linux-kernel - Re: [PATCH] platform/x86: huawei-wmi: Fix misuse of strcmp() function

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Date:   Tue, 15 Oct 2019 15:08:57 -0400
From:   ayman.bagabas@...il.com
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] platform/x86: huawei-wmi: Fix misuse of strcmp()
 function

Hi Gustavo,

On Tue, 2019-10-15 at 13:25 -0500, Gustavo A. R. Silva wrote:
> Comparing the result of strcmp directly with 1 may cause it to be
> misinterpreted. Note that strcmp may return an integer besides -1,
> 0, or 1.
> 
> Fix this by returning -ENODEV only when strcmp() returns a value
> other than 0.
> 
> Addresses-Coverity-ID: 1487035 ("Misuse of memcmp-style function")
> Fixes: b7527d0f4502 ("platform/x86: huawei-wmi: Add battery charging
> thresholds")
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  drivers/platform/x86/huawei-wmi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/platform/x86/huawei-wmi.c
> b/drivers/platform/x86/huawei-wmi.c
> index 6720f78c60c2..b43f76acbfea 100644
> --- a/drivers/platform/x86/huawei-wmi.c
> +++ b/drivers/platform/x86/huawei-wmi.c
> @@ -470,7 +470,7 @@ static DEVICE_ATTR_RW(charge_control_thresholds);
>  static int huawei_wmi_battery_add(struct power_supply *battery)
>  {
>  	/* Huawei laptops come with one battery only */
> -	if (strcmp(battery->desc->name, "BAT") != 1)

Note we don't have a battery number in BATx, strcmp would return 1 if
battery->desc->name is "BAT0" or any one digit. This is a desired
behavior where some Huawei laptops identify the first battery as "BAT1"
and this would match if name is greater than "BAT" by one digit.

Maybe strcmp(battery->desc->name, "BAT") < 0 is a better way to go.

> +	if (strcmp(battery->desc->name, "BAT"))
>  		return -ENODEV;

Now this would always return ENODEV.

Thank you,
Ayman

>  
>  	device_create_file(&battery->dev,
> &dev_attr_charge_control_start_threshold);