Re: [PATCH v3 1/2] ath9k: fix use-after-free in ath9k_hif_usb_rx_cb

Pavel Skripkin
2022-02-08T15:48:38Z

Hi Toke,

On 2/8/22 17:47, Toke Høiland-Jørgensen wrote:
> Pavel Skripkin <paskripkin@gmail.com> 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