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  • FreeBSD Errata Notice FreeBSD-EN-24:12.killpg

    From FreeBSD Errata Notices@21:1/5 to All on Wed Jun 19 22:00:13 2024
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    ============================================================================= FreeBSD-EN-24:12.killpg Errata Notice
    The FreeBSD Project

    Topic: Lock order reversal in killpg causing livelock

    Category: core
    Module: kern
    Announced: 2024-06-19
    Credits: Peter Holm <pho@FreeBSD.org>
    Konstantin Belousov <kib@FreeBSD.org>
    Michael Gmelin <grembo@FreeBSD.org>
    Affects: FreeBSD 13.3
    Corrected: 2024-05-22 23:47:55 UTC (stable/13, 13.3-STABLE)
    2024-06-19 20:37:09 UTC (releng/13.3, 13.3-RELEASE-p3)

    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

    killpg(2) is a system call that sends signals to process groups.
    In order to prevent race conditions with the fork(2) system call,
    locking is required.

    II. Problem Description

    The code designed to prevent lock order reversals between killpg(2)
    and fork(2) did not wait for lock availability before retrying to
    acquire a lock, which could result in a livelock causing very high
    system load.

    III. Impact

    Affected machines are practically unusable. They recover if the
    processes causing the load are killed.

    IV. Workaround

    No workaround is available. Systems that fork a lot are more likely to
    to hit this problem.

    V. Solution

    Upgrade your 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 system via a binary patch:

    Systems running a RELEASE version of FreeBSD on the amd64 or arm64 platforms, or the i386 platform on FreeBSD 13, can be updated via the freebsd-update(8) utility:

    # freebsd-update fetch
    # freebsd-update install
    # shutdown -r +10m "Rebooting for a stability patch"

    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-24:12/killpg.patch
    # fetch https://security.FreeBSD.org/patches/EN-24:12/killpg.patch.asc
    # gpg --verify killpg.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

    This issue is corrected as of the corresponding Git commit hash in the following stable and release branches:

    Branch/path Hash Revision
    - ------------------------------------------------------------------------- stable/13/ cd73b38955f6 stable/13-n257926 releng/13.3/ eb410545d00d releng/13.3-n257435
    - -------------------------------------------------------------------------

    Run the following command to see which files were modified by a
    particular commit:

    # git show --stat <commit hash>

    Or visit the following URL, replacing NNNNNN with the hash:

    <URL:https://cgit.freebsd.org/src/commit/?id=NNNNNN>

    To determine the commit count in a working tree (for comparison against
    nNNNNNN in the table above), run:

    # git rev-list --count --first-parent HEAD

    VII. References

    <URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=279203>

    The latest revision of this advisory is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-24:12.killpg.asc> -----BEGIN PGP SIGNATURE-----

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