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===========================================================================
              AUSCERT External Security Bulletin Redistribution

                             
       ESB-98.088 -- FreeBSD Security Advisory - FreeBSD-SA-98:05.nfs
                            system crash with NFS
                                 05 Jun 1998

===========================================================================

The FreeBSD Security Team has released the following advisory concerning 
an error in the NFS kernel code.  It is possible to crash a FreeBSD 2.2.* 
system by hard linking a device special file to a file on an NFS mounted 
file system.

The following security bulletin is provided as a service to AusCERT's
members.  As AusCERT did not write this document, AusCERT has had no
control over its content.  As such, the decision to use any or all of this
information is the responsibility of each user or organisation, and should
be done so in accordance with site policies and procedures.

NOTE: This is only the original release of the security bulletin.  It will
not be updated when the original bulletin is.  If downloading at a later
date, it is recommended that the bulletin is retrieved from the original
authors to ensure that the information is still current.

Contact information for FreeBSD is included in the Security Bulletin below.  
If you have any questions or need further information, please contact them 
directly.

Previous advisories and external security bulletins can be retrieved from:

	http://www.auscert.org.au/Information/advisories.html

If you believe that your system has been compromised, contact AusCERT or
your representative in FIRST (Forum of Incident Response and Security
Teams).

Internet Email: auscert@auscert.org.au
Facsimile:	(07) 3365 7031
Telephone:	(07) 3365 4417 (International: +61 7 3365 4417)
		AusCERT personnel answer during Queensland business hours
		which are GMT+10:00 (AEST).
		On call after hours for emergencies.


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=============================================================================
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.
=============================================================================

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