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FreeBSD-SA-14:12.ktrace Security Advisory
The FreeBSD Project

Topic: ktrace kernel memory disclosure

Category: core
Module: kern
Announced: 2014-06-03
Credits: Jilles Tjoelker
Affects: FreeBSD 8.4, FreeBSD 9.1 and FreeBSD 9.2
Corrected: 2014-06-03 19:02:33 UTC (stable/9, 9.3-BETA1)
2014-06-03 19:02:33 UTC (stable/9, 9.3-BETA1-p1)
2014-06-03 19:03:11 UTC (releng/9.2, 9.2-RELEASE-p7)
2014-06-03 19:03:11 UTC (releng/9.1, 9.1-RELEASE-p14)
2014-06-03 19:02:42 UTC (stable/8, 8.4-STABLE)
2014-06-03 19:03:23 UTC (releng/8.4, 8.4-RELEASE-p11)
CVE Name: CVE-2014-3873

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:http://security.FreeBSD.org/>.

I. Background

The ktrace utility enables kernel trace logging for the specified processes,
commonly used for diagnostic or debugging purposes. The kernel operations
that are traced include system calls, namei translations, signal processing,
and I/O as well as data associated with these operations.

The utility may be used only with a kernel that has been built with the
“KTRACE” option in the kernel configuration file, which is enabled by
default.

II. Problem Description

Due to an overlooked merge to -STABLE branches, the size for page fault
kernel trace entries was set incorrectly.

III. Impact

A user who can enable kernel process tracing could end up reading the
contents of kernel memory.

Such memory might contain sensitive information, such as portions of the
file cache or terminal buffers. This information might be directly
useful, or it might be leveraged to obtain elevated privileges in some
way; for example, a terminal buffer might include a user-entered
password.

IV. Workaround

The system administrator may set sysctl security.bsd.unprivileged_proc_debug
to 0 to prevent non-privileged users from using all process debugging
facilities provided by the kernel, that includes ktrace functionality.
Please note that this flag have broad effect and may break applications,
as some of them may rely on certain debugging facilities to function.

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.

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 http://security.FreeBSD.org/patches/SA-14:12/ktrace.patch
# fetch http://security.FreeBSD.org/patches/SA-14:12/ktrace.patch.asc
# gpg –verify ktrace.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:http://www.FreeBSD.org/handbook/kernelconfig.html> and reboot the
system.

3) 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

VI. Correction details

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

Branch/path Revision
– ————————————————————————-
stable/8/ r267016
releng/8.4/ r267019
stable/9/ r267015
releng/9.1/ r267018
releng/9.2/ r267018
– ————————————————————————-

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:http://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2014-3873>

The latest revision of this advisory is available at
<URL:http://security.FreeBSD.org/advisories/FreeBSD-SA-14:12.ktrace.asc>
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