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

[Guenter Roeck]

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@xxxxxxxxxxxx> 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@xxxxxxxxx>
> > > > > > > Reported-by: Mathias Payer <mathias.payer@xxxxxxxxxxxxx>
> > > > > > > Signed-off-by: Hui Peng <benquike@xxxxxxxxx>
> > > > > >
> > > > > > FWIW:
> > > > > >
> > > > > > Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>
> > > > > >
> > > > > > 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