Documentation: clarify the purpose of LSMs

00-INDEX

	- this file.

LSM.txt

	- description of the Linux Security Module framework.

SELinux.txt

	- how to get started with the SELinux security enhancement.

Smack.txt

Linux Security Module framework

-------------------------------

The Linux Security Module (LSM) framework provides a mechanism for

various security checks to be hooked by new kernel extensions. The name

"module" is a bit of a misnomer since these extensions are not actually

loadable kernel modules. Instead, they are selectable at build-time via

CONFIG_DEFAULT_SECURITY and can be overridden at boot-time via the

"security=..." kernel command line argument, in the case where multiple

LSMs were built into a given kernel.

The primary users of the LSM interface are Mandatory Access Control

(MAC) extensions which provide a comprehensive security policy. Examples

include SELinux, Smack, Tomoyo, and AppArmor. In addition to the larger

MAC extensions, other extensions can be built using the LSM to provide

specific changes to system operation when these tweaks are not available

in the core functionality of Linux itself.

Without a specific LSM built into the kernel, the default LSM will be the

Linux capabilities system. Most LSMs choose to extend the capabilities

system, building their checks on top of the defined capability hooks.

For more details on capabilities, see capabilities(7) in the Linux

man-pages project.

Based on http://kerneltrap.org/Linux/Documenting_Security_Module_Intent,

a new LSM is accepted into the kernel when its intent (a description of

what it tries to protect against and in what cases one would expect to

use it) has been appropriately documented in Documentation/security/.

This allows an LSM's code to be easily compared to its goals, and so

that end users and distros can make a more informed decision about which

LSMs suit their requirements.

For extensive documentation on the available LSM hook interfaces, please

see include/linux/security.h.

 (5) LSM

     The Linux Security Module allows extra controls to be placed over the

     operations that a task may do.  Currently Linux supports two main

     alternate LSM options: SELinux and Smack.

     operations that a task may do.  Currently Linux supports several LSM

     options.

     Both work by labelling the objects in a system and then applying sets of

     Some work by labelling the objects in a system and then applying sets of

     rules (policies) that say what operations a task with one label may do to

     an object with another label.