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.
People don't understand that the way a backdoor is usually implemented is not going to be obviously saying "backdoor_here", neither it will look like a some magic code loading a large string and unzipping it on the fly -- that's sus af. What you will see is some "play video" functionality that has a very subtle buffer overflow bug that's also not trivially triggerable.
This already happened with WhatsApp.