TUCoPS :: BSD :: ciaci057.txt

FreeBSD Nfs Kernel Code Error



                       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

     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
  retrieving revision
  diff -u -r1.36.2.6 -r1.36.2.7
  --- nfs_vnops.c       1998/05/13 05:48:45
  +++ nfs_vnops.c       1998/05/31 00:07:29
  @@ -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;
        register struct vnode *vp = ap->a_vp;
        register struct vnode *tdvp = ap->a_tdvp;
        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.

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