Shouldn't add XDG_SESSION_ID to dbus and systemd activation environment

[smcv]

Steps to reproduce the behaviour

• Install a Debian 11 system with gdm 3.38, GNOME 3.38, MATE 1.24.x and systemd
• Log in via ssh (for example assume systemd-logind assigns login session ID 2 for this)
• Log in to MATE, as the same user (for example assume systemd-logind assigns login session ID 4 for this)
• Log out from MATE
• Log in to GNOME, as the same user, without rebooting (for example assume systemd-logind assigns login session ID 6 for this)
• Lock the screen
• Try to unlock the screen

Expected behaviour

• When I log in to MATE, mate-session-manager uploads some environment variables to dbus-daemon --session via UpdateActivationEnvironment, and either mate-session-manager itself or dbus-daemon passes on those environment variables to systemd --user via SetEnvironment
• Because the systemd --user and dbus-daemon --session processes are shared between multiple login sessions, these environment variables should not include things that are highly specific to one login session, and in particular XDG_SEAT, XDG_SESSION_ID and XDG_VTNR
• Processes run by systemd --user, including most of GNOME, do not inherit XDG_SESSION_ID
• In particular, GNOME Shell does not inherit XDG_SESSION_ID, correctly determines its own systemd-logind session ID (in my example, session ID 6) by querying systemd-logind, and can lock and unlock correctly

Actual behaviour

• mate-session-manager sends all environment variables to systemd --user, including XDG_SESSION_ID=4 in my example
• Because the ssh login session keeps systemd --user alive, XDG_SESSION_ID=4 stays in the activation environment and is "leaked" into the subsequent GNOME session
• GNOME Shell inherits XDG_SESSION_ID=4 from systemd --user, even though that login session has already ended
• This makes GNOME Shell try to communicate with a logind session that no longer exists, breaking the ability to unlock the screen
  • I contributed a change to gnome-session to work around this, but I don't think it's really a GNOME bug

MATE general version

1.24.1 (not tested with 1.24.2, but none of the changes since 1.24.1 seem like they would affect this)

Package version

1.24.1-1

Linux Distribution

Debian 11

Link to bugreport of your Distribution (requirement)

• MATE bug: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=986100

---

linuxmint/cinnamon-session#141 (comment) lists some other related fixes in the ancestor project gnome-session. It would be a good idea to incorporate those into mate-session-manager at the same time.

Related bug reports:

• equivalent Cinnamon bug: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=986099, Cinnamon session shouldn’t upload XDG_SESSION_ID to systemd —user linuxmint/cinnamon-session#140, util: Blacklist some session-specific variables linuxmint/cinnamon-session#141
• original bug report against GNOME: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=973474
• workaround in GNOME: https://gitlab.gnome.org/GNOME/gnome-session/-/issues/86

[smcv]

A minimal solution is to apply the equivalent of GNOME/gnome-session@646b9bc to mate-session-manager, but all the commits mentioned in linuxmint/cinnamon-session#141 (comment) touch the same file and would be good fixes to have.

[L-U-T-i]

@smcv
based on your posts, I've made a test build of the latest git commit of mate-session-manager 1.25 with the following patches applied (in an order as listed here):

1 - Remove some session-specific environment variables from activation environment:
mate-session-manager-1.25-271-fix-1.patch.txt

2 - Fix environment variables patterns that are accepted:
mate-session-manager-1.25-271-fix-2.patch.txt

3 - Never try to autostart systemd:
mate-session-manager-1.25-271-fix-3.patch.txt

4 - Continue if a client exits during EndSession signal:
mate-session-manager-1.25-continue-if-a-client-exits-during-EndSession-signal.patch.txt

5 - Log a critical when our SIGTERM/SIGINT handler fails to log out:
mate-session-manager-1.25-log-a-critical-when-our-SIGTERM-SIGINT-handler-fails-to-log-out.patch.txt

6 - Stop dbus-daemon instead of restarting it:
mate-session-manager-1.25-stop-dbus-daemon-instead-of-restarting-it.patch.txt

7 - Warn about failures to update the environment:
mate-session-manager-1.25-warn-about-failures-to-update-the-environment.patch.txt

8 - Log variables excluded from environment upload:
mate-session-manager-1.25-log-variables-excluded-from-environment-upload.patch.txt

9 - Create the config directory with 0700:
mate-session-manager-1.25-create-the-config-directory-with-0700.patch.txt

10 - Fix typos in DBus documentation:
mate-session-manager-1.25-fix-typos-in-DBus-documentation.patch.txt

11 - Mention that session saving does not work on systemd:
mate-session-manager-1.25-mention-that-session-saving-does-not-work-on-systemd.patch.txt

12 - Find user's graphical session, not the current pid's session:
mate-session-manager-1.25-gsm-systemd-1.patch.txt

All those patches are ported from gnome-session git commits (and, modified as needed, in some rare cases).

There are more details about each patch within the patch file itself (copied from gnome-session commit descriptions).

I haven't noticed any issues by now (built, installed and launched without any issues...). As I've noticed sessions were not always properly saved / restored in my Mate Desktop (some rare cases, but still...), I've decided to give all this a try. I know some of those patches (a majority of them, in fact ;-)) are not related to this issue at all, but considering I went through all recent git commits of gnome-session, I've decided to simply pull anything that seemd to me appropriate for mate. I am publishing all that here, in case anyone is interested for any part of that...

[smcv]

I'm not a MATE developer or user, so someone from MATE should review those changes, but I think the general principle of sharing non-GNOME-specific fixes between GNOME and MATE is a good one.

[raveit65]

Pull request please.

[sunweaver]

@smcv @raveit65 @L-U-T-i I have already filed a PR for the minimal required changes here: #282