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SELinux


Wikipedia says:

  • Security-Enhanced Linux (SELinux) is an implementation of mandatory access control using Linux Security Modules (LSM) in the Linux kernel, based on the principle of least privilege. It is not a Linux distribution, but rather a set of modifications that can be applied to Unix-like operating systems, such as Linux and BSD.



What is SELinux?

  • A kernel level MAC (Mandatory Access Control) implementation for Linux

  • Originally commissioned and built by/for the NSA

  • A head-ache for the uninitiated

  • Very cool if done right

  • One of three well known MAC implementations

    • Trusted Solaris
    • Mainframe “Top Secret” (as opposed to RACF).


What is MAC?

  • Not an Apple product.

  • MAC: Mandatory Access Control

    • I own it, not you.
    • Ex: Directory “Secret” is owned by “Agent”. “Agent” does not have authority to grant access to others. Only the “Owner” does.
  • DAC: Discretionary Access Control

    • It’s yours, do what you will.
    • Same example: “Agent” can grant access to whomever she cares.
  • RBAC: Role Based Access Control

    • Depending on what your role is, maybe.
    • If “Agent” has the correct Role, she can, otherwise she can’t.


SELinux past tense.

  • Auditing and reporting support very limited and poorly integrated in SELinux.

  • One big ugly policy.

  • No decent interface for managing policies.

    • SLIDE (new tool)
  • Building policies was a flat file hack style.

  • Fresh files got no label. You had to comb the system to find and label them manually.

  • Poor scalability with SMP.



Recent improvements.

  • FC4 policy now has over 120 confined domains, updates in Hardened Gentoo, and support being mainstreamed into Debian.

  • Multi­Level Security support enhanced and mainstreamed.

  • Audit system enhanced and increasingly integrated.

  • RHEL5 entered into evaluation against CAPP (Controlled Access Protection Profile), LSPP (Labeled Security Protection Profile) , and RBAC (Role Based Access Control) with SELinux coverage.

  • Loadable policy modules, build and package policy modules separately.

  • Policy management API (libsemanage)

  • Improved support for policy development: Polgen, SEEdit, SLIDE, CDS Framework.

  • Atomic labeling of new files.

  • File security labels visible for all filesystems exactly as seen by SELinux.

  • Major improvements in SMP scalability.

  • Significant reduction in kernel memory use by policy.



Who Cares?



National Security Administration

  • Researchers in the Information Assurance Research Group of the National Security Agency (NSA) worked with Secure Computing Corporation (SCC) to develop a strong, flexible mandatory access control architecture based on Type Enforcement, a mechanism first developed for the LOCK system. The NSA and SCC developed two Mach-based prototypes of the architecture: DTMach and DTOS. The NSA and SCC then worked with the University of Utah's Flux research group to transfer the architecture to the Fluke research operating system. During this transfer, the architecture was enhanced to provide better support for dynamic security policies. This enhanced architecture was named Flask. The NSA has now integrated the Flask architecture into the Linux operating system to transfer the technology to a larger developer and user community.

  • - NSA Website



What’s the point?

  • Primarily for Government

    • Systems containing certain classifications of data are required to run under a MAC solution.
    • Required for/on many government contracts
  • Helps with audits

    • Though not necessary, a MAC solution can make many of today’s corporate audits MUCH easier.


Terminology:

  • Subject: A domain or process.

  • Object: A resource (file, directory, socket, etc.).

  • Types: A security attribute for files and other objects.

  • Roles: A way to define what “types” a user can use.

  • Identities: Like a username, but specific to SELinux.

  • Contexts: Using a type, role and identity is a “Context.”



How does this apply to “you”?

  • Let’s define “you” first:

    • Hobbiest/Enthusiest
    • Corporate systems guy
      • SysAdmin, Architect, etc.
    • Cracker/Malicious Type


Hobbiest/Enthusiest

  • How it applies

    • Well, it pretty well doesn’t.
    • At this point, the only folks directly impacted by SELinux are those who manage the boxes, audit the boxes, or try to hack the boxes that are running it.
  • Indirectly: you can sleep better



Corporate Systems Guy

  • A *REALLY* big pain.

    • That whole “minimum privileges” thing can suck when you get into the details.
  • A *REALLY* big help.

    • Compliance sucks. Being able to produce the type of reporting available with SELinux is great.
    • For systems running multiple clients or other entity types, think of it as a chroot jail that you can wrap around most anything.
  • An opportunity for training dollars -- “Hey boss, this stuff is a real trick!”



Cracker/Malicious Type

  • Today, extremely annoying.

  • A new (well, kind of anyway) puzzle to tinker with.

  • Not really a big deal unless they’re working against government systems. Very few corporate shops are running it today.

  • Still just another control model, just like DAC (Discretionary Access Control) or RBAC. Granted, a lot tighter than DAC, and has many similarities to RBAC.



Reference material:

  • The NSA Site:

  • http://www.nsa.gov/selinux/

  • The Wikipedia reference:

  • http://en.wikipedia.org/wiki/SELinux

  • Heh, a “symposium”:

  • http://selinux-symposium.org/




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