Comment 3 for bug 1722151

When adding the "debug" parameter to the invokation of pam_env in /etc/pam.d/gdm-password, I'm seeing the following in journalctl:

oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): pam_putenv("PATH=/usr/local/sbin:/usr/local/bin:/usr/
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): pam_putenv("LANG=en_US.UTF-8")
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): pam_putenv("LC_NUMERIC=es_ES.UTF-8")
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): pam_putenv("LC_TIME=es_ES.UTF-8")
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): pam_putenv("LC_MONETARY=es_ES.UTF-8")
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): pam_putenv("LC_PAPER=es_ES.UTF-8")
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): pam_putenv("LC_NAME=es_ES.UTF-8")
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): pam_putenv("LC_ADDRESS=es_ES.UTF-8")
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): pam_putenv("LC_TELEPHONE=es_ES.UTF-8")
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): pam_putenv("LC_MEASUREMENT=es_ES.UTF-8")
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): pam_putenv("LC_IDENTIFICATION=es_ES.UTF-8")
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): pam_putenv("LANGUAGE=en_US")
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): remove variable "LANGUAGE=fr_FR:en_GB:en"
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): remove variable "LANG=fr_FR.UTF-8"
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): remove variable "LC_NUMERIC=es_ES.UTF-8"
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): remove variable "LC_TIME=es_ES.UTF-8"
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): remove variable "LC_MONETARY=es_ES.UTF-8"
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): remove variable "LC_PAPER=es_ES.UTF-8"
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): remove variable "LC_NAME=es_ES.UTF-8"
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): remove variable "LC_ADDRESS=es_ES.UTF-8"
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): remove variable "LC_TELEPHONE=es_ES.UTF-8"
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): remove variable "LC_MEASUREMENT=es_ES.UTF-8"
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): remove variable "LC_IDENTIFICATION=es_ES.UTF-8"
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_env(gdm-password:session): remove variable "PAPERSIZE=a4"
oct 09 09:52:59 artfulvm gdm-password][1072]: pam_unix(gdm-password:session): session opened for user ubuntu by (uid=0)

The code for the _undefine_var() function in pam-env.c (https://github.com/linux-pam/linux-pam/blob/master/modules/pam_env/pam_env.c#L738) calls pam_putenv(pamh, var->name), and this happens to work because var->name == "NAME=value", which is the first token on the line.
This is working, but really by accident, and if in the future pam's parser for conf files becomes stricter, this will cease to work. I think we should consider complying better with the documented way of setting variable values (and we should update the documentation, too).