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

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Date:   Thu, 31 Mar 2022 11:12:55 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Won Chung <wonchung@...gle.com>
Cc:     Takashi Iwai <tiwai@...e.de>, Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Benson Leung <bleung@...omium.org>,
        Prashant Malani <pmalani@...omium.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2] sound/hda: Add NULL check to component match callback function

On Thu, 31 Mar 2022 10:38:34 +0200,
Won Chung wrote:
> 
> On Thu, Mar 31, 2022 at 12:27 AM Takashi Iwai <tiwai@...e.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@...ux.intel.com>
> > > Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> > > Signed-off-by: Won Chung <wonchung@...gle.com>
> > > ---
> > > - Add "Fixes" tag
> > > - Send to stable@...r.kernel.org
> >
> > You rather need to add "Cc: stable@...r.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