Re: [PATCH] Fix a double free bug in rsi_91x_deinit

From: Guenter Roeck <linux@roeck-us.net>
To: Greg KH <greg@kroah.com>
Cc: Kalle Valo <kvalo@codeaurora.org>, 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
Subject: Re: [PATCH] Fix a double free bug in rsi_91x_deinit
Date: Mon, 2 Sep 2019 17:35:59 -0700	[thread overview]
Message-ID: <a3432c17-f3ec-6d1e-77ec-fab43feefcaf@roeck-us.net> (raw)
In-Reply-To: <20190902200635.GA29465@kroah.com>

On 9/2/19 1:06 PM, Greg KH wrote:
> On Mon, Sep 02, 2019 at 12:32:37PM -0700, Guenter Roeck wrote:
>> On 9/2/19 11:47 AM, Greg KH wrote:
>>> On Sun, Sep 01, 2019 at 07:08:29AM -0700, Guenter Roeck wrote:
>>>> 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.
>>>
>>> Yes, but moving from "bad things _can_ happen" to "bad things happen" in
>>> an instance like this will be a tough task.  It also requires physical
>>> access to the machine.
>>>
>>
>> Is this correct even with usbip enabled ?
> 
> Who has usbip enabled anywhere?  :)
> 

It is enabled in Ubuntu, and it looks like it is enabled in Fedora as well.
It is disabled in Chrome OS. I didn't check other distributions.

> I don't know if usbip can trigger this type of thing, maybe someone
> needs to test that...
> 

I seemed to recall someone mentioning that it is possible to use usbip
for remote attacks. This is why I mentioned it. I don't recall details,
though, and I don't know if it is really possible and to what extent.

Guenter