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Date:   Fri, 20 Oct 2023 11:43:11 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Justin Stitt <justinstitt@google.com>
Cc:     Sebastian Reichel <sre@kernel.org>, linux-pm@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] power: supply: bq24190_charger: replace deprecated
 strncpy with strscpy
Message-ID: <202310201140.B6C54194@keescook>
References: <20231020-strncpy-drivers-power-supply-bq24190_charger-c-v1-1-e896223cb795@google.com>
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In-Reply-To: <20231020-strncpy-drivers-power-supply-bq24190_charger-c-v1-1-e896223cb795@google.com>
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On Fri, Oct 20, 2023 at 06:14:47PM +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 bdi->model_name to be NUL-terminated based on its usage with
> sysfs_emit and format strings:
> 
> val->strval is assigned to bdi->model_name in
> bq24190_charger_get_property():
> 1186 | val->strval = bdi->model_name;
> 
> ... then in power_supply_sysfs.c we use value.strval with a format string:
> 311  | ret = sysfs_emit(buf, "%s\n", value.strval);
> 
> we assigned value.strval via:
> 285  | ret = power_supply_get_property(psy, psp, &value);
> ... which invokes psy->desc->get_property():
> 1210 | return psy->desc->get_property(psy, psp, val);
> 
> with bq24190_charger_get_property():
> 1320 | static const struct power_supply_desc bq24190_charger_desc = {
> ...
> 1325 | 	.get_property		= bq24190_charger_get_property,
> 
> Moreover, no NUL-padding is required as bdi is zero-allocated in
> bq24190_charger.c:
> 1798 | bdi = devm_kzalloc(dev, sizeof(*bdi), 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.
> 
> 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
> Signed-off-by: Justin Stitt <justinstitt@google.com>
> ---
> Note: build-tested only.
> 
> Found with: $ rg "strncpy\("
> ---
>  drivers/power/supply/bq24190_charger.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/power/supply/bq24190_charger.c b/drivers/power/supply/bq24190_charger.c
> index 3f99cb9590ba..1db290ee2591 100644
> --- a/drivers/power/supply/bq24190_charger.c
> +++ b/drivers/power/supply/bq24190_charger.c
> @@ -1803,7 +1803,7 @@ static int bq24190_probe(struct i2c_client *client)
>  
>  	bdi->client = client;
>  	bdi->dev = dev;
> -	strncpy(bdi->model_name, id->name, I2C_NAME_SIZE);
> +	strscpy(bdi->model_name, id->name, sizeof(bdi->model_name));

struct bq24190_dev_info {
	...
        char                            model_name[I2C_NAME_SIZE];

Length replacement looks correct.

struct i2c_device_id {
        char name[I2C_NAME_SIZE];

And it looks like this wasn't accidentally leaving strings unterminated,
so that's nice.

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

-- 
Kees Cook