Description of problem:

When a ssh connection is made with X11 forwarding, there is a background task (dbus-kill-process-with-session) which is started and it will kill the dbus-daemon when the ssh connection is over.
This background task while check if the session where the ssh connection was started still exit. If not, it will kill the associated dbus-daemon.

It's working fine up to the usage of the ssh option ControlMaster.
With it, all the ssh connections will share the same session.
That means a new dbus-daemon is created each time a ssh connection is made and it will not be necessary killed when the ssh connection exit.
The dbus-daemon(s) will be killed only when exiting the *last* ssh connection, and therefore terminating the session.

The typical issue is when a client start/close many ssh connections against a server, therefore there are 'zombie dbus daemons' which are still running up the moment when the client close *all* its ssh connections.



Version-Release number of selected component (if applicable):

The backgroup task /usr/libexec/dbus-1/dbus-kill-process-with-session is provided by :
dbus-x11.x86_64 1:1.12.8-23.el8_7.1



How reproducible:

Always



Steps to Reproduce:

1. Install RHEL8.7
[root@bml-el8 ~]# uname -r
4.18.0-425.13.1.el8_7.x86_64

2. Install some "X11 related" packages
[root@bml-el8 ~]# yum install -y gnome-terminal xorg-x11-xauth
...

3. From a client machine with the following ssh option, connect a first time to the server
client-pts1> ssh root@bml-el8 -G | egrep -i 'ForwardX11|ControlMaster'
controlmaster auto
forwardx11 yes
forwardx11trusted yes
forwardx11timeout 1200

4. From the same client, connect to the server with a second term to the server and exit
client-pts2> ssh root@bml-el8 ':'



Actual results:

[root@bml-el8 ~]# who
root     pts/0        Apr 24 12:30 (<IP>)
[root@bml-el8 ~]# loginctl session-status
7 - root (0)
           Since: Mon 2023-04-24 12:30:38 CEST; 23s ago
          Leader: 15664 (sshd)
             TTY: pts/0
          Remote: <IP>
         Service: sshd; type tty; class user
           State: active
            Unit: session-7.scope
                  ├─15664 sshd: root [priv]
                  ├─15667 sshd: root@pts/0
                  ├─15668 -bash
                  ├─15693 /usr/bin/dbus-daemon --syslog --fork --print-pid 7 --print-address 9 --session
                  ├─15696 /bin/bash /usr/libexec/dbus-1/dbus-kill-process-with-session 15693
                  ├─15701 gio monitor -f /run/systemd/sessions/7 /tmp/dbus-session-monitor.sTnGKW
                  ├─15730 /usr/bin/dbus-daemon --syslog --fork --print-pid 7 --print-address 9 --session
                  ├─15733 /bin/bash /usr/libexec/dbus-1/dbus-kill-process-with-session 15730
                  ├─15738 gio monitor -f /run/systemd/sessions/7 /tmp/dbus-session-monitor.Xrrn2w
                  ├─15748 loginctl session-status
                  └─15749 less



Expected results:
[root@bml-el8 ~]# who
root     pts/0        Apr 24 12:30 (<IP>)
[root@bml-el8 ~]# loginctl session-status
7 - root (0)
           Since: Mon 2023-04-24 12:30:38 CEST; 23s ago
          Leader: 15664 (sshd)
             TTY: pts/0
          Remote: <IP>
         Service: sshd; type tty; class user
           State: active
            Unit: session-7.scope
                  ├─15664 sshd: root [priv]
                  ├─15667 sshd: root@pts/0
                  ├─15668 -bash
                  ├─15693 /usr/bin/dbus-daemon --syslog --fork --print-pid 7 --print-address 9 --session
                  ├─15696 /bin/bash /usr/libexec/dbus-1/dbus-kill-process-with-session 15693
                  ├─15701 gio monitor -f /run/systemd/sessions/7 /tmp/dbus-session-monitor.sTnGKW
                  ├─15748 loginctl session-status
                  └─15749 less

It's not a real expected result but it's just for showing that only one dbus-daemon is running while using one ssh connection.



Additional info:

It was implemented in https://bugzilla.redhat.com/show_bug.cgi?id=2089362 where it was assumed that 1 ssh connection = 1 session.