linux-kernel - Re: [PATCH v3 1/2] ath9k: fix use-after-free in ath9k_hif_usb_rx

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Message-ID: <5fd22dda-01d6-cfae-3458-cb3fa23eb84d@I-love.SAKURA.ne.jp>
Date:   Mon, 2 May 2022 15:10:50 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Pavel Skripkin <paskripkin@...il.com>,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        ath9k-devel@....qualcomm.com, kvalo@...nel.org,
        davem@...emloft.net, kuba@...nel.org, linville@...driver.com
Cc:     linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot+03110230a11411024147@...kaller.appspotmail.com,
        syzbot+c6dde1f690b60e0b9fbe@...kaller.appspotmail.com
Subject: Re: [PATCH v3 1/2] ath9k: fix use-after-free in ath9k_hif_usb_rx_cb

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 :)