[Bug 1782152] Re: GDM blocks SIGUSR1 used in PAM scripts
1782152 at bugs.launchpad.net
Thu Aug 2 13:45:00 UTC 2018
Although I originally shared Daniel's doubt, I reported it to Debian and
shared the patch (bug linked above).
** Bug watch added: Debian Bug tracker #905277
** Also affects: gdm3 (Debian) via
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GDM blocks SIGUSR1 used in PAM scripts
Status in gdm3 package in Ubuntu:
Status in gdm3 source package in Xenial:
Status in gdm3 source package in Bionic:
Status in gdm3 source package in Cosmic:
Status in gdm3 package in Debian:
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.
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.
If there were components depending on SIGUSR1 their behavior may change - features that were inactive before may be triggered.
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.
a) Use SIGUSR2 in the scripts.
b) Comment out block_sigusr1() call in daemon/main.c.
To reproduce add the following entries:
auth optional pam_exec.so log=/tmp/auth.log expose_authtok quiet /usr/local/bin/auth.py
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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