Qemu: usb: Infinite loop vulnerability in usb_ehci using siTD process

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

  Hello,

Qemu emulator built with the USB EHCI emulation support is vulnerable to an 
infinite loop issue. It occurs during communication between host controller 
interface(EHCI) and a respective device driver. These two communicate via a 
split isochronous transfer descriptor list(siTD) and an infinite loop unfolds 
if there is a closed loop in this list.

A privileges used inside guest could use this flaw to consume excessive CPU 
cycles & resources on the host.

This issue is similar to CVE-2015-8558, but using siTD instead of iTD.

Upstream patch:
---------------
  -> https://lists.gnu.org/archive/html/qemu-devel/2016-04/msg02691.html

Reference:
----------
  -> https://bugzilla.redhat.com/show_bug.cgi?id=1325129

This issue are discovered by Du Shaobo of Qihoo 360 Inc.

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