From 57b5ead0d007f040ca20cdb595a540a0ccc1a3cb Mon Sep 17 00:00:00 2001
From: Franklin-Qi <yusq77@gmail.com>
Date: Sat, 10 Oct 2026 17:06:08 +0800
Subject: [PATCH] lightdm-session: do not block login on profile stderr

Restore a distro-neutral session wrapper under data/ without the old
modal config-error dialog, so profile stderr is logged only and installing
zenity no longer stalls session start. Add a regression test.

Fixes #482
---
 data/Makefile.am                  |   3 +
 data/lightdm-session              | 124 ++++++++++++++++++++++++++++++
 tests/Makefile.am                 |   1 +
 tests/test-lightdm-session-stderr |  91 ++++++++++++++++++++++
 4 files changed, 219 insertions(+)
 create mode 100755 data/lightdm-session
 create mode 100755 tests/test-lightdm-session-stderr

diff --git a/data/Makefile.am b/data/Makefile.am
index 7f7b4a3fb..ffc3dce75 100644
--- a/data/Makefile.am
+++ b/data/Makefile.am
@@ -4,6 +4,9 @@ dist_init_DATA = init/lightdm.conf
 confdir = $(sysconfdir)/lightdm
 dist_conf_DATA = lightdm.conf users.conf keys.conf
 
+# Default session-wrapper (see Seat:* session-wrapper / src/lightdm.c).
+dist_sbin_SCRIPTS = lightdm-session
+
 dbusconfdir = $(datadir)/dbus-1/system.d
 dist_dbusconf_DATA = org.freedesktop.DisplayManager.conf
 
