CVE-2018-19364 Qemu: 9pfs: Use-after-free due to race condition while updating fid path

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

  Hello,

A use-after-free flaw was found in the VirtFS, host directory sharing via Plan 
9 File System(9pfs) support in QEMU. It could occur due to a race condition in 
updating fid path in worker threads via v9fs_path_copy(), while accessing 
files on a shared host directory.

A user inside guest could use this flaw to crash the QEMU process resulting in 
DoS issue.

Upstream patch:
---------------
  -> https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg01139.html
  -> https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg02795.html

This issue was reported by Zhibin hu.

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