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

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Date:   Sun, 10 Apr 2022 11:17:05 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     duoming@....edu.cn
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        alexander.deucher@....com, gregkh@...uxfoundation.org,
        davem@...emloft.net
Subject: Re: [PATCH] drivers: nfc: nfcmrvl: fix UAF bug in
 nfcmrvl_nci_unregister_dev()

On 10/04/2022 10:30, duoming@....edu.cn wrote:

(...)

> 
>    (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.

Indeed. The code looks racy. It uses the fw_download_in_progress
variable which in core is partially protected with device_lock(). Moving
code around might not solve the issue entirely because there is no
synchronization here.

> 
>>> 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.

Thanks!


Best regards,
Krzysztof