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[Launchpad Bug Tracker <1876600@xxxxxxxxxxxxxxxxxx>]

This bug was fixed in the package systemd - 229-4ubuntu21.29

---------------
systemd (229-4ubuntu21.29) xenial; urgency=medium

  [ Dan Streetman ]
  * d/p/lp1881312/0001-core-don-t-dispatch-load-queue-when-setting-Slice-fo.patch,
    d/p/lp1881312/0002-run-make-slice-work-in-conjunction-with-scope.patch:
    - run new scope unit in specified slice (LP: #1881312)
    https://git.launchpad.net/~ubuntu-core-dev/ubuntu/+source/systemd/commit/?id=b5a778c3cd93e3d684602146f281f315f30778a8
  * d/p/lp1877176-sd-dhcp-client-validate-hostnames-stricter-7308.patch:
    - strictly validate hostname sent to dhcp server (LP: #1877176)
    https://git.launchpad.net/~ubuntu-core-dev/ubuntu/+source/systemd/commit/?id=7a1f1c41dcd860fcba6be42a2153cfe4315ebf17
  * d/e/rules-ubuntu/40-vm-hotadd.rules:
    - Hotadd only offline memory and CPUs
      (LP: #1876018)
    https://git.launchpad.net/~ubuntu-core-dev/ubuntu/+source/systemd/commit/?id=43357bd260a1c3e7b4951d33cbacaebda1d086b3
  * d/p/lp1698388-journal-remote-Ensure-reallocation-of-source-buf-doe.patch:
    - Fix assertion failure when journald source->filled < source->size
      (LP: #1698388)
    https://git.launchpad.net/~ubuntu-core-dev/ubuntu/+source/systemd/commit/?id=d1cc15b88113510227e5a76654e103ef54a8b8f3

  [ Heitor Alves de Siqueira ]
  * d/p/lp1876600-sd-bus-deal-with-cookie-overruns.patch:
    - deal with dbus cookie overruns (LP: #1876600)
    https://git.launchpad.net/~ubuntu-core-dev/ubuntu/+source/systemd/commit/?id=8dc9ef188944349169044d8974a4ffa55c66be9d

 -- Heitor Alves de Siqueira <halves@xxxxxxxxxxxxx>  Tue, 07 Jul 2020
17:28:11 -0400

** Changed in: systemd (Ubuntu Xenial)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1876600

Title:
  cookie overruns can cause org.freedesktop.systemd1 dbus to hang

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

Bug description:
  [Impact]
  Long-running services overflow the sd_bus->cookie counter, causing further communication with org.freedesktop.systemd1 to stall.

  [Description]
  Systemd dbus messages include a "cookie" value to uniquely identify them in their bus context. This value is obtained from the bus header, and incremented for each exchanged message in the same bus object. For services that run for longer periods of time and keep communicating through dbus, it's possible to overflow the cookie value, causing further messages to the org.freedesktop.systemd1 dbus to fail. This can lead to these services becoming unresponsive, as they get stuck trying to communicate with invalid bus cookie values.

  This issue has been fixed upstream by the commit below:
  -  sd-bus: deal with cookie overruns (1f82f5bb4237)

  $ git describe --contains 1f82f5bb4237
  v242-rc1~228

  $ rmadison systemd
   systemd | 229-4ubuntu4     | xenial          | source, ...
   systemd | 229-4ubuntu21.27 | xenial-security | source, ...
   systemd | 229-4ubuntu21.27 | xenial-updates  | source, ...
   systemd | 229-4ubuntu21.28 | xenial-proposed | source, ...
   systemd | 237-3ubuntu10    | bionic          | source, ...
   systemd | 237-3ubuntu10.38 | bionic-security | source, ...
   systemd | 237-3ubuntu10.39 | bionic-updates  | source, ...
   systemd | 237-3ubuntu10.40 | bionic-proposed | source, ... <----
   systemd | 242-7ubuntu3     | eoan            | source, ...

  Releases starting with Eoan already have this fix.

  [Test Case]
  There doesn't seem to be an easy test case for this, as the cookie values start at zero and won't overflow until (1<<32). There have been reports from users hitting this on Kubernetes clusters continuously running for longer periods (~5 months).
  Using GDB, we can construct an artificial test case to test the cookie overflow. The test case below performs the following steps:

  1. Create a new system bus object through sd_bus_default_system()
  2. Allocate and append a new method_call message to the bus
  3. Send the message through sd_bus_call()
  4. Handle the response message and free up the message objects

  It's essentially the example code from the
  sd_bus_message_new_method_call() manpage, with minor modifications:
  this is done continuously, to keep incrementing the bus cookie value.
  We step in with GDB when it reaches 0x10000, and set its value to
  0xffffff00 which then causes the test program to fail shortly
  afterwards. An example test run of an impacted system:

  ubuntu@bionic:~$ gcc -Wall test.c -o cookie -lsystemd -g
  ubuntu@bionic:~$ gdb --batch --command=test.gdb --args ./cookie
  Breakpoint 1 at 0xe61: file test.c, line 38.
  [Thread debugging using libthread_db enabled]
  Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
  (16s) cookie: 0x00010000        reply-cookie: 0x00010000

  Breakpoint 1, print_unit_path (bus=0x555555757290) at test.c:38
  38              r = sd_bus_message_new_method_call(bus, &m,
  $1 = 0x10000
  $2 = 0xffffff00
  Call failed: Operation not supported
  Sleeping and retrying...
  Call failed: Invalid argument
  Assertion 'm->n_ref > 0' failed at ../src/libsystemd/sd-bus/bus-message.c:934, function sd_bus_message_unref(). Aborting.

  Program received signal SIGABRT, Aborted.
  __GI_raise (sig=sig@entry=0x6) at ../sysdeps/unix/sysv/linux/raise.c:51
  51      ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.

  To compile and debug the test case above, libsystemd-dev and libsystemd0-dbgsym are required.
  Both test.c and test.gdb source code are attached to this LP bug.

  [Regression Potential]
  This fix introduces some changes in the way cookie incrementation is handled. We now have a reduced number of available values, since the patch makes use of a high order bit to indicate whether we have overflowed or not. Potential issues could arise from two distinct messages repeating the cookie value, or from us not handling the cookie reuse properly. In practice, this shouldn't cause serious problems as most dbus messages should not stall long enough for a possible overlap in the 2^31 space. The patch has been present in other stable Ubuntu Series and upstream, and has been validated and tested through the systemd test suite and autopkgtests.

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