Let's move pam_systemd_home before pam_unix in the authentication hook.
Since a while we are exposing shadow entries for homed log entries via
NSS. This means that pam_unix now potentially has enough data for
authenticating a user on its own, without letting pam_systemd_home do
that. This is superficially OK, but also means that authentication will
always go via password, even if pkcs11/fido2 is registered.
Let's move this around, but be careful about it: let's list the precise
errors which we think are enough to terminating further PAM processing,
so that pam_unix comes into control in all cases where it's not clear
that pam_systemd_home owns the user record.
This previously wasn't visible to me, because on Fedora until authselect
1.5.1 (released earleir this year) the NSS shadow stuff was not enabled.
This does the same also for the "account" stack, except that the order
there already was as we want it.
Finally, shorten the account stack, by just requiring pam_unix.so and
dropping pam_permit.so, because it doesn't really serve much purpose
(and Fedora doesn't use it by default either.)
Our dumbed down example PAM stacks do not contain cracklib/pwq modules,
hence using use_authtok on the pam_unix.so password change stack won't
work, because it has the effect that pam_unix.so never asks for a
password on its own, expecting the cracklib/pwq modules to have
queried/validated them beforehand.
I noticed this issue because of #30969: Debian's PAM setup suffers by
the same issue – even though they don't actually use our suggested PAM
fragments at all.
See: #30969
This was a copy/paste mistae apparently, there's not "try_authtok" and
this was supposed to copy what Fedora uses, which uses "use_authtok"
correctly. Hence adjust this.
Fixes: #19369
Apparently PAM reacts differently on different systems (?) and if no
authoritative matching module is found might either succeed/fail,
depending on the system.
Let's lock this down explicitly, by hooking in pam_deny.so.
Of course, these PAM files are just examples, and no distro in its right
mind would ship these unmodified, but let's default to something safe.
Fixes: #12950
Stupid PAM, please just go away!
login[26]: pam_limits(login:session): error parsing the configuration file: '/etc/security/limits.conf'
login[26]: pam_unix(login:session): session opened for user root by LOGIN(uid=0)
login[26]: Error in service module
Lennart Poettering
Kay Sievers