linux-kernel - Re: [PATCH] isdn: replace deprecated strncpy with strscpy

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Message-ID: <202309232036.32C3C37@keescook>
Date:   Sat, 23 Sep 2023 20:37:00 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Karsten Keil <isdn@...ux-pingi.de>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] isdn: replace deprecated strncpy with strscpy

On Fri, Sep 22, 2023 at 11:58:06AM +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 `iclock->name` to be NUL-terminated based on its use within
> printk:
> |	printk(KERN_DEBUG "%s: %s %d\n", __func__, iclock->name,
> |	       iclock->pri);
> 
> `iclock` is zero-initialized and as such is already NUL-padded which
> means strncpy is doing extra work here by eagerly NUL-padding the
> destination buffer.
> 
> Considering the above, 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@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Yup, looks like a clean replacement.

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

-- 
Kees Cook