125 lines
4.6 KiB
Text
125 lines
4.6 KiB
Text
-----BEGIN PGP SIGNED MESSAGE-----
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Hash: SHA512
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=============================================================================
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FreeBSD-EN-19:14.epoch Errata Notice
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The FreeBSD Project
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Topic: Incorrect locking in epoch(9)
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Category: core
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Module: kernel
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Announced: 2019-08-06
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Credits: Mark Johnston
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Affects: FreeBSD 12.0
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Corrected: 2019-07-27 16:11:04 UTC (stable/12, 12.0-STABLE)
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2019-08-06 17:07:43 UTC (releng/12.0, 12.0-RELEASE-p9)
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For general information regarding FreeBSD Errata Notices and Security
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Advisories, including descriptions of the fields above, security
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branches, and the following sections, please visit
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<URL:https://security.FreeBSD.org/>.
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I. Background
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Some parts of the kernel use a new synchronization primitive, epoch(9),
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which can be used to implement safe memory reclamation. In this usage,
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threads can use the epoch(9) KPI to ensure that no other threads hold
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a reference to a given object in memory.
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II. Problem Description
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In the case where epoch(9) must wait for a thread that is blocked on
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a lock, it will use the turnstile(9) KPI to propagate the current
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thread's priority to the lock holder. However, in the case where the
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lock has no designated owner - for example, it is a reader-writer lock
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owned by one or more readers - a bug in the interaction with the
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turnstile meant that pair of spin locks were left locked when they
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should have been unlocked.
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III. Impact
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In rare cases and under heavy load, the kernel may panic or lock up.
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IV. Workaround
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No workaround is available.
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V. Solution
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Upgrade your system to a supported FreeBSD stable or release / security
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branch (releng) dated after the correction date, and reboot.
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1) To update your system via a binary patch:
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Systems running a RELEASE version of FreeBSD on the i386 or amd64
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platforms can be updated via the freebsd-update(8) utility:
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# freebsd-update fetch
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# freebsd-update install
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# shutdown -r +10min "Rebooting for errata update"
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2) To update your system via a source code patch:
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The following patches have been verified to apply to the applicable
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FreeBSD release branches.
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a) Download the relevant patch from the location below, and verify the
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detached PGP signature using your PGP utility.
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# fetch https://security.FreeBSD.org/patches/EN-19:14/epoch.patch
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# fetch https://security.FreeBSD.org/patches/EN-19:14/epoch.patch.asc
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# gpg --verify epoch.patch.asc
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b) Apply the patch. Execute the following commands as root:
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# cd /usr/src
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# patch < /path/to/patch
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c) Recompile your kernel as described in
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<URL:https://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
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system.
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VI. Correction details
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The following list contains the correction revision numbers for each
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affected branch.
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Branch/path Revision
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- -------------------------------------------------------------------------
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stable/12/ r350373
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releng/12.0/ r350641
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- -------------------------------------------------------------------------
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To see which files were modified by a particular revision, run the
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following command, replacing NNNNNN with the revision number, on a
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machine with Subversion installed:
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# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base
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Or visit the following URL, replacing NNNNNN with the revision number:
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<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>
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VII. References
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The latest revision of this advisory is available at
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<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-19:14.epoch.asc>
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