[Bug 1782152] Re: GDM blocks SIGUSR1 used in PAM scripts

[Eric Desrochers]

Hi Dariusz,

Before I sponsor the patch in Ubuntu, did you submitted (or at least
forwarded) the patch to gdm3 debian ?

I couldn't find a debian bug about it.

If one exist great, but if none, could you please file one against gdm3 (debian).
This will prevent gdm Ubuntu package to re-introduce the same problem in later future release sync (Debian->Ubuntu).

Once done, I'll gladly sponsor in Cosmic.

- Eric

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Title:
  GDM blocks SIGUSR1 used in PAM scripts

Status in gdm3 package in Ubuntu:
  In Progress
Status in gdm3 source package in Xenial:
  New
Status in gdm3 source package in Bionic:
  New
Status in gdm3 source package in Cosmic:
  In Progress

Bug description:
  https://gitlab.gnome.org/GNOME/gdm/issues/399

  [Impact]
  GDM blocks SIGUSR1 for it's processes, since this is used in communication with X. This signal is later unblocked, however it happens after PAM
  interaction, so if PAM depends on this signal in any way it will get blocked.
  The issue has been fixed upstream.

  [Test Case]
  1. Prepare a setup described in Other Info using the attached scripts.
  2. Log in.
  3. Check logs /tmp/auth.log.

  Expected result: SIGUSR1 has been received.
  Actual result: SIGUSR1 never reaches the process.

  [Regression Potential]
  If there were components depending on SIGUSR1 their behavior may change - features that were inactive before may be triggered.

  [Other Info]

   Original bug description:

  In case of the following scenario:
  1. PAM configured to run auth and session with pam_exec scripts synchronizing via SIGUSR1
  2. Using GDM as the login manager causes SIGUSR1 never reaches the target scripts.

  Workaround:
  a) Use SIGUSR2 in the scripts.
  b) Comment out block_sigusr1() call in daemon/main.c.

  To reproduce add the following entries:
  /etc/pam.d/common-auth:
  auth	optional	pam_exec.so log=/tmp/auth.log expose_authtok quiet /usr/local/bin/auth.py

  /etc/pam.d/common-session:
  session	optional  pam_exec.so   log=/tmp/session.log  /usr/local/bin/session.py

  Attaching example scripts.
  When using SIGUSR1 - sigusr1_handler is never called, with SIGUSR2 it is called without issues.

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