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

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Date:	Tue, 20 May 2014 21:12:22 +0200
From:	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
To:	Tomasz Figa <tomasz.figa@...il.com>
Cc:	Ben Dooks <ben-linux@...ff.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Sangbeom Kim <sbkim73@...sung.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.de>,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix for possible null pointer dereference in dma.c

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.

344b4c48 sound/soc/samsung/dma.c         (Boojin Kim        2011-09-02
09:44:43 +0900 123)              prtd->dma_pos += prtd->dma_period;
344b4c48 sound/soc/samsung/dma.c         (Boojin Kim        2011-09-02
09:44:43 +0900 124)              if (prtd->dma_pos >= prtd->dma_end)
344b4c48 sound/soc/samsung/dma.c         (Boojin Kim        2011-09-02
09:44:43 +0900 125)                      prtd->dma_pos =
prtd->dma_start;
5111c075 sound/soc/s3c24xx/s3c24xx-pcm.c (Mark Brown        2008-04-30
17:19:32 +0200 126)
344b4c48 sound/soc/samsung/dma.c         (Boojin Kim        2011-09-02
09:44:43 +0900 127)              if (substream)
344b4c48 sound/soc/samsung/dma.c         (Boojin Kim        2011-09-02
09:44:43 +0900 128)
snd_pcm_period_elapsed(substream);
c0f41bb1 sound/soc/s3c24xx/s3c24xx-pcm.c (Ben Dooks         2007-02-14
13:20:03 +0100 129)
344b4c48 sound/soc/samsung/dma.c         (Boojin Kim        2011-09-02
09:44:43 +0900 130)              spin_lock(&prtd->lock);


Best regards
Rickard Strandqvist


2014-05-19 12:52 GMT+02:00 Tomasz Figa <tomasz.figa@...il.com>:
> Hi Rickard,
>
> On 15.05.2014 23:57, Rickard Strandqvist wrote:
>> There is otherwise a risk of a possible null pointer dereference.
>>
>> Was largely found by using a static code analysis program called cppcheck.
>>
>> Signed-off-by: Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
>> ---
>>  sound/soc/samsung/dma.c |   10 ++++++----
>>  1 fil ändrad, 6 tillägg(+), 4 borttagningar(-)
>>
>> diff --git a/sound/soc/samsung/dma.c b/sound/soc/samsung/dma.c
>> index dc09b71..b1f6757 100644
>> --- a/sound/soc/samsung/dma.c
>> +++ b/sound/soc/samsung/dma.c
>> @@ -115,17 +115,19 @@ static void dma_enqueue(struct snd_pcm_substream *substream)
>>  static void audio_buffdone(void *data)
>>  {
>>       struct snd_pcm_substream *substream = data;
>> -     struct runtime_data *prtd = substream->runtime->private_data;
>> +     struct runtime_data *prtd = NULL;
>>
>>       pr_debug("Entered %s\n", __func__);
>>
>> -     if (prtd->state & ST_RUNNING) {
>> +     if(substream)
>> +             prtd = substream->runtime->private_data;
>> +
>> +     if (prtd && prtd->state & ST_RUNNING) {
>>               prtd->dma_pos += prtd->dma_period;
>>               if (prtd->dma_pos >= prtd->dma_end)
>>                       prtd->dma_pos = prtd->dma_start;
>>
>> -             if (substream)
>> -                     snd_pcm_period_elapsed(substream);
>> +             snd_pcm_period_elapsed(substream);
>>
>>               spin_lock(&prtd->lock);
>>               if (!samsung_dma_has_circular()) {
>>
>
> Can you find a path (or use case, if possible) on which any of affected
> pointers will be NULL?
>
> Best regards,
> Tomasz
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