NVIDIA UNIX driver -- ARGB cursor buffer overflow in "NoScanout" mode

NVIDIA Unix security team reports:

When the NVIDIA driver for the X Window System is operated in
“NoScanout” mode, and an X client installs an ARGB cursor that
is larger than the expected size (64x64 or 256x256, depending on
the driver version), the driver will overflow a buffer. This
can cause a denial of service (e.g., an X server segmentation
fault), or could be exploited to achieve arbitrary code
execution. Because the X server runs as setuid root in many
configurations, an attacker could potentially use this
vulnerability in those configurations to gain root privileges.