Bug#1039573: cannot authenticate after lock: pam_unix(lightdm:auth): auth could not identify password

[Arturo Borrero Gonzalez]

Package: lightdm
Version: 1.32.0-2
Severity: important

Hi there!

Thanks for your hard work with this package, it is really appreciated.

I just upgraded lightdm from 1.26.0-8 to 1.32.0-2 and now the greeter wont let me
login after a session lock (like a laptop suspend or CTRL+ALT+L on xfce4).

This can be found in the logs:

Jun 27 12:08:28 endurance lightdm[91911]: pam_unix(lightdm-greeter:session): session opened for user lightdm(uid=108) by (uid=0)
Jun 27 12:08:29 endurance lightdm[92079]: pam_unix(lightdm:auth): auth could not identify password for [arturo]
Jun 27 12:08:38 endurance lightdm[935]: Session pid=92114: Invalid string length 1869348864 from child
Jun 27 12:08:38 endurance lightdm[92114]: pam_nologin(lightdm:auth): unexpected response from failed conversation function
Jun 27 12:08:38 endurance lightdm[92114]: No user selected during authentication
Jun 27 12:08:38 endurance lightdm[92114]: pam_nologin(lightdm:auth): cannot determine user name

So I suspect there is a bug somewhere in the stack.

regards.


-- System Information:
Debian Release: trixie/sid
APT prefers stable-security
APT policy: (500, 'stable-security'), (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 6.3.0-1-amd64 (SMP w/4 CPU threads; PREEMPT)
Kernel taint flags: TAINT_PROPRIETARY_MODULE, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=C, LC_CTYPE=C.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages lightdm depends on:
ii adduser 3.134
ii dbus 1.14.8-1
ii debconf [debconf-2.0] 1.5.82
ii libaudit1 1:3.0.9-1
ii libc6 2.36-9
ii libgcrypt20 1.10.2-2
ii libglib2.0-0 2.74.6-2
ii libpam-systemd [logind] 252.11-1
ii libpam0g 1.5.2-6
ii libxcb1 1.15-1
ii libxdmcp6 1:1.1.2-3
ii lightdm-gtk-greeter [lightdm-greeter] 2.0.8-3

Versions of packages lightdm recommends:
ii xserver-xorg 1:7.7+23

Versions of packages lightdm suggests:
ii accountsservice 22.08.8-6
ii upower 0.99.20-2
pn xserver-xephyr <none>

-- Configuration Files:
/etc/lightdm/lightdm.conf changed:
[LightDM]
[Seat:*]
greeter-hide-users=false
display-setup-script=sh -c "xrandr -s 1920x1080"
[XDMCPServer]
[VNCServer]


-- debconf information:
* shared/default-x-display-manager: lightdm
lightdm/daemon_name: /usr/sbin/lightdm

[Yves-Alexis Perez]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

On Tue, 2023-06-27 at 12:22 +0200, Arturo Borrero Gonzalez wrote:
> I just upgraded lightdm from 1.26.0-8 to 1.32.0-2 and now the greeter wont let me
> login after a session lock (like a laptop suspend or CTRL+ALT+L on xfce4).
>
> This can be found in the logs:
>
> Jun 27 12:08:28 endurance lightdm[91911]: pam_unix(lightdm-greeter:session): session opened for user lightdm(uid=108) by (uid=0)
> Jun 27 12:08:29 endurance lightdm[92079]: pam_unix(lightdm:auth): auth could not identify password for [arturo]
> Jun 27 12:08:38 endurance lightdm[935]: Session pid=92114: Invalid string length 1869348864 from child
> Jun 27 12:08:38 endurance lightdm[92114]: pam_nologin(lightdm:auth): unexpected response from failed conversation function
> Jun 27 12:08:38 endurance lightdm[92114]: No user selected during authentication
> Jun 27 12:08:38 endurance lightdm[92114]: pam_nologin(lightdm:auth): cannot determine user name
>
> So I suspect there is a bug somewhere in the stack.

Hi Arturo, it does look like there's something fishy from the "Invalid string
length 1869348864" (which looks way too high). Is that reproducible everytime
? Is there something specific/peculiar about your installation? I assume
you're using light-locker as your screen locker?

Regards,
- --
Yves-Alexis
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[Arturo Borrero Gonzalez]

On 6/27/23 18:14, Yves-Alexis Perez wrote:
> On Tue, 2023-06-27 at 12:22 +0200, Arturo Borrero Gonzalez wrote:
>> I just upgraded lightdm from 1.26.0-8 to 1.32.0-2 and now the greeter wont let me
>> login after a session lock (like a laptop suspend or CTRL+ALT+L on xfce4).
>
>> This can be found in the logs:
>
>> Jun 27 12:08:28 endurance lightdm[91911]: pam_unix(lightdm-greeter:session): session opened for user lightdm(uid=108) by (uid=0)
>> Jun 27 12:08:29 endurance lightdm[92079]: pam_unix(lightdm:auth): auth could not identify password for [arturo]
>> Jun 27 12:08:38 endurance lightdm[935]: Session pid=92114: Invalid string length 1869348864 from child
>> Jun 27 12:08:38 endurance lightdm[92114]: pam_nologin(lightdm:auth): unexpected response from failed conversation function
>> Jun 27 12:08:38 endurance lightdm[92114]: No user selected during authentication
>> Jun 27 12:08:38 endurance lightdm[92114]: pam_nologin(lightdm:auth): cannot determine user name
>
>> So I suspect there is a bug somewhere in the stack.
>
> Hi Arturo, it does look like there's something fishy from the "Invalid string
> length 1869348864" (which looks way too high). Is that reproducible everytime
> ? Is there something specific/peculiar about your installation? I assume
> you're using light-locker as your screen locker?
>

Hi there,

I have experienced the same problem in 2 different systems.
However, I have the strong suspicion that this happened in the same context:
upgrading the system.

I need a few more days to pass by, but I have the hunch that after a reboot this
problem goes away. I didn't see it happening again after being hit by it those 2
times in a row (which triggered me to open this bug).

To your question: yes, I'm using light-locker.

Thanks for the follow up, I'll keep you updated in the next few days.

[Arturo Borrero Gonzalez]

On Wed, 28 Jun 2023 10:58:39 +0200 Arturo Borrero Gonzalez <art...@debian.org>
wrote:

> Thanks for the follow up, I'll keep you updated in the next few days.

I have not experienced this problem again since the update.