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

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Date:	Thu, 13 Jun 2013 10:51:30 +0200
From:	Marek Szyprowski <m.szyprowski@...sung.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	James Bottomley <James.Bottomley@...senpartnership.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 6/12/2013 5:06 PM, Arnd Bergmann wrote:
> 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.

I don't any possibility for userspace to alter the ops pointer, so if you
think that BUG_ON() approach causes additional overhead then I'm fine to
remove it.

Best regards
-- 
Marek Szyprowski
Samsung R&D Institute Poland


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