xserver-nodm-init: improve XDG_RUNTIME_DIR fallback creation

This directory must have mode 0700, and should be under /run/user (as
recommended in the specification, and as weston-init does).

Also check the permissions if the directory already exists and fail
early if they're incorrect.

[ YOCTO #13878 ]

(From OE-Core rev: 5c98609bf7dfb05af722e30adb49731727df9a94)

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-graphics/x11-common/xserver-nodm-init/X11/Xsession.d/13xdgbasedirs.sh

@@ -1,13 +1,19 @@
 # Minimal/stub implementation of the XDG Base Directory specification.
 # http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
-#
-# Wayland needs XDG_RUNTIME_DIR, so set it to /tmp.  This isn't compliant with
-# the specification (wrong mode, wrong owner) but it's mostly sufficient.
-#
-# In the ideal case where SystemD is booting and userspace is initiated by a
-# SystemD user session this will have been set already, so don't overwrite it.
 
+# If the runtime directory hasn't been set already (for example by systemd,
+# elogind, or pam) create a directory in TMPDIR.
 if [ -z "$XDG_RUNTIME_DIR" ]; then
-    XDG_RUNTIME_DIR="/tmp"
+    XDG_RUNTIME_DIR=/run/user/$(id -u)
     export XDG_RUNTIME_DIR
 fi
+
+if [ -d "$XDG_RUNTIME_DIR" ]; then
+    # If the directory exists, check the permissions and ownership
+    if [ "$(stat -c %u-%a "$XDG_RUNTIME_DIR")" != "$(id -u)-700" ]; then
+        echo "ERROR: $XDG_RUNTIME_DIR has incorrect permissions"
+        exit 1
+    fi
+else
+    mkdir --mode 0700 --parents "${XDG_RUNTIME_DIR}"
+fi