linux-kernel - Re: [PATCH] driver core: class: properly reference count class_dev

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Date:   Wed, 17 May 2023 12:41:38 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        syzbot+e7afd76ad060fa0d2605@...kaller.appspotmail.com,
        Mirsad Goran Todorovac <mirsad.todorovac@....unizg.hr>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH] driver core: class: properly reference count class_dev_iter()

On Tue, May 16, 2023 at 9:20 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> When class_dev_iter is initialized, the reference count for the subsys
> private structure is incremented, but never decremented, causing a
> memory leak over time.  To resolve this, save off a pointer to the
> internal structure into the class_dev_iter structure and then when the
> iterator is finished, drop the reference count.
>
> Reported-and-tested-by: syzbot+e7afd76ad060fa0d2605@...kaller.appspotmail.com
> Reported-by: Mirsad Goran Todorovac <mirsad.todorovac@....unizg.hr>
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Cc: Alan Stern <stern@...land.harvard.edu>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

Acked-by: Rafael J. Wysocki <rafael@...nel.org>

> ---
>  drivers/base/class.c         | 2 ++
>  include/linux/device/class.h | 1 +
>  2 files changed, 3 insertions(+)
>
> diff --git a/drivers/base/class.c b/drivers/base/class.c
> index ac1808d1a2e8..05d9df90f621 100644
> --- a/drivers/base/class.c
> +++ b/drivers/base/class.c
> @@ -320,6 +320,7 @@ void class_dev_iter_init(struct class_dev_iter *iter, const struct class *class,
>                 start_knode = &start->p->knode_class;
>         klist_iter_init_node(&sp->klist_devices, &iter->ki, start_knode);
>         iter->type = type;
> +       iter->sp = sp;
>  }
>  EXPORT_SYMBOL_GPL(class_dev_iter_init);
>
> @@ -361,6 +362,7 @@ EXPORT_SYMBOL_GPL(class_dev_iter_next);
>  void class_dev_iter_exit(struct class_dev_iter *iter)
>  {
>         klist_iter_exit(&iter->ki);
> +       subsys_put(iter->sp);
>  }
>  EXPORT_SYMBOL_GPL(class_dev_iter_exit);
>
> diff --git a/include/linux/device/class.h b/include/linux/device/class.h
> index 9deeaeb457bb..abf3d3bfb6fe 100644
> --- a/include/linux/device/class.h
> +++ b/include/linux/device/class.h
> @@ -74,6 +74,7 @@ struct class {
>  struct class_dev_iter {
>         struct klist_iter               ki;
>         const struct device_type        *type;
> +       struct subsys_private           *sp;
>  };
>
>  int __must_check class_register(const struct class *class);
> --
> 2.40.1
>