AppArmor How-To

A short guide to get you started on AppArmor

AppArmor is a linux security module that allows for path based mandatory access control. It’s easy to learn and very effective at both preventing and containing exploits. I suggest you make use of it.

This post is just a short crash course to get you set up and using apparmor.

Step 1:
We first need to install the apparmor-utils package.
sudo apt-get install apparmor-utils
Once it’s done installing you should be able to access these commands:
# aa-logprof
# aa-status
# aa-autodep
# aa-enforce
# aa-complain
Step 2:
Let’s create our first profile. I’ll use pidgin.
# aa-autodep pidgin
This will create the pidign profile in complain mode. Complain mode will audit violations but not stop them.

Step 3:
Close (if open) pidgin and then open it up again. And then close it. Then run the command:
# aa-logprof

At this point you’ll be greeted with some of the “complaints” that were logged. Review and allow what’s needed.

r: r is read access
w: w is write access
a: a is limited write access (append)*
k: k allows the ability to lock a file
m: m lets a file be loaded into memory
x: allows execution
ix: executes the file under the constraints of the profile (inherit)
ux**: executes the file outside of the profile (unconfined)
Px**: executes the file in its own profile, which you will have to define (profile)

*not to be confused with allow. a is the rule, allow is a command that applies it via logprof.

**Capital P or U means that the environment is sanitized before executing the code. You want to sanitize whenever possible.

Step 4:

To test the profile out run:

# aa-enforce /etc/apparmor.d/usr.bin.pidgin

if it isn’t working still set it back to complain:

# aa-complain /etc/apparmor.d/usr.bin.pidgin

The first few times I set up a profile I ended up with a super convoluted mess. It was terrible. I wiped it, started over and actually *thought* before I hit “allow” or “inherit” and in very little time I was able to create many profiles for my programs.
Profiles are stored in /etc/apparmor.d/<path.path.path> so for pidgin it’s /etc/apparmor.d/usr.bin.pidgin. You can manually edit the profiles with a text editor. This is really simple and I suggest you have a look at a few profiles before you start.

Tips:

1) Instead of aa-autodep you can try aa-genprof, which will try to build a partial profile for you.

2) Development profiles can be a great place to start. You can get them here:

https://launchpad.net/apparmor-profiles

3) Apparmor profiles can get complicated. Don’t bother trying to profile something like compiz, there’s no real point. A program like Pidgin or xchat is perfect though.

4) The “owner” tag is your friend. Sometimes you have to give a program really unruly access to your file system (/home/** rw). Using the “owner” tag means that (in the case of /home/** rw) the profiled program can only read/write to files that it has ownership of.

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About insanitybit

Novice programmer interested in computer security. I'll use this blog when I'm bored to post about things I find interesting in that field.

One response to “AppArmor How-To”

  1. Ms. Daisy says :

    Nice quick guide. You may have convinced me to get apparmor running on my systems!

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