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

[quanyang.wang]

Hi Andy,

On 1/30/21 1:26 AM, Andy Shevchenko wrote:
> On Fri, Jan 29, 2021 at 2:01 PM <quanyang.wang@xxxxxxxxxxxxx> wrote:
> > From: Quanyang Wang <quanyang.wang@xxxxxxxxxxxxx>
> >
> > 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?