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Tasklist

FS#68957 - [x11vnc] X11 error with GDM

Attached to Project: Community Packages
Opened by SomeBugCatcher (SomeBugCatcher) - Saturday, 12 December 2020, 17:11 GMT
Last edited by Doug Newgard (Scimmia) - Saturday, 12 December 2020, 19:31 GMT
Task Type Bug Report
Category Packages
Status Closed
Assigned To No-one
Architecture All
Severity Medium
Priority Normal
Reported Version
Due in Version Undecided
Due Date Undecided
Percent Complete 100%
Votes 0
Private No

Details

Description: Since the update 1:0.9.16-4 X11vnc won't work with GDM I get the following error:
Dec 11 16:09:03 PC x11vnc[1032]: caught X11 error:
Dec 11 16:09:03 PC x11vnc[1032]: 11/12/2020 16:09:03 deleted 60 tile_row polling images.
Dec 11 16:09:03 PC x11vnc[1032]: X Error of failed request: BadAccess (attempt to access private resource denied)
Dec 11 16:09:03 PC x11vnc[1032]: Major opcode of failed request: 130 (MIT-SHM)
Dec 11 16:09:03 PC x11vnc[1032]: Minor opcode of failed request: 1 (X_ShmAttach)
Dec 11 16:09:03 PC x11vnc[1032]: Serial number of failed request: 57
Dec 11 16:09:03 PC x11vnc[1032]: Current serial number in output stream: 119

Downgrading to 1:0.9.16-3 fixes the issue and it works perfectly with GDM. I am using the config on the Arch Wiki: https://wiki.archlinux.org/index.php/X11vnc#Run_x11vnc_%22system-wide%22_in_(GDM_and_GNOME_Shell)

Steps to reproduce:
1. Install GDM and X11vnc version 1:0.9.16-4
2. Try to start X11vnc
3. See error
This task depends upon

Closed by  Doug Newgard (Scimmia)
Saturday, 12 December 2020, 19:31 GMT
Reason for closing:  Not a bug
Comment by Jonas Witschel (diabonas) - Saturday, 12 December 2020, 18:43 GMT
This is probably related to the newly applied patch "030-x11vnc-scan-limit-access-to-shared-memory" (https://github.com/LibVNC/x11vnc/commit/69eeb9f7baa14ca03b16c9de821f9876def7a36a), which fixes a security issue where users other than the one running x11vnc could access the server ( FS#68930 ).

My guess is that you need to modify the systemd unit files to run x11vnc as the same user that GDM uses for running its X server instance (probably "gdm").

I confirm that x11vnc 1:0.9.16-4 works fine on my system, running both the X server and x11vnc as my standard user (https://wiki.archlinux.org/index.php/Xorg#Using_xinitrc), so this is not an issue with the package per se, but a configuration issue.
Comment by SomeBugCatcher (SomeBugCatcher) - Saturday, 12 December 2020, 19:25 GMT
Thank you. I can confirm that setting User=gdm to the systemd file and moving the passwd file to a location that the GDM user can access has solved the issue. The Wiki should be updated to reflect this change. Sorry for opening a bug report!
Comment by Jonas Witschel (diabonas) - Saturday, 12 December 2020, 19:31 GMT
No worries at all! Please feel free to update the corresponding section of the ArchWiki with the configuration that worked for you.

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