NetBSD Problem Report #3645

Received: (qmail 9649 invoked from network); 18 May 1997 19:59:44 -0000
Message-Id: <>
Date: Sun, 18 May 1997 16:01:45 -0500 (EST)
Subject: Union mount bug
X-Send-Pr-Version: 3.95

>Number:         3645
>Category:       kern
>Synopsis:       A union mount of a directory onto the same directory causes havoc
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun May 18 13:05:00 +0000 1997
>Last-Modified:  Mon Jun 07 06:42:23 +0000 1999
>Originator:     Rick Byers
>Release:        1.2E - 05/09
	Internet Access Worldwide

System: NetBSD 1.2E NetBSD 1.2E (RICKB) #3: Sat May 10 20:04:10 EST 1997 i386

	A union mount from one directory onto the same directory causes the system to pretty much
	lock up.  For A while, I can ps etc, but any disk activity causes it to look up.  The mount
	process (or any other locked process) cannot be killed.  Generally the entire system
	completely locks up pretty quickly.  No special priveledges are required - any directory
	that the user owns can be used.
	mount_union somedir somedir
	No sure.  Definantly a kernel problem.  I've temporarily disabled the mount_union
	command, but that doesn't stop users from compiling their own program that attempts a 
	union mount.
State-Changed-From-To: open->feedback 
State-Changed-By: hwr 
State-Changed-When: Sat May 8 02:42:23 PDT 1999 
Could you try, is this still happens with actual code? It might be that 
this went away with Lite2 merger. (yes, I know that your PR is 2 years old *sigh*) 

From: Rick Byers <>
Cc:  Subject: kern/3645
Date: Sun, 23 May 1999 17:22:15 -0400

 The mount_union binary will no longer do this, but the kernel will.  A
 modified binary can still easily crash the system when the UNIONFS is in
 the kernel.
State-Changed-From-To: feedback->open 
State-Changed-By: hwr 
State-Changed-When: Sun Jun 6 23:41:42 PDT 1999 
This is still a problem. 

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