donderdag 5 december 2013

Can SELinux be made simpler?

Disclaimer: this is just my opinion

This must be a trick question. There is no easy answer for this.

First we should define SELinux to be able to put the question into a context

SELinux has three components: The LSM-Based system in the kernel, the tools and libraries, and lastly security policy

We also need to determine what defines SELinux in compared to other LSM-Based systems in the kernel

The answer to the latter question is Flexibility and configurability. Thats what defines SELinux. It a main property of SELinux. There are other LSM-Based system with other properties for example SMAC (simple mandatory access control) That system is defined by simplicity (but needless to say it lacks flexibility/configurability, at least compared to SELinux)

It is easy to translate flexibility to complexity but the end result does not always have to be relatively complex

Another thing to consider are constraints, with that i mean that for example SELinux must be optional, additional. It must be an add-on to the existing Linux DAC framework

This prerequisite brings some more "complexity", There 3 more of those prerequisites (one of them is not optional for SELinux to work). To enforce mandatory integrity processes must be able to change type (role base access control).

The other two prerequisites are optional (must be able to compartmentalise, must be able to enforce confidentiality) (multi category security/multi level security)

Back to the question. We now have most considerations briefly explained.

I Believe The core of SELinux (the LSM-Based System) cannot be made simpler. It is already as simple as can be considering all the requirrments.
Can the tools and libraries make the experience simpler? Maybe a bit, but the main concepts and principles will still apply there is little one can do about that.

The last component is what most people experience: the security policy

So Lets look at the state of that. The policy can be build with the minimal set of requirements (e.g. only enforce integrity optionally/additionally e.g. by complementing traditional DAC)

So we already can exclude some complexity and we do. We have different policy models for different requirements. For example if you have confidentiality requirements, which adds complexity, then you need the mls policy model.

Lets look at a operating system: Fedora currently is a single distro that can basically considered general purpose. You can use it as a workstation, server, or your use case can be even more specific.
But a vendor does not know beforehand how you are going to use it, and so every scenario must be supported.

Here is the dilemma: security is never general. If you want to implement mandatory integrity/confidentiality in a flexible/configurable way by complementing traditional DAC on a general purpose system then you have a complex challenge on your hand which requires complex policy.

So compromises were made: Lets not enforce mandatory integrity on the whole system, but only a part of it. Its give and take. Fine now things are a bit simpler but its not cheap. Now user sessions by default are not contained. To me this is already a great compromise because it basically says, were leaving workstation scenarios out in the cold with regard to mandatory integrity in the user space

fortunately some level of mandatory integrity in the user space is still optionally available, but its a compromise and it does not get the attention that i think it deserves

So its all about compromises. We have some ability to make things "simpler" and we already apply it.

So how to make things (a bit) simpler and actually achieve security goals?

We could create "profiles". For example Fedora webs erver edition. is a profile for a web server. web servers have (relatively) specific properties. So that from a security perspective enables us to implement a relatively specific security policy for that profile. We just target the web server. This makes the policy "simpler"

Fedora Desktop edition has a policy that targets the user space.

Does this solve anything? Not really if you still end up focussing on specific cases. it might help a bit but its still a compromise. Unless of course you really commit to all the profules you defined.

There are more (less obvious) options but its all give and take, and its all with regard to the security policy implemented. The core of SELinux cannot be simplified ( with any significance) without SELinux losing its identity.

So what about setroubleshoot? That is a great success story when it comes to simplifying SELinux?! Not really. Its just a buffed audit2why with a lot of bloat. (no offence) Is still a program that cannot make security decisions for you. All it can do is parse. reference and make it easy to report issues. It does not know when to transition or not.

That is not because its a bad piece of software. its just that security policy is not something that is fixed so you cant hard-code solutions. and to put things into context and determine the security requirements and act on it requires a huge base of logic. Is it even worth trying to create that?

Think about it from a security perspective: do you easily trust a third party with security decisions that affect your lively hood? Do you trust some code to make security decisions for you?

And even if you do, youll miss out on the good still: configurability/flexibility.

Why not instead focus on learning the core principles/concepts, and enable people to implement mandatory integrity that is tailored to their specific requirement?

So how do you do that? CIL is a abstraction language/ compiler that aims to make this easier. Its is relatively simple and it can be used as a layer between a policy management program and the SElinux policy language. It makes things less pain full but still wont change the core principles and concepts.

What it does do is optimise. Optimization can, i guess, in some ways be translated to making things more pleasurable and there by perceivably simpler.

You ask me the question can SELinux be made simpler. my answer is no. but things can be improved and optimized. compromises can also be made

But it does not change anything to the core principles and concepts.

If you want (relatively) simple: look into Simple mandatory access control. You want "flexibility/configurability" embrace selinux

For example on the one hand we make things "simpler" by by default not targeting user sessions, But on the other hand we enable an optional security model that adds a layer of complexity to achieve compartmentalization.

Its all a matter of priorities

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