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

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Date:	Wed, 31 Oct 2007 12:05:40 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Jens Axboe <jens.axboe@...cle.com>
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

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.

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

	Jeff

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