There's really no reason to believe in the provenance of any of the code in the Linux kernel. People mail around patchsets, claim they are "signed off by" someone, and they get patched into various trees and merged here and there, and eventually wind up in Linus's tree. It has all of the safety of email, which is to say none at all. Compared to code review practices at software companies, where diffs are reviewed and approved by identities authenticated and authorized by secure computer systems, the linux kernel system is a complete joke.