-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512
=============================================================================
FreeBSD-SA-21:06.xen Security Advisory
The FreeBSD Project
Topic: Xen grant mapping error handling issues
Category: contrib
Module: xen
Announced: 2021-02-24
Credits: See Xen XSA-361 for details
Affects: All supported versions of FreeBSD.
Corrected: 2021-02-23 00:55:14 UTC (stable/13, 13.0-STABLE)
2021-02-24 01:42:35 UTC (releng/13.0, 13.0-BETA3-p1)
2021-02-23 00:58:03 UTC (stable/12, 12.2-STABLE)
2021-02-24 01:43:59 UTC (releng/12.2, 12.2-RELEASE-p4)
2021-02-23 00:59:23 UTC (stable/11, 11.4-STABLE)
2021-02-24 01:41:51 UTC (releng/11.4, 11.4-RELEASE-p8)
CVE Name: CVE-2021-26932
For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.
I. Background
Xen is a type-1 hypervisor which supports FreeBSD as a Dom0 (or host domain).
II. Problem Description
Grant mapping operations often occur in batch hypercalls, where a number of
operations are done in a single hypercall, the success or failure of each one
reported to the backend driver, and the backend driver then loops over the
results, performing follow-up actions based on the success or failure of each
operation.
Unfortunately, when running in HVM/PVH mode, the FreeBSD backend drivers
mishandle this: Some errors are ignored, effectively implying their success
from the success of related batch elements. In other cases, errors resulting
from one batch element lead to further batch elements not being inspected,
and hence successful ones to not be possible to properly unmap upon error
recovery.
III. Impact
A malicious or buggy frontend driver may be able to cause resource leaks
in the domain running the corresponding backend driver.
IV. Workaround
No workaround is available. FreeBSD systems not using Xen are not
affected.
V. Solution
Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date
and reboot.
Perform one of the following:
1) To update your vulnerable system via a binary patch:
Systems running a RELEASE version of FreeBSD on the i386 or amd64
platforms can be updated via the freebsd-update(8) utility:
# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for a security update"
2) To update your vulnerable system via a source code patch:
The following patches have been verified to apply to the applicable
FreeBSD release branches.
a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.
# fetch https://security.FreeBSD.org/patches/SA-21:06/xen.patch
# fetch https://security.FreeBSD.org/patches/SA-21:06/xen.patch.asc
# gpg --verify xen.patch.asc
b) Apply the patch. Execute the following commands as root:
# cd /usr/src
# patch < /path/to/patch
c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.
VI. Correction details
The following list contains the correction revision numbers for each
affected branch.
Branch/path Revision
- -------------------------------------------------------------------------
stable/13/ ab3e1bd3c22a222520c23c2793cc39e3a23c9b46
releng/13.0/ ce9af53d0897a1cb926bd244f499fc09b1626b27
stable/12/ r369341
releng/12.2/ r369358
stable/11/ r369342
releng/11.4/ r369350
- -------------------------------------------------------------------------
[FreeBSD 13.x]
To see which files were modified by a particular revision, run the following
command in a checked out git repository, replacing NNNNNN with the revision
hash:
# git show --stat NNNNNN
Or visit the following URL, replace NNNNNN with the revision hash:
<URL:https://cgit.freebsd.org/src/commit/?id=NNNNNN>
[FreeBSD 11.x, FreeBSD 12.x]
To see which files were modified by a particular revision, run the
following command, replacing NNNNNN with the revision number, on a
machine with Subversion installed:
# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base
Or visit the following URL, replacing NNNNNN with the revision number:
<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>
VII. References
<URL:https://xenbits.xen.org/xsa/advisory-361.html>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-26932>
The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-21:06.xen.asc>
-----BEGIN PGP SIGNATURE-----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=fN2Q
-----END PGP SIGNATURE-----