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NetBSD Security Advisory 2006-014: An audio subsystem race condition may crash the system

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From: NetBSD Security-Officer
Subject: NetBSD Security Advisory 2006-014: An audio subsystem race condition may crash the system
Date: Thursday, April 27, 2006 - 1:40 pm

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		 NetBSD Security Advisory 2006-014
		 =================================

Topic:		An audio subsystem race condition may crash the system

Version:	NetBSD-current:	source prior to April 19, 2006
		NetBSD 3.0:	source prior to April 19, 2006
		NetBSD 2.1:     not affected
		NetBSD 2.0.*:   not affected
		NetBSD 2.0:     not affected
		NetBSD 1.6.*:   not affected
		NetBSD 1.6:     not affected

Severity:	Any local user can crash the system

Fixed:		NetBSD-current:		April 19, 2006
		NetBSD-3-0 branch:	April 19, 2006
					(3.0.1 will include the fix)
		NetBSD-3   branch:	April 19, 2006

Abstract
========

A system crash can occur if a user changes the sample rate of an audio
device during playback.

Technical Details
=================

If the filter list is modified while audio_write() is running, a
kernel crash may occur. While the function is reading data from
userland, it does not check to see if the filter has been changed (via
audiosetinfo ioctl).

The audio_write() function reads data from userland in a loop, runs
any required filters (eg. rate conversion, changing encoding, etc) and
passes the data along to a circular audio buffer. The function
neglected to properly lock against the audiosetinfo() function.

Since this bug was introduced with the new audio filter framework in
NetBSD 3.0, prior releases are unaffected.

Solutions and Workarounds
=========================

For all NetBSD versions, you need to obtain fixed kernel sources,
rebuild and install the new kernel, and reboot the system.

The fixed source may be obtained from the NetBSD CVS repository.

The following instructions briefly summarise how to upgrade your
kernel.  In these instructions, replace:

  ARCH     with your architecture (from uname -m), and 
  KERNCONF with the name of your kernel configuration file.

To update from CVS, re-build, and re-install the kernel:

        # cd src
        # cvs update -d -P sys/dev/audio.c
        # cvs update -d -P sys/dev/audio_if.h
        # cvs update -d -P sys/dev/audiovar.h
	# ./build.sh kernel=KERNCONF
	# mv /netbsd /netbsd.old
	# cp sys/arch/ARCH/compile/obj/KERNCONF/netbsd /netbsd
	# shutdown -r now

For more information on how to do this, see:

   http://www.NetBSD.org/guide/en/chap-kernel.html


Thanks To
=========

Christian Biere for reporting the issue and testing.
Jared D. McNeill for implementing the fixes.

Revision History
================

	2006-04-27	Initial release


More Information
================

Advisories may be updated as new information becomes available.
The most recent version of this advisory (PGP signed) can be found at 
  ftp://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2006-014.txt.asc

Information about NetBSD and NetBSD security can be found at
http://www.NetBSD.org/ and http://www.NetBSD.org/Security/.


Copyright 2006, The NetBSD Foundation, Inc.  All Rights Reserved.
Redistribution permitted only in full, unmodified form.

$NetBSD: NetBSD-SA2006-014.txt,v 1.8 2006/04/27 08:26:30 dan Exp $

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