linux-kernel - Re: [PATCH 2/3] Add rfkill support to compal-laptop

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Date:	Tue, 18 Aug 2009 08:44:38 +0100
From:	Alan Jenkins <sourcejedi.lkml@...glemail.com>
To:	Marcel Holtmann <marcel@...tmann.org>
Cc:	Mario Limonciello <mario_limonciello@...l.com>,
	cezary.jackiewicz@...il.com, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] Add rfkill support to compal-laptop

On 8/18/09, Marcel Holtmann <marcel@...tmann.org> wrote:
> Hi Mario,

...

>> +static int setup_rfkill(void)
>> +{
>> +       int ret;
>> +
>> +       wifi_rfkill = rfkill_alloc("compal-wifi", NULL,
>> RFKILL_TYPE_WLAN,
>> +                                       &compal_rfkill_ops, (void *)
>> WLAN_MASK);
>> +       if (!wifi_rfkill) {
>> +               ret = -ENOMEM;
>> +               goto err_wifi;
>> +       }
>> +       ret = rfkill_register(wifi_rfkill);
>> +       if (ret)
>> +               goto err_wifi;
>> +
>> +       bluetooth_rfkill = rfkill_alloc("compal-bluetooth", NULL,
>> RFKILL_TYPE_BLUETOOTH,
>> +                                       &compal_rfkill_ops, (void *)
>> BT_MASK);
>> +       if (!bluetooth_rfkill) {
>> +               ret = -ENOMEM;
>> +               goto err_bt;
>> +       }
>> +       ret = rfkill_register(bluetooth_rfkill);
>> +       if (ret)
>> +               goto err_bt;
>> +
>> +       return 0;
>> +err_bt:
>> +       rfkill_destroy(bluetooth_rfkill);
>> +       if (bluetooth_rfkill)
>> +               rfkill_unregister(bluetooth_rfkill);
>> +err_wifi:
>> +       rfkill_destroy(wifi_rfkill);
>> +       if (wifi_rfkill)
>> +               rfkill_unregister(wifi_rfkill);
>
> I don't understand how this is not a potential NULL pointer dereference.
> There might some good luck that the pointer is still valid at that time,
> but I highly doubt it. So please unregister before destory.

Wrong as well :-).

If you fail to register wifi_rfkill, you should *only* call
rfkill_destroy().  So I think it should look like this:

+       if (wifi_rfkill)
+               rfkill_unregister(wifi_rfkill);
+err_wifi:
+       rfkill_destroy(wifi_rfkill);

...

>> @@ -420,6 +518,10 @@
>>         platform_device_unregister(compal_device);
>>         platform_driver_unregister(&compal_driver);
>>         backlight_device_unregister(compalbl_device);
>> +       if (wifi_rfkill)
>> +               rfkill_unregister(wifi_rfkill);
>> +       if (bluetooth_rfkill)
>> +               rfkill_unregister(bluetooth_rfkill);
>
> Same here. It should never ever succeeded in the first place. You can
> call it conditionally.

They're already called conditionally.  I assume you mean unconditionally here.

I agree with all your other comments.  Although I wouldn't call the
return/else style issue stupid, I'd just say it was confused :-).

Regards
Alan
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