hwmon: (aspeed-pwm-tacho) Fix -Wstringop-overflow warning in aspeed_create_fan_tach_c...

Based on the documentation below, the maximum number of Fan tach
channels is 16:

Documentation/devicetree/bindings/hwmon/aspeed-pwm-tacho.txt:45:
 45 - aspeed,fan-tach-ch : should specify the Fan tach input channel.
 46                 integer value in the range 0 through 15, with 0 indicating
 47                 Fan tach channel 0 and 15 indicating Fan tach channel 15.
 48                 At least one Fan tach input channel is required.

However, the compiler doesn't know that, and legitimaly warns about a potential
overwrite in array `u8 fan_tach_ch_source[16]` in `struct aspeed_pwm_tacho_data`,
in case `index` takes a value outside the boundaries of the array:

drivers/hwmon/aspeed-pwm-tacho.c:
179 struct aspeed_pwm_tacho_data {
...
184         bool fan_tach_present[16];
...
193         u8 fan_tach_ch_source[16];
196 };

In function ‘aspeed_create_fan_tach_channel’,
    inlined from ‘aspeed_create_fan’ at drivers/hwmon/aspeed-pwm-tacho.c:877:2,
    inlined from ‘aspeed_pwm_tacho_probe’ at drivers/hwmon/aspeed-pwm-tacho.c:936:9:
drivers/hwmon/aspeed-pwm-tacho.c:751:49: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  751 |                 priv->fan_tach_ch_source[index] = pwm_source;
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~
drivers/hwmon/aspeed-pwm-tacho.c: In function ‘aspeed_pwm_tacho_probe’:
drivers/hwmon/aspeed-pwm-tacho.c:193:12: note: at offset [48, 255] into destination object ‘fan_tach_ch_source’ of size 16
  193 |         u8 fan_tach_ch_source[16];
      |            ^~~~~~~~~~~~~~~~~~

Fix this by sanity checking `index` before using it to index arrays of
size 16 elements in `struct aspeed_pwm_tacho_data`. Also, pass `dev` as
argument to function `aspeed_create_fan_tach_channel()`, and add an error
message in case `index` is out-of-bounds, in which case return `-EINVAL`.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/ZVPQJIP26dIzRAr6@work
[groeck: Fixed continuation line alignment]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

diff --git a/drivers/hwmon/aspeed-pwm-tacho.c b/drivers/hwmon/aspeed-pwm-tacho.c
index 997df4b405098ff765acfb0e10875130360fc439..f6e1e55e82922be6f67a98046b4f74c3159625d9 100644 (file)
--- a/drivers/hwmon/aspeed-pwm-tacho.c
+++ b/drivers/hwmon/aspeed-pwm-tacho.c
@@ -166,6 +166,8 @@
 
 #define MAX_CDEV_NAME_LEN 16
 
+#define MAX_ASPEED_FAN_TACH_CHANNELS 16
+
 struct aspeed_cooling_device {
        char name[16];
        struct aspeed_pwm_tacho_data *priv;
@@ -181,7 +183,7 @@ struct aspeed_pwm_tacho_data {
        struct reset_control *rst;
        unsigned long clk_freq;
        bool pwm_present[8];
-       bool fan_tach_present[16];
+       bool fan_tach_present[MAX_ASPEED_FAN_TACH_CHANNELS];
        u8 type_pwm_clock_unit[3];
        u8 type_pwm_clock_division_h[3];
        u8 type_pwm_clock_division_l[3];
@@ -190,7 +192,7 @@ struct aspeed_pwm_tacho_data {
        u16 type_fan_tach_unit[3];
        u8 pwm_port_type[8];
        u8 pwm_port_fan_ctrl[8];
-       u8 fan_tach_ch_source[16];
+       u8 fan_tach_ch_source[MAX_ASPEED_FAN_TACH_CHANNELS];
        struct aspeed_cooling_device *cdev[8];
        const struct attribute_group *groups[3];
 };
@@ -737,20 +739,27 @@ static void aspeed_create_pwm_port(struct aspeed_pwm_tacho_data *priv,
        aspeed_set_pwm_port_fan_ctrl(priv, pwm_port, INIT_FAN_CTRL);
 }
 
-static void aspeed_create_fan_tach_channel(struct aspeed_pwm_tacho_data *priv,
-                                          u8 *fan_tach_ch,
-                                          int count,
-                                          u8 pwm_source)
+static int aspeed_create_fan_tach_channel(struct device *dev,
+                                         struct aspeed_pwm_tacho_data *priv,
+                                         u8 *fan_tach_ch,
+                                         int count,
+                                         u8 pwm_source)
 {
        u8 val, index;
 
        for (val = 0; val < count; val++) {
                index = fan_tach_ch[val];
+               if (index >= MAX_ASPEED_FAN_TACH_CHANNELS) {
+                       dev_err(dev, "Invalid Fan Tach input channel %u\n.", index);
+                       return -EINVAL;
+               }
                aspeed_set_fan_tach_ch_enable(priv->regmap, index, true);
                priv->fan_tach_present[index] = true;
                priv->fan_tach_ch_source[index] = pwm_source;
                aspeed_set_fan_tach_ch_source(priv->regmap, index, pwm_source);
        }
+
+       return 0;
 }
 
 static int
@@ -874,7 +883,10 @@ static int aspeed_create_fan(struct device *dev,
                                        fan_tach_ch, count);
        if (ret)
                return ret;
-       aspeed_create_fan_tach_channel(priv, fan_tach_ch, count, pwm_port);
+
+       ret = aspeed_create_fan_tach_channel(dev, priv, fan_tach_ch, count, pwm_port);
+       if (ret)
+               return ret;
 
        return 0;
 }