Generally the code quality is considered good.
Oh wait, you were just trying to score cheap snark points, weren't you?
[1] - https://www.nsa.gov/ia/mitigation_guidance/security_configur...
https://wiki.debian.org/ReproducibleBuilds
(I gave a talk about this at CCC. The status quo is a reason why free software doesn't have some of the transparency benefits over proprietary software we might expect, if you fear some developer is attacking you or someone is attacking some developers' infrastructure.)
There are many thousands of people who have done the same thing, and this gives us a "web of trust". And if you don't want to trust anyone, you can always compile it yourself.
That's the difference: I have the freedom to learn and study anything and everything. It might not be likely, and it might not be convenient, but it is possible.
Of course, this doesn't do anything against a malicious install environment or a backdoored compiler, but it's a start.