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FreeBSD-EN-20:17.linuxthread                                    Errata Notice
                                                          The FreeBSD Project

Topic:          FreeBSD Linux ABI kernel panic

Category:       core
Module:         kernel
Announced:      2020-09-02
Credits:        Martin Filla
		Henrique L. Amorim, Independent Security Researcher
		Rodrigo Rubira Branco (BSDaemon), Amazon Web Services
Affects:        All supported versions of FreeBSD.
Corrected:      2020-06-25 05:24:35 UTC (stable/12, 12.1-STABLE)
                2020-09-02 16:21:27 UTC (releng/12.1, 12.1-RELEASE-p9)
                2020-06-25 05:35:46 UTC (stable/11, 11.4-STABLE)
                2020-09-02 16:21:27 UTC (releng/11.4, 11.4-RELEASE-p3)
                2020-09-02 16:21:27 UTC (releng/11.3, 11.3-RELEASE-p13)

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

The Linux ABI layer (Linuxulator) allows Linux binaries to be executed on a
FreeBSD kernel.

II.  Problem Description

The kernel function handling exec(3) of a Linux binary did not correctly
handle a calling process with multiple threads.

III. Impact

A multithread non-Linux process execing a Linux binary would fail a kernel
assertion, resuting in a kernel panic "thread_detach: emuldata not found."

IV.  Workaround

No workaround is available.  Systems not using the Linux ABI layer are not
affected.

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 i386 or amd64
platforms can be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for an 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-20:17/linuxthread.patch
# fetch https://security.FreeBSD.org/patches/EN-20:17/linuxthread.patch.asc
# gpg --verify linuxthread.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/                                                        r362605
releng/12.1/                                                      r365253
stable/11/                                                        r362606
releng/11.4/                                                      r365253
releng/11.3/                                                      r365253
- -------------------------------------------------------------------------

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://bugs.freebsd.org/bugzilla/show_bug.cgi?id=247020>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-20:17.linuxthread.asc>
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