The NSA, the original primary developer of SELinux, released the first version to the open source development community under the GNU GPL on December 22, 2000.[6] The software was merged into the mainline Linux kernel 2.6.0-test3, released on 8 August 2003. Other significant contributors include Red Hat, Network Associates, Secure Computing Corporation, Tresys Technology, and Trusted Computer Solutions.
Only because they use Linux too and had to make it public as Linux is a public, open-source kernel
Not really. Do you know how many proprietary, company-specific extensions and modules there are of the Linux kernel out there?
Loads of companies choose not to contribute their stuff back upstream. I don’t know why the NSA did originally in the case of SELinux, but I would guess it had to do with transparency, national defense and not carrying the burden of a module / fork solo. They were also not the only contributors even early on, according to the Wikipedia page
Also, if I recall correctly, there was no other option for MAC back them (no AppArmor or Tomoyo).
Isn’t this GPL license violation? GPL clearly states that the license must be preserved