Ants are known to leave invisible pheromones on their paths in order to inform both themselves and their fellow ants where to go to find food or signal that a path leads to danger. In biology, this phenomenon is known as stigmergy : the act of modifying your environment to manipulate the future behaviour of yourself or others. From the Wikipedia article : Stigmergy (/ˈstɪɡmərdʒi/ STIG-mər-jee) is…
My wife is currently writing her HDR thesis (in France, this is an "accreditation to supervise research"). As part of this, she asked me if it would be possible to split her bibliography into two parts: one containing her own publications and another for the rest of her references. After a tiny bit of searching, I found this stackoverflow answer: https://tex.stackexchange.com/a/407363 However, the…
Much has been written about fuzzing compilers already, but there is not a lot that I could find about fuzzing compilers using more modern fuzzing techniques where coverage information is fed back into the fuzzer to find more bugs. If you know me at all, you know I'll throw anything I can get my hands on at AFL. So I tried gcc. (And clang, and rustc -- but more about Rust in a later post.) Levels…
( EDIT 2017-03-25 : All my patches to make OpenSSH more amenable to fuzzing with AFL are available at https://github.com/vegard/openssh-portable . This also includes improvements to the patches found in this post.) American Fuzzy Lop is a great tool. It does take a little bit of extra setup and tweaking if you want to go into advanced usage, but mostly it just works out of the box. In this post,…
Having done quite a bit of kernel fuzzing and debugging lately I’ve decided to take one of the very latest crashes and write up the whole process from start to finish as I work through it. As you will see, I'm not very familiar with the site of this particular crash, the block layer. Being familiar with some existing kernel code helps, of course, since you recognise a lot of code patterns, but the…
WARNING/DISCLAIMER: Audio programming always carries the risk of damaging your speakers and/or your ears if you make a mistake. Therefore, remember to always turn down the volume completely before and after testing your program. And whatever you do, don't use headphones or earphones. I take no responsibility for damage that may occur as a result of this blog post! Have you ever wondered how a…
The standard C++ pattern for comparing and ordering objects is to overload operator<() for your class. This function is what all the standard containers ( std::set , std::priority_queue , etc.) and algorithms ( std::sort , std::binary_search , etc.) use for comparing objects. So if you have a class that you would like to put in a standard container, you have to overload operator<() . Your class…
After my exams in December, I relaxed by writing a sort of space game using C++/SDL/OpenGL: I ripped the sprites from Space Invaders and Galaga/Galaxian, please forgive me. If whoever wants to play/hack, the source code can be found here: http://github.com/vegard/spaceinv The video is a bit poor, mostly because the frame rate is supposed to be 60 FPS, but the Ogg/Theora capture was 25 FPS while…
So I somewhat promised to say something more on my project for the Google Summer of Code. I participated for the first time, and it was really a great experience. This is the first time I've been paid to do what I would probably have done in either case (because I immensely enjoy it), namely to work on an interesting free software project. So this time it was Jato, a new implementation of the Java…
Here's the recipe for the Jato IRC logger. Nothing fancy, but works surprisingly well. /home/vegard/jato-irc-logger/irssi-config : settings = { core = { real_name = "#jato IRC logger"; user_name = "vegard"; nick = "jato-irc-logger"; }; "fe-text" = { actlist_sort = "refnum"; }; "fe-common/core" = { autolog = "Yes"; autolog_path = "logs/$0/%Y-%m-%d.txt"; }; }; servers = ( { address =…
First of all, I should say that on April 22, I went to Denmark to give a talk on kmemcheck. I was invited to DIKU (Datalogisk Institut på Københavns Universitet) by Julia Lawall, who held a workshop on Coccinelle (or, more generally, "finding bugs in operating system software"). It was really nice to be there, not (just) because I got a chance to talk about kmemcheck, but because I learned so much…
An evening spent with Unicode charts, HTML, CSS, and JavaScript resulted in this: The online Hiragana tutor If you find any errors, please tell me.
