Hi! After asking Markus the status of the gdm3 security upgrade for jessie, he nicely offered me to take it over since he got stuck.
Using his patches, however, I wasn't able to reproduce the problems. Sure, it *looks* like gdm is "crashing", but I /think/ it's actually doing what it's asked. The reproducer issues those two commands: display_path=$(dbus-send --system --dest=org.gnome.DisplayManager --type=method_call --print-reply=literal /org/gnome/DisplayManager/LocalDisplayFactory org.gnome.DisplayManager.LocalDisplayFactory.CreateTransientDisplay) dbus-send --system --dest=org.gnome.DisplayManager --type=method_call $display_path org.gnome.DisplayManager.Display.GetId ie. it's calling `CreateTransientDisplay`. I am not very familiar with the gdm3 D-Bus API, but a quick search online seems to indicate this is used to create a "transient" session, also known as "fast user switching". When running the patched gdm3 under Vagrant / VirtualBox, the reproducer seems to "crash" the display - but what it's doing is actually trying to create that secondary display. There is no actual segfault the Linux kernel can detect, and an attached gdb process happily goes through without detecting anything faulty. I would therefore assert that the patch does what it's designed to do and everything is actually good. Just out of curiosity, I've actually tested the reproducer in Debian buster, which is supposed to be fixed. It could be because I have an exotic session (i3 window manager), but it doesn't work very well either. The display seems to completely crash and return to some virtual terminal. (Just for good measure, all volumes are maxed up as well, bringing down my hearing a few more dBs. :p) But gdm3 doesn't segfault and if I login with my regular user, my session actually returns untouched. So I think this flickering and reset is actually normal. (One thing I *did* find in buster is that gnome-session-check-accelerated segfaults during the procedure: Aug 27 19:34:57 curie kernel: [446832.229288] gnome-session-c[28820]: segfault at 0 ip 0000000000000000 sp 00007fff2cd46d08 error 14 in gnome-session-check-accelerated [5606b821b000+2000] Aug 27 19:34:57 curie kernel: [446832.308946] gnome-session-c[28824]: segfault at 0 ip 0000000000000000 sp 00007fffcd6fb1b8 error 14 in gnome-session-check-accelerated [5589f17d9000+2000] Aug 27 19:34:57 curie gnome-session[28817]: gnome-session-binary[28817]: WARNING: software acceleration check failed: Le processus fils a été tué par le signal 11 Aug 27 19:34:57 curie gnome-session-binary[28817]: WARNING: software acceleration check failed: Le processus fils a été tué par le signal 11 This is likely an unrelated problem, however, so I am ignoring that.) So long story short: apo, your patches were fine! Should I upload the result or do you want to do the honors? If I got no reply tomorrow, I'll complete the DLA. Thanks for the hard work! A. -- In a world where Henry Kissinger wins the Nobel Peace Prize, there is no need for satire. - Tom Lehrer