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__________________________________________________________
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.
CIAC services are available to DOE, DOE contractors, and the NIH. CIAC
can be contacted at:
Voice: +1 925-422-8193
FAX: +1 925-423-8002
STU-III: +1 925-423-2604
E-mail: ciac@llnl.gov
For emergencies and off-hour assistance, DOE, DOE contractor sites,
and the NIH may contact CIAC 24-hours a day. During off hours (5PM -
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or call 800-759-7243 (800-SKY-PAGE) to send a Sky Page. CIAC has two
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Previous CIAC notices, anti-virus software, and other information are
available from the CIAC Computer Security Archive.
World Wide Web: http://www.ciac.org/
(or http://ciac.llnl.gov -- they're the same machine)
Anonymous FTP: ftp.ciac.org
(or ciac.llnl.gov -- they're the same machine)
Modem access: +1 (925) 423-4753 (28.8K baud)
+1 (925) 423-3331 (28.8K baud)
CIAC has several self-subscribing mailing lists for electronic
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2. SPI-ANNOUNCE for official news about Security Profile Inspector
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You will receive an acknowledgment email immediately with a confirmation
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If you include the word 'help' in the body of an email to the above address,
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get past issues of CIAC bulletins via email, etc.
PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing
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