linux-kernel - Re: [PATCH] dma-mapping: Add BUG_ON for uninitialized dma

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Date:	Wed, 12 Jun 2013 17:06:39 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	James Bottomley <James.Bottomley@...senpartnership.com>
Cc:	Marek Szyprowski <m.szyprowski@...sung.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Michal Simek <michal.simek@...inx.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Michal Simek <monstr@...str.eu>,
	"Linux-Arch" <linux-arch@...r.kernel.org>
Subject: Re: [PATCH] dma-mapping: Add BUG_ON for uninitialized dma_ops

On Tuesday 11 June 2013, James Bottomley wrote:
> Really, no, it's not a good idea at all.  It invites tons of patches
> littering the code with BUG_ONs where we might possibly get a NULL
> dereference.  All it does is add extra instructions to a code path for
> no actual benefit.
> 
> If you can answer the question: what more information does the BUG_ON
> give you than the NULL deref Oops would not? then it might be
> reasonable.

The question is if a user can trigger the NULL dereference intentionally,
in which case they might get the kernel to jump into a  user-provided
buffer.

	Arnd
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