ynetd: add nixos module

[haylinmoore]

Introduces a nixos module for setting up ynetd instances. Bear with me this is my first nixos module.

I'm not 100% sure about my way of modeling it with multiple instances. I firmly believe that however it is made should allow for multiple instances since it's more akin to NGINX with multiple virtual hosts, than a service that would just have one instance running per host-machine, I'm just not sure if this is the best way to model it.

It might also make sense to have a toggle to specify what user the systemd service will be running as (or maybe tighten it down to be a non-root user, but then give it all the privileges needed. For this case CAP_SETUID and CAP_SETGID come to mind, but for ynetd.hardened/ctf-ynetd it would also need the ability to manage cgroups and I don't know the proper permissions for that besides CAP_SYS_ADMIN which just basically becomes root. That being said I imagine most users of this where security is a concern (like CTFs where the aim is to pwn a binary) will do it inside of a nix container/vm anyways.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[toastal]

I don’t think this is the place/time to run the formatter on the all-test.nix file unfortunately.

[haylinmoore]

oops, I completely missed how much that formatted. I'll undo that in the morning !

[toastal]

Does this need to be root? Can a systemd user or whatever not be used?

[haylinmoore]

This is the bit I feel a little uneasy regarding, I have a little explanation in the second paragraph of my PR, like we could set it to a less powerful user, but then for cgroups I believe it would need CAP_SYS_ADMIN at which point it's basically root just under another name.

[haylinmoore]

I think if I go through and model more of the flags I can dynamically apply some of the CAP for the unhardened ynetd. I'll go through and see how this looks

[awwpotato]

avoid using with at the top of modules, per nix docs