diff --git a/data/lightdm-session b/data/lightdm-session
new file mode 100755
index 000000000..1dc32edb1
--- /dev/null
+++ b/data/lightdm-session
@@ -0,0 +1,124 @@
+#!/bin/bash
+#
+# LightDM wrapper to run around X sessions.
+#
+# Profile stderr is logged (typically into ~/.xsession-errors) but must not
+# block session startup with a modal warning dialog. Non-empty stderr is not a
+# reliable signal of fatal profile syntax errors (see issue #482).
+
+echo "Running X session wrapper"
+
+message () {
+  # pretty-print messages of arbitrary length; use xmessage if it
+  # is available and $DISPLAY is set
+  MESSAGE="$PROGNAME: $*"
+  echo "$MESSAGE" | fold -s -w ${COLUMNS:-80} >&2
+  if [ -n "$DISPLAY" ] && which xmessage > /dev/null 2>&1; then
+    echo "$MESSAGE" | fold -s -w ${COLUMNS:-80} | xmessage -center -file -
+  fi
+}
+
+errormsg () {
+  # exit script with error
+  message "$*"
+  exit 1
+}
+
+# temporary storage of error messages
+ERR=$(mktemp --tmpdir config-err-XXXXXX)
+trap 'rm -f "$ERR"' EXIT
+
+source_with_error_check () {
+    CONFIG_FILE="$1"
+    echo "Loading $CONFIG_FILE"
+    # Unset BASH_VERSION while sourcing so ~/.profile does not pull in bashrc.
+    BASH_VERSION= . "$CONFIG_FILE" 2>"$ERR"
+    # Keep stderr from profiles in the session log; do not present a blocking
+    # GUI dialog - stderr is not a reliable indicator of fatal syntax errors.
+    if [ -s "$ERR" ]; then
+        cat "$ERR" >&2
+    fi
+    truncate -s 0 "$ERR"
+}
+
+# Load profile
+for file in "/etc/profile" "$HOME/.profile" "/etc/xprofile" "$HOME/.xprofile"; do
+    if [ -f "$file" ]; then
+        source_with_error_check "$file"
+    fi
+done
+
+# Load resources
+if type xrdb >/dev/null 2>&1; then
+    xresourcedir="/etc/X11/Xresources"
+    if [ -d "$xresourcedir" ]; then
+        for file in $xresourcedir/*; do
+            echo "Loading resource: $file"
+            xrdb -merge "$file"
+        done
+    fi
+    xresourcefile="$HOME/.Xresources"
+    if [ -f "$xresourcefile" ]; then
+        echo "Loading resource: $xresourcefile"
+        xrdb -merge "$xresourcefile"
+    fi
+fi
+
+# Load keymaps
+if type setxkbmap >/dev/null 2>&1; then
+    for file in "/etc/X11/Xkbmap" "$HOME/.Xkbmap"; do
+        if [ -f "$file" ]; then
+            echo "Loading keymap: $file"
+            setxkbmap `cat "$file"`
+            XKB_IN_USE=yes
+        fi
+    done
+fi
+
+# Load xmodmap if not using XKB
+if type xmodmap >/dev/null 2>&1; then
+    if [ -z "$XKB_IN_USE" ]; then
+        for file in "/etc/X11/Xmodmap" "$HOME/.Xmodmap"; do
+            if [ -f "$file" ]; then
+               echo "Loading modmap: $file"
+               xmodmap "$file"
+            fi
+        done
+    fi
+fi
+
+unset XKB_IN_USE
+
+# Run all system xinitrc shell scripts.
+xinitdir="/etc/X11/xinit/xinitrc.d"
+if [ -d "$xinitdir" ]; then
+    for script in $xinitdir/*; do
+        echo "Loading xinit script $script"
+        if [ -x "$script" -a ! -d "$script" ]; then
+            . "$script"
+        fi
+    done
+fi
+
+# Load Xsession scripts
+# OPTIONFILE, USERXSESSION, USERXSESSIONRC and ALTUSERXSESSION are required
+# by the scripts to work
+xsessionddir="/etc/X11/Xsession.d"
+OPTIONFILE=/etc/X11/Xsession.options
+USERXSESSION=$HOME/.xsession
+USERXSESSIONRC=$HOME/.xsessionrc
+ALTUSERXSESSION=$HOME/.Xsession
+
+if [ -d "$xsessionddir" ]; then
+    for i in `ls $xsessionddir`; do
+        script="$xsessionddir/$i"
+        echo "Loading X session script $script"
+        if [ -r "$script"  -a -f "$script" ] && expr "$i" : '^[[:alnum:]_-]\+$' > /dev/null; then
+            . "$script"
+        fi
+    done
+fi
+
+echo "X session wrapper complete, running session $@"
+
+exec $@
diff --git a/tests/Makefile.am b/tests/Makefile.am
index fc85348e0..dff3db82e 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -70,6 +70,7 @@ TESTS = \
 	test-session-stderr \
 	test-session-stderr-multi-write \
 	test-session-stderr-backup \
+	test-lightdm-session-stderr \
 	test-xauthority \
 	test-corrupt-xauthority \
 	test-system-xauthority \
diff --git a/tests/test-lightdm-session-stderr b/tests/test-lightdm-session-stderr
new file mode 100755
index 000000000..8b029240e
--- /dev/null
+++ b/tests/test-lightdm-session-stderr
@@ -0,0 +1,91 @@
+#!/bin/sh
+# Regression test for https://github.com/ubuntu/lightdm/issues/482
+#
+# Profile scripts often write non-fatal messages to stderr. The session wrapper
+# must log that output without invoking a blocking zenity/kdialog warning.
+
+set -eu
+
+if [ -n "${srcdir:-}" ]; then
+    ROOT="${srcdir}/.."
+else
+    ROOT=$(CDPATH= cd -- "$(dirname "$0")/.." && pwd)
+fi
+WRAPPER="${ROOT}/data/lightdm-session"
+
+if [ ! -f "$WRAPPER" ]; then
+    echo "lightdm-session not found at $WRAPPER" >&2
+    exit 1
+fi
+
+# Guard: shipped wrapper must not invoke the old blocking dialog helpers.
+if grep -E '(^|[[:space:]])(\.|source)[[:space:]]+/usr/lib/lightdm/config-error-dialog\.sh|(^|[[:space:]])(zenity|kdialog)([[:space:]]|$)' "$WRAPPER" >/dev/null; then
+    echo "data/lightdm-session must not invoke config-error-dialog.sh, zenity, or kdialog" >&2
+    exit 1
+fi
+
+TMP=$(mktemp -d)
+trap 'rm -rf "$TMP"' EXIT
+
+export HOME="${TMP}/home"
+mkdir -p "$HOME" "${TMP}/bin"
+
+cat > "${HOME}/.profile" <<'EOF'
+echo "harmless profile noise" >&2
+EOF
+
+cat > "${TMP}/bin/zenity" <<EOF
+#!/bin/sh
+echo "zenity must not be invoked during session start" >&2
+echo called > "${TMP}/dialog-called"
+exit 1
+EOF
+cat > "${TMP}/bin/kdialog" <<EOF
+#!/bin/sh
+echo "kdialog must not be invoked during session start" >&2
+echo called > "${TMP}/dialog-called"
+exit 1
+EOF
+chmod +x "${TMP}/bin/zenity" "${TMP}/bin/kdialog"
+
+for cmd in xrdb setxkbmap xmodmap; do
+    cat > "${TMP}/bin/${cmd}" <<'EOF'
+#!/bin/sh
+exit 0
+EOF
+    chmod +x "${TMP}/bin/${cmd}"
+done
+
+cat > "${TMP}/bin/test-session" <<EOF
+#!/bin/sh
+touch "${TMP}/session-ran"
+EOF
+chmod +x "${TMP}/bin/test-session"
+
+export PATH="${TMP}/bin:/usr/bin:/bin"
+
+# Capture wrapper stderr (includes forwarded profile noise).
+if ! "$WRAPPER" "${TMP}/bin/test-session" >"${TMP}/wrapper-out" 2>"${TMP}/wrapper-err"; then
+    echo "lightdm-session exited non-zero" >&2
+    cat "${TMP}/wrapper-err" >&2
+    exit 1
+fi
+
+if [ -f "${TMP}/dialog-called" ]; then
+    echo "blocking dialog helper was invoked" >&2
+    exit 1
+fi
+
+if [ ! -f "${TMP}/session-ran" ]; then
+    echo "session command was not executed" >&2
+    cat "${TMP}/wrapper-err" >&2
+    exit 1
+fi
+
+if ! grep -F "harmless profile noise" "${TMP}/wrapper-err" >/dev/null; then
+    echo "profile stderr was not forwarded to the session log stream" >&2
+    cat "${TMP}/wrapper-err" >&2
+    exit 1
+fi
+
+exit 0