Hurrah for LADSPA. I started (yet another) project, this time it's a sort of audio synthesisizer and sequencer library. I've always been fascinated with digital audio, since there are so many cool things we can do with it! Like e.g. create and apply filters, warp the sound waves any way we want, add cool effects, and generally do things that I can't otherwise do. Not to mention that I like…
I found two exploits of the Linux kernel back in January. The first one is a crash in inotify, where a locking imbalance would unlock the inotify mutex twice before returning to userspace. It happens only if the buffer passed to read() was an invalid userspace address. It's fixed in mainline and went into -stable last month (if I recall correctly), though I can't say the fix has showed up in the…
This week was Brain Awareness Week . I found that my university was giving some lectures on the brain, so I attended them all. As expected, it was quite interesting. I knew the basic concepts from before, but it really helps to hear different people talk about different subtopics, as it gives me a fuller picture of how this wonderful organ works. In any case, I couldn't help feeling inspired, so…
I've been playing with Chipmunk lately. It is a C library that simulates physics in two dimensions, and is intended for use in games. It's quite easy to use, but there is a bit of overhead in setting up graphics since I have to do that on my own. I'm using OpenGL through the SDL library, and it works quite smoothly. Here is the result of today's dabbling: There are two important fundamental…
Richard M. Stallman was at the university (University of Oslo) today, and he gave a talk titled "Copyright vs. Community in the Age of Computer Networks - Free software and beyond". I was there, of course. It was an interesting topic, though I cannot say that I agree with everything he stands for. He explained about the Four Freedoms of the Free Software Foundation…
Dear Gnome, This is completely ridiculous. According to top, "clock-applet" is using 353M virtual memory, of which 17M is resident. I have no swap partition, so it really makes me wonder why those 336M were allocated in the first place. If they are not resident, and not in swap, what are they? Blank pages? mmap()ed files which can be swapped in on demand? There is also a column for "shared…
Hi, It's been a while -- I've been mostly busy with university. Maybe I won't try to follow four classes next year. In other news, we didn't make it (with kmemcheck) for 2.6.28 either. Oh well. We did at least make an impression by discovering two more bugs in 2.6.28-rc. Now for the topic of this post: Recursive type definitions in C. More specifically, the types I want to write about are not…
Hi, First of all: Scribe. That is my new pet project. Actually, I don't know how serious it is yet. But I've made a Project out of it; maybe somebody else who is interested will come along and help. We'll see. But what is it? Well, it's really just a demo so far. A demo of a "3D pixel engine". It started out as an experiment to see how the graphics from "The Legend of Zelda: Link's awakening"…
I finally did it. I fixed the problem with single-stepping REP STOS (and MOVS) instructions on the P4. (Look in the blog archive to find the original post.) At first, I wanted emulate the instructions completely. But it wasn't really that easy. My naïve implementation did support different register/data widths. But I soon hit some real show-stoppers. It turned out that the kernel will use REP STOS…
(This post contains some reflections on the hypothetical design of an ideal programming language...) Don't use or support the use of preprocessing source code. Preprocessing means that all the tools which operate on the source code (including editors, compilers, static analyzers, etc.) will necessarily need to either support preprocessing themselves, or call the preprocessor before operating on…
I've recently made a startling discovery that explains a LOT about how kmemcheck has been working (or not) on one of my machines. Yesterday I added the kmemcheck hooks into the DMA API, which means that we should now not give any false-positive errors about DMA-able memory. The patch was essentially a one-liner, since the rest of the DMA API deals with whole pages only (and they come straight from…
Yesterday, I decided that it was time to try out Fedora 9; after all, it's been a few months since it was released, and having just made a backup, I found that this was a convenient time to perform the upgrade. Things did not start out so well, though. The installer seemed incredibly slow this time. There is a progress bar which shows how many packages that have been installed, but this could…