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NetBSD-SA1999-009 i386 SVR4 compatibility problems Print E-mail
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Posted by Team   
NetBSD SVR4 compatibility device creation vulnerability

                 NetBSD Security Advisory 1999-009

Topic:          SVR4 compatibility device creation vulnerability
Version:        NetBSD 1.3.3 and prior; NetBSD-current until 19990420
Severity:       Local users can access and modify any data on first IDE disk


In order to provide a system environment capable of executing System V
Release 4 (`SVR4') binaries, it is necessary to create a set of device
special files; to simplify this task, a shell script is shipped with
the system.  Due to a mismatch of device major numbers between NetBSD
platforms, one device special file is erroneously created with a wrong
major number, which may allow a regular user to arbitrarily read or
write any data stored on the NetBSD portion of the first IDE disk
configured by the system.

This vulnerability is restricted to the i386 port of NetBSD with SVR4
emulation additionally configured only.

Technical Details

The SVR4 /dev/wabi character device special file, usually created
below the /emul/svr4 hierarchy, is currently supposed to be a synonym
for the /dev/null device special file.

Originally developed on the sparc port of NetBSD, the SVR4_MAKEDEV
shell script creates this file with a major number of 3 and a minor
number of 2, setting these properties equivalent to those of the
/dev/null device special file on that platform.  On the i386 port of
NetBSD, the character device major number 3 is associated with the
wd(4) driver, which supports IDE (and compatible) disks, and whose
minor number 2 denotes the NetBSD portion of the first such disk
configured by the systems; this corresponds to the special device file
/dev/rwd0c in the base distribution.  As the /dev/wabi special device
file is created with world read and write permissions, a regular user
may read and write any data stored on that portion of the disk.

The effects of actually running the WABI software on a vulnerable system
have not been investigated.

Solutions and Workarounds

A patch is available for the NetBSD 1.3.3 which makes the SVR4_MAKEDEV
shell script create the wabi device special file with the correct
properties.  You may find this patch on the NetBSD ftp server:


NetBSD-current since 19990420 is not vulnerable.  Users of
NetBSD-current should upgrade to a source tree later than 19990420.

Once the SVR4_MAKEDEV script is updated, re-run it to recreate the
wabi device with the correct parameters.

If this action cannot be taken, an immediate workaround is to remove
the existing device special file and creating a new one, which can be
done by executing the following shell command sequence as the super-user:

        # /bin/rm -f /emul/svr4/dev/wabi
        # /sbin/mknod /emul/svr4/dev/wabi c 2 2
        # /bin/chmod u=rw,g=rw,o=rw /emul/svr4/dev/wabi

Thanks To

The vulnerability was discovered by Klaus Klein ,
who also provided the solution and authored this advisory.

Revision History

        1999/04/17 - initial version

        1999/04/19 - dates were incorrect

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-SA1999-009.txt,v 1.2 1999/04/19 15:07:52 mrg Exp $

Version: 2.6.3ia
Charset: noconv

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