[Bug 1796808] Re: frontend locking regression: dpkg::post-invoke scripts can't install packages

[Brian Murray]

Hello Julian, or anyone else affected,

Accepted apt into bionic-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/apt/1.6.6 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 and change the tag from
verification-needed-bionic to verification-done-bionic. If it does not
fix the bug for you, please add a comment stating that, and change the
tag to verification-failed-bionic. 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: apt (Ubuntu Bionic)
       Status: Triaged => Fix Committed

** Tags added: verification-needed-bionic

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https://bugs.launchpad.net/bugs/1796808

Title:
  frontend locking regression: dpkg::post-invoke scripts can't install
  packages

Status in apt package in Ubuntu:
  Fix Released
Status in apt source package in Xenial:
  Fix Committed
Status in apt source package in Bionic:
  Fix Committed
Status in apt source package in Cosmic:
  Fix Released

Bug description:
  [Impact]
  The switch to frontend locking in 1.2.28/1.6.5/1.7~ caused scripts registered in

  DPkg::Pre-Install-Pkgs
  DPkg::Pre-Invoke
  DPkg::Post-Invoke

  To be run with the frontend lock held. This caused problems with some
  installer packages like libdvd-pkg which install a locally built
  package in such a hook.

  To reduce the impact, a fix has been applied in 1.7.0 which exports
  the DPKG_FRONTEND_LOCKED variable when running those scripts, allowing
  dpkg to be run from those scripts.

  [Test case]
  Make sure that the test-frontend-lock test run by autopkgtest succeeds. This checks that:

  (1) the variable is correctly exported to those scripts
  (2) the frontend lock is still held
  (3) dpkg can be run from the post-invoke script

  [Regression potential]
  Depending on the script (for example, if the script starts a daemon manually or something like that), DPKG_FRONTEND_LOCKED might leak to other processes which might survive the apt call and thus revert surviving process to not using frontend locking.

  [Other info]
  This fix is for backwards compatibility only. Starting with the dd cycle, it will be dropped for the Pre-Install-Pkgs and Pre-Invoke scripts. Potentially for post-invoke as well, if we find a better solution for it.

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