composite: Fix use-after-free of the COW

ZDI-CAN-19866/CVE-2023-1393

If a client explicitly destroys the compositor overlay window (aka COW),
we would leave a dangling pointer to that window in the CompScreen
structure, which will trigger a use-after-free later.

Make sure to clear the CompScreen pointer to the COW when the latter gets
destroyed explicitly by the client.

This vulnerability was discovered by:
Jan-Niklas Sohn working with Trend Micro Zero Day Initiative

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
(cherry picked from commit 26ef545b3502f61ca722a7a3373507e88ef64110)

0 files changed, 0 insertions, 0 deletions