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  • [FreeBSD-Announce] FreeBSD Errata Notice FreeBSD-EN-19:14.epoch

    From FreeBSD Errata Notices@21:1/5 to All on Tue Aug 13 05:48:38 2019
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    ============================================================================= FreeBSD-EN-19:14.epoch Errata Notice
    The FreeBSD Project

    Topic: Incorrect locking in epoch(9)

    Category: core
    Module: kernel
    Announced: 2019-08-06
    Credits: Mark Johnston
    Affects: FreeBSD 12.0
    Corrected: 2019-07-27 16:11:04 UTC (stable/12, 12.0-STABLE)
    2019-08-06 17:07:43 UTC (releng/12.0, 12.0-RELEASE-p9)

    For general information regarding FreeBSD Errata Notices and Security Advisories, including descriptions of the fields above, security
    branches, and the following sections, please visit <URL:https://security.FreeBSD.org/>.

    I. Background

    Some parts of the kernel use a new synchronization primitive, epoch(9),
    which can be used to implement safe memory reclamation. In this usage,
    threads can use the epoch(9) KPI to ensure that no other threads hold
    a reference to a given object in memory.

    II. Problem Description

    In the case where epoch(9) must wait for a thread that is blocked on
    a lock, it will use the turnstile(9) KPI to propagate the current
    thread's priority to the lock holder. However, in the case where the
    lock has no designated owner - for example, it is a reader-writer lock
    owned by one or more readers - a bug in the interaction with the
    turnstile meant that pair of spin locks were left locked when they
    should have been unlocked.

    III. Impact

    In rare cases and under heavy load, the kernel may panic or lock up.

    IV. Workaround

    No workaround is available.

    V. Solution

    Upgrade your system to a supported FreeBSD stable or release / security
    branch (releng) dated after the correction date, and reboot.

    1) To update your 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 errata update"

    2) To update your 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/EN-19:14/epoch.patch
    # fetch https://security.FreeBSD.org/patches/EN-19:14/epoch.patch.asc
    # gpg --verify epoch.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/12/ r350373 releng/12.0/ r350641
    - -------------------------------------------------------------------------

    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

    The latest revision of this advisory is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-19:14.epoch.asc> -----BEGIN PGP SIGNATURE-----

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