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 new_bus->id to be NUL-terminated but not NUL-padded based on
its prior assignment through snprintf:
|       snprintf(new_bus->id, MII_BUS_ID_SIZE, "gpio-%x", bus_id);

Due to this, 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: linux-hardening@vger.kernel.org
Signed-off-by: Justin Stitt <justinstitt@google.com>
---
Note: build-tested only.

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

diff --git a/drivers/net/mdio/mdio-gpio.c b/drivers/net/mdio/mdio-gpio.c
index 0fb3c2de0845..a1718d646504 100644
--- a/drivers/net/mdio/mdio-gpio.c
+++ b/drivers/net/mdio/mdio-gpio.c
@@ -125,7 +125,7 @@ static struct mii_bus *mdio_gpio_bus_init(struct device *dev,
 	if (bus_id != -1)
 		snprintf(new_bus->id, MII_BUS_ID_SIZE, "gpio-%x", bus_id);
 	else
-		strncpy(new_bus->id, "gpio", MII_BUS_ID_SIZE);
+		strscpy(new_bus->id, "gpio", sizeof(new_bus->id));
 
 	if (pdata) {
 		new_bus->phy_mask = pdata->phy_mask;

---
base-commit: cbf3a2cb156a2c911d8f38d8247814b4c07f49a2
change-id: 20231012-strncpy-drivers-net-mdio-mdio-gpio-c-bddd9ed0c630

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

On Thu, 12 Oct 2023 21:43:02 +0000, Justin Stitt wrote:
> 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 new_bus->id to be NUL-terminated but not NUL-padded based on
> its prior assignment through snprintf:
> |       snprintf(new_bus->id, MII_BUS_ID_SIZE, "gpio-%x", bus_id);
> 
> [...]

Applied to for-next/hardening, thanks!

[1/1] net: mdio: replace deprecated strncpy with strscpy
      https://git.kernel.org/kees/c/3247bb945786

Take care,

-- 
Kees Cook

On Thu, 30 Nov 2023 14:00:33 -0800 Kees Cook wrote:
> Applied to for-next/hardening, thanks!
> 
> [1/1] net: mdio: replace deprecated strncpy with strscpy
>       https://git.kernel.org/kees/c/3247bb945786

newer version of this was posted...

On Thu, Nov 30, 2023 at 10:43:34PM -0800, Jakub Kicinski wrote:
> On Thu, 30 Nov 2023 14:00:33 -0800 Kees Cook wrote:
> > Applied to for-next/hardening, thanks!
> > 
> > [1/1] net: mdio: replace deprecated strncpy with strscpy
> >       https://git.kernel.org/kees/c/3247bb945786
> 
> newer version of this was posted...

Hm, I didn't see anything land for this for the other with the same
subject. I've dropped both from my tree now.

Justin, can you chase down the mdio patches?

-- 
Kees Cook

On Thu, Oct 12, 2023 at 09:43:02PM +0000, Justin Stitt wrote:
> 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 new_bus->id to be NUL-terminated but not NUL-padded based on
> its prior assignment through snprintf:
> |       snprintf(new_bus->id, MII_BUS_ID_SIZE, "gpio-%x", bus_id);
> 
> Due to this, 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: linux-hardening@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>
> ---
> Note: build-tested only.
> 
> Found with: $ rg "strncpy\("
> ---
>  drivers/net/mdio/mdio-gpio.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/mdio/mdio-gpio.c b/drivers/net/mdio/mdio-gpio.c
> index 0fb3c2de0845..a1718d646504 100644
> --- a/drivers/net/mdio/mdio-gpio.c
> +++ b/drivers/net/mdio/mdio-gpio.c
> @@ -125,7 +125,7 @@ static struct mii_bus *mdio_gpio_bus_init(struct device *dev,
>  	if (bus_id != -1)
>  		snprintf(new_bus->id, MII_BUS_ID_SIZE, "gpio-%x", bus_id);
>  	else
> -		strncpy(new_bus->id, "gpio", MII_BUS_ID_SIZE);
> +		strscpy(new_bus->id, "gpio", sizeof(new_bus->id));

struct mii_bus {
	...
        char id[MII_BUS_ID_SIZE];

Yup, looks good. (I wonder about changing to sizeof() in the snprintf()
above it, but for a strscpy() refactor, I think this is fine.)

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

On Thu, Oct 12, 2023 at 09:43:02PM +0000, Justin Stitt wrote:
> 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 new_bus->id to be NUL-terminated but not NUL-padded based on
> its prior assignment through snprintf:
> |       snprintf(new_bus->id, MII_BUS_ID_SIZE, "gpio-%x", bus_id);
> 
> Due to this, 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: linux-hardening@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Reviewed-by: Andrew Lunn <andrew@lunn.ch>

    Andrew