linux-kernel - Re: [PATCH] rfkill: Fix use-after-free in rfkill

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Date:   Wed, 11 Nov 2020 11:23:17 +0800
From:   Claire Chang <tientzu@...omium.org>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     davem@...emloft.net, kuba@...nel.org, hdegoede@...hat.com,
        marcel@...tmann.org,
        "open list:NETWORKING DRIVERS (WIRELESS)" 
        <linux-wireless@...r.kernel.org>, netdev@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rfkill: Fix use-after-free in rfkill_resume()

On Wed, Nov 11, 2020 at 1:35 AM Johannes Berg <johannes@...solutions.net> wrote:
>
> On Tue, 2020-11-10 at 16:49 +0800, Claire Chang wrote:
> > If a device is getting removed or reprobed during resume, use-after-free
> > might happen. For example, h5_btrtl_resume()[drivers/bluetooth/hci_h5.c]
> > schedules a work queue for device reprobing. During the reprobing, if
> > rfkill_set_block() in rfkill_resume() is called after the corresponding
> > *_unregister() and kfree() are called, there will be an use-after-free
> > in hci_rfkill_set_block()[net/bluetooth/hci_core.c].
>
>
> Not sure I understand. So you're saying
>
>  * something (h5_btrtl_resume) schedules a worker
>  * said worker run, when it runs, calls rfkill_unregister()
>  * somehow rfkill_resume() still gets called after this
>
> But that can't really be right, device_del() removes it from the PM
> lists?

If device_del() is called right before the device_lock() in device_resume()[1],
it's possible the rfkill device is unregistered, but rfkill_resume is
still called.
We actually hit this during the suspend/resume stress test, although it's rare.

I also have a patch with multiple msleep that can 100% reproduce this
use-after-free. Happy to share here if needed.

[1] https://elixir.bootlin.com/linux/v5.10-rc3/source/drivers/base/power/main.c#L919

Thanks,
Claire

>
>
> johannes
>
>