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FreeBSD-SA-16:03.linux                                      Security Advisory
                                                          The FreeBSD Project

Topic:          Linux compatibility layer incorrect futex handling

Category:       core
Module:         kernel
Announced:      2016-01-14
Credits:        Mateusz Guzik
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-2016-1880

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 handling of Linux futex robust lists may result
in incorrect memory locations being accessed.

III. Impact

It is possible for a local attacker to read portions of kernel memory, which
may result in a privilege escalation. 

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.

2) 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-16:03/linux.patch
# fetch https://security.FreeBSD.org/patches/SA-16:03/linux.patch.asc

b) Apply the patch.

# 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 and modules 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 revision numbers of each file that was
corrected in FreeBSD.

Subversion:

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

VII. References

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-1880>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:03.linux.asc>
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