Re: [PATCH 4/4] ALSA: pcm_dmaengine: Properly synchronize DMA on shutdown

[Takashi Iwai <tiwai@suse.de>]

On Tue, 20 Oct 2015 11:46:31 +0200,
Lars-Peter Clausen wrote:
> 
> Use the new dmaengine_synchronize() function to make sure that all complete
> callbacks have finished running before the runtime data, which is accessed
> in the completed callback, is freed.
> 
> This fixes a long standing use-after-free race condition that has been
> observed on some systems.

What if a substream is restarted immediately after the stop?


Takashi

> 
> Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
> ---
>  sound/core/pcm_dmaengine.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/sound/core/pcm_dmaengine.c b/sound/core/pcm_dmaengine.c
> index fba365a..697c166 100644
> --- a/sound/core/pcm_dmaengine.c
> +++ b/sound/core/pcm_dmaengine.c
> @@ -202,13 +202,13 @@ int snd_dmaengine_pcm_trigger(struct snd_pcm_substream *substream, int cmd)
>  		if (runtime->info & SNDRV_PCM_INFO_PAUSE)
>  			dmaengine_pause(prtd->dma_chan);
>  		else
> -			dmaengine_terminate_all(prtd->dma_chan);
> +			dmaengine_terminate_async(prtd->dma_chan);
>  		break;
>  	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
>  		dmaengine_pause(prtd->dma_chan);
>  		break;
>  	case SNDRV_PCM_TRIGGER_STOP:
> -		dmaengine_terminate_all(prtd->dma_chan);
> +		dmaengine_terminate_async(prtd->dma_chan);
>  		break;
>  	default:
>  		return -EINVAL;
> @@ -346,6 +346,7 @@ int snd_dmaengine_pcm_close(struct snd_pcm_substream *substream)
>  {
>  	struct dmaengine_pcm_runtime_data *prtd = substream_to_prtd(substream);
>  
> +	dmaengine_synchronize(prtd->dma_chan);
>  	kfree(prtd);
>  
>  	return 0;
> @@ -362,9 +363,11 @@ int snd_dmaengine_pcm_close_release_chan(struct snd_pcm_substream *substream)
>  {
>  	struct dmaengine_pcm_runtime_data *prtd = substream_to_prtd(substream);
>  
> +	dmaengine_synchronize(prtd->dma_chan);
>  	dma_release_channel(prtd->dma_chan);
> +	kfree(prtd);
>  
> -	return snd_dmaengine_pcm_close(substream);
> +	return 0;
>  }
>  EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_close_release_chan);
>  
> -- 
> 2.1.4
> 
>