Re: [PATCH v4] usb: core: Prevent null pointer dereference in update_port_device_state

[Udipto Goswami]

On 1/10/2024 2:52 PM, Sergei Shtylyov wrote:
> On 1/10/24 12:14 PM, Udipto Goswami wrote:
>
> > Currently,the function update_port_device_state gets the usb_hub from
>
>     Need space between comma and "the"...
got it.
> > udev->parent by calling usb_hub_to_struct_hub.
> > However, in case the actconfig or the maxchild is 0, the usb_hub would
> > be NULL and upon further accessing to get port_dev would result in null
> > pointer dereference.
> >
> > Fix this by introducing an if check after the usb_hub is populated.
> >
> > Fixes: 83cb2604f641 ("usb: core: add sysfs entry for usb device state")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Udipto Goswami <quic_ugoswami@xxxxxxxxxxx>
> [...]
>
> > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> > index ffd7c99e24a3..5ba1875e6bf4 100644
> > --- a/drivers/usb/core/hub.c
> > +++ b/drivers/usb/core/hub.c
> > @@ -2053,9 +2053,22 @@ static void update_port_device_state(struct usb_device *udev)
> >   
> >   	if (udev->parent) {
> >   		hub = usb_hub_to_struct_hub(udev->parent);
> > -		port_dev = hub->ports[udev->portnum - 1];
> > -		WRITE_ONCE(port_dev->state, udev->state);
> > -		sysfs_notify_dirent(port_dev->state_kn);
> > +
> > +		/*
> > +		 * The Link Layer Validation System Driver (lvstest)
> > +		 * has step to unbind the hub before running the rest
> > +		 * of the procedure. This triggers hub_disconnect which
> > +		 * will set the hub's maxchild to 0, further resulting
>
>     Resulting in.

got it.
> > +		 * usb_hub_to_struct_hub returning NULL.
> > +		 *
> > +		 * Add if check to avoid running into NULL pointer
> > +		 * de-reference.
>
>     This is obvious from the code below, I think...
ok will remove this.

Thanks,
-Udipto