Re: [PATCH] fix potential NULL pointer deref in snd_sb8dsp_midi_interrupt()

[Alexey Dobriyan]

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.

> --- 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;
>  	}

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