Android 4.3 and below do not use Security-Enhanced Linux (SELinux) for mandatory access control, which means that a process with root access can gain access to the kernel.
android-developers.googleblog.com/2008/09/announcing-android-10-sdk-release-1.html
googleblog.blogspot.com/2013/10/android-for-all-and-new-nexus-5.html
source.android.com/security/selinux