linux-hardening - Re: [PATCH] hwmon: pmbus: refactor deprecated strncpy

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Date:   Fri, 15 Sep 2023 11:35:32 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] hwmon: pmbus: refactor deprecated strncpy

On Fri, Sep 15, 2023 at 06:28:41PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> We should prefer more robust and less ambiguous string interfaces.
> 
> A suitable replacement is `strscpy` [2] due to the fact that it guarantees
> NUL-termination on the destination buffer without unnecessarily NUL-padding.
> 
> `label` is zero-allocated and as such the NUL-padding behavior of
> strncpy is not required here.
> 
> 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>
> ---
>  drivers/hwmon/pmbus/pmbus_core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> index 1363d9f89181..dcc8b12387cc 100644
> --- a/drivers/hwmon/pmbus/pmbus_core.c
> +++ b/drivers/hwmon/pmbus/pmbus_core.c
> @@ -1394,7 +1394,7 @@ static int pmbus_add_label(struct pmbus_data *data,
>  	snprintf(label->name, sizeof(label->name), "%s%d_label", name, seq);
>  	if (!index) {
>  		if (phase == 0xff)
> -			strncpy(label->label, lstring,
> +			strscpy(label->label, lstring,
>  				sizeof(label->label) - 1);

'label' is allocated with kzalloc(), and, by copying one byte less
than the size of the field into label->label, it is guaranteed to be
terminated. Using strscpy() instead of strncpy() results in dropping
the last character of lstring if its length is sizeof(label->label) - 1.

Really, I am not going to accept any of your patches, sorry.

Guenter