Who controls glibc?

No it's not as simple as that. Depending on the nature of the change, you as maintainer are trusted to decide how long you'd like to wait for agreement and how many people you'd like to review the change before committing it. Every once in a while you might get it wrong but that's not the end because we can always discuss to gather consensus either way.

Again, I'm simplifying, please read the consensus wiki page (linked in the article) which is way more exhaustive.