GLVND: Set current thread state to NULL in teardown

[Aidan Foster]

A new fix has been merged into the libglvnd repo at https://gitlab.freedesktop.org/glvnd/libglvnd

This change fixes an issue where if eglReleaseThread gets externally called after the EGL destructor, a double free occurs due to the threadState that eglReleaseThread checks is not null being not null despite being freed by the destuctor.
The change makes the threadState null in the destructor to fix this.

Can this make it into the libs in 20.04 LTS?

Source package where the issue is encountered: https://launchpad.net/ubuntu/+source/libglvnd/1.3.2-1~ubuntu0.20.04.2

[Launchpad Janitor (janitor)]

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

[Sebastien Bacher (seb128)]

Thank you for the bug report. It seems like a fix worth cherrypicking but could you maybe give an example of impact the issue has which is user visible? It would help especially for a stable update to have a testcase to verify the fix and to justify the importance. If it's not impacting anyone in a visible fashion then maybe it's not such an issue

[Aidan Foster (aidanf)]

The bug was observed running the Vulkan CTS on an Nvidia Jetson AGX Xavier Developer Kit and on a Jetson AGX Orin Developer Kit. Running the testcase dEQP-VK.api.object_management.alloc_callback_fail.instance without an X display should cause the double free to occur.
I confirmed that this is a GLVND issue, as when I built libglvnd with small fix that was merged and used it instead of the provided libs, the issue went away.

[Sebastien Bacher (seb128)]

Thanks, it seems a pretty special case and in practice not something most users are going to hit, the fix is trivial though so would be easy to cherry pick for a next upload, https://gitlab.freedesktop.org/glvnd/libglvnd/-/commit/5024e579

[Aidan Foster (aidanf)]

I do think it is worth mentioning that since it is a in issue that shows up in the Vulkan CTS, it is likely that it will also show up in other applications. It may also occur on other platforms, but the two I listed are the only ones that I confirmed the issue is reproducing on.