In short

I’m delroth, or Pierre Bourdon. Originally from France, currently living in Zürich, Switzerland. I’m an open source developer, mainly contributing to NixOS these days. In the past, I was a core developer for the Dolphin Emulator, and I was the main infrastructure maintainer as well as treasurer for the project.

In my working life, I’ve worked for around 10 years as a Software Engineer at Google. I’ve spent around 3 years each specializing in site reliability, counter-abuse technologies, then infrastructure security. Along the way, I also became privacy reviewer for new infrastructure projects, as well as teacher/mentor for new C++ developers at the company.

I’m currently on a sabbatical leave, spending my free time learning more about the country I’ve lived in for 10 years, and finally learning the local language.

This article was co-authored with Samuel Chevet.

During the Nuit du Hack 2012 Prequals contest, we often had to remote exploit some services running in a custom VM (which was recently released on GitHub). After injecting a shellcode in the services (through a remote stack buffer overflow) we were able to run VM code, which can execute interesting syscalls: readwriteopenexit, and a lot more. However there was not a way to directly execute a random x86 binary or to list directories (no getdents), which made it really hard to explore the server filesystem.

After the event ended we got an idea that we could have used to bypass this security and execute any shell command line on the remote server. Using /proc/self/cmdline, we can get the path to the VM binary and download it. Then, using /proc/self/mem we can replace some symbols from the binary by our custom x86 code. This method works because without the grsecurity patchset /proc/self/mem completely overrides NX and allows writing to read-only memory locations (like .text).

Once upon a time, Stefan Esser from the Hitmen programmed an IDA loader plugin to be able to analyze DOL files, which is the executable format used for Gamecube and Wii. Builds are published for versions up to 5.2, but nothing more recent.

Fortunately they also released the source to their plugin, which allowed me (with some very minor modifications to the code to use linput_t instead of C FILE structures) to build a version of the IDA DOL loader plugin for IDA 6.1, the version I’m using in my day to day reverse engineering. Here is a link to this build.

Have fun with it!

My Stripe CTF writeup

- 6 mins read

Recently Stripe (a startup trying to improve online payments for web developers) put online a fun CTF challenge with simple security exercises. Now that the challenge is done and the CTF is offline, I wanted to share my solutions with people who were interested in this CTF but were not able to solve it before the time limit.

Unfortunately I don’t have the original source code of the exercises here. I hope that the Stripe CTF organizers will publish those so that I can explain my exploits better 🙂

What I mean by reading a Wii disc is simple: from a Wii DVD image, being able to get metadata about the game, like its name or its unique ID, but also being able to read the filesystem on the disc to access the game executable and data. We’ll do this in three parts: first, we’ll decrypt the disc clusters to be able to access the raw partition data, then we’ll parse the filesystem to access files and directories, and we’ll end this by a presentation of wiiodfs, the software I created to mount Wii discs on Linux using FUSE.

I currently only have one game disc image on my computer: the one from Tales of Symphonia: Dawn of the New World, PAL version, whose ID is RT4PAF (sha1sum: b2fb05a7fdf172ea61b5d1872e6b121140c95822). I’m going to work on this disc image for my tests, and if needed fix things when I’ll have to open another game DVD image which doesn’t work. To write this article, I’m using documentation from WiiBrew, a wiki about Wii homebrew with a lot of technical informations, and the source code of Dolphin, the Wii emulator (mostly in the Source/Core/DiscIO directory). Thanks a lot to all of the contributors to these projects.

Most games nowadays avoid hardcoding behavior in the main program code. It makes the development process a lot easier by allowing people with less programming experience than the core engine developers to contribute by writing scripts which defines how conversations happen in the game, how menus work, how cinematic scenes go, etc. Scripts are usually written in a higher level language than the game engine, as they require less performance and must be portable when the game needs to run on different platforms. Easy, common script languages like Lua or Python are often used (for example, CCP uses Python to describe the EVE Online client GUI, and Microsoft uses Lua in Freelancer to describe cinematics), but some companies like to create their own language and their own interpreter to do this job.

I’m a fan of Namco’s “Tales of” RPG games. I was given a Wii last december as a gift, and bought “Tales of Symphonia: Dawn of the New World”. As a true hacker interested in game development, after finishing the game, I started investigating how this game actually works behind the scenes. After writing software to read the encrypted Wii disc of the game, I analyzed the data contained on the DVD, trying to find what was each file and how the game engine made all of this into a game.

As in the other binary l33tness problems, only a single file was provided in the problem description:

b300_b258110ad2d6100c4b8: gzip compressed data

Decompressing this gives us a tar archive containing these files:


The binary is classes.dex, which is bytecode for the Dalvik virtual machine found on Android devices. The hprof file is a heap profiler output file which contains the state of the program heap at some point during the execution. The .jpgs files seems to contain random data at first, which leaded us to think it was encrypted data we needed to decrypt.

gb100 took a lot of time to pwn for us as we ran out of ideas really fast and it was mostly guessing. Anyway, this is a small writeup about this really simple problem from the DEFCON 19 CTF.

The description of this problem contained only a host:port which we had to connect to. For the first 4 to 6 hours of the contest the server simply closed any incoming connection on the specified port, which caused us to try a lot of strange protocols, only to find out 4 hours later that the problem was fixed and was simply an HTTP server.

Eri HaKawai is a new exploit for PAL Wiis, which works for all currently released System Menu versions (<= 4.3). It works by using a bug in the savegame loading code of Tales of Symphonia: Dawn of the New World, the sequel to the Gamecube game Tales of Symphonia.

I’m releasing it in a source format (no binary data.bin) under the GPLv2. You’ll need a Broadway cross-compilation toolchain, as well as a checkout of Segher’s Wii Git repository. Do whatever you want with it (as long as it is allowed by the license, of course!), I’m just too lazy to distribute binaries.

Download Eri HaKawai v0.1

This last Christmas I was happy to get gifted a brand new Nintendo Wii (“25 years of Mario” version) from someone in my family. Quickly my interests shifted from “playing games on the system” to trying to understand how the console works, and whether I could potentially run my own code on it. This led to an article on this blog about the Wii DVD file format, but also a lot of research and reverse engineering to understand how games themselves work.

However, while I did learn a lot, I was still not able to run my own code on the console. It’s kind of sad, I would have loved to be able to do more than just reading about the hardware. To run unapproved code on a closed/locked platform, one must use what is called a jailbreak. This usually involves exploiting a security vulnerability in software that already runs on the device (for example, on the Nintendo Wii, a game). Through this vulnerability, arbitrary code gets executed, then this entry point is used to further root the device. The iPhone, for example, was jailbroken via a vulnerability in its PDF reading code, allowing rooting by direct access to a web page. On the Wii, the Bannerbomb exploit allowed until last year jailbreaking a Wii by making it read a malformed image. There are many similar examples.