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

Johan Hovold
2022-12-10T10:59:38Z

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.

> Remove the call to usb_set_intfdata(intf, NULL). The core will take
> care of setting it to NULL after ems_usb_disconnect() at [3].
>
> [1] c/27ef17849779 ("usb: add usb_set_intfdata() documentation")
> Link: https://git.kernel.org/gregkh/usb/c/27ef17849779

The claim in this commit is not correct either.

> [2] thread about usb_set_intfdata() on linux-usb mailing.
> Link: https://lore.kernel.org/linux-usb/Y4OD70GD4KnoRk0k@rowland.harvard.edu/
>
> [3] function usb_unbind_interface() from drivers/usb/core/driver.c
> Link: https://elixir.bootlin.com/linux/v6.0/source/drivers/usb/core/driver.c#L497
>
> Fixes: 702171adeed3 ("ems_usb: Added support for EMS CPC-USB/ARM7 CAN/USB interface")
> Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
> ---
> drivers/net/can/usb/ems_usb.c | 2 --
> 1 file changed, 2 deletions(-)
>
> diff --git a/drivers/net/can/usb/ems_usb.c b/drivers/net/can/usb/ems_usb.c
> index 050c0b49938a..c64cb40ac8de 100644
> --- a/drivers/net/can/usb/ems_usb.c
> +++ b/drivers/net/can/usb/ems_usb.c
> @@ -1062,8 +1062,6 @@ static void ems_usb_disconnect(struct usb_interface *intf)
> {
> struct ems_usb *dev = usb_get_intfdata(intf);

The interface data pointer is only used in this function so there is no
risk for any NULL pointer dereference here. I only checked one of the
other drivers you patch, but I'm pretty sure all of your claims about
fixing NULL-pointer dereferences in this series are equally bogus.

>
> - usb_set_intfdata(intf, NULL);
> -
> if (dev) {
> unregister_netdev(dev->netdev);

Johan