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FreeBSD Applications using libkvm may leak sensitive descriptors


FreeBSD-SA-02:39.libkvm                                     Security Advisory
                                                          The FreeBSD Project

Topic:          Applications using libkvm may leak sensitive descriptors

Category:       core
Module:         libkvm
Announced:      2002-09-16
Credits:        David Endler <DEndler@iDefense.com>,
Affects:        All releases prior to and including 4.6.2-RELEASE.
                Security branch releases prior to 4.4-RELEASE-p27,
                4.5-RELEASE-p20, and 4.6.2-RELEASE-p2.
Corrected:      2002-09-13 14:53:43 UTC (RELENG_4)
                2002-09-13 15:04:22 UTC (RELENG_4_6)
                2002-09-13 15:07:26 UTC (RELENG_4_5)
                2002-09-13 15:09:07 UTC (RELENG_4_4)
FreeBSD only:   NO

I.   Background

The kvm(3) library provides a uniform interface for accessing kernel
virtual memory images, including live systems and crash dumps.  Access
to live systems is via /dev/mem and /dev/kmem.  Memory can be read and
written, kernel symbol addresses can be looked up efficiently, and
information about user processes can be gathered.

The kvm_openfiles(3) function opens the special device files /dev/mem
and /dev/kmem, and returns an opaque handle that must be passed
to the other library functions.

II.  Problem Description

Applications that wish to present system information such as swap
utilization, virtual memory utilization, CPU utilization, and
so on may use the kvm(3) library to read kernel memory directly
And gather this information.  Such applications typically must
be run set-group-ID kmem so that the call to kvm_openfiles(3)
can access /dev/mem and /dev/kmem.

If the application then uses exec(2) to start another application,
the new application will continue to have open file descriptors to
/dev/mem and /dev/kmem.  This is usually avoided by marking file
descriptors as close-on-exec, but since the handle returned by
kvm_openfiles(3) is opaque, there is no direct way for the application
to determine what file descriptors have been opened by the library.
As a result, application writers may neglect to take these file
descriptors into account.

III. Impact

Set-group-ID kmem applications which use kvm(3) and start other
applications may leak /dev/mem and /dev/kmem file descriptors.  If
those applications can be specified by a local user, they may be
used to read kernel memory, resulting in disclosure of sensitive
information such as file, network, and tty buffers, authentication
tokens, and so on.

Several applications in the FreeBSD Ports Collection were identified
that are affected: asmon, ascpu, bubblemon, wmmon, and wmnet2.  There
may be other applications as well.

IV.  Workaround

Remove the set-group-ID bit on affected applications.  This will
result in the applications losing some functionality.

V.   Solution

Do one of the following:

1) Upgrade your vulnerable system to 4.6-STABLE; or to the RELENG_4_6,
RELENG_4_5, or RELENG_4_4 security branch dated after the correction
date (4.6.2-RELEASE-p2, 4.5-RELEASE-p20, or 4.4-RELEASE-p27).

2) To patch your present system:

The following patch has been verified to apply to FreeBSD 4.4, FreeBSD
4.5, FreeBSD 4.6, and FreeBSD 4.6.2 systems.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:39/libkvm.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:39/libkvm.patch.asc

b) Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch
# cd /usr/src/lib/libkvm
# make depend && make && make install

VI.  Correction details

The following list contains the revision numbers of each file that was
corrected in FreeBSD.

Path                                                             Revision
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Version: GnuPG v1.0.7 (FreeBSD)


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