[PATCH v2] hwmon: refactor deprecated strncpy

[PATCH v2] hwmon: refactor deprecated strncpy

[Justin Stitt]

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

A trailing zero is already handled by the kcalloc
|	*str = kcalloc(element->string.length + 1, sizeof(u8), GFP_KERNEL);
... which makes memcpy() a suitable replacement to strncpy.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
Link: https://github.com/KSPP/linux/issues/90
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Changes in v2:
- use memcpy over strscpy (thanks Kees)
- Link to v1: https://lore.kernel.org/r/20230914-strncpy-drivers-hwmon-acpi_power_meter-c-v1-1-905297479fe8@google.com
---
 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..82e99aec4a33 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);
+		memcpy(*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 <justinstitt@google.com>

Re: [PATCH v2] hwmon: refactor deprecated strncpy

[Thomas Weißschuh]

On 2023-09-19 05:07:55+0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> A trailing zero is already handled by the kcalloc
> |	*str = kcalloc(element->string.length + 1, sizeof(u8), GFP_KERNEL);
> ... which makes memcpy() a suitable replacement to strncpy.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>
> ---
> Changes in v2:
> - use memcpy over strscpy (thanks Kees)
> - Link to v1: https://lore.kernel.org/r/20230914-strncpy-drivers-hwmon-acpi_power_meter-c-v1-1-905297479fe8@google.com
> ---
>  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..82e99aec4a33 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);
> +		memcpy(*str, element->string.pointer, element->string.length);

Isn't this now essentially the same as kmemdup_nul()?

>  		str++;
>  	}
>  
> 
> ---
> base-commit: 3669558bdf354cd352be955ef2764cde6a9bf5ec
> change-id: 20230914-strncpy-drivers-hwmon-acpi_power_meter-c-c9f2d8053bef
> 
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
> 

Re: [PATCH v2] hwmon: refactor deprecated strncpy

[Kees Cook]

On Tue, Sep 19, 2023 at 09:02:49AM +0200, Thomas Weißschuh wrote:
> On 2023-09-19 05:07:55+0000, Justin Stitt wrote:
> > `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> > 
> > A trailing zero is already handled by the kcalloc
> > |	*str = kcalloc(element->string.length + 1, sizeof(u8), GFP_KERNEL);
> > ... which makes memcpy() a suitable replacement to strncpy.
> > 
> > Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> > Link: https://github.com/KSPP/linux/issues/90
> > Cc: linux-hardening@vger.kernel.org
> > Signed-off-by: Justin Stitt <justinstitt@google.com>
> > ---
> > Changes in v2:
> > - use memcpy over strscpy (thanks Kees)
> > - Link to v1: https://lore.kernel.org/r/20230914-strncpy-drivers-hwmon-acpi_power_meter-c-v1-1-905297479fe8@google.com
> > ---
> >  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..82e99aec4a33 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);
> > +		memcpy(*str, element->string.pointer, element->string.length);
> 
> Isn't this now essentially the same as kmemdup_nul()?

Ah, yeah, good catch. I should add a note that the reverse of strtomem()
is kmemdup_nul() :)

Justin, can you refactor this to use kmemdup_nul() instead?

-Kees

-- 
Kees Cook