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

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Date: Thu, 30 Nov 2023 12:31:26 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
 Kees Cook <keescook@...omium.org>, Jim Cromie <jim.cromie@...il.com>
Cc: Jean Delvare <jdelvare@...e.com>, 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 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@...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>
> 

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