Bug#878069: lightdm: xdmcp broken

Anton Ivanov

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Oct 9, 2017, 9:10:02 AM10/9/17

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Package: lightdm
Version: 1.18.3-1
Severity: important

Dear Maintainer,

After upgrade to stretch XDMCP no longer works. Setup has worked
virtually unchanged for a decade, with the last 5+ years using
lightdm.

Lightdm shows a greeter, you can enter username and password
after which it bombs out straight back to greeter.

lighdm log snippet for the connecting client:

[+146895.21s] DEBUG: Greeter connected version=1.18.3 resettable=false
[+146895.66s] DEBUG: Greeter start authentication
[+146895.66s] DEBUG: Session: Not setting XDG_VTNR
[+146895.66s] DEBUG: Session pid=13183: Started with service 'lightdm', username '(null)'
[+146895.66s] DEBUG: Session pid=13183: Got 1 message(s) from PAM
[+146895.66s] DEBUG: Prompt greeter with 1 message(s)
[+147067.77s] DEBUG: Greeter start authentication for aivanov
[+147067.77s] DEBUG: Session pid=13183: Sending SIGTERM
[+147067.77s] DEBUG: Session: Not setting XDG_VTNR
[+147067.77s] DEBUG: Session pid=18969: Started with service 'lightdm', username 'aivanov'
[+147067.77s] DEBUG: Session pid=13183: Terminated with signal 15
[+147067.77s] DEBUG: Session: Failed during authentication
[+147067.77s] DEBUG: Seat (null): Session stopped
[+147067.78s] DEBUG: Session pid=18969: Got 1 message(s) from PAM
[+147067.78s] DEBUG: Prompt greeter with 1 message(s)
[+147072.36s] DEBUG: Continue authentication
[+147072.38s] DEBUG: Session pid=18969: Authentication complete with return value 0: Success
[+147072.38s] DEBUG: Authenticate result for user aivanov: Success
[+147072.38s] DEBUG: User aivanov authorized
[+147072.39s] DEBUG: Greeter sets language en_GB.utf8
[+147072.46s] DEBUG: Greeter requests session xfce
[+147072.47s] DEBUG: Seat (null): Stopping greeter; display server will be re-used for user session
[+147072.47s] DEBUG: Session pid=13148: Sending SIGTERM
[+147072.48s] DEBUG: Greeter closed communication channel
[+147072.48s] DEBUG: Session pid=13148: Exited with return value 0
[+147072.48s] DEBUG: Seat (null): Session stopped
[+147072.48s] DEBUG: Seat (null): Greeter stopped, running session
[+147072.48s] DEBUG: Registering session with bus path /org/freedesktop/DisplayManager/Session12
[+147072.48s] DEBUG: Session pid=18969: Not setting XDG_VTNR
[+147072.48s] DEBUG: Session pid=18969: Running command /etc/X11/Xsession startxfce4
[+147072.48s] DEBUG: Session pid=18969: Logging to .xsession-errors
[+147072.51s] DEBUG: Activating login1 session 618
[+147072.51s] WARNING: Error activating login1 session: GDBus.Error:org.freedesktop.DBus.Error.NotSupported: Operation not supported
[+147072.75s] DEBUG: Session pid=18969: Exited with return value 0
[+147072.75s] DEBUG: Seat (null): Session stopped
[+147072.75s] DEBUG: Seat (null): Stopping display server, no sessions require it
[+147072.75s] DEBUG: Seat (null): Display server stopped
[+147072.75s] DEBUG: Seat (null): Active display server stopped, starting greeter
[+147072.75s] DEBUG: Seat (null): Stopping; failed to start a greeter
[+147072.75s] DEBUG: Seat (null): Stopping
[+147072.75s] DEBUG: Seat (null): Stopped
[+147072.76s] DEBUG: Got Query(authentication_names=[]) from 192.168.3.145:43839
[+147072.76s] DEBUG: Send Willing(authentication_name='' hostname='wyvern' status='') to 192.168.3.145:43839
[+147072.96s] DEBUG: Got Request(display_number=0 connections=[192.168.3.145 fe80::21e:bff:fe7b:6513] authentication_name='' authentication_data= authorization_names=['MIT-MAGIC-COOKIE-1' 'XDM-AUTHORIZATION-1' 'SUN-DES-1'] manufacturer_display_id='') from 192.168.3.145:43839
[+147072.96s] CRITICAL: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
[+147072.96s] DEBUG: Send Accept(session_id=51275 authentication_name='' authentication_data= authorization_name='MIT-MAGIC-COOKIE-1' authorization_data=936E7D99E7EF9DC62998E48D97972425) to 192.168.3.145:43839
[+147072.96s] DEBUG: Got Manage(session_id=51275 display_number=0 display_class='MIT-unspecified') from 192.168.3.145:43839
[+147072.96s] DEBUG: Seat (null): Loading properties from config section Seat:*
[+147072.96s] DEBUG: Seat (null): Starting
[+147072.96s] DEBUG: Seat (null): Creating greeter session
[+147072.96s] DEBUG: Seat (null): Creating display server of type x
[+147072.96s] DEBUG: DisplayServer x-192.168.3.145-0: Connecting to XServer 192.168.3.145:0
[+147072.96s] DEBUG: Seat (null): Display server ready, starting session authentication
[+147072.96s] DEBUG: Session: Not setting XDG_VTNR
[+147072.96s] DEBUG: Session pid=19127: Started with service 'lightdm-greeter', username 'lightdm'
[+147072.96s] DEBUG: Registering seat with bus path /org/freedesktop/DisplayManager/Seat10
[+147072.98s] DEBUG: Session pid=19127: Authentication complete with return value 0: Success
[+147072.98s] DEBUG: Seat (null): Session authenticated, running command
[+147072.98s] DEBUG: Session pid=19127: Not setting XDG_VTNR
[+147072.98s] DEBUG: Session pid=19127: Running command /usr/sbin/lightdm-gtk-greeter
[+147072.98s] DEBUG: Session pid=19127: Logging to /var/log/lightdm/(null)-greeter.log
[+147073.00s] DEBUG: Activating login1 session c36
[+147073.00s] WARNING: Error activating login1 session: GDBus.Error:org.freedesktop.DBus.Error.NotSupported: Operation not supported

