[Bug 1628687] Update Released

[Martin Pitt]

The verification of the Stable Release Update for systemd has completed
successfully and the package has now been released to -updates.
Subsequently, the Ubuntu Stable Release Updates Team is being
unsubscribed and will not receive messages about this bug report.  In
the event that you encounter a regression using the package from
-updates please report a new bug using ubuntu-bug and tag the bug report
regression-update so we can easily find any regressions.

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https://bugs.launchpad.net/bugs/1628687

Title:
  Assertion failure when PID 1 receives a zero-length message over
  notify socket

Status in systemd:
  Fix Released
Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Xenial:
  Fix Released
Status in systemd source package in Yakkety:
  Fix Released

Bug description:
  Environment:

  Xenial 16.04.1
  Amd64

  Description.

  Systemd fails an assertion in manager_invoke_notify_message when a
  zero-length message is received over /run/systemd/notify. This allows
  a local user to perform a denial-of-service attack against PID 1.

  How to trigger the bug:

  $ while true; do NOTIFY_SOCKET=/run/systemd/notify systemd-notify "";
  done

  The following entries are written into /var/log/syslog, at this point
  systemd is crashed.

  Sep 28 20:57:20 ubuntu systemd[1]: Started User Manager for UID 1000.
  Sep 28 20:57:28 ubuntu systemd[1]: Assertion 'n > 0' failed at ../src/core/manager.c:1501, function manager_invoke_notify_message(). Aborting.
  Sep 28 20:57:29 ubuntu systemd[1]: Caught <ABRT>, dumped core as pid 1307.
  Sep 28 20:57:29 ubuntu systemd[1]: Freezing execution.

  Public bug: https://github.com/systemd/systemd/issues/4234

  The original USN/security fix in
  https://launchpad.net/ubuntu/+source/systemd/229-4ubuntu10 introduced
  another local DoS due to fd exhaustion:

    NOTIFY_SOCKET=/run/systemd/notify python3 -c 'from systemd import
  daemon; daemon.notify("", fds=[0]*100)'

  Run this a few times and watch "sudo ls -l /proc/1/fd" grow.

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