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Date:   Mon, 2 May 2022 15:10:50 +0900
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Subject: Re: [PATCH v3 1/2] ath9k: fix use-after-free in ath9k_hif_usb_rx_cb
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To:     Pavel Skripkin <paskripkin@gmail.com>,
        =?UTF-8?Q?Toke_H=c3=b8iland-J=c3=b8rgensen?= <toke@toke.dk>,
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        davem@davemloft.net, kuba@kernel.org, linville@tuxdriver.com
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        linux-kernel@vger.kernel.org,
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 <87h799a007.fsf@toke.dk> <6f0615da-aa0b-df8e-589c-f5caf09d3449@gmail.com>
From:   Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
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On 2022/02/09 0:48, Pavel Skripkin wrote:
>> ath9k_htc_suspend()
>> ath9k_htc_resume()
>> ath9k_hif_usb_disconnect()
>>
>> What guarantees that none of these will be called midway through
>> ath9k_htc_probe_device() (which would lead to a NULL deref after this
>> change)?
>>
> 
> IIUC, situation you are talking about may happen even without my change.
> I was thinking, that ath9k_htc_probe_device() is the real ->probe() function, but things look a bit more tricky.
> 
> 
> So, the ->probe() function may be completed before ath9k_htc_probe_device()
> is called, because it's called from fw loader callback function.

Yes, ath9k_hif_usb_probe() may return before complete_all(&hif_dev->fw_done)
is called by ath9k_hif_usb_firmware_cb() or ath9k_hif_usb_firmware_fail().

> If ->probe() is completed, than we can call ->suspend(), ->resume() and
> others usb callbacks, right?

Yes, but ath9k_hif_usb_disconnect() and ath9k_hif_usb_suspend() are calling
wait_for_completion(&hif_dev->fw_done) before checking HIF_USB_READY flag.
hif_dev->fw_done serves for serialization.

> And we can meet NULL defer even if we leave drv_priv = priv initialization
> on it's place.

I didn't catch the location. As long as "htc_handle->drv_priv = priv;" is done
before complete_all(&hif_dev->fw_done) is done, is something wrong?

> 
> Please, correct me if I am wrong somewhere :)