2023-09-14 22:52:42

by Justin Stitt

Subject: [PATCH] hwmon: refactor deprecated strncpy

`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.

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: [email protected]
Signed-off-by: Justin Stitt <[email protected]>
---
drivers/hwmon/acpi_power_meter.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hwmon/acpi_power_meter.c b/drivers/hwmon/acpi_power_meter.c
index fa28d447f0df..9bafe7c85ff7 100644
--- a/drivers/hwmon/acpi_power_meter.c
+++ b/drivers/hwmon/acpi_power_meter.c
@@ -803,7 +803,7 @@ static int read_capabilities(struct acpi_power_meter_resource *resource)
goto error;
}

- strncpy(*str, element->string.pointer, element->string.length);
+ strscpy(*str, element->string.pointer, element->string.length);
str++;
}


---
base-commit: 3669558bdf354cd352be955ef2764cde6a9bf5ec
change-id: 20230914-strncpy-drivers-hwmon-acpi_power_meter-c-c9f2d8053bef

Best regards,
--
Justin Stitt <[email protected]>

2023-09-15 12:20:02

by Kees Cook

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

On Thu, Sep 14, 2023 at 10:50:15PM +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.
>
> 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: [email protected]
> Signed-off-by: Justin Stitt <[email protected]>
> ---
> drivers/hwmon/acpi_power_meter.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/hwmon/acpi_power_meter.c b/drivers/hwmon/acpi_power_meter.c
> index fa28d447f0df..9bafe7c85ff7 100644
> --- a/drivers/hwmon/acpi_power_meter.c
> +++ b/drivers/hwmon/acpi_power_meter.c
> @@ -803,7 +803,7 @@ static int read_capabilities(struct acpi_power_meter_resource *resource)
> goto error;
> }
>
> - strncpy(*str, element->string.pointer, element->string.length);
> + strscpy(*str, element->string.pointer, element->string.length);

This will truncate the destination by 1 training character. This is better
replaced with just memcpy() (all the size information has already been
calculated and %NUL termination space made in the kcalloc() above it.

-Kees

> str++;
> }
>
>
> ---
> base-commit: 3669558bdf354cd352be955ef2764cde6a9bf5ec
> change-id: 20230914-strncpy-drivers-hwmon-acpi_power_meter-c-c9f2d8053bef
>
> Best regards,
> --
> Justin Stitt <[email protected]>
>

--
Kees Cook