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AUSCERT External Security Bulletin Redistribution
ESB-2002.401 -- FreeBSD-SA-02:37.kqueue
local users can panic the system using the kqueue mechanism
8 August 2002
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AusCERT Security Bulletin Summary
---------------------------------
Product: kqueue
Vendor: FreeBSD
Operating System: FreeBSD 4.6-STABLE prior to the correction date
FreeBSD 4.6-RELEASE
FreeBSD 4.5-RELEASE
FreeBSD 4.4-RELEASE
FreeBSD 4.3-RELEASE
Impact: Denial of Service
Access Required: Existing Account
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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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