linux-hardening - Re: [PATCH] video: fbdev: au1200fb: replace deprecated strncpy with strscpy

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Date: Wed, 20 Mar 2024 08:56:21 +0100
From: Helge Deller <deller@....de>
To: Justin Stitt <justinstitt@...gle.com>
Cc: linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
 Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] video: fbdev: au1200fb: replace deprecated strncpy with
 strscpy

On 3/19/24 00:46, 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.
>
> Let's use the new 2-argument strscpy() which guarantees NUL-termination
> on the destination buffer while also simplifying the syntax. Note that
> strscpy() will not NUL-pad the destination buffer like strncpy() does.
>
> However, the NUL-padding behavior of strncpy() is not required since
> fbdev is already NUL-allocated from au1200fb_drv_probe() ->
> frameuffer_alloc(), rendering any additional NUL-padding redundant.
> |	p = kzalloc(fb_info_size + size, GFP_KERNEL);
>
> 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@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> ---
> Note: build-tested only.
>
> Found with: $ rg "strncpy\("
> ---
>   drivers/video/fbdev/au1200fb.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/video/fbdev/au1200fb.c b/drivers/video/fbdev/au1200fb.c
> index 6f20efc663d7..e718fea63662 100644
> --- a/drivers/video/fbdev/au1200fb.c
> +++ b/drivers/video/fbdev/au1200fb.c
> @@ -1557,7 +1557,7 @@ static int au1200fb_init_fbinfo(struct au1200fb_device *fbdev)
>   		return ret;
>   	}
>
> -	strncpy(fbi->fix.id, "AU1200", sizeof(fbi->fix.id));
> +	strscpy(fbi->fix.id, "AU1200");

I wonder if you really build-tested this, as this driver is for the mips architecture...
And I don't see a strscpy() function which takes just 2 arguments.
But I might be wrong....

Helge