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

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Message-ID: <202310181623.FB6FA17@keescook>
Date:   Wed, 18 Oct 2023 16:23:47 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] net: mdio: replace deprecated strncpy with strscpy

On Thu, Oct 12, 2023 at 09:53:03PM +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 mdiodev->modalias to be NUL-terminated based on its usage with
> strcmp():
> |       return strcmp(mdiodev->modalias, drv->name) == 0;
> 
> Moreover, mdiodev->modalias is already zero-allocated:
> |       mdiodev = kzalloc(sizeof(*mdiodev), GFP_KERNEL);
> ... which means the NUL-padding strncpy provides is not necessary.
> 
> 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>

Looks good!

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

-- 
Kees Cook