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FreeBSD-SA-16:10.linux Security Advisory
The FreeBSD Project

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

Category: core
Module: kernel
Announced: 2016-01-27
Credits: Isaac Dunham, Brent Cook, Warner Losh
Affects: All supported versions of FreeBSD.
Corrected: 2016-01-27 07:28:55 UTC (stable/10, 10.2-STABLE)
2016-01-27 07:41:31 UTC (releng/10.2, 10.2-RELEASE-p11)
2016-01-27 07:41:31 UTC (releng/10.1, 10.1-RELEASE-p28)
2016-01-27 07:34:23 UTC (stable/9, 9.3-STABLE)
2016-01-27 07:42:11 UTC (releng/9.3, 9.3-RELEASE-p35)
CVE Name: CVE-2016-1883

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 could cause the
issetugid(2) system call to return incorrect information.

III. Impact

If an application relies on output of the issetugid(2) system call
and that information is incorrect, this could lead to 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.

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-16:10/linux.patch
# fetch https://security.FreeBSD.org/patches/SA-16:10/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

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/ r294903
releng/9.3/ r294905
stable/10/ r294901
releng/10.1/ r294904
releng/10.2/ r294904
– ————————————————————————-

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-2016-1883>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:10.linux.asc>
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