-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

=============================================================================
FreeBSD-SA-16:04.linux                                      Security Advisory
                                                          The FreeBSD Project

Topic:          Linux compatibility layer setgroups(2) system call
                vulnerability

Category:       core
Module:         kernel
Announced:      2016-01-14
Credits:        Dmitry Chagin
Affects:        All supported versions of FreeBSD
Corrected:      2016-01-14 09:11:42 UTC (stable/10, 10.2-STABLE)
                2016-01-14 09:10:46 UTC (releng/10.2, 10.2-RELEASE-p9)
                2016-01-14 09:11:16 UTC (releng/10.1, 10.1-RELEASE-p26)
                2016-01-14 09:11:48 UTC (stable/9, 9.3-STABLE)
                2016-01-14 09:11:26 UTC (releng/9.3, 9.3-RELEASE-p33)
CVE Name:       CVE-2016-1881

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

FreeBSD is binary-compatible with the Linux operating system through a
loadable kernel module/optional kernel component.  The support is
provided on amd64 and i386 machines.

II.  Problem Description

A programming error in the Linux compatibility layer setgroups(2) system
call can lead to an unexpected results, such as overwriting random kernel
memory contents.

III. Impact

It is possible for a local attacker to overwrite portions of kernel
memory, which may result in a privilege escalation or cause a system
panic.

IV.  Workaround

No workaround is available, but systems not using the Linux binary
compatibility layer are not vulnerable.

The following command can be used to test if the Linux binary
compatibility layer is loaded:

# kldstat -m linuxelf

V.   Solution

Perform one of the following:

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

Reboot the system or unload and reload the linux.ko kernel module.

2) 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

Reboot the system or unload and reload the linux.ko kernel module.

3) 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-16:04/linux.patch
# fetch https://security.FreeBSD.org/patches/SA-16:04/linux.patch.asc
# gpg --verify linux.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch
# cd /usr/src/amd64/linux32
# make sysent
# cd /usr/src/i386/linux
# make sysent

c) Recompile your kernel as described in
<URL:https://www.FreeBSD.org/handbook/kernelconfig.html>.

Reboot the system or unload and reload the linux.ko kernel module.

VI.  Correction details

The following list contains the correction revision numbers for each
affected branch.

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/9/                                                         r293898
releng/9.3/                                                       r293896
stable/10/                                                        r293897
releng/10.1/                                                      r293894
releng/10.2/                                                      r293893
- -------------------------------------------------------------------------

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://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-1881>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:04.linux.asc>
-----BEGIN PGP SIGNATURE-----
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=JKVW
-----END PGP SIGNATURE-----