-----BEGIN PGP SIGNED MESSAGE----- __________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN FreeBSD NFS Kernel Code Error June 16, 1998 21:00 GMT Number I-057 ______________________________________________________________________________ PROBLEM: FreeBSD has identified a error in the NFS kernel code. PLATFORM: FreeBSD 2.2.* and FreeBSD-stable before 1998/05/31 DAMAGE: By creating a hard link to a file on a NFS mounted file system, it is possible to cause the system to crash. SOLUTION: Apply one of the patches. No workaround is known except to unmount your NFS file systems. ______________________________________________________________________________ VULNERABILITY If your systems is vulnerable, patches should be applied as ASSESSMENT: soon as possible. ______________________________________________________________________________ [ Start FreeBSD Advisory ] ============================================================================= FreeBSD-SA-98:05 Security Advisory FreeBSD, Inc. Topic: system crash with NFS Category: core Module: kernel Announced: 1998-06-04 Affects: FreeBSD 2.2.* and FreeBSD-stable before 1998/05/31 this problem. Corrected: FreeBSD-current as of 1998/05/31 FreeBSD only: no (also other 4.4BSD based systems may be affected) Patches: ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-98:05/ ============================================================================= IMPORTANT MESSAGE: The FreeBSD security officer now uses the policy ftp://ftp.freebsd.org/pub/FreeBSD/POLICY.asc for sending out advisories. ============================================================================= I. Background NFS can be used to mount remote file systems. Apart from being remote, it acts like a normal UFS file system. Among others, This means that creating hard links can be done in NFS file systems II. Problem Description When creating hard links on file systems, the kernel checks that both the original file and the link to it are located on the same file system. Unfortunately, there is an error in the NFS kernel code in FreeBSD 2.2.* systems that performs this check. III. Impact It is possible to crash a FreeBSD 2.2.* system by hard linking a device special files to a file on an NFS mounted file system. FreeBSD-current is not vulnerable. IV. Workaround No real work around is known (except for unmounting your NFS file systems). V. Solution Apply one of the following patches, rebuild your kernel, install it and reboot your system. The patches below can be found on ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-98:05/ Patch for 2.2.5 and 2.2.6 systems: Index: nfs_vnops.c =================================================================== RCS file: /home/cvsup/freebsd/CVS/src/sys/nfs/nfs_vnops.c,v retrieving revision 1.36.2.6 retrieving revision 1.36.2.7 diff -u -r1.36.2.6 -r1.36.2.7 --- nfs_vnops.c 1998/05/13 05:48:45 1.36.2.6 +++ nfs_vnops.c 1998/05/31 00:07:29 1.36.2.7 @@ -1755,17 +1755,8 @@ struct componentname *a_cnp; } */ *ap; { -#if defined(__NetBSD__) - /* - * Since the args are reversed in the VOP_LINK() calls, - * switch them back. Argh! - */ - register struct vnode *vp = ap->a_tdvp; - register struct vnode *tdvp = ap->a_vp; -#else register struct vnode *vp = ap->a_vp; register struct vnode *tdvp = ap->a_tdvp; -#endif register struct componentname *cnp = ap->a_cnp; register u_long *tl; register caddr_t cp; @@ -1776,11 +1767,8 @@ int v3 = NFS_ISV3(vp); if (vp->v_mount != tdvp->v_mount) { - VOP_ABORTOP(vp, cnp); - if (tdvp == vp) - vrele(tdvp); - else - vput(tdvp); + VOP_ABORTOP(tdvp, cnp); + vput(tdvp); return (EXDEV); } ============================================================================= FreeBSD, Inc. Web Site: http://www.freebsd.org/ Confidential contacts: security-officer@freebsd.org Security notifications: security-notifications@freebsd.org Security public discussion: freebsd-security@freebsd.org PGP Key: ftp://ftp.freebsd.org/pub/FreeBSD/CERT/public_key.asc Notice: Any patches in this document may not apply cleanly due to modifications caused by digital signature or mailer software. Please reference the URL listed at the top of this document for original copies of all patches if necessary. ============================================================================= [ End FreeBSD Advisory ] ______________________________________________________________________________ CIAC wishes to acknowledge the contributions of FreeBSD, Inc. for the information contained in this bulletin. ______________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. 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Your agency's team will coordinate with CIAC. The Forum of Incident Response and Security Teams (FIRST) is a world-wide organization. A list of FIRST member organizations and their constituencies can be obtained via WWW at http://www.first.org/. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC) I-047: HP-UX OpenMail Vulnerability I-048: SunOS mountd Vulnerability I-049: SunOS ufsrestore Vulnerability I-050: Digital UNIX softlinks - advfs Vulnerability I-051: FreeBSD T/TCP Vulnerability I-052: 3Com(r) CoreBuilder and SuperStack II LAN Vulnerabilities I-053: ISC DHCP Distribution Vulnerability I-054: Cisco Web Cache Control Protocol Router Vulnerability I-055: SGI IRIX Vulnerabilities (NetWare Client, diskperf/diskalign I-056: Cisco PIX Private Link Key Processing and Cryptography Vulnerability -----BEGIN PGP SIGNATURE----- Version: 4.0 Business Edition iQCVAwUBNYbe4bnzJzdsy3QZAQGACAQA0OOkoR48SauV+51CQDh/kWmzA+NwDsRA DS+PHAZ7SBlaXguj+77fe/3LzOfV0IRvxbhwAI7VJJ+vEIPwel95dgNnZXLmGbYm vH1RJON5ktLhm+c7LSF/FvSCyiZXJIftNeXnE2EJaq9bV20fsVfVHQz9XxAOLsnN N3xXv/U17+A= =UlN6 -----END PGP SIGNATURE-----