ALSA: rme9652: Fix potential Spectre v1 vulnerability

info->channel is indirectly controlled by user-space, hence leading to
a potential exploitation of the Spectre variant 1 vulnerability.

This issue was detected with the help of Smatch:

sound/pci/rme9652/hdsp.c:4100 snd_hdsp_channel_info() warn: potential spectre issue 'hdsp->channel_map' [r] (local cap)

Fix this by sanitizing info->channel before using it to index hdsp->channel_map

Notice that given that speculation windows are large, the policy is
to kill the speculation on the first load and not worry if it can be
completed with a dependent load/store [1].

Also, notice that I refactored the code a bit in order to get rid of the
following checkpatch warning:

ERROR: do not use assignment in if condition
FILE: sound/pci/rme9652/hdsp.c:4103:
	if ((mapped_channel = hdsp->channel_map[info->channel]) < 0)

[1] https://marc.info/?l=linux-kernel&m=152449131114778&w=2

Cc: stable@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
CVE-2017-5753

(cherry picked from commit 0b84304ef5da92add8dc75a1b07879c5374cdb05)
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/sound/pci/rme9652/hdsp.c b/sound/pci/rme9652/hdsp.c
index 1bff4b1b39cd04651f16efa1e151ca87c2804d9c..ba99ff0e93e0307aebc79d7dd2e59fb2d7a3b5fb 100644 (file)
--- a/sound/pci/rme9652/hdsp.c
+++ b/sound/pci/rme9652/hdsp.c
@@ -30,6 +30,7 @@
 #include <linux/math64.h>
 #include <linux/vmalloc.h>
 #include <linux/io.h>
+#include <linux/nospec.h>
 
 #include <sound/core.h>
 #include <sound/control.h>
@@ -4092,15 +4093,16 @@ static int snd_hdsp_channel_info(struct snd_pcm_substream *substream,
                                    struct snd_pcm_channel_info *info)
 {
        struct hdsp *hdsp = snd_pcm_substream_chip(substream);
-       int mapped_channel;
+       unsigned int channel = info->channel;
 
-       if (snd_BUG_ON(info->channel >= hdsp->max_channels))
+       if (snd_BUG_ON(channel >= hdsp->max_channels))
                return -EINVAL;
+       channel = array_index_nospec(channel, hdsp->max_channels);
 
-       if ((mapped_channel = hdsp->channel_map[info->channel]) < 0)
+       if (hdsp->channel_map[channel] < 0)
                return -EINVAL;
 
-       info->offset = mapped_channel * HDSP_CHANNEL_BUFFER_BYTES;
+       info->offset = hdsp->channel_map[channel] * HDSP_CHANNEL_BUFFER_BYTES;
        info->first = 0;
        info->step = 32;
        return 0;