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		 NetBSD Security Advisory 2006-016

		 =================================
Topic:		IPv6 socket options can crash the system
Version:	NetBSD-current:	source prior to May 23, 2006

		NetBSD 3.0:	affected

		NetBSD 2.1:     affected

		NetBSD 2.0.*:   affected

		NetBSD 2.0:     affected
Severity:	Any local user can crash the system
Fixed:		NetBSD-current:		May 23, 2006

		NetBSD-3-0 branch:	May 24, 2006

						(3.0.1 will include the fix)

		NetBSD-3   branch:	May 24, 2006

		NetBSD-2-1 branch:      May 24, 2006

						(2.1.1 will include the fix)

		NetBSD-2-0 branch:      May 24, 2006

						(2.0.4 will include the fix)

		NetBSD-2 branch:        May 24, 2006
Abstract

========
Insufficient validation when parsing IPv6 socket options can lead to a

system crash.  This can be triggered by a local non-privileged user.
Technical Details

=================
IPv6 sockets can be used with IPv4-mapped addresses, and thus IPv4

packets may be sent and delivered through an IPv6 socket.
When sending an IPv6 packet, the NetBSD kernel needs to call the

ip6_savecontrol() function in order to process the SO_TIMESTAMP socket

option.  This function should process options for IPv6 packets only,

but wasn't checking for IPv4-mapped sockets. If such a socket had this

option set, it would traverse the mbuf chain by later calling

ip6_pullexthdr(), causing a panic.
Either net.inet6.ip6.v6only sysctl MIB (global) or IPV6_V6ONLY socket

option (per-socket) need to be 0 (zero) for this code path to occur.
Solutions and Workarounds

=========================
By default on NetBSD net.inet6.ip6.v6only is set to 1 (disabled).

However, any user can set IPV6_V6ONLY on their own sockets.
The only workaround available is to rebuild a kernel with

"options BIND_V6ONLY".
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/netinet6/ip6_input.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

=========
Christian Biere for finding the problem.

JINMEI Tatuya from the KAME project for the fix.

Rui Paulo for implementing the fixes.
Revision History

================
	2006-06-08	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-SA2006-016.tx...
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-SA2006-016.txt,v 1.2 2006/06/08 16:21:43 adrianp Exp $
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