linux-kernel - Re: [PATCH] power: supply: bq2515x: replace deprecated strncpy with strscpy

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Message-ID: <202310201206.2D1271C209@keescook>
Date:   Fri, 20 Oct 2023 12:06:25 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Sebastian Reichel <sre@...nel.org>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] power: supply: bq2515x: replace deprecated strncpy with
 strscpy

On Fri, Oct 20, 2023 at 06:59:34PM +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 bq2515x->model_name to be NUL-terminated based on its usage with
> sysfs_emit and format strings:
> 
> val->strval is assigned to bq2515x->model_name in
> bq2515x_mains_get_property():
> |       val->strval = bq2515x->model_name;
> 
> ... then in power_supply_sysfs.c we use value.strval with a format string:
> |       ret = sysfs_emit(buf, "%s\n", value.strval);
> 
> we assigned value.strval via:
> |       ret = power_supply_get_property(psy, psp, &value);
> ... which invokes psy->desc->get_property():
> |       return psy->desc->get_property(psy, psp, val);
> 
> with bq2515x_mains_get_property():
> |       static const struct power_supply_desc bq2515x_mains_desc = {
> ...
> |       	.get_property		= bq2515x_mains_get_property,
> 
> Moreover, no NUL-padding is required as bq2515x is zero-allocated in
> bq2515x_charger.c:
> |       bq2515x = devm_kzalloc(dev, sizeof(*bq2515x), GFP_KERNEL);
> 
> 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.
> 
> Let's also opt to use the more idiomatic strscpy() usage of (dest, src,
> sizeof(dest)) as this more closely ties the destination buffer and the
> length.
> 
> 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>

This looks like a good replacement, just like the prior I2C change.

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

-- 
Kees Cook