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            Xen Security Advisory CVE-2022-33743 / XSA-405
                               version 3

       network backend may cause Linux netfront to use freed SKBs

UPDATES IN VERSION 3
====================

Public release.

ISSUE DESCRIPTION
=================

While adding logic to support XDP (eXpress Data Path), a code label was
moved in a way allowing for SKBs having references (pointers) retained
for further processing to nevertheless be freed.

IMPACT
======

A misbehaving or malicious backend may cause a Denial of Service (DoS)
in the guest.  Information leaks or privilege escalation cannot be
ruled out.

VULNERABLE SYSTEMS
==================

Linux versions 5.9 - 5.18 are vulnerable.  Linux versions 5.8 and
earlier are not vulnerable.

This vulnerability only increases the capability of an attacker in systems
with less than fully privileged network backends (e.g. network driver
domains).  For systems where netback runs in dom0 (the default
configuration), this vulnerability does not increase the capabilities of
an attacker.

MITIGATION
==========

There is no mitigation available other than not using PV devices in case
a backend is suspected to be potentially malicious.

CREDITS
=======

This issue was discovered by Jan Beulich of SUSE.

RESOLUTION
==========

Applying the appropriate attached patch resolves this issue.

Note that patches for released versions are generally prepared to
apply to the stable branches, and may not apply cleanly to the most
recent release tarball.  Downstreams are encouraged to update to the
tip of the stable branch before applying these patches.

xsa405-linux.patch     Linux 5.9 - 5.19-rc

$ sha256sum xsa405*
69716b78fbd996bce0414079bbb5f002029c5a82924aaae0db78a13c4b385f0a  xsa405-linux.patch
$

DEPLOYMENT DURING EMBARGO
=========================

Deployment of patches or mitigations is NOT permitted (except where
all the affected systems and VMs are administered and used only by
organisations which are members of the Xen Project Security Issues
Predisclosure List).  Specifically, deployment on public cloud systems
is NOT permitted.

This is because the patches need to be applied in the affected guests.
Switching from PV to non-PV devices is observable by the guests and has
usually a bad performance impact.

Deployment is permitted only AFTER the embargo ends.

(Note: this during-embargo deployment notice is retained in
post-embargo publicly released Xen Project advisories, even though it
is then no longer applicable.  This is to enable the community to have
oversight of the Xen Project Security Team's decisionmaking.)

For more information about permissible uses of embargoed information,
consult the Xen Project community's agreed Security Policy:
  http://www.xenproject.org/security-policy.html
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