Category Archives: Linux

Abstract sent to LinuxCon

So I’ve decided to see if I can get a speaking slot at LinuxCon in San Diego this year. Here is the abstract that I sent them. Wish me luck!

I will talk about hooking into pre-compiled distribution linux kernels to add security hardening. This allows for certain security frameworks to be used on kernels that are either 1) too old, 2) don’t have certain config flags set, or 3) don’t use non-mainline security patches. The primary example I’ll be discussing is my implementation of “Trusted Path Execution” as a linux kernel module, the source code of which is here: . I may also demo installing AppArmor on a RHEL6 system via a kernel module, if I get the module stable before July.

The audience would be system administrators and developers who manage systems that they can not change the kernel on, or don’t want to manage custom kernel builds. This is important because it allows access to kernel hardening to a lot of people who have their hands tied either by policy or lack of experience.

AppArmor in a RHEL/CentOS kernel

Not long after I gave up on getting a MAC system in userspace, I had the thought that LSM functions in the kernel are all visible as kernel symbols, and already implemented mandatory access control systems use just those kernel functions to do their work. I already have a working module that hooks into kernel functions (tpe-lkm), so it isn’t such a far leap to think that using the same method, one could implement a kernel-based MAC system with some creative function hijacking.

So, I’m currently working on porting the AppArmor LSM to my tpe-lkm style kernel hijack code so that it can be used on a RHEL/CentOS kernel. So far so good, I have all the basics done, but in order to get things to work right I just need to figure out how to handle something. The kernel has a task->cred->security area on every process on the system, and on module load, I need to figure out how to safely convert that from the currently loaded LSM into an apparmor profile. Once I have that figured out and a basic policy working, I’ll publish the source to github.

Wish me luck.

So the glguard thing didn’t go anywhere

I previously talked about wrapping glibc functions and the possibility of doing a mandatory control system out of it. Well, the short version is, it doesn’t work right on multi-arch systems, which is pretty much a deal breaker for me. So unless you want this error spat out on every single command that is ran:

ERROR: object '/usr/lib/' from /etc/
       cannot be preloaded: ignored.

Then you’re SOL. Oh well, it was worth a try. On to other things!

Bug reported and fixed in tpe-lkm, new version ready

Early this morning I got a bug report from someone that, when the full path to a file is sufficiently long enough, a denied execution of it will throw a NULL pointer exception in the kernel. This evening I researched the issue and coded in a fix. Basically, the error reporting tried to print out a NULL pointer under those conditions. How embarrassing for me to not notice this.

If you’re using the tpe-lkm module, you’ll want to update it. I’ve also bumped the version number.

Many thanks to Panos Sakkos for the bug report!

Intercepting glibc functions

The other day I came across an old forum post about logging exec calls to syslog without modifying code anywhere. I was intrigued; I didn’t know you could hook into glibc function calls like this. I wonder how far can this go? Naturally, I decided to take a quick whack at it myself, and I ended up coding a very basic implementation of Trusted Path Execution with it. I got good (although puzzling) results:

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grsecurity kernel rpm spec file for EL6

I used to maintain a grsecurity kernel rpm repository, but haven’t kept it online due to lack of proper build infrastructure. The servers, the code, the effort in keeping everything working order – I admire what the CentOS guys have put together, and look forward to the possibility of them releasing their reimzul for everyone to use. Maybe one day I’ll do the repository thing again.

Anyway, I get asked occasionally about the rpms, if I still make them, and how they were made. So, in the absence of me pre-building the RPM files, here is my kernel-grsec rpm spec file that I used to build them. Hope you find it useful.

tpe-lkm is ready for a wider deployment

About a year ago, I posted about me coding a TPE module for distribution kernels. In that time I’ve added some features, fixed some bugs, and deployed it to all of my non-grsecurity systems. With the last known outstanding bug (that I know about) being fixed a little over two weeks ago (and tested) I’m excited to say that, you guessed it, tpe-lkm is ready for wider deployment.

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Repacking an RPM from files on the system

Have you ever had an RPM installed on the system that you needed installed on another system, but didn’t have the .rpm file for it? Or, have you wanted to make a .rpm file with just a minor change without having to completely rebuilt it? Or perhaps forge an RPM with some naughty scripts or binaries in it? 😉

Check out my rpm-repack script. Simply run it with the package name that’s installed on the system:

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nagios snmp check all disks plugin

Having to manage a wide array of servers with vastly different disk configurations, I found that things began to be very tedious with the nagios configuration file for disks checks. It seemed as if no two server disk configuration was the same, and coming up with a scheme to have different partitions be a consistent index number across systems was proving to be difficult.

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