Re: [PATCH v2 1/9] can: ems_usb: ems_usb_disconnect(): fix NULL pointer dereference

Vincent MAILHOL
2022-12-11T11:24:47Z

On Tue. 10 déc. 2022 à 20:02, Johan Hovold <johan@kernel.org> wrote:
> On Sat, Dec 10, 2022 at 06:01:49PM +0900, Vincent Mailhol wrote:
> > ems_usb sets the driver's priv data to NULL before waiting for the
> > completion of outsdanding urbs. This can results in NULL pointer
> > dereference, c.f. [1] and [2].
>
> Please stop making hand-wavy claims like this. There is no risk for a
> NULL-pointer deference here, and if you think otherwise you need to
> explain how that can happen in detail for each driver.

Understood.

*My* mistake comes from this message from Alan [1]:

| But if a driver does make the call, it should be careful to
| ensure that the call happens _after_ the driver is finished
| using the interface-data pointer. For example, after all
| outstanding URBs have completed, if the completion handlers
| will need to call usb_get_intfdata().

I did not pay enough attention to the "if the completion handlers will
need to call usb_get_intfdata()" part and jumped into the incorrect
conclusion that any use of usb_set_intfdata(intf, NULL) before URB
completion was erroneous.

My deep apologies for all the noise. Please forget this series and one
more time, thank you for your patience.

[1] https://lore.kernel.org/linux-usb/Y4OD70GD4KnoRk0k@rowland.harvard.edu/