[PATCH 4.19 057/134] ALSA: rawmidi: Fix potential Spectre v1 vulnerability

From: Greg Kroah-Hartman
Date: Mon Apr 01 2019 - 13:15:16 EST

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


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

commit 2b1d9c8f87235f593826b9cf46ec10247741fff9 upstream.

info->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/rawmidi.c:604 __snd_rawmidi_info_select() warn: potential spectre issue 'rmidi->streams' [r] (local cap)

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

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://lore.kernel.org/lkml/20180423164740.GY17484@xxxxxxxxxxxxxx/

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

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

--- a/sound/core/rawmidi.c
+++ b/sound/core/rawmidi.c
@@ -30,6 +30,7 @@
#include <linux/module.h>
#include <linux/delay.h>
#include <linux/mm.h>
+#include <linux/nospec.h>
#include <sound/rawmidi.h>
#include <sound/info.h>
#include <sound/control.h>
@@ -601,6 +602,7 @@ static int __snd_rawmidi_info_select(str
return -ENXIO;
if (info->stream < 0 || info->stream > 1)
return -EINVAL;
+ info->stream = array_index_nospec(info->stream, 2);
pstr = &rmidi->streams[info->stream];
if (pstr->substream_count == 0)
return -ENOENT;