power: supply: bq256xx: replace deprecated strncpy with strscpy

strncpy() is deprecated for use on NUL-terminated destination strings
[1] and as such we should prefer more robust and less ambiguous string
interfaces.

We expect bq->model_name to be NUL-terminated based on its usage with
sysfs_emit and format strings:

val->strval is assigned to bq->model_name in
bq256xx_get_charger_property():
|       val->strval = bq->model_name;

... then in power_supply_sysfs.c we use value.strval with a format string:
|       ret = sysfs_emit(buf, "%s\n", value.strval);

we assigned value.strval via:
|       ret = power_supply_get_property(psy, psp, &value);
... which invokes psy->desc->get_property():
|       return psy->desc->get_property(psy, psp, val);

with bq256xx_get_charger_property():
|       static const struct power_supply_desc bq256xx_power_supply_desc = {
...
|       	.get_property = bq256xx_get_charger_property,

Moreover, no NUL-padding is required as bq is zero-allocated in
bq256xx_charger.c:
|       bq = devm_kzalloc(dev, sizeof(*bq), GFP_KERNEL);

Considering the above, a suitable replacement is `strscpy` [2] due to
the fact that it guarantees NUL-termination on the destination buffer
without unnecessarily NUL-padding.

Let's also opt to use the more idiomatic strscpy() usage of (dest, src,
sizeof(dest)) as this more closely ties the destination buffer and the
length.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Similar-to: https://lore.kernel.org/all/20231020-strncpy-drivers-power-supply-bq24190_charger-c-v1-1-e896223cb795@google.com/
Similar-to: https://lore.kernel.org/all/20231020-strncpy-drivers-power-supply-bq2515x_charger-c-v1-1-46664c6edf78@google.com/
Signed-off-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20231020-strncpy-drivers-power-supply-bq256xx_charger-c-v1-1-2fad856124f9@google.com
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

diff --git a/drivers/power/supply/bq256xx_charger.c b/drivers/power/supply/bq256xx_charger.c
index 474201815a27fc959b654ea3c3cd7f6ac3201837..789a31bd70c39f2954527bfb565dc53fda0d6c21 100644 (file)
--- a/drivers/power/supply/bq256xx_charger.c
+++ b/drivers/power/supply/bq256xx_charger.c
@@ -1706,7 +1706,7 @@ static int bq256xx_probe(struct i2c_client *client)
 
        mutex_init(&bq->lock);
 
-       strncpy(bq->model_name, id->name, I2C_NAME_SIZE);
+       strscpy(bq->model_name, id->name, sizeof(bq->model_name));
 
        bq->regmap = devm_regmap_init_i2c(client,
                                        bq->chip_info->bq256xx_regmap_config);