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

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Message-ID: <CAOvb9yiO_n48JPZ3f0+y-fQ_YoOmuWF5c692Jt5_SKbxdA4yAw@mail.gmail.com>
Date:   Thu, 31 Mar 2022 01:38:34 -0700
From:   Won Chung <wonchung@...gle.com>
To:     Takashi Iwai <tiwai@...e.de>
Cc:     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, 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.

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.

Thanks,
Won