ALSA: pcm: Add missing copy ops check before clearing buffer

[ this is a fix specific to 4.4.y and 4.9.y stable trees;
  4.14.y and older already contain the right fix ]

The stable 4.4.y and 4.9.y backports of the upstream commit
add9d56d7b37 ("ALSA: pcm: Avoid possible info leaks from PCM stream
buffers") dropped the check of substream->ops->copy_user as copy_user
is a new member that isn't present in the older kernels.
Although upstream drivers should work without this NULL check, it may
cause a regression with a downstream driver that sets some
inaccessible address to runtime->dma_area, leading to a crash at
worst.

Since such drivers must have ops->copy member on older kernels instead
of ops->copy_user, this patch adds the missing check of ops->copy for
fixing the regression.

Reported-and-tested-by: Andreas Schneider <asn@cryptomilk.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 2376b09..23e17a5 100644 (file)
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -588,7 +588,7 @@ static int snd_pcm_hw_params(struct snd_pcm_substream *substream,
                runtime->boundary *= 2;
 
        /* clear the buffer for avoiding possible kernel info leaks */
-       if (runtime->dma_area)
+       if (runtime->dma_area && !substream->ops->copy)
                memset(runtime->dma_area, 0, runtime->dma_bytes);
 
        snd_pcm_timer_resolution_change(substream);