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SELinux Cookbook

By : Sven Vermeulen
Book Image

SELinux Cookbook

By: Sven Vermeulen

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SELinux Cookbook
Sven Vermeulen
Sep, 2014 | 240 pages
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Table of Contents (17 chapters)
SELinux Cookbook
SELinux Cookbook
Credits
Credits
About the Author
About the Author
About the Reviewers
About the Reviewers
www.PacktPub.com
www.PacktPub.com
Preface
Preface
Free Chapter
1
The SELinux Development Environment
The SELinux Development Environment
Introduction
Creating the development environment
Building a simple SELinux module
Calling refpolicy interfaces
Creating our own interface
Using the refpolicy naming convention
Distributing SELinux policy modules
2
Dealing with File Labels
Dealing with File Labels
Introduction
Defining file contexts through patterns
Using substitution definitions
Enhancing an SELinux policy with file transitions
Setting resource-sensitivity labels
Configuring sensitivity categories
3
Confining Web Applications
Confining Web Applications
Introduction
Listing conditional policy support
Enabling user directory support
Assigning web content types
Using different web server ports
Using custom content types
Creating a custom CGI domain
Setting up mod_selinux
Starting Apache with limited clearance
Mapping HTTP users to contexts
Using source address mapping to decide on contexts
Separating virtual hosts with mod_selinux
4
Creating a Desktop Application Policy
Creating a Desktop Application Policy
Introduction
Researching the application's logical design
Creating a skeleton policy
Setting context definitions
Defining application role interfaces
Testing and enhancing the policy
Ignoring permissions we don't need
Creating application resource interfaces
Adding conditional policy rules
Adding build-time policy decisions
5
Creating a Server Policy
Creating a Server Policy
Introduction
Understanding the service
Choosing resource types wisely
Differentiating policies based on use cases
Creating resource-access interfaces
Creating exec, run, and transition interfaces
Creating a stream-connect interface
Creating the administrative interface
6
Setting Up Separate Roles
Setting Up Separate Roles
Introduction
Managing SELinux users
Mapping Linux users to SELinux users
Running commands in a specified role with sudo
Running commands in a specified role with runcon
Switching roles
Creating a new role
Initial role based on entry
Defining role transitions
Looking into access privileges
7
Choosing the Confinement Level
Choosing the Confinement Level
Introduction
Finding common resources
Defining common helper domains
Documenting common privileges
Granting privileges to all clients
Creating a generic application domain
Building application-specific domains using templates
Using fine-grained application domain definitions
8
Debugging SELinux
Debugging SELinux
Introduction
Identifying whether SELinux is to blame
Analyzing SELINUX_ERR messages
Logging positive policy decisions
Looking through SELinux constraints
Ensuring an SELinux rule is never allowed
Using strace to clarify permission issues
Using strace against daemons
Auditing system behavior
9
Aligning SELinux with DAC
Aligning SELinux with DAC
Introduction
Assigning a different root location to regular services
Using a different root location for SELinux-aware applications
Sharing user content with file ACLs
Enabling polyinstantiated directories
Configuring capabilities instead of setuid binaries
Using group membership for role-based access
Backing up and restoring files
Governing application network access
10
Handling SELinux-aware Applications
Handling SELinux-aware Applications
Introduction
Controlling D-Bus message flows
Restricting service ownership
Understanding udev's SELinux integration
Using cron with SELinux
Checking the SELinux state programmatically
Querying SELinux userland configuration in C
Interrogating the SELinux subsystem code-wise
Running new processes in a new context
Reading the context of a resource
Index
Index

Creating a skeleton policy

With the logical setup now in place, we can draft a skeleton policy. This policy will be a translation from the logical setup we encountered to SELinux policy rules.

The entire policy is written in a myskype.te file. The final result of this set of recipes is also available through the download pack of this book as a reference.

How to do it…

We start with a base skeleton that we can enhance later. This skeleton is developed as follows:

  1. We start with the declaration of the various types. From the design, we can deduce four types:

    • skype_t as the main process domain

    • skype_exec_t as the label for the Skype executable(s)

    • skype_home_t for the user configuration files and directories of the skype_t domain

    • skype_tmpfs_t is needed for shared memory and the X11 interaction

    The code to deduce these four types is as follows:

    policy_module(myskype, 0.1)

attribute_role skype_roles;

type skype_t;
type skype_exec_t;
userdom_user_application_domain(skype_t, skype_exec_t)
role skype_roles...
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