linux-kernel - Re: Re: [PATCH] drivers: nfc: nfcmrvl: fix UAF bug in nfcmrvl_nci_unregister

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Date:   Sun, 10 Apr 2022 16:30:55 +0800 (GMT+08:00)
From:   duoming@....edu.cn
To:     "Krzysztof Kozlowski" <krzysztof.kozlowski@...aro.org>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        alexander.deucher@....com, gregkh@...uxfoundation.org,
        davem@...emloft.net
Subject: Re: Re: [PATCH] drivers: nfc: nfcmrvl: fix UAF bug in
 nfcmrvl_nci_unregister_dev()

Hello,

I am sorry for the delay.

On Sat, 9 Apr 2022 17:10:05 +0200 Krzysztof Kozlowski wrote:

> > There is a potential UAF bug in nfcmrvl usb driver between
> > unregister and resume operation.
> > 
> > The race that cause that UAF can be shown as below:
> > 
> >    (FREE)                   |      (USE)
> >                             | nfcmrvl_resume
> >                             |  nfcmrvl_submit_bulk_urb
> >                             |   nfcmrvl_bulk_complete
> >                             |    nfcmrvl_nci_recv_frame
> >                             |     nfcmrvl_fw_dnld_recv_frame
> >                             |      skb_queue_tail
> > nfcmrvl_disconnect          |
> >  nfcmrvl_nci_unregister_dev |
> >   nfcmrvl_fw_dnld_deinit    |      ...
> >    destroy_workqueue //(1)  |
> >    ...                      |      queue_work //(2)
> > 
> > When nfcmrvl usb driver is resuming, we detach the device.
> > The workqueue is destroyed in position (1), but it will be
> > latter used in position (2), which leads to data race.
> 
> I miss here something. How can you queue work on a destroyed workqueue?
> When workqueue is destroyed, no more work should be executed. Unless you
> mean the case that draining the work (during destroying, not after)
> causes the (2) to happen?

Sorry, I make a mistake in my patch. The destroy_workqueue() will not 
return until all work is finished. So the UAF bug is not exist.

Actually, there is a double free bug in nfcmrvl_nci_unregister_dev(). The root
cause is shown below:

   (FREE)                   |      (USE)
                            | nfcmrvl_resume
                            |  nfcmrvl_submit_bulk_urb
                            |   nfcmrvl_bulk_complete
                            |    nfcmrvl_nci_recv_frame
                            |     nfcmrvl_fw_dnld_recv_frame
                            |      queue_work
                            |       fw_dnld_rx_work
                            |        fw_dnld_over
                            |         release_firmware
                            |          kfree(fw); //(1)
nfcmrvl_disconnect          |
 nfcmrvl_nci_unregister_dev |
  nfcmrvl_fw_dnld_abort     |
   fw_dnld_over             |         ...
    if (priv->fw_dnld.fw)   |
    release_firmware        |
     kfree(fw); //(2)       |
     ...                    |         fw = NULL;

When nfcmrvl usb driver is resuming, we detach the device.
The release_firmware() will deallocate firmware in position (1),
but firmware will be deallocate again in position (2), which
leads to double free.

> > This patch reorders the nfcmrvl_fw_dnld_deinit after
> > nci_unregister_device in order to prevent UAF. Because
> > nci_unregister_device will not return until finish all
> > operations from upper layer.
> > 
> > Signed-off-by: Duoming Zhou <duoming@....edu.cn>
> > ---
> >  drivers/nfc/nfcmrvl/main.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/drivers/nfc/nfcmrvl/main.c b/drivers/nfc/nfcmrvl/main.c
> > index 2fcf545012b..5ed17b23ee8 100644
> > --- a/drivers/nfc/nfcmrvl/main.c
> > +++ b/drivers/nfc/nfcmrvl/main.c
> > @@ -186,12 +186,11 @@ void nfcmrvl_nci_unregister_dev(struct nfcmrvl_private *priv)
> >  	if (priv->ndev->nfc_dev->fw_download_in_progress)
> >  		nfcmrvl_fw_dnld_abort(priv);
> >  
> > -	nfcmrvl_fw_dnld_deinit(priv);
> > -
> >  	if (gpio_is_valid(priv->config.reset_n_io))
> >  		gpio_free(priv->config.reset_n_io);
> >  
> >  	nci_unregister_device(ndev);
> > +	nfcmrvl_fw_dnld_deinit(priv);
> 
> The new order matches reverse-probe, so actually makes sense.
> 
> >  	nci_free_device(ndev);
> >  	kfree(priv);
> >  }

I will send "[PATCH] drivers: nfc: nfcmrvl: fix double free bug in
nfcmrvl_nci_unregister_dev()" as soon as possible.

Best regards,
Duoming Zhou