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From: Takashi Iwai <>
Cc: Robin Gong <>, Lars-Peter Clausen <>
Subject: [PATCH 2/2] ALSA: pcm: Clear the full allocated memory at hw_params
Date: Fri, 18 Dec 2020 15:56:25 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

The PCM hw_params core function tries to clear up the PCM buffer
before actually using for avoiding the information leak from the
previous usages or the usage before a new allocation.  It performs the
memset() with runtime->dma_bytes, but this might still leave some
remaining bytes untouched; namely, the PCM buffer size is aligned in
page size for mmap, hence runtime->dma_bytes doesn't necessarily cover
all PCM buffer pages, and the remaining bytes are exposed via mmap.

This patch changes the memory clearance to cover the all buffer pages
if the stream is supposed to be mmap-ready (that guarantees that the
buffer size is aligned in page size).

Signed-off-by: Takashi Iwai <>
 sound/core/pcm_native.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 47b155a49226..9f3f8e953ff0 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -755,8 +755,13 @@ 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 && !substream->ops->copy_user)
-		memset(runtime->dma_area, 0, runtime->dma_bytes);
+	if (runtime->dma_area && !substream->ops->copy_user) {
+		size_t size = runtime->dma_bytes;
+		if (runtime->info & SNDRV_PCM_INFO_MMAP)
+			size = PAGE_ALIGN(size);
+		memset(runtime->dma_area, 0, size);
+	}
 	snd_pcm_set_state(substream, SNDRV_PCM_STATE_SETUP);

  parent reply	other threads:[~2020-12-18 14:58 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-18 14:56 [PATCH 0/2] ALSA: Clear PCM buffers more properly Takashi Iwai
2020-12-18 14:56 ` [PATCH 1/2] ALSA: memalloc: Align buffer allocations in page size Takashi Iwai
2020-12-18 15:31   ` Lars-Peter Clausen
2020-12-18 14:56 ` Takashi Iwai [this message]
2020-12-18 15:32   ` [PATCH 2/2] ALSA: pcm: Clear the full allocated memory at hw_params Lars-Peter Clausen

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