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

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Message-ID: <87h799a007.fsf@toke.dk>
Date:   Tue, 08 Feb 2022 15:47:20 +0100
From:   Toke Høiland-Jørgensen <toke@...e.dk>
To:     Pavel Skripkin <paskripkin@...il.com>,
        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,
        Pavel Skripkin <paskripkin@...il.com>,
        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

Pavel Skripkin <paskripkin@...il.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