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FreeBSD-SA-02:37.kqueue                                     Security Advisory
                                                          The FreeBSD Project

Topic:          local users can panic the system using the kqueue mechanism

Category:       core
Module:         kqueue
Announced:      2002-08-05
Credits:        Mark Delany <markd@bushwire.net>
Affects:        FreeBSD 4.3-RELEASE
                FreeBSD 4.4-RELEASE
                FreeBSD 4.5-RELEASE
                FreeBSD 4.6-RELEASE
                FreeBSD 4.6-STABLE prior to the correction date
Corrected:      2002-08-05 15:05:15 (RELENG_4)
                2002-08-05 15:13:48 (RELENG_4_6)
                2002-08-05 15:13:44 (RELENG_4_5)
                2002-08-05 15:13:40 (RELENG_4_4)
FreeBSD only:   YES

I.   Background

The kqueue mechanism allows a process to register interest in
particular events on particular file descriptors, and receive
asynchronous notification when these events occur on the selected
descriptors.

II.  Problem Description

If a pipe was created with the pipe(2) system call, and one end of the
pipe was closed, registering an EVFILT_WRITE filter on the other end
would cause a kernel panic.

A common scenario in which this could occur is when a process uses a
pipe to communicate with a child and uses kqueue to monitor the pipe,
and the child dies shortly after the fork(2) call, before the parent
has had time to register the filter.

III. Impact

A local attacker may cause the system to panic by executing their own
malicious application.

IV.  Workaround

There is no known workaround.

V.   Solution

The following patch has been verified to apply to FreeBSD 4.4, 4.5, and
4.6 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-02:37/kqueue.patch
# fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-02:37/kqueue.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.

Path                                                             Revision
  Branch
- -------------------------------------------------------------------------
sys/kern/sys_pipe.c
  RELENG_4                                                      1.60.2.13
  RELENG_4_6                                                1.60.2.12.2.1
  RELENG_4_5                                                1.60.2.11.2.1
  RELENG_4_4                                                1.60.2.10.2.1
- -------------------------------------------------------------------------
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