From e0f2f7f9eadadab6d464ea63ab4dda04fe075d75 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B8rn=20Forsman?= <bjorn.forsman@gmail.com>
Date: Tue, 12 Jul 2022 09:03:29 +0200
Subject: [PATCH] nixos/ddclient: don't leak password in process listings

...by using `replace-secret` instead of `sed` when injecting the
password into the ddclient config file. (Verified with `execsnoop`.)

Ref https://github.com/NixOS/nixpkgs/issues/156400.
---
 nixos/modules/services/networking/ddclient.nix | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/nixos/modules/services/networking/ddclient.nix b/nixos/modules/services/networking/ddclient.nix
index faee99b175eb..43a50af8f9b5 100644
--- a/nixos/modules/services/networking/ddclient.nix
+++ b/nixos/modules/services/networking/ddclient.nix
@@ -13,7 +13,7 @@ let
     foreground=YES
     use=${cfg.use}
     login=${cfg.username}
-    password=${lib.optionalString (cfg.protocol == "nsupdate") "/run/${RuntimeDirectory}/ddclient.key"}
+    password=${if cfg.protocol == "nsupdate" then "/run/${RuntimeDirectory}/ddclient.key" else "@password_placeholder@"}
     protocol=${cfg.protocol}
     ${lib.optionalString (cfg.script != "") "script=${cfg.script}"}
     ${lib.optionalString (cfg.server != "") "server=${cfg.server}"}
@@ -33,10 +33,9 @@ let
     ${lib.optionalString (cfg.configFile == null) (if (cfg.protocol == "nsupdate") then ''
       install ${cfg.passwordFile} /run/${RuntimeDirectory}/ddclient.key
     '' else if (cfg.passwordFile != null) then ''
-      password=$(printf "%q" "$(head -n 1 "${cfg.passwordFile}")")
-      sed -i "s|^password=$|password=$password|" /run/${RuntimeDirectory}/ddclient.conf
+      "${pkgs.replace-secret}/bin/replace-secret" "@password_placeholder@" "${cfg.passwordFile}" "/run/${RuntimeDirectory}/ddclient.conf"
     '' else ''
-      sed -i '/^password=$/d' /run/${RuntimeDirectory}/ddclient.conf
+      sed -i '/^password=@password_placeholder@$/d' /run/${RuntimeDirectory}/ddclient.conf
     '')}
   '';