Re: [PATCH 1/4] mmc: vub300: fix NULL-deref on disconnect

[Johan Hovold <johan@kernel.org>]

On Tue, Mar 31, 2026 at 12:13:41PM +0200, Ulf Hansson wrote:
> On Fri, 27 Mar 2026 at 11:52, Johan Hovold <johan@kernel.org> wrote:
> >
> > Make sure to deregister the controller before dropping the reference to
> > the driver data on disconnect to avoid NULL-pointer dereferences or
> > use-after-free.
> >
> > Fixes: 88095e7b473a ("mmc: Add new VUB300 USB-to-SD/SDIO/MMC driver")
> > Cc: stable@vger.kernel.org      # 3.0
> > Cc: Tony Olech <tony.olech@elandigitalsystems.com>
> > Signed-off-by: Johan Hovold <johan@kernel.org>
> > ---
> >  drivers/mmc/host/vub300.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/mmc/host/vub300.c b/drivers/mmc/host/vub300.c
> > index ff49d0770506..f173c7cf4e1a 100644
> > --- a/drivers/mmc/host/vub300.c
> > +++ b/drivers/mmc/host/vub300.c
> > @@ -2365,8 +2365,8 @@ static void vub300_disconnect(struct usb_interface *interface)
> >                         usb_set_intfdata(interface, NULL);
> >                         /* prevent more I/O from starting */
> >                         vub300->interface = NULL;
> > -                       kref_put(&vub300->kref, vub300_delete);
> >                         mmc_remove_host(mmc);
> > +                       kref_put(&vub300->kref, vub300_delete);
> 
> While this seems like a step in the right direction, I don't see why
> calling usb_set_intfdata(interface, NULL)

The interface data is only used in the USB bus callbacks and is not
needed after disconnect().

> and assigning
> vub300->interface = NULL is safe.
>
> For example, some of the workqueues might be running a work that uses
> the vub300->interface, isn't that a problem too?

The driver uses this pointer to indicate that the device has been
disconnected. That doesn't mean that the implementation is correct (e.g.
the check in vub300_pollwork_thread() should use some locking) but that
would be pre-existing issues.

Johan