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

[Udipto Goswami]

On 1/9/2024 8:10 PM, Sergei Shtylyov wrote:
> On 1/9/24 2:57 PM, 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"
>
>     That seems parsable. :-)
>
> > > > +         * 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.
>
>     Probably "in this function" should be dropped altogether...

sure, i'll remove in v4.

Thanks,
-Udipto