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

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Date:   Mon, 1 Feb 2021 16:49:58 +0100
From:   Bartosz Golaszewski <bgolaszewski@...libre.com>
To:     "quanyang.wang" <quanyang.wang@...driver.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        "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

On Sat, Jan 30, 2021 at 4:45 AM quanyang.wang
<quanyang.wang@...driver.com> wrote:
>
> 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?
> >

Andy,

gdev->dev.release is assigned as the very last step in
gpiochip_add_data_with_key() so the patch looks correct to me. Do you
still have objections? Maybe I'm not seeing something.

Bart