Abstract

Kernel syscall implementations must perform appropriate sanity checks on
data passed from userland. The native system calls perform appropriate
checks.

Some of the functions in /usr/src/sys/compat/* which implement execution
of foreign binaries (such as Linux, FreeBSD, IRIX, OSF1, SVR4, HPUX, and
ULTRIX) used argument data in unsafe ways prior to calling the kernel
syscall.

This issue was reported by Evgeny Demidov.

Technical Details

The compat subsystem, in /usr/src/sys/compat/*, allows NetBSD users to
run binaries compiled for other operating systems which run on the same
CPU architecture as the NetBSD host.

Typically, the foreign OS supports a set of system calls which are very
similar to NetBSD's. Native instructions do not need to be translated,
but calls to the operating system do.

A binary's native OS is determined at exec() time. The kernel maps the
syscall table for the native OS so that each syscall is delivered to a
foreign OS -> NetBSD translation function, if needed.

These translation functions reorder arguments, reformat them, perform
mapping of constants (such as signal(3) IDs) and call the appropriate
native NetBSD system call to service the application's needs.

Some of the translation functions performed unsafe operations using the
syscall arguments, and were exploitable to cause kernel traps. Some of
the flaws may be exploitable and result in privilege escalation.

All of these attacks require local access to the system. A system with
only trusted user accounts is not immediately at risk.

A system running a custom kernel with all 'options COMPAT_' commented
out is not at risk.


See also Evgeny Demidov's advisory:

http://gleg.net/advisory_netbsd2.shtml

Solutions and Workarounds

The NetBSD 2.0 release already includes the fixes for this
vulnerability.

Since the NetBSD-1-5 branch has reached End of Life, updating to
NetBSD-1-6 or NetBSD-2-0 is recommended.


netbsd-1-6, netbsd-2-0 (pre-release), netbsd-current:

*** Patching from sources:

The fix for this issue is contained in changes to several files, all
within the subdirectory:

sys/compat

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 (netbsd-1-6,
                netbsd-2-0, HEAD)
    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/compat
# cd sys/arch/ARCH/conf
# config KERNCONF
# cd ../compile/KERNCONF
# make depend; make
# mv /netbsd /netbsd.old
# cp netbsd /
# shutdown -fr now

Thanks To

Evgeny Demidov for notification, review of patches, and considerable patience.

Christos Zoulas, David Maxwell, and Simon Burge for patches and review.

Revision History

2004-12-16 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-SA2004-010.txt.asc

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

Copyright 2004, The NetBSD Foundation, Inc. All Rights Reserved.
Redistribution permitted only in full, unmodified form.