settings allow arbitrarily large user pictures which makes the user lock themselves out at lightdm.

[Lyn Perrine]

To reproduce on a fresh install of ubuntu mate 16.04 start lightdm-gtk-greeter-settings and authenticate to start editing lightdm settings. Please do not try to reproduce this on a production machine as it will involve locking yourself out of lightdm.

In the settings for lightdm GTK+ greeter settings select a really large image from a digial camera or high resolution screenshot as your user image that is larger than your screen resolution hit save and then log out.

You will be taken to a lightdm screen that has a user image so large you cannot login.

Description: Ubuntu Xenial Xerus (development branch)
Release: 16.04
lightdm-gtk-greeter-settings:
  Installed: 1.2.0-0ubuntu1
  Candidate: 1.2.0-0ubuntu1
  Version table:
 *** 1.2.0-0ubuntu1 0
        500 http://us.archive.ubuntu.com/ubuntu/ xenial/universe amd64 Packages
        100 /var/lib/dpkg/status

I would expect the greeter to check that it would not set such redicolous file sizes that block the user from logging in or at least provide a warning dialog that this could make you unable to login similar to things that cause data loss on a partition in ubuquity or gparted.

As this prevents even loggin into guest session graphically. I did manage to get back in editing /etc/lightdm/lightdm-gtk-greeter.conf by hand with vim.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: lightdm-gtk-greeter-settings 1.2.0-0ubuntu1
ProcVersionSignature: Ubuntu 4.2.0-16.19-generic 4.2.3
Uname: Linux 4.2.0-16-generic x86_64
ApportVersion: 2.19.2-0ubuntu1
Architecture: amd64
CurrentDesktop: MATE
Date: Tue Nov 3 22:51:13 2015
InstallationDate: Installed on 2015-11-03 (0 days ago)
InstallationMedia: Ubuntu-MATE 16.04 LTS "Xenial Xerus" - Alpha amd64 (20151103)
PackageArchitecture: all
SourcePackage: lightdm-gtk-greeter-settings
UpgradeStatus: No upgrade log present (probably fresh install)

[finny388 (alteahandle-launchpad)]

Ubuntu Mate 16.04
Same here. Workaround: Tab 3 times, enter pw, Enter.

Pretty lame.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[James Lu (jlu5)]

Is there any specific limit on the largest file size / resolution LightDM GTK+ Greeter supports?

[Sean Davis (bluesabre)]

Resolved with this commit. User images provided by AccountsService were scaled while default images were not.
http://bazaar.launchpad.net/~lightdm-gtk-greeter-team/lightdm-gtk-greeter/trunk/revision/366