CVE-2017-13673 Qemu: vga: reachable assert failure during during display update

[P J P <ppandit () redhat com>]

  Hello,

Quick emulator(Qemu) built with the VGA display emulator support is vulnerable 
to an assert failure issue. It could occur while updating graphics display, 
due to miscalculating region for dirty bitmap snapshot in split screen mode.

A privileged user/process inside guest could use this flaw to crash the Qemu 
process on the host resulting in DoS.

Upstream patch:
---------------
  -> https://lists.gnu.org/archive/html/qemu-devel/2017-08/msg04685.html

Reference:
----------
  -> https://bugzilla.redhat.com/show_bug.cgi?id=1486588

This issue was reported by David Buchanan.

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
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