linux-kernel - [PATCH AUTOSEL 5.10 28/31] ALSA: pcm: Clear the full allocated memory at hw

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Date:   Wed, 30 Dec 2020 08:03:10 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Takashi Iwai <tiwai@...e.de>, Lars-Peter Clausen <lars@...afoo.de>,
        Sasha Levin <sashal@...nel.org>, alsa-devel@...a-project.org
Subject: [PATCH AUTOSEL 5.10 28/31] ALSA: pcm: Clear the full allocated memory at hw_params

From: Takashi Iwai <tiwai@...e.de>

[ Upstream commit 618de0f4ef11acd8cf26902e65493d46cc20cc89 ]

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).

Reviewed-by: Lars-Peter Clausen <lars@...afoo.de>
Link: https://lore.kernel.org/r/20201218145625.2045-3-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 47b155a49226f..9f3f8e953ff04 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_timer_resolution_change(substream);
 	snd_pcm_set_state(substream, SNDRV_PCM_STATE_SETUP);
-- 
2.27.0