linux-kernel - Re: [PATCH] driver core : Fix use after free of dev->parent in device

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Date:	Wed, 25 Sep 2013 09:14:46 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Benson Leung <bleung@...omium.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	olofj@...omium.org, stable <stable@...r.kernel.org>
Subject: Re: [PATCH] driver core : Fix use after free of dev->parent in device_shutdown

On Wed, Sep 25, 2013 at 5:39 AM, Benson Leung <bleung@...omium.org> wrote:
> The put_device(dev) at the bottom of the loop of device_shutdown
> may result in the dev being cleaned up. In device_create_release,
> the dev is kfreed.
>
> However, device_shutdown attempts to use the dev pointer again after
> put_device by referring to dev->parent.
>
> Copy the parent pointer instead to avoid this condition.

Right.

>
> This bug was found on Chromium OS's chromeos-3.8, which is based on v3.8.11.
> See bug report : https://code.google.com/p/chromium/issues/detail?id=297842
> This can easily be reproduced when shutting down with
> hidraw devices that report battery condition.
> Two examples are the HP Bluetooth Mouse X4000b and the Apple Magic Mouse.
> For example, with the magic mouse :
> The dev in question is "hidraw0"
> dev->parent is "magicmouse"
>
> In the course of the shutdown for this device, the input event cleanup calls
> a put on hidraw0, decrementing its reference count.
> When we finally get to put_device(dev) in device_shutdown, kobject_cleanup
> is called and device_create_release does kfree(dev).
> dev->parent is no longer valid, and we may crash in
> put_device(dev->parent).
>
> This change should be applied on any kernel with this change :
> d1c6c030fcec6f860d9bb6c632a3ebe62e28440b
>
> Cc: stable@...r.kernel.org
> Signed-off-by: Benson Leung <bleung@...omium.org>
> ---
>  drivers/base/core.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index c7cfadc..34bd546 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -2026,6 +2026,8 @@ void device_shutdown(void)
>          * devices offline, even as the system is shutting down.
>          */
>         while (!list_empty(&devices_kset->list)) {
> +               struct device *parent;
> +
>                 dev = list_entry(devices_kset->list.prev, struct device,
>                                 kobj.entry);
>
> @@ -2034,7 +2036,8 @@ void device_shutdown(void)
>                  * prevent it from being freed because parent's
>                  * lock is to be held
>                  */
> -               get_device(dev->parent);
> +               parent = dev->parent;
> +               get_device(parent);

It is better to save one line by below:

                    parent = get_device(dev->parent);

>                 get_device(dev);
>                 /*
>                  * Make sure the device is off the kset list, in the
> @@ -2044,8 +2047,8 @@ void device_shutdown(void)
>                 spin_unlock(&devices_kset->list_lock);
>
>                 /* hold lock to avoid race with probe/release */
> -               if (dev->parent)
> -                       device_lock(dev->parent);
> +               if (parent)
> +                       device_lock(parent);
>                 device_lock(dev);
>
>                 /* Don't allow any more runtime suspends */
> @@ -2063,11 +2066,11 @@ void device_shutdown(void)
>                 }
>
>                 device_unlock(dev);
> -               if (dev->parent)
> -                       device_unlock(dev->parent);
> +               if (parent)
> +                       device_unlock(parent);
>
>                 put_device(dev);
> -               put_device(dev->parent);
> +               put_device(parent);
>
>                 spin_lock(&devices_kset->list_lock);
>         }

Reviewed-by: Ming Lei <ming.lei@...onical.com>

Thanks,
--
Ming Lei
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