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

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[ 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>
This commit is contained in:
Takashi Iwai 2020-01-29 10:40:41 +01:00 committed by prashantpaddune
parent 5835450858
commit 96abf3db0d
1 changed files with 1 additions and 1 deletions
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2
sound/core/pcm_native.c
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@ -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);