-----BEGIN PGP SIGNED MESSAGE----- NetBSD Security Advisory 2004-004 ================================= Topic: shmat reference counting bug Version: NetBSD-current: source prior to February 6th, 2004 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 privilege escalation Fixed: NetBSD-current: February 7th, 2004 NetBSD-1.6 branch: February 8th, 2004 (1.6.2 will include the fix) NetBSD-1.5 branch: This fix is not yet pulled up. This advisory will be updated when it has. Updating to NetBSD 1.6.2 is advised. Abstract ======== A programming error in the shmat(2) system call can result in a shared memory segment's reference count being erroneously incremented. This system call is part of the System-V Shared Memory subsystem; although this is enabled in the default (GENERIC*) kernels, custom kernels built without "options SYSVSHM" are not affected. Technical Details ================= The shmat(2) function maps a shared memory segment, previously created with the shmget(2) function, into the address space of the calling process. The shmat(2) function first increases the reference count on the underlying vm_object and then attempts to insert the vm_object into the process address space. The vulnerability occurs because the shmat(2) function forgets to decrease the reference count if the vm_map_find function returns failure. Since the caller of shmat(2) can specify the address at which the segment should be mapped it is possible to have vm_map_find return failure and thus end up with stale references. In the end, an unprivileged user may have write access to an unreferenced piece of kernel memory, which could later become part of a privileged object. Solutions and Workarounds ========================= If you are unable to apply the patch as described below, you may workaround the problem by removing SYSVSHM from your kernel config file and rebuilding and reinstalling your kernel. *** Patching from sources: Otherwise, the fix for this issue is contained in the one file, sys/kern/sysv_shm.c. The following table lists the fixed revisions and dates of this file for each branch: CVS branch revision date ------------- ----------- ---------------- HEAD 1.74 2004/02/05 netbsd-1-6 1.64.4.1 2004/02/08 netbsd-1-5 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/sysv_shm.c # cd sys/arch/ARCH/conf # config KERNCONF # cd ../compile/KERNCONF # make depend;make # mv /netbsd /netbsd.old # cp netbsd / # reboot * Binary Patch: Binary patches are being provided, in the form of replacement kernels built with the patches from the GENERIC kernel configuration. If you use a custom kernel configuration, these may not be suitable for you. NOTE: The path below says SA2004-002-kernel intentionally. The same kernel includes fixes for NetBSD-SA2004-002 and NetBSD-SA2004-004. If you already updated for 2004-002, you do not need to perform these steps again. To apply the binary patch, perform the following steps, replacing ARCH with the NetBSD architecture you are running (i.e. i386): ftp://ftp.netbsd.org/pub/NetBSD/security/patches/SA2004-002-kernel/netbsd-1-6/ARCH-kernel.tgz cd / && cp /path/to/ARCH-kernel.gz / gzip -d ARCH-kernel.gz The tar file will extract a new copy of: ARCH-kernel Back up your old kernel: mv netbsd netbsd.old Then either rename: mv ARCH-kernel netbsd or link, as per local site policy: ln ARCH-kernel netbsd Then, reboot. Thanks To ========= Joost Pol of Pine Digital Security FreeBSD Security-Officer Christos Zoulas for supplying a fix. Revision History ================ 2004-02-18 Initial release More Information ================ ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-04:02.shmat.asc http://www.pine.nl/press/pine-cert-20040201.txt http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-0114 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-SA2004-004.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. $NetBSD: NetBSD-SA2004-004.txt,v 1.4 2004/02/19 03:17:33 david Exp $ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.4 (NetBSD) iQCVAwUBQDU2XT5Ru2/4N2IFAQGG2QP/ddFLWToVaTe1ddbPWOZdIwidnpNHmEeP WGdwXW6l435QrwhKsMVHc9E/UvkxaDy8riRysuIMu4ok8hBZUgoZuMmvWhO43bJN 5iUXsPoLANj/twI8/7w0cLhFKuEx9d6OJ0IWUNAr9r3LlyXqKnGTvUEZ/sQg4HT2 dOgWBHlvmSY= =KJw/ -----END PGP SIGNATURE-----