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Date: Mon, 8 Feb 99 22:41:12 +0000 (GMT)
From: dwmalone@maths.tcd.ie
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Subject: kern/9970: NFS cross device links cause vrele: negative ref cnt
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>Number:         9970
>Category:       kern
>Synopsis:       NFS cross device links cause vrele: negative ref cnt
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Mon Feb  8 14:50:00 PST 1999
>Closed-Date:
>Last-Modified:
>Originator:     David Malone
>Release:        FreeBSD 2.2.7-STABLE i386
>Organization:
School of Mathematics, Trinity College, Dublin.
>Environment:

FreeBSD-3.0 or FreeBSD-4.0.

>Description:

The vrele: negative reference count problem that we have been seeing is
caused by attempting a cross device link to a directory on an nfs
filesystem. The machine may not panic for a while until the last real
reference is gone.

This is quite dramatic as anyone with write access to a nfs filesystem
can kill the machine!

This problem was introduced in version 1.108 of nfs_vnops.c.
In version 1.84 some of the vrele, etc were removed when there
was a change in filesystem behavior. The fact that the man page
for VOP_LINK(9) still says that you should release the directory
obviously doesn't help.

>How-To-Repeat:

cd /tmp
touch hello
ln hello /nfs/filesystem	(Repeat until *BOOM*)

>Fix:

The following seems to fix the problem, but the VOP_* man pages
should also be updated by someone who understands the changes
about the time of 1.84.

--- nfs_vnops.c.orig	Mon Feb  8 22:09:51 1999
+++ nfs_vnops.c	Mon Feb  8 22:11:48 1999
@@ -1686,7 +1686,6 @@
 
 	if (vp->v_mount != tdvp->v_mount) {
 		VOP_ABORTOP(tdvp, cnp);
-		vput(tdvp);
 		return (EXDEV);
 	}
 
>Release-Note:
>Audit-Trail:
>Unformatted:

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