linux-kernel - Re: Should snd_card_free() check for null pointer?

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Date:	Wed, 10 Feb 2016 02:41:38 -0500 (EST)
From:	Jerome Marchand <jmarchan@...hat.com>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	Jaroslav Kysela <perex@...ex.cz>, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org
Subject: Re: Should snd_card_free() check for null pointer?

----- Original Message -----
> From: "Takashi Iwai" <tiwai@...e.de>
> To: "Jerome Marchand" <jmarchan@...hat.com>
> Cc: "Jaroslav Kysela" <perex@...ex.cz>, alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
> Sent: Tuesday, February 9, 2016 10:56:39 PM
> Subject: Re: Should snd_card_free() check for null pointer?
> 
> On Tue, 09 Feb 2016 15:30:16 +0100,
> Jerome Marchand wrote:
> > 
> > Hi,
> > 
> > Before commit f24640648186b (ALSA: Use standard device refcount for card
> > accounting), snd_card_free() would return -EINVAL on a null pointer. Now
> > it ends up in a null pointer dereference. There is at least one driver
> > that can call snd_card_free() with null argument: saa7134_alsa. It can
> > easily be triggered by just inserting and removing the module (no need
> > to have the hardware).
> > I don't think that is a rule, but it seems that the standard behavior of
> > *_free() functions is to check for null pointer. What do you think?
> 
> Well, I have a mixed feeling about this.  Allowing NULL sometimes
> makes the code easier.  OTOH, caling snd_card_free() with NULL is
> really an unexpected situation, and if a driver does it, most likely
> it does something weird.
> 
> So, at this moment, I would fix the caller side.  But, it's not a
> final call, just my gut feeling.

I have no strong opinion either way and I have a patch that fixes saa7134
driver ready to be sent if that is your preference.

Thanks,
Jerome

> 
> 
> thanks,
> 
> Takashi
>