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FreeBSD Security Advisory FreeBSD-SA-04:02.shmat


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Date: Thu, 5 Feb 2004 10:40:34 -0800 (PST)
From: FreeBSD Security Advisories <security-advisories@freebsd.org.>
To: Bugtraq <bugtraq@securityfocus.com.>
Subject: FreeBSD Security Advisory FreeBSD-SA-04:02.shmat

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FreeBSD-SA-04:02.shmat Security Advisory The FreeBSD Project Topic: shmat reference counting bug Category: core Module: kernel Announced: 2004-02-05 Credits: Joost Pol <joost@pine.nl.> Affects: All FreeBSD releases Corrected: 2004-02-04 18:00:40 UTC (RELENG_4) 2004-02-04 18:00:47 UTC (RELENG_5_2, 5.2-RELEASE-p2) 2004-02-04 18:00:55 UTC (RELENG_5_1, 5.1-RELEASE-p14) 2004-02-04 18:01:03 UTC (RELENG_5_0, 5.0-RELEASE-p20) 2004-02-04 18:01:10 UTC (RELENG_4_9, 4.9-RELEASE-p2) 2004-02-04 18:01:18 UTC (RELENG_4_8, 4.8-RELEASE-p15) 2004-02-04 18:01:25 UTC (RELENG_4_7, 4.7-RELEASE-p25) CVE Name: CAN-2004-0114 FreeBSD only: NO I. Background The System V Shared Memory interface provides primitives for sharing memory segments between separate processes. FreeBSD supports this interface when the kernel is built with SYSVSHM option, or the sysvshm module is loaded. By default, the FreeBSD kernel is built with the SYSVSHM option. The shmat(2) system call, which is part of the System V Shared Memory interface, is used to attach a shared memory segment to the calling process's address space. II. Problem Description A programming error in the shmat(2) system call can result in a shared memory segment's reference count being erroneously incremented. III. Impact It may be possible to cause a shared memory segment to reference unallocated kernel memory, but remain valid. This could allow a local attacker to gain read or write access to a portion of kernel memory, resulting in sensitive information disclosure, bypass of access control mechanisms, or privilege escalation. IV. Workaround NOTE: These workarounds could cause applications that use shared memory, such as the X Window System, to exhibit erratic behavior or to fail completely. Do one of the following: 1) Disable the System V Shared Memory interface entirely by following these steps: - Remove or comment out any lines mentioning `SYSVSHM' from your kernel configuration file, and recompile your kernel as described in <URL:http://www.freebsd.org/handbook/kernelconfig.html>;. - Remove or comment out any lines mentioning `sysvshm' from /boot/loader.conf and /etc/rc.conf. - On FreeBSD 5.x systems only , System V Shared Memory support may be provided as a kld(4). To be absolutely safe, remove any files named `sysvshm.ko' in /modules, /boot, and any subdirectories. - Finally, reboot your system. OR 2) Configure the System V Shared Memory parameters so that no new shared memory segments may be created, terminate all processes using shared memory, and delete all existing shared memory segments. Run the following commands as root: # sysctl -w kern.ipc.shmmax=0 # echo 'kern.ipc.shmmax=0' >> /etc/sysctl.conf # ipcs | awk '/^m/ { print $2 }' | xargs -n 1 ipcrm -m V. Solution Do one of the following: 1) Upgrade your vulnerable system to 4-STABLE, or to the RELENG_5_2, RELENG_5_1, RELENG_4_9, or RELENG_4_8 security branch dated after the correction date. NOTE WELL: Due to release engineering in progress at the time of this writing, the RELENG_5_2 security branch (5.2-RELEASE-p2) also includes numerous other critical bug fixes, most of which are not security related. Please read src/UPDATING for details on these changes. OR 2) Patch your present system: The following patch has been verified to apply to FreeBSD 4.x and 5.x systems. a) Download the relevant patch from the location below, and verify the detached PGP signature using your PGP utility. # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-04:02/shmat.patch # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-04:02/shmat.patch.asc b) Apply the patch. # cd /usr/src # patch < /path/to/patch c) Recompile your kernel as described in <URL:http://www.freebsd.org/handbook/kernelconfig.html>; and reboot the system. VI. Correction details The following list contains the revision numbers of each file that was corrected in FreeBSD. Path Revision Branch - ------------------------------------------------------------------------- RELENG_4 src/sys/kern/sysv_shm.c 1.45.2.8 RELENG_5_2 src/UPDATING 1.282.2.5 src/sys/conf/newvers.sh 1.56.2.5 src/sys/kern/sysv_shm.c 1.89.2.1 RELENG_5_1 src/UPDATING 1.251.2.15 src/sys/conf/newvers.sh 1.50.2.15 src/sys/kern/sysv_shm.c 1.83.2.1 RELENG_5_0 src/UPDATING 1.229.2.26 src/sys/conf/newvers.sh 1.48.2.21 src/sys/kern/sysv_shm.c 1.74.2.1 RELENG_4_9 src/UPDATING 1.73.2.89.2.3 src/sys/conf/newvers.sh 1.44.2.32.2.3 src/sys/kern/sysv_shm.c 1.45.2.6.4.1 RELENG_4_8 src/UPDATING 1.73.2.80.2.18 src/sys/conf/newvers.sh 1.44.2.29.2.16 src/sys/kern/sysv_shm.c 1.45.2.6.2.1 RELENG_4_7 src/UPDATING 1.73.2.74.2.29 src/sys/conf/newvers.sh 1.44.2.26.2.27 src/sys/kern/sysv_shm.c 1.45.2.5.6.1 - ------------------------------------------------------------------------- VII. References <URL:http://www.pine.nl/press/pine-cert-20040201.txt>; -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.4 (FreeBSD) iD8DBQFAIocaFdaIBMps37IRAtO8AJ9pP86snAwE67qdkwsat1CoJ+gFGACeJLtU PjD0jexX+1QaN7q2JvgVXmc= =IEvj -----END PGP SIGNATURE-----

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