Share Next Entry
Linux fragmentation - a view from the Security community
Some History
I have lived the Unix wars over the past 20 years. I worked on Project
Athena back at Digital Equipment (DEC) in the late 1980's and remember
all the effort that it took to make it work on multiple UNIX versions.

We had the best technology at the time. MIT and DEC had awesome
technology including instant messaging (Zephyr), security (Kerberos),
distributed management (Moira), secure file systems with Kerberized NFS
and AFS, shared name service via DNS and Hesiod, and a network windowing
system (X). You could walk up to any machine and log in and have the
same environment. We had single sign-on. We had universities working on
the product. It was a perfect system. But then we decided it need to run
on multiple different Unixes. We spent untold dollars making it work.
The problem was instead of improving the overall product, we spent all
of our time dealing with differences between the platforms. During this
time Microsoft was developing NT group-ware products and ended up
blowing us out of the water. The Unix wars had destroyed a great

Linux consistency refocuses Unix developers
After a few years of working on Microsoft platforms for managing
security infrastructure on Unix and Non-Unix platforms, I came to Linux.
Linux seemed to have corrected the problems of the UNIX wars. It was
community based, all vendors shared the same code and worked together to
build a common platform. Sure, there were multiple competing layered
products, but almost all could run on all the different distributions.
Third party vendors could fairly easily build to a single API and it
worked on everyone's Linux.

Three years ago, I was asked to work on the SELinux Team at Red Hat to
bring Mandatory Access Control to a mainstream operating system (OS).
MAC had been attempted before but had always failed or became a one-off
OS. OS vendors would ship the primary OS and then a "Trusted" version.
This "Trusted" version would quickly become out of date as the main
development efforts would always go into the primary OS and eventually
be ported to the "Trusted" version.

With SELinux we decided we could do both at the same time, using the
Open Source method, we could get multiple companies, and customers
working on it. We had some stumbles along the way, but through the use
of the Fedora Core collaborative development process we came up with a
single OS that uses MAC and handles everything from your laptop to a the
highest levels of security specified by government.

Today we have great technology. We have many companies and government
organizations collaboratively working on SELinux together, including Red
Hat, IBM, HP, NSA, DOD, Tresys, Trusted Computing Systems. We have a
significant open source community built around SELinux, colleges and
universities contributing and doing experiments with it. We have
multiple distributions shipping with SELinux including Fedora Core
(2,3,4 and soon 5), Red Hat Enterprise Linux 4, Gentoo, Debian, Ubuntu,
Suse and Slackware.

Security Deja Vu
Everything seems to be going great, but ... Novell, who last year
claimed to be the first Linux distribution to ship with SELinux
technology, suddenly announced that they are dropping support for it. To
replace it, they bought a product called AppArmor and are now asking
third party developers to use it instead of SELinux. Is this the
beginning of the Unix wars all over again?

Not only is AppArmor divergent from upstream/community, but it is also not
suitable as a real alternative to SELinux, because it lacks the flexibility
and scalability of SELinux to address the full range of security concerns,
and its limitations are not just in implementation but architectural.

Novell claims that AppArmor is easier to use for third parties. But now
users and developers have to choose one or the other mechanism for
providing MAC, and ignore the other platform's security mechanism. Or do
twice as much work, to support both. Think back to the Project Athena
example. Is this easier? Couldn't Novell have spent their money on
making SELinux easier to use? No, Novel chooses to split the user and
developer community. I am not sure what their goals are, but I feel this
hurts Linux and the open source movement. The community has now gotten
SELinux to the point where "easier" is coming, but built upon a solid

My fear now is that the Linux OS community has given application
developers an excuse to support neither security infrastructure, because
supporting either of them would prevent their product from running in
the other environment. So, for a developer, supporting neither SELinux
or AppArmor is the cheapest alternative, and maximizes the potential
customer base.

Instead of leveraging collaborative open source development to make
Linux the most secure operating system in the world, the now fragmented
Linux security community will be doing battle over who has the prettier
GUI. And the ISV community will ignore us.

The best outcome would be to have Novell work with the SELinux/open source
community to bring the benefits of AppArmor to the architecture/infrastucture
that is SELinux. This collaboration would benefit the entire Linux community.

  • 1

Re: Comments

Our goal is to give administrators choices of how they want to run their system, without forcing them to write policies.

This works only for basic applications and environments. It obviously does not provide room for much customization. That said, I think Selinux is great once administrators can write their own policies. As has been said before this leads back to the discussion on documentation and tutorials; the Selinux project simply needs more of it. Or at the very least a visual tool which allows you to see appropriate context of changes made or programs added to policy and how they affect other packages. Or maybe using a macro for something would be bad in some form or combination etc etc.

Interestingly enough I came across this thread, while trying to figure out if Selinux was included in RHEL v3. I came across apparmor yesterday which from what I can tell is just Immunix. The main difference between the two? Documentation. The guide for lets say RHEL V4 and AppArmor are worlds apart.

You get to Chapter 8 in the RHEL V4 guide and what?

Presenting a comprehensive guide to writing policy is not within the scope for this book. For more information on writing policy, refer to the resources in Chapter 9 References.

You click on the HOWTO on writing Policy, learn about attributes, users, te's, etc etc and then you think you're gonna get some good answers you get:

We'll now get in to the fun part of actually editing SE Linux policy. This takes a fair bit of practise. The best thing to do is just play around with it all. It can be quite a challenge to get started with as a lot of stuff isn't documented and you'll most likely take the trial-and-error approach. Make sure you look at other policies already written in /etc/selinux/domains/program/ and the corresponding file_contexts file in /etc/selinux/file_contexts/program/

Considering that a major part of Selinux is enforcing policy. You can't expect someone to place all their security in the fact that others have written policy for programs. Not only that but what about ones own program which Redhat hasn't written policy for? Also, considering that Selinux the actual project is being built on a Fedora machine with core system packages being patched and modified, acquiring the patches for fedora first become a pain. Binding lets say Novell to Fedora, there is much involved in that alone. I say after going through it all myself, its a steep hill and alot of time involved in even setting it up. Then understanding how to write policy? Thats even more time, since there really is no documentation its just all trial and error.

This is why I suspect most distros provide Selinux support in the kernel/userland and just stop there. It ships, selinux=0.

Redhat just needs to provide proper documentation on writing policy. Otherwise the lazies will indeed choose AppArmor. I can't speak on the technical merits of it mind you but it does look like the easy way out. I suspect the reason everyone does Selinux=0 is because no one understands it and no one understands it because there is no good howto, no good documentation and seemingly no one wants to write any.

Anyway, yeah.. rhelv3.. no selinux.. so now my selinux skills go back in the closet.

Christopher Warner

Re: Comments

Your concerns are legit, but there is quite a bit of work in progress to deal with them, including the reference policy (, a policy IDE (should be released soon, being presented at the SELinux Symposium), and a book on policy writing that is in progress.

  • 1

Log in