Re: [PATCH v3] usb: core: Prevent null pointer dereference in update_port_device_state

[Udipto Goswami]

Hi Sergei,

On 1/9/2024 3:01 PM, Sergei Shtylyov wrote:
> On 1/9/24 9:17 AM, Udipto Goswami wrote:
>
> > Currently,the function update_port_device_state gets the usb_hub from
> > 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>
> > ---
> > v3: Re-wrote the comment for better context.
> > v2: Introduced comment for the if check & CC'ed stable.
> >
> >   drivers/usb/core/hub.c | 20 +++++++++++++++++---
> >   1 file changed, 17 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> > index ffd7c99e24a3..6b514546e59b 100644
> > --- a/drivers/usb/core/hub.c
> > +++ b/drivers/usb/core/hub.c
> > @@ -2053,9 +2053,23 @@ 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 procedure of unbinding the hub before running
> > +		 * the rest of the procedure. This triggers
> > +		 * hub_disconnect will set the hub's maxchild to 0.
>
>     I can't parse this sentence, s/th is missing...
Thanks for the review.
Maybe this would sound better?

"This triggers hub_disconnect which will set hub's maxchild to 0"
> > +		 * This would result usb_hub_to_struct_hub in this
> > +		 * function to return NULL.
>
>     "This would result in usb_hub_to_struct_hub in this function
> returning NULL", perhaps?

yah sound better. Will take care of it in next version.

Thanks,
-Udipto