ALSA: pcm: Avoid possible info leaks from PCM stream buffers

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>
Link: https://lore.kernel.org/r/20191211155742.3213-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 1fe581167b7b9aad19be6a06c3c5d98d3183cf45..d083225344a06d7a5aadb5b9afb5d7918f459c02 100644 (file)
--- 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);