linux-kernel - Re: [PATCH] sound: hdmi: avoid dereferencing uninitialized 'jack' pointer

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Message-ID: <3395859.dhsfOsmVIe@wuerfel>
Date:	Tue, 16 Feb 2016 23:08:13 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Takashi Iwai <tiwai@...e.de>, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org, Jaroslav Kysela <perex@...ex.cz>,
	Mark Brown <broonie@...nel.org>, Han Lu <han.lu@...el.com>,
	Libin Yang <libin.yang@...ux.intel.com>,
	Thierry Reding <treding@...dia.com>,
	David Henningsson <david.henningsson@...onical.com>
Subject: Re: [PATCH] sound: hdmi: avoid dereferencing uninitialized 'jack' pointer

On Tuesday 16 February 2016 18:26:09 Arnd Bergmann wrote:
> >                 return err;
> >         per_pin->acomp_jack = jack;
> > -       jack->private_data = per_pin;
> > -       jack->private_free = free_acomp_jack_priv;
> > +       if (jack) {
> > +               jack->private_data = per_pin;
> > +               jack->private_free = free_acomp_jack_priv;
> > +       }
> >         return 0;
> >  }
> > 
> Looks good to me.
> 
> Acked-by: Arnd Bergmann <arnd@...db.de>
> 

Actually, on second thought, there is one notable downside
of this approach: 'jack' is guaranteed to be NULL here, so gcc
won't produce a warning if another driver makes the same mistake:

By default, we only get a warning for uses of uninitialized
variables, but not those that are known to be NULL. I think
some compiler warnings are able to warn about that too, but I
forgot the details.

	Arnd