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FreeBSD-SA-09:13.pipe                                       Security Advisory
                                                          The FreeBSD Project

Topic:          kqueue pipe race conditions
Category:       core
Module:         kern
Announced:      2009-10-02
Credits:        Przemyslaw Frasunek
Affects:        FreeBSD 6.x
Corrected:      2009-10-02 18:09:56 UTC (RELENG_6, 6.4-STABLE)
                2009-10-02 18:09:56 UTC (RELENG_6_4, 6.4-RELEASE-p7)
                2009-10-02 18:09:56 UTC (RELENG_6_3, 6.3-RELEASE-p13)

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

Pipes are a form of inter-process communication (IPC) provided by the
FreeBSD kernel.  kqueue is an event management API that applications can
use to monitor pipes and other kernel services.

II.  Problem Description

A race condition exists in the pipe close() code relating to kqueues,
causing use-after-free for kernel memory, which may lead to an
exploitable NULL pointer vulnerability in the kernel, kernel memory
corruption, and other unpredictable results.

III. Impact

Successful exploitation of the race condition can lead to local kernel
privilege escalation, kernel data corruption and/or crash.

To exploit this vulnerability, an attacker must be able to run code on
the target system.

IV.  Workaround

An errata notice, FreeBSD-EN-09:05.null has been released simultaneously to
this advisory, and contains a kernel patch implementing a workaround for a
more broad class of vulnerabilities.  However, prior to those changes, no
workaround is available.

V.   Solution

Perform one of the following:

1) Upgrade your vulnerable system to 6-STABLE, or to the RELENG_6_4, or
RELENG_6_3 security branch dated after the correction date.

2) To patch your present system:

The following patches have been verified to apply to FreeBSD 6.3 and 6.4.

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-09:13/pipe.patch
# fetch http://security.FreeBSD.org/patches/SA-09:13/pipe.patch.asc

b) Apply the patch.

# 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.

VI.  Correction details

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

CVS:

Branch                                                           Revision
  Path
- -------------------------------------------------------------------------
RELENG_6
  src/sys/kern/kern_event.c                                      1.93.2.7
  src/sys/kern/kern_fork.c                                      1.252.2.8
  src/sys/kern/sys_pipe.c                                       1.184.2.6
  src/sys/sys/event.h                                            1.32.2.1
  src/sys/sys/pipe.h                                             1.29.2.1
RELENG_6_4
  src/UPDATING                                            1.416.2.40.2.11
  src/sys/conf/newvers.sh                                  1.69.2.18.2.13
  src/sys/kern/kern_event.c                                  1.93.2.6.6.2
  src/sys/kern/kern_fork.c                                  1.252.2.7.4.2
  src/sys/kern/sys_pipe.c                                   1.184.2.4.2.3
  src/sys/sys/event.h                                           1.32.12.2
  src/sys/sys/pipe.h                                            1.29.16.2
RELENG_6_3
  src/UPDATING                                            1.416.2.37.2.18
  src/sys/conf/newvers.sh                                  1.69.2.15.2.17
  src/sys/kern/kern_event.c                                  1.93.2.6.4.1
  src/sys/kern/kern_fork.c                                  1.252.2.7.2.1
  src/sys/kern/sys_pipe.c                                   1.184.2.2.6.3
  src/sys/sys/event.h                                           1.32.10.1
  src/sys/sys/pipe.h                                            1.29.12.1
- -------------------------------------------------------------------------

Subversion:

Branch/path                                                      Revision
- -------------------------------------------------------------------------
stable/6/                                                         r197715
releng/6.4/                                                       r197715
releng/6.3/                                                       r197715
- -------------------------------------------------------------------------

VII. References

http://svn.freebsd.org/viewvc/base?view=revision&revision=179243

The latest revision of this advisory is available at
http://security.FreeBSD.org/advisories/FreeBSD-SA-09:13.pipe.asc
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