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

Toke Høiland-Jørgensen
2022-02-08T14:54:38Z

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)?

-Toke