CVE-2014-3672 libvirt: DoS via excessive logging

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

  Hello,

A while back, Mr Andrew Sorensen reported a Qemu logging issue wherein Libvirt 
OR Xen directed 'stderr' of Qemu to a log file on the host.

This can be easily exploited by a user inside guest to flood the log file with 
endless messages, resulting in a DoS situation on the host, affecting other 
services and guests alike.

'CVE-2014-3672' was assigned to it by Red Hat Inc.

Until recently there was no remedy in sight, but quoting Mr Daniel P Berrange 
of libvirt

  "Since libvirt version 1.3.3, libvirt has 'virtlogd' daemon running. The
   QEMU stdout/err are no longer connected directly to a file on disk, instead
   they go to a pipe connected to virtlogd. virtlogd only allows 128 kb of
   data to be written before rolling over the logs, and only keeps 3 backups,
   so there is no longer an uncontrolled denial of service.

   With QEMU 2.6, it is further possible to use virtlogd in association with
   QEMU serial ports that need to log to a file, for the same reason."

Upstream patch:
---------------
  -> https://libvirt.org/git/?p=libvirt.git;a=commit;h=0d968ad715475a1660779bcdd2c5b38ad63db4cf

Note: It's probably not feasible to back port this solution to older versions.

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