Unless you want to tell me that the Android kernel is the first OS kernel without bugs, it takes at the very least one bug to be left intentionally unfixed and shared with the feds to introduce a backdoor. I wouldn't consider it infeasible with how large the android kernel is, and how high a barrier of entry kernel dev is. If the bug is found, just move to the next one. Normally I wouldn't be so paranoid, but this is Google we're dealing with, on one of, if not the most popular kernels on the planet.