linux-kernel - [PATCH] power: supply: bq256xx: replace deprecated strncpy with strscpy

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Message-ID: <20231020-strncpy-drivers-power-supply-bq256xx_charger-c-v1-1-2fad856124f9@google.com>
Date:   Fri, 20 Oct 2023 19:05:25 +0000
From:   Justin Stitt <justinstitt@...gle.com>
To:     Sebastian Reichel <sre@...nel.org>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org,
        Justin Stitt <justinstitt@...gle.com>
Subject: [PATCH] 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 [1]
Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@...r.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@...gle.com>
---
Note: build-tested only.

Found with: $ rg "strncpy\("
---
 drivers/power/supply/bq256xx_charger.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/power/supply/bq256xx_charger.c b/drivers/power/supply/bq256xx_charger.c
index 82d3cd5ee2f9..85e1185275b9 100644
--- 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);

---
base-commit: bb55d7f7f7445abcc8db50e6a65d4315e79f75c7
change-id: 20231020-strncpy-drivers-power-supply-bq256xx_charger-c-be69c58602e6

Best regards,
--
Justin Stitt <justinstitt@...gle.com>