-----BEGIN PGP SIGNED MESSAGE----- =============================================================================== Security Advisory CERT-NL =============================================================================== Author/Source : Gert Meijerink Index : S-98-35 Distribution : World Page : 1 Classification: External Version: 2 Subject : FreeBSD system crash with NFS Date : 05-Jun-98 =============================================================================== By courtesy of FreeBSD, Inc. we received information on a vulnerability in NFS. 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. CERT-NL recommends to follow the FreeBSD recommendation, which is to apply the patches. ============================================================================== ============================================================================= 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. ============================================================================= ============================================================================== CERT-NL is the Computer Emergency Response Team for SURFnet customers. SURFnet is the Dutch network for educational, research and related institutes. CERT-NL is a member of the Forum of Incident Response and Security Teams (FIRST). All CERT-NL material is available under: http://www.surfnet.nl/surfnet/security/cert-nl.html ftp://ftp.surfnet.nl/surfnet/net-security In case of computer or network security problems please contact your local CERT/security-team or CERT-NL (if your institute is NOT a SURFnet customer please address the appropriate (local) CERT/security-team). CERT-NL is one/two hour(s) ahead of UTC (GMT) in winter/summer, i.e. UTC+0100 in winter and UTC+0200 in summer (DST). Email: cert-nl@surfnet.nl ATTENDED REGULARLY ALL DAYS Phone: +31 302 305 305 BUSINESS HOURS ONLY Fax: +31 302 305 329 BUSINESS HOURS ONLY Snailmail: SURFnet bv Attn. CERT-NL P.O. Box 19035 NL - 3501 DA UTRECHT The Netherlands NOODGEVALLEN: 06 52 87 92 82 ALTIJD BEREIKBAAR EMERGENCIES : +31 6 52 87 92 82 ATTENDED AT ALL TIMES CERT-NL'S EMERGENCY PHONENUMBER IS ONLY TO BE USED IN CASE OF EMERGENCIES: THE SURFNET HELPDESK OPERATING THE EMERGENCY NUMBER HAS A *FIXED* PROCEDURE FOR DEALING WITH YOUR ALERT AND WILL IN REGULAR CASES RELAY IT TO CERT-NL IN AN APPROPRIATE MANNER. CERT-NL WILL THEN CONTACT YOU. ============================================================================== -----BEGIN PGP SIGNATURE----- Version: 2.6.3i Charset: cp850 iQCVAwUBNXfXRVpSTqmIRWKVAQGfEwP8CoGoMb+e51V5aN3voeRirZ4R6Zte50cQ 5QzrfVg+QtuysEeAhZCAVr6/n2v6L6wI+X7SfjTM3hqjWyTz9XhygWCHaZsOwdtO 30IlrsoOZkXN0Fc18jhTl0gfi4tS+Vhms9ljULgkcFgH8u50GVk1nYRNYImMjdhv 4emTKL3btr0= =+F/8 -----END PGP SIGNATURE-----