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

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Date:   Mon,  3 Feb 2020 16:18:53 +0000
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Takashi Iwai <tiwai@...e.de>,
        Andreas Schneider <asn@...ptomilk.org>
Subject: [PATCH 4.4 01/53] ALSA: pcm: Add missing copy ops check before clearing buffer

From: Takashi Iwai <tiwai@...e.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@...ptomilk.org>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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);