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Date:   Wed, 18 Oct 2023 16:23:47 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Justin Stitt <justinstitt@google.com>
Cc:     Andrew Lunn <andrew@lunn.ch>,
        Heiner Kallweit <hkallweit1@gmail.com>,
        Russell King <linux@armlinux.org.uk>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] net: mdio: replace deprecated strncpy with strscpy
Message-ID: <202310181623.FB6FA17@keescook>
References: <20231012-strncpy-drivers-net-phy-mdio_bus-c-v1-1-15242e6f9ec4@google.com>
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In-Reply-To: <20231012-strncpy-drivers-net-phy-mdio_bus-c-v1-1-15242e6f9ec4@google.com>
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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@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Looks good!

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

-- 
Kees Cook