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Home » Security Advisories» NetBSD » Sysctl local denial of service

Sysctl local denial of service

The user supplied buffer where results of the sysctl call are stored is locked into physical memory without checking its size. This way, a malicious user can cause a system lockup by allocating all available physical memory on most systems.

  • Vendor: NetBSD
  • Vendor ID: 2006-013
  • Date: April 12, 2006


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NetBSD Security Advisory 2006-013
=================================

Topic: sysctl(3) local denial of service

Version: NetBSD-current: source prior to March 15, 2005
NetBSD 3.0: affected
NetBSD 2.1: affected
NetBSD 2.0.*: affected
NetBSD 2.0: affected
NetBSD 1.6.*: affected
NetBSD 1.6: affected

Severity: Any local user can crash the system

Fixed: NetBSD-current: March 15, 2005
NetBSD-3-0 branch: March 24, 2006
(3.0.1 will include the fix)
NetBSD-3 branch: March 24, 2006
NetBSD-2-1 branch: March 24, 2006
(2.1.1 will include the fix)
NetBSD-2-0 branch: March 24, 2006
(2.0.4 will include the fix)
NetBSD-2 branch: March 24, 2006

Abstract
========

The user supplied buffer where results of the sysctl(3) call are stored is
locked into physical memory without checking its size. This way, a malicious
user can cause a system lockup by allocating all available physical memory on
most systems.

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

The system call implementing the sysctl(3) library call tries to lock the user
supplied result buffer into physical memory, to avoid the interferences of
information collection with other system activity. The size of that buffer is
not checked against system limits.

The VM system checks whether the virtual address of the buffer is part of the
user address space, but since the amount of virtual memory a single user is
able to allocate exceeds the available physical memory on most systems, a
user can cause a system lockup by exhaustion of physical memory.

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/kern/kern_sysctl.c
# ./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
=========

Matthias Drochner for PoC code and implementing the fixes.

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

2006-04-12 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-SA2006-013.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-SA2006-013.txt,v 1.4 2006/04/12 22:09:50 adrianp Exp $

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