[PATCH] hwmon: pmbus: refactor deprecated strncpy

[PATCH] hwmon: pmbus: refactor deprecated strncpy

[Justin Stitt]

`strncpy` is deprecated for use on NUL-terminated destination strings [1].

We should prefer more robust and less ambiguous string interfaces.

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

`label` is zero-allocated and as such the NUL-padding behavior of
strncpy is not required here.

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@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
 drivers/hwmon/pmbus/pmbus_core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
index 1363d9f89181..dcc8b12387cc 100644
--- a/drivers/hwmon/pmbus/pmbus_core.c
+++ b/drivers/hwmon/pmbus/pmbus_core.c
@@ -1394,7 +1394,7 @@ static int pmbus_add_label(struct pmbus_data *data,
 	snprintf(label->name, sizeof(label->name), "%s%d_label", name, seq);
 	if (!index) {
 		if (phase == 0xff)
-			strncpy(label->label, lstring,
+			strscpy(label->label, lstring,
 				sizeof(label->label) - 1);
 		else
 			snprintf(label->label, sizeof(label->label), "%s.%d",

---
base-commit: 3669558bdf354cd352be955ef2764cde6a9bf5ec
change-id: 20230915-strncpy-drivers-hwmon-pmbus-pmbus_core-c-8279663960a3

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

Re: [PATCH] hwmon: pmbus: refactor deprecated strncpy

[Guenter Roeck]

On Fri, Sep 15, 2023 at 06:28:41PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> We should prefer more robust and less ambiguous string interfaces.
> 
> A suitable replacement is `strscpy` [2] due to the fact that it guarantees
> NUL-termination on the destination buffer without unnecessarily NUL-padding.
> 
> `label` is zero-allocated and as such the NUL-padding behavior of
> strncpy is not required here.
> 
> 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@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>
> ---
>  drivers/hwmon/pmbus/pmbus_core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> index 1363d9f89181..dcc8b12387cc 100644
> --- a/drivers/hwmon/pmbus/pmbus_core.c
> +++ b/drivers/hwmon/pmbus/pmbus_core.c
> @@ -1394,7 +1394,7 @@ static int pmbus_add_label(struct pmbus_data *data,
>  	snprintf(label->name, sizeof(label->name), "%s%d_label", name, seq);
>  	if (!index) {
>  		if (phase == 0xff)
> -			strncpy(label->label, lstring,
> +			strscpy(label->label, lstring,
>  				sizeof(label->label) - 1);

'label' is allocated with kzalloc(), and, by copying one byte less
than the size of the field into label->label, it is guaranteed to be
terminated. Using strscpy() instead of strncpy() results in dropping
the last character of lstring if its length is sizeof(label->label) - 1.

Really, I am not going to accept any of your patches, sorry.

Guenter