[PATCH 10/11] vivid-sdr-cap: fix potential Spectre variant 1

[Gustavo A. R. Silva]

band->index can be controlled by user-space, hence leading to
a potential exploitation of the Spectre variant 1 vulnerability.

Smatch warning:
drivers/media/platform/vivid/vivid-sdr-cap.c:323 vivid_sdr_enum_freq_bands() warn: potential spectre issue 'bands_adc'

Fix this by sanitizing band->index before using it to index
bands_adc and bands_fm.

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

Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
---
 drivers/media/platform/vivid/vivid-sdr-cap.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/media/platform/vivid/vivid-sdr-cap.c b/drivers/media/platform/vivid/vivid-sdr-cap.c
index cfb7cb4..684d8a2 100644
--- a/drivers/media/platform/vivid/vivid-sdr-cap.c
+++ b/drivers/media/platform/vivid/vivid-sdr-cap.c
@@ -22,6 +22,8 @@
 #include "vivid-ctrls.h"
 #include "vivid-sdr-cap.h"
 
+#include <linux/nospec.h>
+
 /* stream formats */
 struct vivid_format {
 	u32	pixelformat;
@@ -320,11 +322,15 @@ int vivid_sdr_enum_freq_bands(struct file *file, void *fh,
 	case 0:
 		if (band->index >= ARRAY_SIZE(bands_adc))
 			return -EINVAL;
+		band->index = array_index_nospec(band->index,
+						 ARRAY_SIZE(bands_adc));
 		*band = bands_adc[band->index];
 		return 0;
 	case 1:
 		if (band->index >= ARRAY_SIZE(bands_fm))
 			return -EINVAL;
+		band->index = array_index_nospec(band->index,
+						 ARRAY_SIZE(bands_fm));
 		*band = bands_fm[band->index];
 		return 0;
 	default:
-- 
2.7.4