-- System Information:
Debian Release: 9.0
APT prefers stable
APT policy: (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.9.0-3-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8), LANGUAGE=en_GB:en (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages lightdm depends on:
ii adduser 3.115
ii consolekit 0.4.6-6
ii dbus 1.10.18-1
ii debconf [debconf-2.0] 1.5.61
ii libaudit1 1:2.6.7-2
ii libc6 2.24-11+deb9u1
ii libgcrypt20 1.7.6-2+deb9u1
ii libglib2.0-0 2.50.3-2
ii libpam-systemd 232-25
ii libpam0g 1.1.8-3.6
ii libxcb1 1.12-1
ii libxdmcp6 1:1.1.2-3
ii lightdm-gtk-greeter [lightdm-greeter] 2.0.2-1

Versions of packages lightdm recommends:
ii xserver-xorg 1:7.7+19

Versions of packages lightdm suggests:
ii accountsservice 0.6.43-1
pn upower <none>
ii xserver-xephyr 2:1.19.2-1+deb9u1

-- Configuration Files:
/etc/lightdm/lightdm.conf changed:
[LightDM]
[SeatDefaults]
xserver-command=X -dpi 100
xserver-allow-tcp=true
greeter-session=lightdm-greeter
greeter-hide-users=true
user-session=xfce
session-wrapper=/etc/X11/Xsession
[XDMCPServer]
enabled=true
port=177
[VNCServer]

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

Yves-Alexis Perez

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Oct 9, 2017, 10:10:03 AM10/9/17

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On Mon, 2017-10-09 at 14:03 +0100, Anton Ivanov wrote:
> After upgrade to stretch XDMCP no longer works. Setup has worked
> virtually unchanged for a decade, with the last 5+ years using
> lightdm.
>
> Lightdm shows a greeter, you can enter username and password
> after which it bombs out straight back to greeter.

Hi,

thanks for the report. Unfortunately I don't have an XDMCP setup so I can't
really test that, you'll have to investigate that by yourself.

Regards,
--
Yves-Alexis

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Anton Ivanov

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Oct 9, 2017, 2:00:03 PM10/9/17

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This looks related.

https://ubuntuforums.org/showthread.php?t=2332313

It smells like something similar - not doing the correct auth for the X
connection resulting in an IO error which immediately terminates the
session. Anything else would have been less immediate (it returns to the
login screen straight away).

A

Anton Ivanov

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Mar 28, 2019, 5:40:04 PM3/28/19

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I can no longer observe it for up-to-date stretch clients vs stretch
server and buster clients versus stretch server.

Both sides are amd64

(the original reported crash was with a 32 bit client which I no longer
have so cannot re-test).

A.

On 09/10/2017 14:06, Debian Bug Tracking System wrote:
> Thank you for filing a new Bug report with Debian.
>
> You can follow progress on this Bug here: 878069: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=878069.
>
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> Debian Xfce Maintainers <pkg-xfc...@lists.alioth.debian.org>
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--
Anton R. Ivanov
https://www.kot-begemot.co.uk/