gnome-control-center crashed when switching to mirror mode and monitors don't have matched resolution

[Dirk Su]

[Impact]
gnome-control-center crashed when switching to mirror mode and monitors don't have matched resolution

[Test case]
Mirror mode is only an option if there are only 2 monitors connected even if one monitor is disabled. A laptop's internal screen counts as one of the monitors.

This particular bug requires two screens that have a screen resolution that they don't both share. (See comment 12 for an example).

1. Connect the monitors
2. Open the GNOME Settings app (gnome-control-center)
3. On the left sidebar, click Displays to switch to the Display panel
4. Switch to mirror mode
3. gnome-control-center won't crash

[Where problems could occur]
This only modifies the code related to mirror mode in Displays panel.

For Lunar, check variable (best_mode) before using it. This patch is backported from GNOME 45 Alpha.

For Jammy, include the Lunar patch and update the way to find cloning mode. These 2 additional patches are backported from gnome-control-center 43.

[Other info]
Two Merge Request are related
1. Check best_mode exist before adding flag (https://gitlab.gnome.org/GNOME/gnome-control-center/-/merge_requests/1835)
2. Use virtual clone modes when mirroring (https://gitlab.gnome.org/GNOME/gnome-control-center/-/merge_requests/1376)

[Sebastien Bacher (seb128)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. It sounds like some part of the system has crashed. To help us find the cause of the crash please follow these steps:

1. Look in /var/crash for crash files and if found run:
    ubuntu-bug YOURFILE.crash
Then tell us the ID of the newly-created bug.

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Please take care to avoid attaching .crash files to bugs as we are unable to process them as file attachments. It would also be a security risk for yourself.

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "lunar_ubuntu5_ubuntu6.debdiff" seems to be a debdiff. The ubuntu-sponsors team has been subscribed to the bug report so that they can review and hopefully sponsor the debdiff. If the attachment isn't a patch, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are member of the ~ubuntu-sponsors, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issue please contact him.]

[Athos Ribeiro (athos-ribeiro)]

Thanks, Dirk.

I wonder why only the jammy debdiff contains the second patch. Is it applied in the other series (kk and ll) already?

Also, as per the SRU guidelines in https://wiki.ubuntu.com/StableReleaseUpdates#SRU_Bug_Template, regarding the "[ Where problems could occur ]" section,

> * This must '''never''' be "None" or "Low", or entirely an argument as to why
   your upload is low risk.

Describing where problems could occur and how they would manifest is a nice way to show to the SRU team that we did consider possible unwanted outcomes for the SRU and that we'd be ready to address them in case they do occur. It also helps people testing the SRU, guiding them on what to look for when checking for regressions.

[Dirk Su (dirksu)]

The second patch included in gnome-42. KK use gnome-43 and LL use gnome-44 as base, both of distribution had the second patch.

[Jeremy Bícha (jbicha)]

I am closing the Kinetic task. Ubuntu 22.10 "Kinetic" will be End of Life on July 20 and there is not enough time under normal Stable Release Update procedures for this fix to land in kinetic-updates before July 20.

[Jeremy Bícha (jbicha)]

I have uploaded your patch to Mantic.

When I tested this on Lunar, I was unable to reproduce the crash. I had set my second monitor to a different screen resolution than the first but gnome-control-center made the 2 monitors have the same resolution when I enabled Mirror Mode. Are you able to reproduce the crash on Lunar?

[Launchpad Janitor (janitor)]

This bug was fixed in the package gnome-control-center - 1:44.3-1ubuntu2

---------------
gnome-control-center (1:44.3-1ubuntu2) mantic; urgency=medium

  * Add patch to fix mirror mode crash when resolution of
    the 2 monitors don't match (LP: #2026228)

 -- Dirk Su <email address hidden> Wed, 12 Jul 2023 13:29:55 -0400

[Jeremy Bícha (jbicha)]

Please don't subscribe ubuntu-sru to bugs. You can subscribe ubuntu-sponsors (as was already done here) if you need someone to upload your work to a stable Ubuntu release.

[Dirk Su (dirksu)]

I can reproduced the gnome-control-center crash on Lunar. The crash only happened when two monitor can't find match resolution. My laptop's internal display only has one resolution 1920x1200, external monitor's highest resolution is 1920x1080. When switching to mirror mode in gnome-control-center, it will crashed.

[Jeremy Bícha (jbicha)]

Thank you for helping to make Ubuntu better. I have uploaded these fixes for Jammy and Lunar. They will need to be manually approved by a member of the Ubuntu SRU team before they will be made available as proposed updates.

I am unsubscribing ubuntu-sponsors now. Feel free to resubscribe if you have something else that needs to be sponsored.

[Steve Langasek (vorlon)]

Hello Dirk, or anyone else affected,

Accepted gnome-control-center into lunar-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/gnome-control-center/1:44.0-1ubuntu6 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-lunar to verification-done-lunar. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-lunar. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

[Steve Langasek (vorlon)]

Hello Dirk, or anyone else affected,

Accepted gnome-control-center into jammy-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/gnome-control-center/1:41.7-0ubuntu0.22.04.7 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed. Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested, what testing has been performed on the package and change the tag from verification-needed-jammy to verification-done-jammy. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-jammy. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance for helping!

N.B. The updated package will be released to -updates after the bug(s) fixed by this package have been verified and the package has been in -proposed for a minimum of 7 days.

[Dirk Su (dirksu)]

Tested with laptop 202211-30793 which only has 1920x1200 for internal display. Install stock 23.04 iso image and update gnome-control-center 1:44.0-1ubuntu6 from lunar-proposed. Connected DUT with external monitor which had resolution 1920x1080. Open gnome-control-center, switch to Display panel and select mirror mode. And gnome-control-center won't crash.

[Dirk Su (dirksu)]

Tested with laptop 202211-30793 which only has 1920x1200 for internal display. Install stock 22.04 iso image and update gnome-control-center 1:41.7-0ubuntu0.22.04.7 from jammy-proposed. Connected DUT with external monitor which had resolution 1920x1080. Open gnome-control-center, switch to Display panel and select mirror mode. And gnome-control-center won't crash.

[Andreas Hasenack (ahasenack)]

The verification of the Stable Release Update for gnome-control-center has completed successfully and the package is now being released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.

[Launchpad Janitor (janitor)]

This bug was fixed in the package gnome-control-center - 1:44.0-1ubuntu6

---------------
gnome-control-center (1:44.0-1ubuntu6) lunar; urgency=medium

  * Add patch to fix mirror mode crash when resolution of
    the 2 monitors don't match (LP: #2026228)

 -- Dirk Su <email address hidden> Fri, 07 Jul 2023 09:15:28 +0800

[Launchpad Janitor (janitor)]

This bug was fixed in the package gnome-control-center - 1:41.7-0ubuntu0.22.04.7

---------------
gnome-control-center (1:41.7-0ubuntu0.22.04.7) jammy; urgency=medium

  * Cherry-pick 3 patches to fix mirror mode crash
    when resolution of the 2 monitors don't match (LP: #2026228)

 -- Dirk Su <email address hidden> Fri, 07 Jul 2023 12:45:49 +0800