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FreeBSD-SA-16:18.atkbd Security Advisory
The FreeBSD Project

Topic: Buffer overflow in keyboard driver

Category: core
Module: atkbd
Announced: 2016-05-17
Credits: CTurt and the HardenedBSD team
Affects: All supported versions of FreeBSD.
Corrected: 2016-05-17 22:29:59 UTC (stable/10, 10.3-STABLE)
2016-05-17 22:28:27 UTC (releng/10.3, 10.3-RELEASE-p3)
2016-05-17 22:28:20 UTC (releng/10.2, 10.2-RELEASE-p17)
2016-05-17 22:28:11 UTC (releng/10.1, 10.1-RELEASE-p34)
2016-05-17 22:31:12 UTC (stable/9, 9.3-STABLE)
2016-05-17 22:28:36 UTC (releng/9.3, 9.3-RELEASE-p42)
CVE Name: CVE-2016-1886

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

The atkbd(4) driver, together with the atkbdc(4) driver, provides access
to the AT 84 keyboard or the AT enhanced keyboard which is connected to
the AT keyboard controller. The driver is required for the console driver
syscons(4) or vt(4). The driver exposes its own ioctl(2) interface to allow
it to be configured from userland through the kbdcontrol(1) utility.

II. Problem Description

Incorrect signedness comparison in the ioctl(2) handler allows a malicious
local user to overwrite a portion of the kernel memory.

III. Impact

A local user may crash the kernel, read a portion of kernel memory and
execute arbitrary code in kernel context. The result of executing an
arbitrary kernel code is privilege escalation.

IV. Workaround

Disallow keymap changes for non-privileged users:

sysctl hw.kbd.keymap_restrict_change=4

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 is required.

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 is required.

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-16:18/atkbd.patch
# fetch https://security.FreeBSD.org/patches/SA-16:18/atkbd.patch.asc
# gpg –verify atkbd.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/9/ r300093
releng/9.3/ r300088
stable/10/ r300091
releng/10.1/ r300085
releng/10.2/ r300086
releng/10.3/ r300087
– ————————————————————————-

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:http://cturt.github.io/SETFKEY.html>
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2016-1886>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:18.atkbd.asc>
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