linux-kernel - Re: [PATCH] net: dsa: remove deprecated strncpy

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Date:   Tue, 18 Jul 2023 11:08:00 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     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, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] net: dsa: remove deprecated strncpy

On Mon, Jul 17, 2023 at 5:04 PM <justinstitt@...gle.com> wrote:
>
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
>
> Even call sites utilizing length-bounded destination buffers should
> switch over to using `strtomem` or `strtomem_pad`. In this case,
> however, the compiler is unable to determine the size of the `data`
> buffer which renders `strtomem` unusable. Due to this, `strscpy`
> should be used.
>
> It should be noted that most call sites already zero-initialize the
> destination buffer. However, I've opted to use `strscpy_pad` to maintain
> the same exact behavior that `strncpy` produced (zero-padded tail up to
> `len`).
>
> Also see [3].
>
> [1]: www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings
> [2]: elixir.bootlin.com/linux/v6.3/source/net/ethtool/ioctl.c#L1944
> [3]: manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html
>
> Link: https://github.com/KSPP/linux/issues/90
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> ---
>  net/dsa/slave.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/net/dsa/slave.c b/net/dsa/slave.c
> index 527b1d576460..c9f77b7e5895 100644
> --- a/net/dsa/slave.c
> +++ b/net/dsa/slave.c
> @@ -1056,10 +1056,10 @@ static void dsa_slave_get_strings(struct net_device *dev,
>         if (stringset == ETH_SS_STATS) {
>                 int len = ETH_GSTRING_LEN;
>
> -               strncpy(data, "tx_packets", len);
> -               strncpy(data + len, "tx_bytes", len);
> -               strncpy(data + 2 * len, "rx_packets", len);
> -               strncpy(data + 3 * len, "rx_bytes", len);
> +               strscpy_pad(data, "tx_packets", len);
> +               strscpy_pad(data + len, "tx_bytes", len);
> +               strscpy_pad(data + 2 * len, "rx_packets", len);
> +               strscpy_pad(data + 3 * len, "rx_bytes", len);

Thanks for the patch!

Consider adding a #include <linux/string.h> so that we stop having
such an indirect dependency in this TU.

Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

>                 if (ds->ops->get_strings)
>                         ds->ops->get_strings(ds, dp->index, stringset,
>                                              data + 4 * len);
>
> ---
> base-commit: fdf0eaf11452d72945af31804e2a1048ee1b574c
> change-id: 20230717-net-dsa-strncpy-844ca1111eb2
>
> Best regards,
> --
> Justin Stitt <justinstitt@...gle.com>
>


-- 
Thanks,
~Nick Desaulniers