[PATCH AUTOSEL 5.4 14/24] hwmon: (pc87360) Bounds check data->innr usage

[Sasha Levin]

From: Kees Cook <keescook@xxxxxxxxxxxx>

[ Upstream commit 4265eb062a7303e537ab3792ade31f424c3c5189 ]

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@xxxxxxxxx>
Cc: Jean Delvare <jdelvare@xxxxxxxx>
Cc: Guenter Roeck <linux@xxxxxxxxxxxx>
Cc: linux-hwmon@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20231130200207.work.679-kees@xxxxxxxxxx
[groeck: Added comment into code clarifying context]
Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/hwmon/pc87360.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/pc87360.c b/drivers/hwmon/pc87360.c
index 94f4b8b4a2ba..0cf603c8c9f9 100644
--- a/drivers/hwmon/pc87360.c
+++ b/drivers/hwmon/pc87360.c
@@ -1605,7 +1605,11 @@ static struct pc87360_data *pc87360_update_device(struct device *dev)
 		}
 
 		/* Voltages */
-		for (i = 0; i < data->innr; i++) {
+		/*
+		 * The min() below does not have any practical meaning and is
+		 * only needed to silence a warning observed with gcc 12+.
+		 */
+		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 */
-- 
2.43.0