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From: NetBSD Security Officer (security-officerNetBSD.org)
Date: Tue Feb 02 2010 - 13:04:17 CST
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NetBSD Security Advisory 2010-001
Topic: File system module autoloading Denial of Service attack
Version: NetBSD-current: affected prior to 2009-12-19 20:28:27 UTC
NetBSD 5.0.1: not affected
NetBSD 5.0: not affected
NetBSD 4.0.*: not affected
NetBSD 4.0: not affected
Severity: Local Denial of Service
Fixed: NetBSD-current: Dec 19, 2009
Please note that NetBSD releases prior to 4.0 are no longer supported.
It is recommended that all users upgrade to a supported release.
A coding error in the NetBSD VFS code allows a local attacker to
crash the local system by passing a soon-to-be-unmapped pointer
as a file system name to the mount system call.
When entering the mount_get_vfsops() function, the string "fstype",
containing the file system name, is first copied from userspace into the
kernel address space variable "fstypename". Upon invocation of the file
system kernel module autoloader, however, the module_autoload() function
was passed the "fstype" variable, which points to userspace memory.
If a pointer passed to the mount system call as the file system name is
unmapped before being used by the module autoloader, the module autoloader
will access unmapped memory, causing an unresolvable page fault in kernel
space and subsequently a kernel panic.
The same occurrs unconditionally on architectures with completely separate
kernel and user address spaces.
Please note that this vulnerability does not affect NetBSD 5.0 and 5.0.1,
as the file system module autoloading code is not enabled in these
Solutions and Workarounds
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/kern/vfs_syscalls.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:
Martin Husemann for finding and reporting the vulnerability, and for
developing a patch for it.
2010-01-12 Initial release
2010-02-02 Removed NetBSD-5 from the list of vulnerable versions
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 2010, The NetBSD Foundation, Inc. All Rights Reserved.
Redistribution permitted only in full, unmodified form.
$NetBSD: NetBSD-SA2010-001.txt,v 1.2 2010/02/02 18:21:54 tonnerre Exp $
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