Hi Toke,
On 2/8/22 17:47, Toke Høiland-Jørgensen wrote:
> Pavel Skripkin <[email protected]> writes:
>
>> Syzbot reported use-after-free Read in ath9k_hif_usb_rx_cb(). The
>> problem was in incorrect htc_handle->drv_priv initialization.
>>
>> Probable call trace which can trigger use-after-free:
>>
>> ath9k_htc_probe_device()
>> /* htc_handle->drv_priv = priv; */
>> ath9k_htc_wait_for_target() <--- Failed
>> ieee80211_free_hw() <--- priv pointer is freed
>>
>> <IRQ>
>> ...
>> ath9k_hif_usb_rx_cb()
>> ath9k_hif_usb_rx_stream()
>> RX_STAT_INC() <--- htc_handle->drv_priv access
>>
>> In order to not add fancy protection for drv_priv we can move
>> htc_handle->drv_priv initialization at the end of the
>> ath9k_htc_probe_device() and add helper macro to make
>> all *_STAT_* macros NULL save.
>
> I'm not too familiar with how the initialisation flow of an ath9k_htc
> device works. Looking at htc_handle->drv_priv there seems to
> be three other functions apart from the stat counters that dereference
> it:
>
> 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. If ->probe() is completed, than we can call
->suspend(), ->resume() and others usb callbacks, right? And we can meet
NULL defer even if we leave drv_priv = priv initialization on it's place.
Please, correct me if I am wrong somewhere :)
With regards,
Pavel Skripkin
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 :)
Hi Tetsuo,
On 5/2/22 09:10, Tetsuo Handa wrote:
>> 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?
>
I don't really remember why I said that, but looks like I just haven't
opened callbacks' code.
My point was that my patch does not change the logic, but only fixes 2
problems: UAF and NULL deref.
With regards,
Pavel Skripkin