ptrace(2)'d processes can gain "kernel" privileges on vax.

-----BEGIN PGP SIGNED MESSAGE-----

===========================================================================
              AUSCERT External Security Bulletin Redistribution
                             
              ESB-2000.027 -- NetBSD Security Advisory 1999-012
         ptrace(2)'d processes can gain "kernel" privileges on vax.
                              16 February 2000

===========================================================================

The NetBSD Foundation, Inc. has released the following advisory concerning 
a possible security vulnerability in the NetBSD kernel versions prior to 
and including 1.4.1.  

This vulnerability may allow a wrapper program, constructed by a local 
user, to modify modify the hardware privileges of a ptrace(2)'d process. 
This vulnerability may allow local users to gain privileged access.

- --------------------------BEGIN INCLUDED TEXT--------------------

- -----BEGIN PGP SIGNED MESSAGE-----

                 NetBSD Security Advisory 1999-012
                 =================================

Topic:		ptrace(2)'d processes can gain "kernel" privileges on vax.
Version:	NetBSD/vax 1.4.1 and earlier; -current prior to 19991212
Severity:	Theoretical problem only, no known exploits


Abstract
========

As part of an ongoing effort to construct a secure kernel and application
environment, the NetBSD project has identified and corrected a possible
security issue.

A wrapper program can be constructed by a local user that can modify the
hardware privileges of a ptrace(2)'d process.

It might be possible to write a security-related exploit via this mechanism.


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

NetBSD uses the ptrace(2) system call to trace and debug other processes.
The debugging process can also modify the internal registers, including
the status (PSL) register, for the process being debugged.

Besides the normal user-accessible flags, the VAX hardware also stores
information about privilege levels and used stacks in the PSL. Those
flags are only altered via the instruction REI (return from interrupt)
or LDPCTX (load process context) and cannot be modified while running
in "user" mode.

When the PSL contents are altered by the debugging process, the debugged
process is in the kernel, and will get the privileges defined by the 
PSL when it REI to userspace to continue execution.

Solutions and Workarounds
=========================

Upgrade to NetBSD-current, or apply the following patch to 1.4.1:

Index: machdep.c
===================================================================
RCS file: /cvsroot/syssrc/sys/arch/vax/vax/machdep.c,v
retrieving revision 1.76.2.1
diff -c -r1.76.2.1 machdep.c
*** machdep.c   1999/04/16 16:26:01     1.76.2.1
- - --- machdep.c   1999/12/12 11:08:46
***************
*** 770,776 ****
        tf->fp = regs->fp;
        tf->sp = regs->sp;
        tf->pc = regs->pc;
!       tf->psl = regs->psl;
        return 0;
  }
  
- - --- 770,777 ----
        tf->fp = regs->fp;
        tf->sp = regs->sp;
        tf->pc = regs->pc;
!       tf->psl = (regs->psl|PSL_U|PSL_PREVU) &
!           ~(PSL_MBZ|PSL_IS|PSL_IPL1F|PSL_CM); /* Allow compat mode? */
        return 0;
  }



Thanks To
=========

Discovery of the problem by Klaus Klein (kleink@netbsd.org)


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

	1999/12/12 - initial version


More Information
================

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


Copyright 1999, The NetBSD Foundation, Inc.  All Rights Reserved.

$NetBSD: NetBSD-SA1999-012.txt,v 1.3 2000/02/15 13:33:47 dan Exp $

- -----BEGIN PGP SIGNATURE-----
Version: 2.6.3ia
Charset: noconv

iQCVAwUBOKlXcD5Ru2/4N2IFAQEvPAP+IXJ+48+eC/iDXTDXTG4QLNsqBZT4QRki
Y6DI7j0NqioiEvuJScW54dVpL0rUOd7XJH5bI27q2XEBy2J9furOwjFDb3Y4gpoU
4GWyQyw1oCd3tGecfUETlFtBdPNM6qVObEeKeQr87kbUsugSZUW+RuY4OA6Lywf7
rTMlmyoYuss=
=xqwx
- -----END PGP SIGNATURE-----

- --------------------------END INCLUDED TEXT--------------------

This security bulletin is provided as a service to AusCERT's members.  As
AusCERT did not write the document quoted above, AusCERT has had no control
over its content.  The decision to use any or all of this information is
the responsibility of each user or organisation, and should be done so in
accordance with site policies and procedures.

NOTE: This is only the original release of the security bulletin.  It may
not be updated when updates to the original are made.  If downloading at
a later date, it is recommended that the bulletin is retrieved directly
from the original authors to ensure that the information is still current.

Contact information for the authors of the original document is included
in the Security Bulletin above.  If you have any questions or need further
information, please contact them directly.

Previous advisories and external security bulletins can be retrieved from:

	http://www.auscert.org.au/Information/advisories.html

If you believe that your system has been compromised, contact AusCERT or
your representative in FIRST (Forum of Incident Response and Security
Teams).

Internet Email: auscert@auscert.org.au
Facsimile:	(07) 3365 7031
Telephone:	(07) 3365 4417 (International: +61 7 3365 4417)
		AusCERT personnel answer during Queensland business hours
		which are GMT+10:00 (AEST).
		On call after hours for emergencies.


-----BEGIN PGP SIGNATURE-----
Version: 2.6.3i
Charset: noconv
Comment: ftp://ftp.auscert.org.au/pub/auscert/AUSCERT_PGP.key

iQCVAwUBOMy1cih9+71yA2DNAQH9pwP8CTv3BUs+RH2y9UYOA5GgNlW8An+uVk/z
QfgITqcP0k08uvsDe2DgI/ihnlbb59Z+cUej9FnNfLBonF9RObrhSL/AnnWcKD6P
GIMqPycSr04dwVejfIKIIaVafcoCxjhxqL8mRXeXlLGKULAFAA7HQXU45m4mjOJ3
j9Cwf3sCpZI=
=/Rtl
-----END PGP SIGNATURE-----