[Bug 1934147] Re: systemd leaks abandoned session scopes

[Chris Halse Rogers]

Hello Nicolas, or anyone else affected,

Accepted systemd into hirsute-proposed. The package will build now and
be available at
https://launchpad.net/ubuntu/+source/systemd/247.3-3ubuntu3.5 in a few
hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
hirsute to verification-done-hirsute. If it does not fix the bug for
you, please add a comment stating that, and change the tag to
verification-failed-hirsute. In either case, without details of your
testing we will not be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

** Changed in: systemd (Ubuntu Hirsute)
       Status: In Progress => Fix Committed

** Tags added: verification-needed-hirsute

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https://bugs.launchpad.net/bugs/1934147

Title:
  systemd leaks abandoned session scopes

Status in snapd:
  New
Status in systemd:
  New
Status in systemd package in Ubuntu:
  Fix Committed
Status in systemd source package in Bionic:
  Fix Committed
Status in systemd source package in Focal:
  In Progress
Status in systemd source package in Groovy:
  Won't Fix
Status in systemd source package in Hirsute:
  Fix Committed
Status in systemd source package in Impish:
  Fix Committed

Bug description:
  [impact]

  systemd may leak sessions, leaving empty cgroups around as well as
  abandoned session scopes.

  [test case]

  on a system where the user has a ssh key that allows noninteractive
  login to localhost, and also has noninteractive sudo, run:

  $ for i in {1..100}; do sudo -b -i -u ubuntu ssh localhost -- sleep 1;
  done; for i in {1..20}; do echo 'Reloading...'; sudo systemctl daemon-
  reload; done

  check the sessions to see there have been leaked sessions:

  $ loginctl list-sessions

  SESSION  UID USER   SEAT TTY
        1 1000 ubuntu      ttyS0
      350 1000 ubuntu      
      351 1000 ubuntu      
      360 1000 ubuntu      
  ...

  to verify the sessions were leaked, clear them out with:

  $ echo '' | sudo tee
  /sys/fs/cgroup/unified/user.slice/user-1000.slice/session-*.scope/cgroup.events

  that should result in all the leaked sessions being cleaned up.

  [regression potential]

  issues during systemd pid1 reexec/reload, or issues while cleaning up
  sessions, including leaking sessions/cgroups

  [scope]

  this is needed for all releases

  upstream bug linked above, and upstream PR:
  https://github.com/systemd/systemd/pull/20199

  [original description]

  On a system that is monitored via telegraf I found many abandoned
  systemd session which I believe are created by a potential race where
  systemd is reloading unit files and at the same time a user is
  connecting to the system via ssh or is executing the su command.

  The simple reproducer

  $ for i in {1..100}; do sleep 0.2; ssh localhost sudo systemctl
  daemon-reload & ssh localhost sleep 1 & done

  Wait > 1 second

  $ jobs -p | xargs --verbose --no-run-if-empty kill -KILL

  To clean out STOPPED jobs and

  $ systemctl status --all 2> /dev/null | grep --before-context 3
  abandoned

  will produce something similar to

             │ ├─  175 su - ubuntu
             │ ├─  178 -su
             │ ├─62375 systemctl status --all
             │ └─62376 grep --color=auto --before-context 3 abandoned
  --
  ● session-273.scope - Session 273 of user ubuntu
     Loaded: loaded (/run/systemd/transient/session-273.scope; transient)
  Transient: yes
     Active: active (abandoned) since Wed 2021-06-30 13:32:03 UTC; 4min 7s ago
  --
  ● session-274.scope - Session 274 of user ubuntu
     Loaded: loaded (/run/systemd/transient/session-274.scope; transient)
  Transient: yes
     Active: active (abandoned) since Wed 2021-06-30 13:32:03 UTC; 4min 7s ago
  --
  ● session-30.scope - Session 30 of user ubuntu
     Loaded: loaded (/run/systemd/transient/session-30.scope; transient)
  Transient: yes
     Active: active (abandoned) since Wed 2021-06-30 10:05:56 UTC; 3h 30min ago
  --
  ● session-302.scope - Session 302 of user ubuntu
     Loaded: loaded (/run/systemd/transient/session-302.scope; transient)
  Transient: yes
     Active: active (abandoned) since Wed 2021-06-30 13:32:04 UTC; 4min 6s ago
  --
             │ ├─  175 su - ubuntu
             │ ├─  178 -su
             │ ├─62375 systemctl status --all
             │ └─62376 grep --color=auto --before-context 3 abandoned

  The system in question is running Bionic, systemd-237-3ubuntu10.48

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