[alsa-devel] [PATCH] ALSA: pcm: Avoid possible info leaks from PCM stream buffers

[alsa-devel] [PATCH] ALSA: pcm: Avoid possible info leaks from PCM stream buffers

[Takashi Iwai]

The current PCM code doesn't initialize explicitly the buffers
allocated for PCM streams, hence it might leak some uninitialized
kernel data or previous stream contents by mmapping or reading the
buffer before actually starting the stream.

Since this is a common problem, this patch simply adds the clearance
of the buffer data at hw_params callback.  Although this does only
zero-clear no matter which format is used, which doesn't mean the
silence for some formats, but it should be OK because the intention is
just to clear the previous data on the buffer.

Reported-by: Lionel Koenig <lionel.koenig@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---

This is a revised patch of the previous one
  20191210130219.27919-1-tiwai@suse.de

 sound/core/pcm_native.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 1fe581167b7b..d083225344a0 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -739,6 +739,10 @@ static int snd_pcm_hw_params(struct snd_pcm_substream *substream,
 	while (runtime->boundary * 2 <= LONG_MAX - runtime->buffer_size)
 		runtime->boundary *= 2;
 
+	/* clear the buffer for avoiding possible kernel info leaks */
+	if (runtime->dma_area && !substream->ops->copy_user)
+		memset(runtime->dma_area, 0, runtime->dma_bytes);
+
 	snd_pcm_timer_resolution_change(substream);
 	snd_pcm_set_state(substream, SNDRV_PCM_STATE_SETUP);
 
-- 
2.16.4

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Re: [alsa-devel] [PATCH] ALSA: pcm: Avoid possible info leaks from PCM stream buffers

[Lionel Koenig]

On Wed, Dec 11, 2019 at 04:57:42PM +0100, Takashi Iwai wrote:
> The current PCM code doesn't initialize explicitly the buffers
> allocated for PCM streams, hence it might leak some uninitialized
> kernel data or previous stream contents by mmapping or reading the
> buffer before actually starting the stream.
> 
> Since this is a common problem, this patch simply adds the clearance
> of the buffer data at hw_params callback.  Although this does only
> zero-clear no matter which format is used, which doesn't mean the
> silence for some formats, but it should be OK because the intention is
> just to clear the previous data on the buffer.

I have tested this patch on the same way I tested the previous one and
didn't experience any leakage of data. 
Thanks for helping putting that together.

Kind regards,
Lionel

> 
> Reported-by: Lionel Koenig <lionel.koenig@gmail.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> ---
> 
> This is a revised patch of the previous one
>   20191210130219.27919-1-tiwai@suse.de
> 
>  sound/core/pcm_native.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
> index 1fe581167b7b..d083225344a0 100644
> --- a/sound/core/pcm_native.c
> +++ b/sound/core/pcm_native.c
> @@ -739,6 +739,10 @@ static int snd_pcm_hw_params(struct snd_pcm_substream *substream,
>  	while (runtime->boundary * 2 <= LONG_MAX - runtime->buffer_size)
>  		runtime->boundary *= 2;
>  
> +	/* clear the buffer for avoiding possible kernel info leaks */
> +	if (runtime->dma_area && !substream->ops->copy_user)
> +		memset(runtime->dma_area, 0, runtime->dma_bytes);
> +
>  	snd_pcm_timer_resolution_change(substream);
>  	snd_pcm_set_state(substream, SNDRV_PCM_STATE_SETUP);
>  
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