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Subject: Re: [PATCH] Fix a double free bug in rsi_91x_deinit
To:     Kalle Valo <kvalo@codeaurora.org>
Cc:     Hui Peng <benquike@gmail.com>, security@kernel.org,
        Mathias Payer <mathias.payer@nebelwelt.net>,
        "David S. Miller" <davem@davemloft.net>,
        linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20190819220230.10597-1-benquike@gmail.com>
 <20190831181852.GA22160@roeck-us.net>
 <87k1asqw87.fsf@kamboji.qca.qualcomm.com>
From:   Guenter Roeck <linux@roeck-us.net>
Message-ID: <385361d3-048e-9b3f-c749-aa5861e397e7@roeck-us.net>
Date:   Sun, 1 Sep 2019 07:08:29 -0700
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On 9/1/19 1:03 AM, Kalle Valo wrote:
> Guenter Roeck <linux@roeck-us.net> writes:
> 
>> On Mon, Aug 19, 2019 at 06:02:29PM -0400, Hui Peng wrote:
>>> `dev` (struct rsi_91x_usbdev *) field of adapter
>>> (struct rsi_91x_usbdev *) is allocated  and initialized in
>>> `rsi_init_usb_interface`. If any error is detected in information
>>> read from the device side,  `rsi_init_usb_interface` will be
>>> freed. However, in the higher level error handling code in
>>> `rsi_probe`, if error is detected, `rsi_91x_deinit` is called
>>> again, in which `dev` will be freed again, resulting double free.
>>>
>>> This patch fixes the double free by removing the free operation on
>>> `dev` in `rsi_init_usb_interface`, because `rsi_91x_deinit` is also
>>> used in `rsi_disconnect`, in that code path, the `dev` field is not
>>>   (and thus needs to be) freed.
>>>
>>> This bug was found in v4.19, but is also present in the latest version
>>> of kernel.
>>>
>>> Reported-by: Hui Peng <benquike@gmail.com>
>>> Reported-by: Mathias Payer <mathias.payer@nebelwelt.net>
>>> Signed-off-by: Hui Peng <benquike@gmail.com>
>>
>> FWIW:
>>
>> Reviewed-by: Guenter Roeck <linux@roeck-us.net>
>>
>> This patch is listed as fix for CVE-2019-15504, which has a CVSS 2.0 score
>> of 10.0 (high) and CVSS 3.0 score of 9.8 (critical).
> 
> A double free in error path is considered as a critical CVE issue? I'm
> very curious, why is that?
> 

You'd have to ask the people assigning CVSS scores. However, if the memory
was reallocated, that reallocated memory (which is still in use) is freed.
Then all kinds of bad things can happen.

Guenter

>> Are there any plans to apply this patch to the upstream kernel anytime
>> soon ?
> 
> I was on vacation last week and hence I have not been able to apply any
> wireless patches. I should be able to catch up next week.
>