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Home » Security Advisories» NetBSD » Audio subsystem race condition

Audio subsystem race condition

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

  • Vendor: NetBSD
  • Vendor ID: 2006-014
  • Date: April 27, 2006

Hash: SHA1

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


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
# ./ 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:

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

Information about NetBSD and NetBSD security can be found at and

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 $

Version: GnuPG v1.4.3 (NetBSD)


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