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		 NetBSD Security Advisory 2013-013
		 =================================

Topic:		Memory leak when trying to execute bogus ELF binaries

Version:	NetBSD-current:		affected prior to 2013-12-18
		NetBSD 6.1*:		affected
		NetBSD 6.0:		affected
		NetBSD 5.2*:		not affected
		NetBSD 5.1*:		not affected

Severity:	Local user denial of service

Fixed:		NetBSD-current:		December 17, 2013
		NetBSD-6-0 branch:	December 17, 2013
		NetBSD-6-1 branch:	December 17, 2013
		NetBSD-6 branch:	December 17, 2013


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 a kernel bug a buffer was not freed when probing a binary for
execution if the "interpreter" of that binary did not exist, an
authenticated attacker can exhaust kernel memory by running binaries
with non-existent ELF interpreter paths.

On systems with the standard toolchain installed, creating such bogus
binaries is very easy.


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

When trying to execute a binary (or script), the kernel looks up
the corresponding "interpreter" (in case of native dynamic ELF
binaries: the dynamic linker ld.elf_so). If this interpreter does
not exist, the path buffer memory allocated for that interpreter
during the probe was not freed.

If a standard toolchain is installed, a local user can easily create
such broken binaries by passing the -dynamic-linker switch to the
linker.

Trying to execute such a broken binary in a loop would cause the
kernel to run out of memory and eventually crash.


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.    
  VERSION  with the file version below

File versions containing the fix:

branch		VERSION
HEAD		1.45
netbsd-6	1.44.14.1
netbsd-6-1	1.44.28.1
netbsd-6-0	1.44.20.1

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

	# cd src
	# cvs update -d -P -r VERSION src/sys/compat/common/compat_util.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
=========

Maxime Villard for notifying us of the issue and providing a patch.


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

	2013-12-19	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-SA2013-013.txt.asc

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

Copyright 2013, The NetBSD Foundation, Inc.  All Rights Reserved.
Redistribution permitted only in full, unmodified form.

$NetBSD: NetBSD-SA2013-013.txt,v 1.1 2013/12/19 20:36:48 tonnerre Exp $

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