Date: Thu, 4 Jun 1998 19:56:36 +0200 (MET DST) From: FreeBSD Security Officer <security-officer@FreeBSD.ORG> To: undisclosed-recipients:; Subject: FreeBSD Security Advisory: FreeBSD-SA-98:05.nfs Message-ID: <199806041756.TAA22999@gvr.gvr.org>
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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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