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

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Message-ID: <6f0615da-aa0b-df8e-589c-f5caf09d3449@gmail.com>
Date:   Tue, 8 Feb 2022 18:48:24 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     Toke Høiland-Jørgensen <toke@...e.dk>,
        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,
        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

Hi Toke,

On 2/8/22 17:47, Toke Høiland-Jørgensen wrote:
> 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)?
> 

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