[Bug 1977870] Re: SRU fix for LP#1807628

[Kellen Renshaw]

I haven't had any luck reproducing the issue. It appears to be a race
between the enumeration in lxcfs and the teardown of a cgroup hierarchy.

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Title:
  SRU fix for LP#1807628

Status in lxcfs package in Ubuntu:
  New

Bug description:
  [Impact]

   * lxcfs on Bionic will segfault if there are no non-directory files in a cgroup. This necessitates restarting running containers.
   * See LP#1807628 (https://bugs.launchpad.net/ubuntu/+source/lxcfs/+bug/1807628) for details on the impact.
   * Timing of crash seems to indicate that a reload or race happens with logrotate rotating LXD's logfiles.

  [Test Plan]

   * Install lxd on an Ubuntu Bionic machine. "sudo apt install lxd"
   * Use the guide at https://linuxcontainers.org/lxd/getting-started-cli/#initial-configuration to create some LXD/lxc containers.
   * Reproduction is difficult, even on affected systems. A better test plan will be put in place should a reliable or synthetic reproducer be found.
   * Exercise the logrotate configuration with running containers.
   * Segfault should not occur.

  [Where problems could occur]

   * Correcting the null pointer dereference could allow previously
  undetected bugs masked by the segfault to be encountered.

  [Other Info]

   * Proposed fix is upstream since version 3.0.4 with no negative impacts.
   * Proposed fix is a minimal cherry-pick of the fix, without other functional changes.

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