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Date:      Fri, 5 Apr 1996 09:35:25 +0000
From:      "Frank ten Wolde" <franky@pinewood.nl>
To:        Terry Lambert <terry@lambert.org>
Cc:        freebsd-current@FreeBSD.org
Subject:   Re: 2.2-960323 Panic in mount_msdos
Message-ID:  <9604050935.ZM9063@pwood1.pinewood.nl>
In-Reply-To: Terry Lambert <terry@lambert.org> "Re: 2.2-960323 Panic in mount_msdos" (Apr  4, 13:10)
References:  <199604042010.NAA22425@phaeton.artisoft.com>

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Hi,
> > I just tried to mount a Windows NT file system (NTFS) using:
> > 
> > 	mount -t msdos /dev/sd0s2 /dos
> > 
> > (I thought it was an MSDOS-FAT file system :-).  The 2.2-960223-SNAPSHOT
> > of FreeBSD immediately paniced:
> 
> [ ... ]
> 
> > I know you cannot mount an NTFS under FreeBSD, but at least the system
> > should not crash.
> > 
> > I just report this problem as I have too little knowledge of the internals
> > of the kernel to fix the problem myself :-)
> 
> A file system operates by copying on disk strucutures into memory
> and then using the offsets in the coppy to access additional memory.
> 
> It does not bounds-check these accesses.
Yep, I found out :-)

> Not bounds-checking dereferences isn't an error; it an optimization,
> and it's allowable because mount is not a user accessable command
> (you have to be root).
I slightly disagree. Even as root I could make a typo and by mistake
specifiy the wrong partition/slice to mount, causing the entire system
to die.

It would have been nice if some sanity checking would have been performed,
so that the kernel simply would abort the mount(2) system call with an
appropriate error (wrong FS type, or something similar).

[...]

> The DOSFS is being rewritten (not by me).
Neither by me.  Don't get me wrong, I *really* like FreeBSD and my
remarks are not ment to critisize anyone.  I, for sure, do *not* have the
time and resources to contribute significantly to FreeBSD and I certainly
do not make demands of any kind :-)
I simply pointed out the panic.  Maybe the code maintainer of the DOSFS
can use this info to make the system even more stable.

-Frank

-- 
----------------------------------------------------------------------
F.W. ten Wolde (PA3FMT)                       Pinewood Automation B.V.
E-mail: franky@pinewood.nl                    Kluyverweg 2a
Phone: +31-15 2682543                         2629 HT  Delft



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