From 5fbe320b9173b1ef0725a79548f34f967ad16130 Mon Sep 17 00:00:00 2001
From: tv <tv@krebsco.de>
Date: Fri, 19 Apr 2019 16:32:00 +0200
Subject: krebs.shadow: init

---
 krebs/3modules/default.nix |  1 +
 krebs/3modules/shadow.nix  | 79 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+)
 create mode 100644 krebs/3modules/shadow.nix

diff --git a/krebs/3modules/default.nix b/krebs/3modules/default.nix
index 4d40f385..fddb6a31 100644
--- a/krebs/3modules/default.nix
+++ b/krebs/3modules/default.nix
@@ -49,6 +49,7 @@ let
       ./rtorrent.nix
       ./secret.nix
       ./setuid.nix
+      ./shadow.nix
       ./syncthing.nix
       ./tinc.nix
       ./tinc_graphs.nix
diff --git a/krebs/3modules/shadow.nix b/krebs/3modules/shadow.nix
new file mode 100644
index 00000000..cff66492
--- /dev/null
+++ b/krebs/3modules/shadow.nix
@@ -0,0 +1,79 @@
+with import <stockholm/lib>;
+{ config, pkgs, ... }: let
+
+  cfg = config.krebs.shadow;
+
+  mergeShadowsJq = pkgs.writeJq "merge-shadows.jq" ''
+    def fields_3_to_9: ["1", "", "", "", "", "", ""];
+
+    def read_value:
+      split(":") |
+      if length == 9 then
+        if .[2:] == fields_3_to_9 then
+          .
+        else
+          error("unrecognized field contents")
+        end
+      elif length == 2 then
+        if .[1] | test("^\\$6\\$") then
+          . + fields_3_to_9
+        else
+          error("unrecognized hashed password")
+        end
+      else
+        error("unexpected field count: expected 9 or 2, got \(length)")
+      end;
+
+    def write_value:
+      join(":");
+
+    split("\n") |
+    map(select(length > 0) | read_value) |
+
+    reverse |
+    unique_by(.[0]) |
+    map(write_value) |
+    sort |
+
+    join("\n")
+  '';
+
+in {
+
+  options.krebs.shadow = {
+    enable = mkEnableOption "krebs.shadow" // {
+      default = cfg.overridesFile != null;
+    };
+    overridesFile = mkOption {
+      apply = x: if typeOf x == "path" then toString x else x;
+      default = null;
+      description = ''
+        Path to a file containing additional shadow entries, used for adding
+        encrypted passwords  which should not be placed into the Nix store.
+
+        The overrides file may contain either regular shadow(5) entries like:
+
+        <code>&lt;login-name&gt;:&lt;hashed-password&gt;:1::::::</code>
+
+        Or shortened entries only containing login name and password like:
+
+        <code>&lt;login-name&gt;:&lt;hashed-password&gt</code>
+      '';
+      type = types.nullOr (types.either types.path types.absolute-pathname);
+    };
+  };
+
+  config = let
+  in mkIf cfg.enable {
+    system.activationScripts.users-tv = stringAfter [ "users" ] /* sh */ ''
+      (
+        set -efu
+        umask 77
+        ${pkgs.jq}/bin/jq -Rrs -f ${mergeShadowsJq} \
+            /etc/shadow ${cfg.overridesFile} > /etc/shadow~
+        ${pkgs.coreutils}/bin/mv /etc/shadow /etc/shadow-
+        ${pkgs.coreutils}/bin/mv /etc/shadow~ /etc/shadow
+      )
+    '';
+  };
+}
-- 
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