If you have been reading this blog, you have probably noticed how all the debugging and analysis of applications have been on Windows executables, and although I did create my own Linux distribution, Dapper Linux, I haven’t written much about debugging on Linux.
Time to change that. Today, we are going to look into how debugging Linux kernel crash dumps works on Ubuntu 18.10 Cosmic Cuttlefish. Fire up a virtual machine, and follow along.
We will cover how to install and configure
kdump, a little on how each tool works, and finding the root cause of a basic panic.
Let’s get started.
Here we are, back again for my third bug bounty! It really is a good time trying to break an applications security, and especially so when there is some Bitcoin waiting as a reward.
As always, I was on Reddit and saw that u/cryptocomicon has made some changes to TimeLock, and is ready for them to be tested again.
u/cryptocomicon has acknowledged that writing secure software is extremely hard, and is absolutely correct in that statement. We also see that a new challenge is issued:
Designing an un-hackable TimeLock is challenging. This is my third version and the third challenge, with a 0.02 BTC reward.
Please give it a try.
Will do. Challenge accepted.
Recently I was asked to do some homework to prepare for an interview on Linux kernel internals, and I was given the following to analyse:
Specifically, we would like you to study and be able to discuss
the code path that is exercised when a kernel caller allocates an object
from the kernel memory allocator using a call of the form:
object = kmalloc(sizeof(*object), GFP_KERNEL);
For this discussion, assume that (a) sizeof(*object) is 128, (b)
there is no process context associated with the allocation, and (c)
we’re referencing an Ubuntu 4.4 series kernel, as found at
In addition, we will discuss the overall architecture of the
SLUB allocator and memory management in the kernel, and the specifics of
the slab_alloc_node() function in mm/slub.c.
I spent quite a lot of time, maybe 8-10 hours, studying how the SLUB memory allocator functions, and looking at the implementation of
kmalloc(). It’s a pretty interesting process, and it is well worth writing up.
Let’s get started, and I will try to keep this simple.
I’m back again for my second bug bounty! Searching for bugs is actually pretty fun, especially when it comes with a generous reward in my favourite cryptocurrency, Bitcoin!
I was scrolling Reddit like usual, and u/cryptocomicon has returned with a new version of TimeLock! That’s great news.
If we remember back to last week, I solved the original TimeLock challenge, and wrote a detailed writeup.
u/cryptocomicon issued a new challenge:
I’m so confident in this technology that I’ve created a challenge LockBox file which holds the private key to an address with 0.02 BTC.
Please give it a try.
NOTE: This is going to be much harder than last time.
Much harder than last time? Sounds interesting.
I was lucky enough to be selected to speak at linux.conf.au 2019, which was held in Christchurch, at the University of Canterbury.
My talk, Maintaining the Unmaintainable: Picking up the Baton of a Secure Kernel Patchset is about my experience in attempting to forward port the last release of the grsecurity patchset to newer kernels, and my time maintaining a public release that targets Linux 4.9 LTS.
I put a lot of time into practising the talk at least once a day for about two weeks straight, and I am happy with how it turned out.
The talk has been uploaded to YouTube, so check it out below, and also have a look at the other talks - there was a lot of interesting talks by the open source community this year.
You can find a copy of the slides here.