1===========================
2Linux Security Module Usage
3===========================
4
5The Linux Security Module (LSM) framework provides a mechanism for
6various security checks to be hooked by new kernel extensions. The name
7"module" is a bit of a misnomer since these extensions are not actually
8loadable kernel modules. Instead, they are selectable at build-time via
9CONFIG_DEFAULT_SECURITY and can be overridden at boot-time via the
10``"security=..."`` kernel command line argument, in the case where multiple
11LSMs were built into a given kernel.
12
13The primary users of the LSM interface are Mandatory Access Control
14(MAC) extensions which provide a comprehensive security policy. Examples
15include SELinux, Smack, Tomoyo, and AppArmor. In addition to the larger
16MAC extensions, other extensions can be built using the LSM to provide
17specific changes to system operation when these tweaks are not available
18in the core functionality of Linux itself.
19
20The Linux capabilities modules will always be included. This may be
21followed by any number of "minor" modules and at most one "major" module.
22For more details on capabilities, see ``capabilities(7)`` in the Linux
23man-pages project.
24
25A list of the active security modules can be found by reading
26``/sys/kernel/security/lsm``. This is a comma separated list, and
27will always include the capability module. The list reflects the
28order in which checks are made. The capability module will always
29be first, followed by any "minor" modules (e.g. Yama) and then
30the one "major" module (e.g. SELinux) if there is one configured.
31
32Process attributes associated with "major" security modules should
33be accessed and maintained using the special files in ``/proc/.../attr``.
34A security module may maintain a module specific subdirectory there,
35named after the module. ``/proc/.../attr/smack`` is provided by the Smack
36security module and contains all its special files. The files directly
37in ``/proc/.../attr`` remain as legacy interfaces for modules that provide
38subdirectories.
39
40.. toctree::
41   :maxdepth: 1
42
43   apparmor
44   LoadPin
45   SELinux
46   Smack
47   tomoyo
48   Yama
49   SafeSetID
50