TUCoPS :: BSD :: 2003-14.txt

sysctl(2) arg check vuln


		 NetBSD Security Advisory 2003-014

Topic:		Insufficient argument checking in sysctl(2)

Version:	NetBSD-current:	source prior to October 3, 2003 (*)
		NetBSD 1.6.1:	affected
		NetBSD 1.6:	affected
		NetBSD-1.5.3:	affected
		NetBSD-1.5.2:	affected
		NetBSD-1.5.1:	affected
		NetBSD-1.5:	affected

Severity:	local DoS, read protected kernel memory

Fixed:		NetBSD-current:		October 3, 2003
		NetBSD-1.6 branch:	October 3, 2003 (1.6.2 will include the fix)
		NetBSD-1.5 branch:	October 9, 2003

(*) - This advisory has been updated with additional sysctl issues. See
the details below, or the revision history.


Three unrelated problems with inappropriate argument handling were
found in the kernel sysctl(2) code, which could be exploited by
a malicious local user:

  Some sysctl nodes could cause the kernel to dereference a NULL
  pointer, resulting in a panic. (item 1 in technical details section)

  Passing the process id of a zombie process could cause the kernel to
  dereference invalid process data, and panic. (item 2)

  Other sysctl nodes had an insufficient range check, which could be
  abused to read arbitrary locations in kernel memory space. (item 3 and 4)

NOTE: previous revision of the advisory did not catch (4) in the technical

Technical Details

There are four unrelated problems which were found during an effort to
reimplement the sysctl(2) infrastructure.

1) A pointer variable was reused for pointing user-level addresses
   (sysctl(2) argument) and kernel addresses, and there was a code path
   which would allow a local user to set the pointer to NULL.

2) The proc.* sysctl tree could be invoked on a zombie process, but
   made assumptions that the processes were in a valid state, and so
   could attempt to reference process information that is invalid or
   non-existent for zombies.  This is no longer possible.

3) Under the proc.curproc.rlimit subtree there are a number of nodes
   representing the process resource limits, soft and hard. The sysctl
   helper function used to manipulate these values had an insufficient
   range check, and could be used to read values outside of the working
   copy of the rlimit structure.  Writes have been changed to check

4) The code that supports the debug.* subtree had an insufficient range
   check, and could be used to read/write values outside of the intended
   variables.  The flaw will exist only if "options DEBUG" is specified
   in the kernel configuration file, which is not the case in the
   GENERIC or INSTALL kernel configurations.

Solutions and Workarounds

To correct this problem, a kernel upgrade (and reboot) is required.
There is no practical work-around for systems running the vulnerable
code in the kernel.

The fixes for all of these issues are contained in the one file,
sys/kern/kern_sysctl.c. The following table lists the fixed revisions
and dates of this file for each branch:

  CVS branch     revision     date
  -------------  -----------  ----------------
  HEAD           1.147        2003/10/03
  netbsd-1-6    2003/10/03
  netbsd-1-5     2003/10/09

The following instructions describe how to upgrade your kernel
binaries by updating your source tree and rebuilding and installing a
new version of the kernel. In these instructions, replace: 

  BRANCH   with the appropriate CVS branch (from the above table)
  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 -r BRANCH sys/kern/kern_sysctl.c
	# cd sys/arch/ARCH/conf
	# config KERNCONF
	# cd ../compile/KERNCONF
	# make depend;make
	# mv /netbsd /netbsd.old
	# cp netbsd /
	# reboot

Thanks To

Andrew Brown 

Eike Dehling for corrections to the advisory.


Revision History

	2003-09-17	Initial release
	2003-09-18	Correct path in rebuild instructions.
	2003-10-09	Additional issues - details updated

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
http://www.NetBSD.org/ and http://www.NetBSD.org/Security/.

Copyright 2003, The NetBSD Foundation, Inc.  All Rights Reserved.
Redistribution permitted only in full, unmodified form.

$NetBSD: NetBSD-SA2003-014.txt,v 1.16 2003/10/09 02:24:33 david Exp $

Version: GnuPG v1.0.6 (NetBSD)
Comment: For info see http://www.gnupg.org


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