linux-kernel - Re: [PATCH v2] net: dsa: lan9303: use ethtool_sprintf() for lan9303_get

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Message-ID: <202310051539.B2D34DB@keescook>
Date:   Thu, 5 Oct 2023 15:42:08 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...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,
        Alexander Lobakin <aleksander.lobakin@...el.com>
Subject: Re: [PATCH v2] net: dsa: lan9303: use ethtool_sprintf() for
 lan9303_get_strings()

On Thu, Oct 05, 2023 at 06:56:50PM +0000, Justin Stitt wrote:
> This pattern of strncpy with some pointer arithmetic setting fixed-sized
> intervals with string literal data is a bit weird so let's use
> ethtool_sprintf() as this has more obvious behavior and is less-error
> prone.
> 
> Nicely, we also get to drop a usage of the now deprecated strncpy() [1].
> 
> One might consider this pattern:
> |       ethtool_sprintf(&buf, lan9303_mib[u].name);
> ... but this triggers a -Wformat-security warning.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Cc: Kees Cook <keescook@...omium.org>
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>

Ah, cool ethtool_sprintf() works. Maybe some day we can fix the whole
API to actually have bounds, but yes, this is fine.

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

-- 
Kees Cook