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

commit add9d56d7b3781532208afbff5509d7382fb6efe upstream.

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>
Link: https://lore.kernel.org/r/20191211155742.3213-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index a0ee065a9f8c4526f90ececfe41b9ead118cb2ec..4195e3c8b641eb56f985a20945a153667072595b 100644 (file)
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -459,6 +459,10 @@ 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)
+               memset(runtime->dma_area, 0, runtime->dma_bytes);
+
        snd_pcm_timer_resolution_change(substream);
        snd_pcm_set_state(substream, SNDRV_PCM_STATE_SETUP);