0 compiler (Visual Studio Community 2015).

Building Ogre can take some time and things don't always go smoothly, which is why I decided to document the entire process. I will follow the basic process as documented in the official guides:

Just be aware that I may be using a slightly different directory structure within my build. Substitute my paths for yours where applicable.

The latest stable release is 1.9 and has been around for a long time, so it should build without too much trouble.

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Setting up a LAMP server (Linux + Apache + MySQL + PHP)

nospam@example.com (Sylvester Rac) — Wed, 02 Dec 2015 11:54:00 +0000

Linux + Apache + MySQL + PHP

Probably the most common installation of web server, at least for a Linux system, is Linux, Apache, MySQL and PHP. Also possible on a Windows system, in which case it would be known as WAMP. I will cover setting up the former here.

I assume you already have a working Debian based Linux distribution. If not then I highly recommend Debian, or for Raspberry Pi users, Raspbian.

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