Keyring isn't suid on nixos

Hi, @SebTM. Thank you for building that module, as it got me over a significant hurdle in just approaching this problem. I've pulled your branch and am able to reproduce this on my machine, too.

Nothing is wrong with your module or the derivation (that I can see, so far, if we make progress we may find more problems...). Our executable verification process figures out the exact file path of the running process and checks the permissions on the file itself. I can see now where and why we're failing, and it looks like we didn't consider the possibility that write permission would be globally disabled.

I'm getting a new build and will try it out.