SELinux was originally a development project from the National Security Agency (NSA
) and others. It is an implementation of the Flask
operating system security architecture.The NSA integrated SELinux into the Linux kernel using the Linux Security Modules
) framework. SELinux motivated the creation of LSM
, at the suggestion of Linus Torvalds, who wanted a modular approach to security instead of just accepting SELinux into the kernel.
Originally, the SELinux implementation used persistent security IDs
) stored in an unused field of the ext2 inode. These numerical representations (i.e., non-human-readable) were mapped by SELinux to a security context label. Unfortunately, this required modifying each file system type to support PSID
s, so was not a scalable solution or one that would be supported upstream in the Linux kernel.
The next evolution of SELinux was as a loadable kernel module for the 2.4.<x>
series of Linux kernels. This module stored PSID
s in a normal file, and SELinux was able to support more file systems. This solution was not optimal for performance, and was inconsistent across platforms. Finally, the SELinux code was integrated upstream to the 2.6.x
kernel, which has full support for LSM
and has extended attributes
) in the ext3 file system. SELinux was moved to using xattrs
to store security context information. The xattr
namespace provides useful separation for multiple security modules existing on the same system.
Much of the work to get the kernel ready for upstream, as well as subsequent SELinux development, has been a joint effort between the NSA, Red Hat, and the community of SELinux developers.