xdg-portal-gtk crashes if a RemoteDesktop request is received after the session is closed

[ofourdan]

Summary

This is a corollary of https://github.com/flatpak/xdg-desktop-portal/issues/508

If a client sends a RemoteDesktop request such as NotifyPointerMotion after the session is closed from the service side, xdg-desktop-portal-gtk segfaults.

Steps to reproduce

Same as https://github.com/flatpak/xdg-desktop-portal/issues/508

1. Save https://gitlab.gnome.org/snippets/1122 as xdp-pointer-events.py
2. Run python xdp-pointer-events.py
3. Select pointer in the list
4. Click [Share] to start the RemoteDesktop session
5. From gnome-shell, select "Screen is being shared" → "Turn off" to terminate terminate the session

Actual results

xdg-desktop-portal-gtk segfaults with the following backtrace: xdg-portal-gtk-crash.txt

Expected results

No crash - Either xdg-portal or xdg-portal-gtk should do some sanity checks on the session state.

[ofourdan]

Small clarification, xdg-desktop-portal-gtk crashes because:

Program terminated with signal SIGSEGV, Segmentation fault.

#0  0x0000560d74095b1d in handle_notify_pointer_motion (object=0x560d75e8ee10, invocation=0x560d75ec71f0, arg_session_handle=<optimized out>, 
    arg_options=<optimized out>, dx=0, dy=1) at src/remotedesktop.c:612
612	  org_gnome_mutter_remote_desktop_session_call_notify_pointer_motion_relative (proxy,

(gdb) list
607	
608	  remote_desktop_session =
609	    (RemoteDesktopSession *)lookup_session (arg_session_handle);
610	  proxy = remote_desktop_session->mutter_session_proxy;
611	
612	  org_gnome_mutter_remote_desktop_session_call_notify_pointer_motion_relative (proxy,
613	                                                                               dx, dy,
614	                                                                               NULL, NULL, NULL);
615	
616	  xdp_impl_remote_desktop_complete_notify_pointer_motion (object, invocation);
(gdb) p proxy
Cannot access memory at address 0x48
(gdb) p remote_desktop_session
$1 = (RemoteDesktopSession *) 0x0