I do see the Tor-Issue - a botnet or a well-supplied malicious actor could just flood it. And if you flip it - if you'd need agreement about the build output, it could also be poisoned with enough nodes to prevent releases for a critical security issue. I agree, I don't solve all supply chain issues in one comment :)
But that in turn could be helped with reputation. Maybe a node needs to supply 6 months of perfect builds - for testing as well - to become eligible. Which would be defeated by patience, but what isn't? It'd just have to be more annoying to breach the distributed build infrastructure than to plant a malicious developer.
This combination of reproducible, deterministic builds, tests across a number of probably-trustworthy sources is quite interesting, as it allows very heavy decentralization. I could just run an old laptop or two here to support. And then come compromise hundreds of these all across the world.
It really wouldn't. You don't even need a powerful build server since you can mirror whatever someone else built. You can also buy / hack nodes of existing trusted people.
I have yet to experience a straight shot install or build of anything in an air gapped environment. Always need to hack things to make it work.
That's not always the silver bullet you seem to think it is. Have you ever tried to build something like Chromium, Firefox, or LLVM yourself? It's not realistic to do that on a mid tier let alone low end device.
Even when you go to the trouble of getting a local build set up, more often than not the build system immediately attempts to download opaque binary blobs of uncertain provenance. Try building some common pieces of software in a network isolated environment and you will likely be surprised at how poorly it goes.
If projects actually took this stuff seriously then you'd be able to bootstrap from a sectorlisp and pure human readable source code without any binary blobs or network access involved. Instead we have the abomination that is npm.
https://buildd.debian.org/status/package.php?p=firefox-esr
See Bootstrappable Builds for starting from almost nothing, so far only GNU Guix and StageX have worked out how to start from the BB work to get a full distro. Should be fairly trivial for other distros too if they cared.
https://bootstrappable.org/ https://guix.gnu.org/blog/2023/the-full-source-bootstrap-bui... https://stagex.tools/
Most importantly you need to pay attention to RAM usage, if necessary reducing parallelism so that it doesn't need to swap.
Of course you can. You can also read the ToS before clicking accept, but who does that?
The build infrastructure is, of course, a juicy target: infect the artifact after building but before signing, and pwn millions of boxes before this is detected.
This is why bit-perfect reproducible builds are so important. OpenWRT in particular have that: https://openwrt.org/docs/guide-developer/security#reproducib...