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IDProjectCategoryView StatusLast Update
0014022CentOS-7gdmpublic2018-01-26 09:34
Status newResolutionopen 
Platformx86_64OSCentOSOS Version7.4.1708
Product Version7.4.1708 
Target VersionFixed in Version 
Summary0014022: GDM crashes with XDMCP when locking screen
DescriptionI have enabled XDMCP in GDM and set up Xvnc to use it.

I can log in fine via VNC to the Xvnc server using the GDM with XDMCP, but when the screen is locked I cannot unlock the screen. An attempt to unlock the screen crashes gdm. Also, after this occurs I also have trouble simple login in, gdm often crashes as well.

According to ABRT, gdm crashes in _int_malloc() within libc, so it looks like gdm is doing some heap corruption.
Steps To ReproduceThe following are simple steps to reproduce the issue (simpler than setting up Xvnc with systemd).

1. Enable XDMCP in gdm in /etc/gdm/custom.conf



2. Restart gdm with "systemctl restart gdm.service"

3. Install tigervnc-server

4. Open port 5901 on the firewall: firewall-cmd --add-port=5901/tcp

5. Setup a VNC password with: vncpassword

6. Log in as a regular user via SSH and run

/usr/bin/Xvnc :1 -query localhost -once -geometry 1024x768 passwordfile=$HOME/.vnc/passwd

7. Connect from a VNC client on display :1

8. Lock the screen of the VNC session

9. Unlock the screen, GDM will crash just after typing the password
Additional InformationGDM version: gdm-3.22.3-12.el7.x86_64

Apparently this is just this bug: and the fix is

I got the sources from the debuginfo and the above problem is there. I also attached gdb and confirmed that it is doing a free of a dangling pointer.

The Red Hat bug could also be related.
TagsNo tags attached.




2018-01-26 09:34

reporter   ~0031057

This has been fixed by gdm-3.22.3-13.el7_4.x86_64, see

As far as I could test the issue no longer occurs and the source rpm does contain the above fix.

Issue History

Date Modified Username Field Change
2017-10-16 15:43 diego.santacruz New Issue
2018-01-26 09:34 diego.santacruz Note Added: 0031057