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

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Message-ID: <cdc00899-cf44-44dd-b708-6cf7dc4b8375@embeddedor.com>
Date: Thu, 30 Nov 2023 14:11:49 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Kees Cook <keescook@...omium.org>, Jim Cromie <jim.cromie@...il.com>
Cc: Jean Delvare <jdelvare@...e.com>, Guenter Roeck <linux@...ck-us.net>,
 linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-hardening@...r.kernel.org
Subject: Re: [PATCH] hwmon: (pc87360) Bounds check data->innr usage



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@...il.com>
> Cc: Jean Delvare <jdelvare@...e.com>
> Cc: Guenter Roeck <linux@...ck-us.net>
> Cc: linux-hwmon@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>

Looks good to me.

Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.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 */