[alsa-devel] [PATCH 4/4] ALSA: pcm_dmaengine: Properly synchronize DMA on shutdown

[Lars-Peter Clausen]

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.

Signed-off-by: Lars-Peter Clausen <lars at 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