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NetBSD Security Advisory 2014-011: User-controlled memory allocation in the modctl system call

27 August, 2014 by security-officer@NetBSD.org | netbsd 

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		NetBSD Security Advisory 2014-011
		=================================

Topic:		User-controlled memory allocation in the modctl system call


Version:	NetBSD-current:		source prior to Thu, Jul 10th 2014
		NetBSD 6.1 - 6.1.4:	affected
		NetBSD 6.0 - 6.0.5:	affected
		NetBSD 5.1 - 5.1.4:	affected
		NetBSD 5.2 - 5.2.2:	affected

Severity:	Local DoS

Fixed:		NetBSD-current:		Thu, Jul 10th 2014
		NetBSD-6-1 branch:	Mon, Jul 14th 2014
		NetBSD-6-0 branch:	Mon, Jul 14th 2014
		NetBSD-6 branch:	Mon, Jul 14th 2014
		NetBSD-5.2 branch:	Mon, Jul 14th 2014
		NetBSD-5.1 branch:	Mon, Jul 14th 2014
		NetBSD-5 branch:	Mon, Jul 14th 2014

Teeny versions released later than the fix date will contain the fix.

Please note that NetBSD releases prior to 5.1 are no longer supported.
It is recommended that all users upgrade to a supported release.


Abstract
========

Due to missing input validation checks, a local (un)privileged user
could cause the kernel to perform a zero-sized or unbounded memory
allocation, resulting in a crash.


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

The modctl system call takes as second argument a buffer which is
represented as a structure when loading a kernel module. This structure
indicates special information on how to load a module, including a
string pointer and the length of the string pointed to. A kernel buffer
of the same size is allocated, but no check was performed to ensure the
size is neither too low nor too high, thus allowing a local user to
crash the system.


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),               
  KERNCONF with the name of your kernel configuration file and  
  VERSION  with the file version below

File versions containing the fixes:

FILE  HEAD  netbsd-6  netbsd-6-1  netbsd-6-0  netbsd-5  netbsd-5-2  netbsd-5-1
- ----  ----  --------  ----------  ----------  --------  ----------  ----------
sys/kern/sys_module.c
      1.15  1.13.8.1  1.13.14.1   1.13.12.1   1.8.4.2   1.8.4.1.6.1 1.8.4.1.2.1

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

	# cd src
	# cvs update -d -P -r VERSION sys/kern/sys_module.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
=========

Thanks to Maxime Villard, who found the issue and provided a fix.


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

	2014-08-27	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 
  http://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2014-011.txt.asc

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


Copyright 2014, The NetBSD Foundation, Inc.  All Rights Reserved.
Redistribution permitted only in full, unmodified form.

$NetBSD: NetBSD-SA2014-011.txt,v 1.1 2014/08/27 00:33:51 tonnerre Exp $

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