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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

Switching roles

When a role transition is needed for more than just a couple of commands, it is necessary to open a shell with the new role. This will ensure that the entire session is now running with the new role assigned to it. Every activity performed from within this session will then run with the target role.

How to do it…

Switching roles with sudo or newrole is done as follows:

  1. Switching a role can be done using sudo -i or sudo -s if allowed by the sudoers file. If the ROLE and TYPE attributes are set, then the target shell will have the proper context assigned:

    ~$ id -Z
dbadm_u:staff_r:staff_t:s0
~$ sudo -u postgres -i
Password: 
~$ id -Z
dbadm_u:dbadm_r:dbadm_t:s0

  2. Switching roles can also be done using newrole:

    ~$ newrole -r dbadm_r

How it works…

Getting a shell after switching roles is not all that different from executing commands. However, the SELinux policy might not allow running shells and regular binaries in the target domain. For instance, a user who is allowed the puppetca_t...

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