[PATCH v8 1/2] img/app: Create needed directories in early boot

[Demi Marie Obenour <demiobenour@gmail.com>]

This moves various calls to mkdir(1) to very early boot, before any
services are running.  This has two advantages:

1. These directories are guaranteed to exist.  Code can just assume that
   they are there without checking for them.

2. Malicious code running as an unprivileged user cannot create
   directories under /tmp before legitimate code has done so.

The following directories are created under /tmp:

- /tmp/.font-unix (used by obsolete X Font Server) is created with mode
  0000.
- The directories used by X11 are created with 1700 permissions:
  - /tmp/.X11-unix (X server)
  - /tmp/.ICE-unix (Inter-Client Exchange)
  - /tmp/.XIM-unix (X Input Methods)
- $XDG_RUNTIME_DIR (/run/user/0) is created with 0700 permissions, as
  expected by the XDG specification.

The copyright notice for directory creation is not kept because making
one directories with well-known names and permissions is not
copyrightable and the code has been rewritten.

Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
---
Changes since v6:

- Add missing S-o-b
- Add comments explaining why each directory needs to be created.
- Fix spelling errors in commit messages.

Changes since v5:

- Remove "directories" service in favor of creating the directories from
  rc.init.
---
 img/app/etc/s6-linux-init/scripts/rc.init  | 13 +++++++++++++
 img/app/etc/s6-rc/wayland-proxy-virtwl/run | 10 ----------
 2 files changed, 13 insertions(+), 10 deletions(-)

diff --git a/img/app/etc/s6-linux-init/scripts/rc.init b/img/app/etc/s6-linux-init/scripts/rc.init
index c5a59245ff3761e94acb974edde967806fb3b234..7744286d0282bb8e0cc40973c6a6eae4c9401630 100755
--- a/img/app/etc/s6-linux-init/scripts/rc.init
+++ b/img/app/etc/s6-linux-init/scripts/rc.init
@@ -1,10 +1,23 @@
 #!/bin/execlineb -P
 # SPDX-License-Identifier: EUPL-1.2+
 # SPDX-FileCopyrightText: 2020-2022 Alyssa Ross <hi@alyssa.is>
+# SPDX-FileCopyrightText: 2025 Demi Marie Obenour <demiobenour@gmail.com>
 
 if { s6-rc-init -c /etc/s6-rc /run/service }
 
 if { modprobe overlay }
 if { mount -a --mkdir }
 
+# X Font Server is obsolete
+if { mkdir -m 0000 /tmp/.font-unix }
+
+# /tmp/.X11-unix: X11 server
+# /tmp/.ICE-unix: X11 Inter-Client Exchange
+# /tmp/.XIM-unix: X11 input methods
+# Some documentation states sticky bit is required.
+if { mkdir -m 1700 /tmp/.X11-unix /tmp/.ICE-unix /tmp/.XIM-unix }
+
+# /run/user/0: "$XDG_RUNTIME_DIR"
+if { mkdir -m 0700 /run/user/0 }
+
 s6-rc change ok-all
diff --git a/img/app/etc/s6-rc/wayland-proxy-virtwl/run b/img/app/etc/s6-rc/wayland-proxy-virtwl/run
index 0715d912953c8a1d326059dfd37c29799fcbb053..c1e0e088c789ab8c5fde7e50c9f4b856fff0e477 100755
--- a/img/app/etc/s6-rc/wayland-proxy-virtwl/run
+++ b/img/app/etc/s6-rc/wayland-proxy-virtwl/run
@@ -1,16 +1,6 @@
 #!/bin/execlineb -P
 # SPDX-License-Identifier: EUPL-1.2+
 # SPDX-FileCopyrightText: 2023-2024 Alyssa Ross <hi@alyssa.is>
-#
-# Directory creation (if it's copyrightable):
-# SPDX-License-Identifier: MIT
-# SPDX-FileCopyrightText: 2022 Unikie
-
-foreground { mkdir /tmp/.X11-unix }
-foreground {
-  umask 077
-  mkdir /run/user/0
-}
 
 s6-ipcserver-socketbinder -B /run/user/0/wayland-0
 fdmove -c 3 0
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)