[PATCH 4.4 01/53] ALSA: pcm: Add missing copy ops check before clearing buffer

Greg Kroah-Hartman
2020-02-03T16:19:55Z

From: Takashi Iwai <tiwai@suse.de>

[ 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>
---
sound/core/pcm_native.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -588,7 +588,7 @@ static int snd_pcm_hw_params(struct snd_
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);