[PATCH 4.19 062/170] ALSA: pcm: Fix potential Spectre v1 vulnerability

From: Greg Kroah-Hartman
Date: Mon Jan 07 2019 - 07:50:52 EST

4.19-stable review patch. If anyone has any objections, please let me know.


From: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>

commit 94ffb030b6d31ec840bb811be455dd2e26a4f43e upstream.

stream 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/core/pcm.c:140 snd_pcm_control_ioctl() warn: potential spectre issue 'pcm->streams' [r] (local cap)

Fix this by sanitizing stream before using it to index pcm->streams

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].

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

Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

sound/core/pcm.c | 2 ++
1 file changed, 2 insertions(+)

--- a/sound/core/pcm.c
+++ b/sound/core/pcm.c
@@ -25,6 +25,7 @@
#include <linux/time.h>
#include <linux/mutex.h>
#include <linux/device.h>
+#include <linux/nospec.h>
#include <sound/core.h>
#include <sound/minors.h>
#include <sound/pcm.h>
@@ -129,6 +130,7 @@ static int snd_pcm_control_ioctl(struct
return -EFAULT;
if (stream < 0 || stream > 1)
return -EINVAL;
+ stream = array_index_nospec(stream, 2);
if (get_user(subdevice, &info->subdevice))
return -EFAULT;