[PATCH] ALSA: pcm_dmaengine: Run complete cb only if runtime check passes

[PATCH] ALSA: pcm_dmaengine: Run complete cb only if runtime check passes

[Misael Lopez Cruz]

The DMA complete callback uses substream's runtime data, so make
sure the runtime check passes before going forward.

The callback could run while the stream is closing or after it's
already closed.  By then, the substream's runtime data might already
been freed and cause NULL pointer dereferences.

Signed-off-by: Misael Lopez Cruz <misael.lopez@ti.com>
Reviewed-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
---
 sound/core/pcm_dmaengine.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/sound/core/pcm_dmaengine.c b/sound/core/pcm_dmaengine.c
index fba365a..061a8f7 100644
--- a/sound/core/pcm_dmaengine.c
+++ b/sound/core/pcm_dmaengine.c
@@ -133,7 +133,12 @@ EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_set_config_from_dai_data);
 static void dmaengine_pcm_dma_complete(void *arg)
 {
 	struct snd_pcm_substream *substream = arg;
-	struct dmaengine_pcm_runtime_data *prtd = substream_to_prtd(substream);
+	struct dmaengine_pcm_runtime_data *prtd;
+
+	if (PCM_RUNTIME_CHECK(substream))
+		return;
+
+	prtd = substream_to_prtd(substream);
 
 	prtd->pos += snd_pcm_lib_period_bytes(substream);
 	if (prtd->pos >= snd_pcm_lib_buffer_bytes(substream))
-- 
1.7.9.5

Re: [PATCH] ALSA: pcm_dmaengine: Run complete cb only if runtime check passes

[Lars-Peter Clausen]

On 07/15/2015 07:23 PM, Misael Lopez Cruz wrote:
> The DMA complete callback uses substream's runtime data, so make
> sure the runtime check passes before going forward.
>
> The callback could run while the stream is closing or after it's
> already closed.  By then, the substream's runtime data might already
> been freed and cause NULL pointer dereferences.

If the callback runs after the stream has been closed that's a bug in the 
DMAengine driver. This patch does not fix the issue, the sub-stream itself 
might have been freed as well, so things will still crash.

To fix a potential race condition that can happen if one cpu is running the 
callback handlers and the stream is closed from another see this thread: 
http://www.spinics.net/lists/dmaengine/msg05126.html

- Lars

>
> Signed-off-by: Misael Lopez Cruz <misael.lopez@ti.com>
> Reviewed-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
> ---
>   sound/core/pcm_dmaengine.c |    7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/sound/core/pcm_dmaengine.c b/sound/core/pcm_dmaengine.c
> index fba365a..061a8f7 100644
> --- a/sound/core/pcm_dmaengine.c
> +++ b/sound/core/pcm_dmaengine.c
> @@ -133,7 +133,12 @@ EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_set_config_from_dai_data);
>   static void dmaengine_pcm_dma_complete(void *arg)
>   {
>   	struct snd_pcm_substream *substream = arg;
> -	struct dmaengine_pcm_runtime_data *prtd = substream_to_prtd(substream);
> +	struct dmaengine_pcm_runtime_data *prtd;
> +
> +	if (PCM_RUNTIME_CHECK(substream))
> +		return;
> +
> +	prtd = substream_to_prtd(substream);
>
>   	prtd->pos += snd_pcm_lib_period_bytes(substream);
>   	if (prtd->pos >= snd_pcm_lib_buffer_bytes(substream))
>