• [FreeBSD-Announce] FreeBSD Security Advisory FreeBSD-SA-21:06.xen

    From FreeBSD Security Advisories@21:1/5 to All on Wed Feb 24 07:00:02 2021
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    ============================================================================= 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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