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

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

[Jesper Juhl]

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.
Also remove some blank comments.

Found by the Coverity checker as bug #367

Patch is compile testted only due to lack of hardware.


Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
---

 sound/isa/sb/sb8_midi.c |   20 +++++++-------------
 1 files changed, 7 insertions(+), 13 deletions(-)


--- linux-2.6.17-rc4-git2-orig/sound/isa/sb/sb8_midi.c	2006-03-20 06:53:29.000000000 +0100
+++ linux-2.6.17-rc4-git2/sound/isa/sb/sb8_midi.c	2006-05-14 04:12:33.000000000 +0200
@@ -32,20 +32,22 @@
 #include <sound/core.h>
 #include <sound/sb.h>
 
-/*
 
- */
-
-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;
 	}
+
 	spin_lock(&chip->midi_input_lock);
 	while (max-- > 0) {
 		if (inb(SBP(chip, DATA_AVAIL)) & 0x80) {
@@ -59,10 +61,6 @@ irqreturn_t snd_sb8dsp_midi_interrupt(st
 	return IRQ_HANDLED;
 }
 
-/*
-
- */
-
 static int snd_sb8dsp_midi_input_open(struct snd_rawmidi_substream *substream)
 {
 	unsigned long flags;
@@ -252,10 +250,6 @@ static void snd_sb8dsp_midi_output_trigg
 		snd_sb8dsp_midi_output_write(substream);
 }
 
-/*
-
- */
-
 static struct snd_rawmidi_ops snd_sb8dsp_midi_output =
 {
 	.open =		snd_sb8dsp_midi_output_open,

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;
>  	}

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

[Willy Tarreau]

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