From 6e6df72eb25ff1ace89e8c497fb164e57ff798f7 Mon Sep 17 00:00:00 2001
From: Peder Bergebakken Sundt <pbsds@hotmail.com>
Date: Sat, 12 Oct 2024 16:07:20 +0200
Subject: [PATCH] fix nixbld-remote

---
 hosts/known-hosts.toml   |  2 ++
 profiles/known-hosts.nix | 36 ++++++++++++++++++++++++++++--------
 2 files changed, 30 insertions(+), 8 deletions(-)

diff --git a/hosts/known-hosts.toml b/hosts/known-hosts.toml
index 8c454b2..ff04125 100644
--- a/hosts/known-hosts.toml
+++ b/hosts/known-hosts.toml
@@ -191,6 +191,8 @@ ssh.userPrivateKey = "/run/secrets/nix-community-builders-ssh-key"
 # ssh.listenPublicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIPIQCZc54poJ8vqawd8TraNryQeJnvH1eLpIDgbiqymM";
 # ssh.userPrivateKey = "/run/secrets/nixbuild-dot-net-ssh-key"
 
+# TODO: https://exozy.me/about
+
 
 ["clab01.idi.ntnu.no"] # gtx 4090
 # buildMachine.maxJobs = 1 # 24 threads 64GB
diff --git a/profiles/known-hosts.nix b/profiles/known-hosts.nix
index db65661..a0a7cf9 100644
--- a/profiles/known-hosts.nix
+++ b/profiles/known-hosts.nix
@@ -1,7 +1,4 @@
-{ config, lib, ... }:
-
-# TODO: make a remote-build user on nixos boxes, instead of giving access to pbsds
-# TODO: https://exozy.me/about
+{ config, lib, pkgs, ... }:
 
 let
   inherit (builtins)
@@ -14,6 +11,22 @@ let
     attrValues
     ;
 
+  # TODO: test ssh-ng
+  # https://discourse.nixos.org/t/wrapper-to-restrict-builder-access-through-ssh-worth-upstreaming/25834
+  nix-ssh-wrapper = pkgs.writeShellScript "nix-ssh-wrapper" ''
+    case $SSH_ORIGINAL_COMMAND in
+      "nix-daemon --stdio")
+        exec ${config.nix.package}/bin/nix-daemon --stdio
+        ;;
+      "nix-store --serve --write")
+        exec ${config.nix.package}/bin/nix-store --serve --write
+        ;;
+      *)
+        echo "Access only allowed for using the nix remote builder" 1>&2
+        exit
+    esac
+  '';
+
   known-hosts = let
     known-hosts' = lib.importTOML ../hosts/known-hosts.toml; # TODO: eww
   in
@@ -91,14 +104,21 @@ let
 
     })
     # in
-    (lib.mkIf ((thisHostIsBuilder || thisHostIsHopHost) && thatHostIsBuildee) {
+    (lib.mkIf ((thisHostIsBuilder || thisHostIsHopHost) && thatHostIsBuildee && !thatHost.isAlias) {
+      # TODO: ensure the user is "nixbld-remote"?
+      users.groups.${thisHost.ssh.listenUser} = { };
       users.users.${thisHost.ssh.listenUser} = {
         isSystemUser = lib.mkDefault (!config.users.users.${thisHost.ssh.listenUser}.isNormalUser);
-        openssh.authorizedKeys.keys = [ thatHost.ssh.userPublicKey ];
-        group = lib.mkOptionDefault "nogroup";
+        useDefaultShell = lib.mkDefault true;
+        openssh.authorizedKeys.keys = [
+          # https://man.archlinux.org/man/core/openssh/sshd.8.en#AUTHORIZED_KEYS_FILE_FORMAT
+          # TODO: lib.getExe
+          ''restrict,pty,command="${nix-ssh-wrapper}" ${thatHost.ssh.userPublicKey}''
+        ];
+        group = lib.mkOverride 1499 "${thisHost.ssh.listenUser}"; # mkOptionDefault - 1,
       };
     })
-    (lib.mkIf (thisHostIsBuilder && thatHostIsBuildee) {
+    (lib.mkIf (thisHostIsBuilder && thatHostIsBuildee && !thatHost.isAlias) {
       nix.settings.allowed-users = [ thisHost.ssh.listenUser ];
       nix.settings.trusted-users = [ thisHost.ssh.listenUser ];
     })