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

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Date:	Tue, 09 Feb 2016 22:56:39 +0100
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>
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.


thanks,

Takashi