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

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Message-Id: <20231130200207.work.679-kees@kernel.org>
Date:   Thu, 30 Nov 2023 12:02:07 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Jim Cromie <jim.cromie@...il.com>
Cc:     Kees Cook <keescook@...omium.org>,
        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: [PATCH] hwmon: (pc87360) Bounds check data->innr usage

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>
---
 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