Re: [PATCH v2] sound/hda: Add NULL check to component match callback function

[Takashi Iwai <tiwai@suse.de>]

On Thu, 31 Mar 2022 10:38:34 +0200,
Won Chung wrote:
> 
> On Thu, Mar 31, 2022 at 12:27 AM Takashi Iwai <tiwai@suse.de> wrote:
> >
> > On Wed, 30 Mar 2022 23:19:13 +0200,
> > Won Chung wrote:
> > >
> > > Component match callback function needs to check if expected data is
> > > passed to it. Without this check, it can cause a NULL pointer
> > > dereference when another driver registers a component before i915
> > > drivers have their component master fully bind.
> > >
> > > Fixes: 7b882fe3e3e8b ("ALSA: hda - handle multiple i915 device instances")
> > > Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
> > > Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> > > Signed-off-by: Won Chung <wonchung@google.com>
> > > ---
> > > - Add "Fixes" tag
> > > - Send to stable@vger.kernel.org
> >
> > You rather need to add "Cc: stable@vger.kernel.org" line to the patch
> > itself (around sign-off block), not actually Cc'ing the mail.
> > I edited manually, but please do it so at the next time.
> >
> > Although I applied the patch as-is now, I wonder...
> >
> >
> > > -     if (!strcmp(dev->driver->name, "i915") &&
> > > +     if (dev->driver && !strcmp(dev->driver->name, "i915") &&
> >
> > Can NULL dev->driver be really seen?  I thought the components are
> > added by the drivers, hence they ought to have the driver field set.
> > But there can be corner cases I overlooked.
> >
> >
> > thanks,
> >
> > Takashi
> 
> Hi Takashi,
> 
> When I try using component_add in a different driver (usb4 in my
> case), I think dev->driver here is NULL because the i915 drivers do
> not have their component master fully bound when this new component is
> registered. When I test it, it seems to be causing a crash.

Hm, from where component_add*() is called?  Basically dev->driver must
be already set before the corresponding driver gets bound at
__driver_probe_deviec().  So, if the device is added to component from
the corresponding driver's probe, dev->driver must be non-NULL.

> Would it be okay for me to resend a new patch with the flags
> corrected? I have mistakenly added Heikki and Mika as "Signed-off-by"
> instead of "Suggested-by". I am sorry for that.

Ah that's bad.  I'll reset the branch, then.  Please resubmit
properly.


thanks,

Takashi