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From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@toke.dk>
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To:     Pavel Skripkin <paskripkin@gmail.com>,
        ath9k-devel@qca.qualcomm.com, kvalo@kernel.org,
        davem@davemloft.net, kuba@kernel.org, linville@tuxdriver.com
Cc:     linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Pavel Skripkin <paskripkin@gmail.com>,
        syzbot+03110230a11411024147@syzkaller.appspotmail.com,
        syzbot+c6dde1f690b60e0b9fbe@syzkaller.appspotmail.com
Subject: Re: [PATCH v3 1/2] ath9k: fix use-after-free in ath9k_hif_usb_rx_cb
In-Reply-To: <80962aae265995d1cdb724f5362c556d494c7566.1644265120.git.paskripkin@gmail.com>
References: <80962aae265995d1cdb724f5362c556d494c7566.1644265120.git.paskripkin@gmail.com>
Date:   Tue, 08 Feb 2022 15:47:20 +0100
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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