linux-kernel - Re: "Fix ATAPI transfer lengths" causes CD writing regression

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Message-ID: <20071031175543.GB11514@kernel.dk>
Date:	Wed, 31 Oct 2007 18:55:44 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, Daniel Drake <dsd@...too.org>,
	linux list <linux-kernel@...r.kernel.org>,
	linux-ide@...r.kernel.org
Subject: Re: "Fix ATAPI transfer lengths" causes CD writing regression

On Wed, Oct 31 2007, Jeff Garzik wrote:
> Jens Axboe wrote:
> >Right, that's of course problematic... There has to be a way to recover
> >that situation though, or you can't export any user command issue
> >facility.
> 
> You cannot hope to handle all possible effects arising from an app 
> providing an invalid sg header / cdb.
> 
> Once you start talking "recovery" you are already screwed:  we are 
> talking about low-level hardware commands that are passed straight to 
> the hardware.  It is trivial to lock up hardware, brick hardware, and 
> corrupt data at that level.
> 
> 
> If this is NOT a privileged app, we must update the command validation 
> to ensure that invalid commands are not transported to the hardware.
> 
> If this is a privileged app, our work is done.  Fix the app.  We gave 
> root rope, and he took it.

Woaw, back the truck up a bit :-)

I'm talking about simple things - like asking for 8 bytes of sense data.
Simple mistakes. You cannot possibly check for everything like that in a
command filter, it's utterly impossible.

> I even venture to say that "accept anything, clean up afterwards" is 
> /impossible/ to implement, in addition to being dangerous.

Certainly, that's not what I'm talking about.

-- 
Jens Axboe

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