Date: Sun, 14 May 2006 16:40:54 +0200
From: Willy Tarreau <willy@w.ods.org>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Jesper Juhl <jesper.juhl@gmail.com>, linux-kernel@vger.kernel.org,
       perex@suse.cz
Subject: Re: [PATCH] fix potential NULL pointer deref in snd_sb8dsp_midi_interrupt()
Message-ID: <20060514144054.GM11191@w.ods.org>
References: <200605140420.52710.jesper.juhl@gmail.com> <20060514142409.GC23387@mipter.zuzino.mipt.ru>
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On Sun, May 14, 2006 at 06:24:09PM +0400, Alexey Dobriyan wrote:
> On Sun, May 14, 2006 at 04:20:52AM +0200, Jesper Juhl wrote:
> > First testing if a pointer is NULL and if it is (or might be), proceeding
> > with code that dereferences that same pointer is clearly a mistake.
> > This happens in sound/isa/sb/sb8_midi.c::snd_sb8dsp_midi_interrupt()
> > The patch below reworks the code so this unfortunate case doesn't happen.
> 
> All callers of snd_sb8dsp_midi_interrupt() dereference "chip" right
> before calling.

So the "if (chip == NULL)" part should be removed to avoid confusion.

> 
> > --- linux-2.6.17-rc4-git2-orig/sound/isa/sb/sb8_midi.c
> > +++ linux-2.6.17-rc4-git2/sound/isa/sb/sb8_midi.c
> > -irqreturn_t snd_sb8dsp_midi_interrupt(struct snd_sb * chip)
> > +irqreturn_t snd_sb8dsp_midi_interrupt(struct snd_sb *chip)
> >  {
> >  	struct snd_rawmidi *rmidi;
> >  	int max = 64;
> >  	char byte;
> >  
> > -	if (chip == NULL || (rmidi = chip->rmidi) == NULL) {
> > +	if (!chip)
> > +		return IRQ_NONE;
> > +	
> > +	rmidi = chip->rmidi;
> > +	if (!rmidi) {
> >  		inb(SBP(chip, DATA_AVAIL));	/* ack interrupt */
> >  		return IRQ_NONE;
> >  	}

Willy

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