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