| 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. |
| |
| A list of the active security modules can be found by reading |
| /sys/kernel/security/lsm. This is a comma separated list, and |
| will always include the capability module. The list reflects the |
| order in which checks are made. The capability module will always |
| be first, followed by any "minor" modules (e.g. Yama) and then |
| the one "major" module (e.g. SELinux) if there is one configured. |
| |
| Based on https://lkml.org/lkml/2007/10/26/215, |
| 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. |
