564ccf2ce9
PointerWindows[] keeps a reference to the last window our sprite entered - changes are usually handled by CheckMotion(). If we switch between screens via XWarpPointer our dev->spriteInfo->sprite->win is set to the new screen's root window. If there's another window at the cursor location CheckMotion() will trigger the right enter/leave events later. If there is not, it skips that process and we never trigger LeaveWindow() - PointerWindows[] for the device still refers to the previous window. If that window is destroyed we have a dangling reference that will eventually cause a use-after-free bug when checking the window hierarchy later. To trigger this, we require: - two protocol screens - XWarpPointer to the other screen's root window - XDestroyWindow before entering any other window This is a niche bug so we hack around it by making sure we reset the PointerWindows[] entry so we cannot have a dangling pointer. This doesn't handle Enter/Leave events correctly but the previous code didn't either. CVE-2023-5380, ZDI-CAN-21608 This vulnerability was discovered by: Sri working with Trend Micro Zero Day Initiative Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net> Reviewed-by: Adam Jackson <ajax@redhat.com>
X Server
The X server accepts requests from client applications to create windows, which are (normally rectangular) "virtual screens" that the client program can draw into.
Windows are then composed on the actual screen by the X server (or by a separate composite manager) as directed by the window manager, which usually communicates with the user via graphical controls such as buttons and draggable titlebars and borders.
For a comprehensive overview of X Server and X Window System, consult the following article: https://en.wikipedia.org/wiki/X_server
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