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FreeBSD Security Advisory FreeBSD-SA-16:20.linux



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FreeBSD-SA-16:20.linux                                      Security Advisory
                                                          The FreeBSD Project

Topic:          Kernel stack disclosure in Linux compatibility layer

Category:       core
Module:         linux(4)
Announced:      2016-05-31
Credits:        CTurt
Affects:	All supported versions of FreeBSD.
Corrected:      2016-05-31 16:57:42 UTC (stable/10, 10.3-STABLE)
                2016-05-31 16:55:50 UTC (releng/10.3, 10.3-RELEASE-p4)
                2016-05-31 16:55:45 UTC (releng/10.2, 10.2-RELEASE-p18)
                2016-05-31 16:55:41 UTC (releng/10.1, 10.1-RELEASE-p35)
                2016-05-31 16:58:00 UTC (stable/9, 9.3-STABLE)
                2016-05-31 16:55:37 UTC (releng/9.3, 9.3-RELEASE-p43)

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
for amd64 and i386 machines.

II.  Problem Description

The implementation of the TIOCGSERIAL ioctl(2) does not clear the output
struct before copying it out to userland.

The implementation of the Linux sysinfo() system call does not clear the
output struct before copying it out to userland.

III. Impact

An unprivileged user can read a portion of uninitialised kernel stack data,
which may contain sensitive information, such as the stack guard, portions
of the file cache or terminal buffers, which an attacker might leverage to
obtain elevated privileges.

IV.  Workaround

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

The Linux compatibility layer is not included in the default GENERIC kernel.

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 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-16:20/linux.patch
# fetch https://security.FreeBSD.org/patches/SA-16:20/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/                                                         r301055
releng/9.3/                                                       r301049
stable/10/                                                        r301054
releng/10.1/                                                      r301050
releng/10.2/                                                      r301051
releng/10.3/                                                      r301052
- -------------------------------------------------------------------------

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/compat-info-leaks.html>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-16:20.linux.asc>
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