linux-kernel - Re: [alsa-devel] [PATCH] Fix for possible null pointer dereference in dma.c

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Date:	Tue, 20 May 2014 23:21:08 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Tomasz Figa <tomasz.figa@...il.com>
CC:	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>,
	Mark Brown <broonie@...nel.org>, alsa-devel@...a-project.org,
	Kukjin Kim <kgene.kim@...sung.com>,
	Sangbeom Kim <sbkim73@...sung.com>,
	linux-kernel@...r.kernel.org, Liam Girdwood <lgirdwood@...il.com>,
	Takashi Iwai <tiwai@...e.de>,
	linux-samsung-soc@...r.kernel.org, Ben Dooks <ben-linux@...ff.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [alsa-devel] [PATCH] Fix for possible null pointer dereference
 in dma.c

On 05/20/2014 09:16 PM, Tomasz Figa wrote:
> Hi Rickard,
>
> On 20.05.2014 21:12, Rickard Strandqvist wrote:
>> Hi Tomasz
>>
>> What I based my patch on is really because of this line:
>> if (substream)
>>           snd_pcm_period_elapsed(substream);
>>
>> Boojin Kim thought that this was needed, if this is true anymore..? I
>> have not been able to immerse myself so much in all patches.
>> I'm working on about 100 similar patches.
>
> To me having NULL as either data argument of buffer done callback or
> private_data would be a serious driver bug and IMHO it's better to let
> it crash with a NULL pointer dereference to let someone notice than mask
> it by adding a condition.
>
> Still, I'm not too experienced with ALSA and ASoC, so I might be wrong.
> Mark, what do you think about this?

Given that there is a patch[1] which removes the whole file I think we can stop 
the discussion about this patch here.

But for the record, substream will never ever be NULL in this function. prtd 
might be though if the DMA completion callback races against the closing of the 
PCM stream.

[1] http://mailman.alsa-project.org/pipermail/alsa-devel/2014-May/076860.html

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