Re: [PATCH] drm/nouveau/core: refactor deprecated strncpy

[Kees Cook <keescook@chromium.org>]

On Thu, Sep 14, 2023 at 09:40:49PM +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.
> 
> There is likely no bug in the current implementation due to the safeguard:
> | 	cname[sizeof(cname) - 1] = '\0';
> ... however we can provide simpler and easier to understand code using
> the newer (and recommended) `strscpy` api.
> 
> 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/gpu/drm/nouveau/nvkm/core/firmware.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nvkm/core/firmware.c b/drivers/gpu/drm/nouveau/nvkm/core/firmware.c
> index 91fb494d4009..374212da9e95 100644
> --- a/drivers/gpu/drm/nouveau/nvkm/core/firmware.c
> +++ b/drivers/gpu/drm/nouveau/nvkm/core/firmware.c
> @@ -79,8 +79,7 @@ nvkm_firmware_get(const struct nvkm_subdev *subdev, const char *fwname, int ver,
>  	int i;
>  
>  	/* Convert device name to lowercase */
> -	strncpy(cname, device->chip->name, sizeof(cname));
> -	cname[sizeof(cname) - 1] = '\0';
> +	strscpy(cname, device->chip->name, sizeof(cname));
>  	i = strlen(cname);
>  	while (i) {
>  		--i;

Yup, consumed by strlen() and snprintf(). Looks like a standard
conversion. :)

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

-Kees

> 
> ---
> base-commit: 3669558bdf354cd352be955ef2764cde6a9bf5ec
> change-id: 20230914-strncpy-drivers-gpu-drm-nouveau-nvkm-core-firmware-c-791223838b72
> 
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
> 

-- 
Kees Cook