hwmon: (nct6775) Fix potential Spectre v1

val can be 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:

vers/hwmon/nct6775.c:2698 store_pwm_weight_temp_sel() warn: potential
spectre issue 'data->temp_src' [r]

Fix this by sanitizing val before using it to index data->temp_src

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@vger.kernel.org
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
CVE-2017-5753

(cherry picked from commit d49dbfade96d5b0863ca8a90122a805edd5ef50a)
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/drivers/hwmon/nct6775.c b/drivers/hwmon/nct6775.c
index f5f3f8cf57ea66d1a95bd4511d767611fb0fb338..f6fbdb63f5768fcc951bd4c246d538c93c94b903 100644 (file)
--- a/drivers/hwmon/nct6775.c
+++ b/drivers/hwmon/nct6775.c
@@ -63,6 +63,7 @@
 #include <linux/bitops.h>
 #include <linux/dmi.h>
 #include <linux/io.h>
+#include <linux/nospec.h>
 #include "lm75.h"
 
 #define USE_ALTERNATE
@@ -2642,6 +2643,7 @@ store_pwm_weight_temp_sel(struct device *dev, struct device_attribute *attr,
                return err;
        if (val > NUM_TEMP)
                return -EINVAL;
+       val = array_index_nospec(val, NUM_TEMP + 1);
        if (val && (!(data->have_temp & BIT(val - 1)) ||
                    !data->temp_src[val - 1]))
                return -EINVAL;