Subject: kern/2426: pererse union fs mounts can causes system crash, other miscfs dangers
To: None <gnats-bugs@NetBSD.ORG>
From: Greg Stark <email@example.com>
Date: 05/17/1996 04:51:44
>Synopsis: mount_union a/ b/; mount_union -b a/ b/
>Responsible: kern-bug-people (Kernel Bug People)
>Arrival-Date: Fri May 17 05:20:01 1996
>Originator: Greg Stark
The Student Information Processing Board
System: NetBSD limekiller 1.1B NetBSD 1.1B (LIMEKILLER) #13: Sat May 11 17:43:31 EDT 1996 ghudson@zygorthian-space-raiders:/afs/sipb.mit.edu/project/netbsd/dev/current-source/build/i386_nbsd1/sys/arch/i386/compile/LIMEKILLER i386
from strings mount_union
$NetBSD: mount_union.c,v 1.2 1995/03/18 14:58:24 cgd Exp $
$NetBSD: getmntopts.c,v 1.3 1995/03/18 14:56:58 cgd Exp $
Some combinations of circular or otherwise confusing union mounts and
presumably nullfs mounts cause the machine to crash.
I verified this remotely so i didn't see exactly how the failure
occured. The machine seemed ok for a while; it responded to finger,
but a second login froze and it eventually crashed.
I fear this isn't the only danger, what would happen if you nullfs
mount a over b and b over a? Or the same with union mounts?
This was recently reported as a "security hole" in FreeBSD 2.1 by
"Krzysztof Labanowski" <CHRISL@gazeta.pl> and Adam Kubicki.
mkdir a b
mount_union a/ b/
mount_union -b a/ b/
# for me this second command never returned.
<synopsis of the problem (one line)>