Messages in this thread | | | Date | Fri, 2 Jan 2015 09:07:32 +0000 | From | Qais Yousef <> | Subject | Re: [PATCH] ALSA: ASoC: soc-compress.c: fix NULL dereference |
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On 12/29/2014 04:13 PM, Mark Brown wrote: > On Tue, Dec 23, 2014 at 09:09:27AM +0000, Qais Yousef wrote: >> In soc_new_compress() when rtd->dai_link->daynmic is set, we create the pcm >> substreams with this call: >> >> ret = snd_pcm_new_internal(rtd->card->snd_card, new_name, num, >> 1, 0, &be_pcm); >> >> which passes 0 as capture_count leading to >> >> be_pcm->streams[SNDRV_PCM_STREAM_CAPTURE].substream >> >> being NULL, hence when trying to set rtd a few lines below we get an oops. >> Fix by removing this line of code since CAPTURE substream will always be NULL. > Why will the capture stream always be NULL? There should be no > intrinsic reason why we can't have hardware support for capturing > compressed audio.
I think because we pass 0 as capture_count in snd_pcm_new_internal(). If I read the code correctly this will lead to _snd_pcm_new() to be called which in return will call snd_pcm_new_stream(pcm, SNDRV_PCM_STREAM_CAPTURE, capture_count) which will cause no substream to be allocated for the capture case, hence being NULL. I get an oops in my experimental driver when I set dynamic = 1 in FE dai link. If I did something wrong there that caused this, it's not obvious to me how.
Maybe a better fix would be to replace the 1 and 0 in snd_pcm_new_internal() call with rtd->dai_link->dpcm_playback and rtd->dai_link->dpcm_capture.
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