Re: [PATCH] power: supply: bq256xx: replace deprecated strncpy with strscpy

[Kees Cook <keescook@chromium.org>]

On Fri, Oct 20, 2023 at 07:05:25PM +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 bq->model_name to be NUL-terminated based on its usage with
> sysfs_emit and format strings:
> 
> val->strval is assigned to bq->model_name in
> bq256xx_get_charger_property():
> |       val->strval = bq->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 bq256xx_get_charger_property():
> |       static const struct power_supply_desc bq256xx_power_supply_desc = {
> ...
> |       	.get_property = bq256xx_get_charger_property,
> 
> Moreover, no NUL-padding is required as bq is zero-allocated in
> bq256xx_charger.c:
> |       bq = devm_kzalloc(dev, sizeof(*bq), 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@vger.kernel.org
> Similar-to: https://lore.kernel.org/all/20231020-strncpy-drivers-power-supply-bq24190_charger-c-v1-1-e896223cb795@google.com/
> Similar-to: https://lore.kernel.org/all/20231020-strncpy-drivers-power-supply-bq2515x_charger-c-v1-1-46664c6edf78@google.com/
> Signed-off-by: Justin Stitt <justinstitt@google.com>

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

-- 
Kees Cook