linux-kernel - Re: [PATCH v2] net: mdio-gpio: replace deprecated strncpy with strscpy

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Message-ID: <ZXJNwrcSfgUFhaz6@shell.armlinux.org.uk>
Date:   Thu, 7 Dec 2023 22:57:06 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "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 v2] net: mdio-gpio: replace deprecated strncpy with
 strscpy

On Thu, Dec 07, 2023 at 09:54:31PM +0000, Justin Stitt wrote:
> We expect new_bus->id to be NUL-terminated but not NUL-padded based on
> its prior assignment through snprintf:
> |       snprintf(new_bus->id, MII_BUS_ID_SIZE, "gpio-%x", bus_id);
> 
> We can also use sizeof() instead of a length macro as this more closely
> ties the maximum buffer size to the destination buffer.

Honestly, this looks machine generated and unreviewed by the submitter,
because...

>  	if (bus_id != -1)
>  		snprintf(new_bus->id, MII_BUS_ID_SIZE, "gpio-%x", bus_id);
>  	else
> -		strncpy(new_bus->id, "gpio", MII_BUS_ID_SIZE);
> +		strscpy(new_bus->id, "gpio", sizeof(new_bus->id));

If there is an argument for not using MII_BUS_ID_SIZE in one place,
then the very same argument applies to snprintf(). If one place
changes the other also needs to be changed.

-- 
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