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FreeBSD-SA-14:07.devfs Security Advisory
The FreeBSD Project

Topic: devfs rules not applied by default for jails

Category: core
Module: etc_rc.d
Announced: 2014-04-30
Affects: FreeBSD 10.0
Corrected: 2014-04-30 04:03:05 UTC (stable/10, 10.0-STABLE)
2014-04-30 04:04:42 UTC (releng/10.0, 10.0-RELEASE-p2)
CVE Name: CVE-2014-3001

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 device file system, or devfs(5), provides access to kernel’s device
namespace in the global file system namespace.

The devfs(5) rule subsystem provides a way for the administrator of a system
to control the attributes of DEVFS nodes. Each DEVFS mount-point has a
“ruleset”, or a list of rules, associated with it, allowing the
administrator to change the properties, including the visibility, of certain
nodes.

II. Problem Description

The default devfs rulesets are not loaded on boot, even when jails are used.
Device nodes will be created in the jail with their normal default access
permissions, while most of them should be hidden and inaccessible.

III. Impact

Jailed processes can get access to restricted resources on the host system.
For jailed processes running with superuser privileges this implies access
to all devices on the system. This level of access could lead to information
leakage and privilege escalation.

IV. Workaround

Systems that do not run jails are not affected.

The system administrator can do the following to load the default ruleset:

/etc/rc.d/devfs onestart

Then apply the default ruleset for jails on a devfs mount using:

devfs -m ${devfs_mountpoint} rule -s 4 applyset

Or, alternatively, the following command will apply the ruleset over all devfs
mountpoints except the host one:

mount -t devfs | grep -v ‘^devfs on /dev ‘ | awk ‘{print $3;}’ | \
xargs -n 1 -J % devfs -m % rule -s 4 applyset

After this, the system administrator should add the following configuration
to /etc/rc.conf to make it permanent, so the above operations do not have
to be done each time the host system reboots.

devfs_load_rulesets=”YES”

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-14:07/devfs.patch
# fetch http://security.FreeBSD.org/patches/SA-14:07/devfs.patch.asc
# gpg –verify devfs.patch.asc

b) Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch
# install -o root -g wheel -m 444 etc/defaults/rc.conf /etc/defaults/

Follow the steps described in the “Workaround” section, or 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/10/ r265122
releng/10.0/ r265124
– ————————————————————————-

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-2014-3001>

The latest revision of this advisory is available at
<URL:http://security.FreeBSD.org/advisories/FreeBSD-SA-14:07.devfs.asc>
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