linux-kernel - Re: [PATCH] gpiolib: free device name on error path to fix kmemleak

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Date:   Sat, 30 Jan 2021 11:44:50 +0800
From:   "quanyang.wang" <quanyang.wang@...driver.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpiolib: free device name on error path to fix kmemleak

Hi Andy,

On 1/30/21 1:26 AM, Andy Shevchenko wrote:
> On Fri, Jan 29, 2021 at 2:01 PM <quanyang.wang@...driver.com> wrote:
>> From: Quanyang Wang <quanyang.wang@...driver.com>
>>
>> In gpiochip_add_data_with_key, we should check the return value of
>> dev_set_name to ensure that device name is allocated successfully
>> and then add a label on the error path to free device name to fix
>> kmemleak as below:
> Thanks for the report.
> Unfortunately...
>
>> +       ret = dev_set_name(&gdev->dev, GPIOCHIP_NAME "%d", gdev->id);
>> +       if (ret)
>> +               goto err_free_ida;
> ...
>
>> +err_free_dev_name:
>> +       kfree(dev_name(&gdev->dev));
> ...this approach seems to  create a possible double free if I'm not mistaken.
Thanks for your comment.  I didn't catch the double free. Would you 
please point it out?
>
> The idea is that device name should be cleaned in kobject ->release()
> callback when device is put.

Yes, the device name should be freed by calling put_device(&gdev->dev). 
But int gpiochip_add_data_with_key,

when running dev_set_name, "gdev->dev.release" hasn't been installed 
until in the tail of gpiochip_add_data_with_key.

So we couldn't call put_device here.

Any suggestion is much appreciated.

Thanks,

Quanyang

> Can you elaborate?
>