[PATCH] hwmon: (pc87360) Bounds check data->innr usage

[PATCH] hwmon: (pc87360) Bounds check data->innr usage

[Kees Cook]

Without visibility into the initializers for data->innr, GCC suspects
using it as an index could walk off the end of the various 14-element
arrays in data. Perform an explicit clamp to the array size. Silences
the following warning with GCC 12+:

../drivers/hwmon/pc87360.c: In function 'pc87360_update_device':
../drivers/hwmon/pc87360.c:341:49: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
  341 |                                 data->in_max[i] = pc87360_read_value(data,
      |                                 ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
  342 |                                                   LD_IN, i,
      |                                                   ~~~~~~~~~
  343 |                                                   PC87365_REG_IN_MAX);
      |                                                   ~~~~~~~~~~~~~~~~~~~
../drivers/hwmon/pc87360.c:209:12: note: at offset 255 into destination object 'in_max' of size 14
  209 |         u8 in_max[14];          /* Register value */
      |            ^~~~~~

Cc: Jim Cromie <jim.cromie@gmail.com>
Cc: Jean Delvare <jdelvare@suse.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: linux-hwmon@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/hwmon/pc87360.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hwmon/pc87360.c b/drivers/hwmon/pc87360.c
index 926ea1fe133c..db80394ba854 100644
--- a/drivers/hwmon/pc87360.c
+++ b/drivers/hwmon/pc87360.c
@@ -323,7 +323,7 @@ static struct pc87360_data *pc87360_update_device(struct device *dev)
 		}
 
 		/* Voltages */
-		for (i = 0; i < data->innr; i++) {
+		for (i = 0; i < min(data->innr, ARRAY_SIZE(data->in)); i++) {
 			data->in_status[i] = pc87360_read_value(data, LD_IN, i,
 					     PC87365_REG_IN_STATUS);
 			/* Clear bits */
-- 
2.34.1

Re: [PATCH] hwmon: (pc87360) Bounds check data->innr usage

[Gustavo A. R. Silva]

On 11/30/23 14:02, Kees Cook wrote:
> Without visibility into the initializers for data->innr, GCC suspects
> using it as an index could walk off the end of the various 14-element
> arrays in data. Perform an explicit clamp to the array size. Silences
> the following warning with GCC 12+:
> 
> ../drivers/hwmon/pc87360.c: In function 'pc87360_update_device':
> ../drivers/hwmon/pc87360.c:341:49: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
>    341 |                                 data->in_max[i] = pc87360_read_value(data,
>        |                                 ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
>    342 |                                                   LD_IN, i,
>        |                                                   ~~~~~~~~~
>    343 |                                                   PC87365_REG_IN_MAX);
>        |                                                   ~~~~~~~~~~~~~~~~~~~
> ../drivers/hwmon/pc87360.c:209:12: note: at offset 255 into destination object 'in_max' of size 14
>    209 |         u8 in_max[14];          /* Register value */
>        |            ^~~~~~
> 
> Cc: Jim Cromie <jim.cromie@gmail.com>
> Cc: Jean Delvare <jdelvare@suse.com>
> Cc: Guenter Roeck <linux@roeck-us.net>
> Cc: linux-hwmon@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Looks good to me.

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks!
--
Gustavo

> ---
>   drivers/hwmon/pc87360.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/pc87360.c b/drivers/hwmon/pc87360.c
> index 926ea1fe133c..db80394ba854 100644
> --- a/drivers/hwmon/pc87360.c
> +++ b/drivers/hwmon/pc87360.c
> @@ -323,7 +323,7 @@ static struct pc87360_data *pc87360_update_device(struct device *dev)
>   		}
>   
>   		/* Voltages */
> -		for (i = 0; i < data->innr; i++) {
> +		for (i = 0; i < min(data->innr, ARRAY_SIZE(data->in)); i++) {
>   			data->in_status[i] = pc87360_read_value(data, LD_IN, i,
>   					     PC87365_REG_IN_STATUS);
>   			/* Clear bits */

Re: [PATCH] hwmon: (pc87360) Bounds check data->innr usage

[Guenter Roeck]

On 11/30/23 12:11, Gustavo A. R. Silva wrote:
> 
> 
> On 11/30/23 14:02, Kees Cook wrote:
>> Without visibility into the initializers for data->innr, GCC suspects
>> using it as an index could walk off the end of the various 14-element
>> arrays in data. Perform an explicit clamp to the array size. Silences
>> the following warning with GCC 12+:
>>
>> ../drivers/hwmon/pc87360.c: In function 'pc87360_update_device':
>> ../drivers/hwmon/pc87360.c:341:49: warning: writing 1 byte into a region of size 0 [-Wstringop-overflow=]
>>    341 |                                 data->in_max[i] = pc87360_read_value(data,
>>        |                                 ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
>>    342 |                                                   LD_IN, i,
>>        |                                                   ~~~~~~~~~
>>    343 |                                                   PC87365_REG_IN_MAX);
>>        |                                                   ~~~~~~~~~~~~~~~~~~~
>> ../drivers/hwmon/pc87360.c:209:12: note: at offset 255 into destination object 'in_max' of size 14
>>    209 |         u8 in_max[14];          /* Register value */
>>        |            ^~~~~~
>>
>> Cc: Jim Cromie <jim.cromie@gmail.com>
>> Cc: Jean Delvare <jdelvare@suse.com>
>> Cc: Guenter Roeck <linux@roeck-us.net>
>> Cc: linux-hwmon@vger.kernel.org
>> Signed-off-by: Kees Cook <keescook@chromium.org>
> 
> Looks good to me.
> 
> Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
> 

Guess I'll apply it, even though it is quite pointless. But arguing against
such changes seems like shouting into the wind, so whatever.

There are several other similar "unchecked" loops, including loops for
fannr and tempnr. The driver would misbehave badly if any of those would
ever be outside the valid range, both when accessing the hardware and
writing into various arrays.

Guenter