[2.6.19 patch] drivers/block/aoe/aoedev.c: fix NULL dereference

[2.6.19 patch] drivers/block/aoe/aoedev.c: fix NULL dereference

[Adrian Bunk]

This patch fixes a NULL dereference introduced by
commit e407a7f6cd143b3ab4eb3d7e1cf882e96b710eb5:

This quite unusual error handling through a switch introduces NULL 
dereferences if exactly one of the two k{c,z}alloc's failed.

That wouldn't be unfixable, but considering that the Linux kernel is not 
part of the obfuscated C contest (and silent fallthroughs in switches do 
not improve readability) I've converted it to a normal error handling.

The NULL dereference was spotted by the Coverity checker.

Signed-off-by: Adrian Bunk <bunk@stusta.de>

---

 drivers/block/aoe/aoedev.c |   46 ++++++++++++++++++-------------------
 1 file changed, 23 insertions(+), 23 deletions(-)

--- linux-2.6/drivers/block/aoe/aoedev.c.old	2006-10-31 23:56:46.000000000 +0100
+++ linux-2.6/drivers/block/aoe/aoedev.c	2006-11-01 00:23:49.000000000 +0100
@@ -64,30 +64,25 @@
 
 	d = kzalloc(sizeof *d, GFP_ATOMIC);
 	f = kcalloc(nframes, sizeof *f, GFP_ATOMIC);
- 	switch (!d || !f) {
- 	case 0:
- 		d->nframes = nframes;
- 		d->frames = f;
- 		e = f + nframes;
- 		for (; f<e; f++) {
- 			f->tag = FREETAG;
- 			f->skb = new_skb(ETH_ZLEN);
- 			if (!f->skb)
- 				break;
- 		}
- 		if (f == e)
- 			break;
- 		while (f > d->frames) {
- 			f--;
- 			dev_kfree_skb(f->skb);
- 		}
- 	default:
- 		if (f)
- 			kfree(f);
- 		if (d)
- 			kfree(d);
-		return NULL;
+
+ 	if (!d || !f)
+		goto out_err;
+
+	d->nframes = nframes;
+	d->frames = f;
+	e = f + nframes;
+	for (; f < e; f++) {
+		f->tag = FREETAG;
+		f->skb = new_skb(ETH_ZLEN);
+		if (!f->skb) {
+			while (f > d->frames) {
+				f--;
+				dev_kfree_skb(f->skb);
+			}
+			goto out_err;
+		}
 	}
+
 	INIT_WORK(&d->work, aoecmd_sleepwork, d);
 	spin_lock_init(&d->lock);
 	init_timer(&d->timer);
@@ -101,6 +96,11 @@
 	devlist = d;
 
 	return d;
+
+out_err:
+	kfree(f);
+	kfree(d);
+	return NULL;
 }
 
 void

Re: [2.6.19 patch] drivers/block/aoe/aoedev.c: fix NULL dereference

[Ed L. Cashin]

On Wed, Nov 01, 2006 at 01:40:25AM +0100, Adrian Bunk wrote:
> This patch fixes a NULL dereference introduced by
> commit e407a7f6cd143b3ab4eb3d7e1cf882e96b710eb5:
> 
> This quite unusual error handling through a switch introduces NULL 
> dereferences if exactly one of the two k{c,z}alloc's failed.

Hmm.  If exactly one of the two fails, then the value of the switch
conditional is 1 (well, certainly not zero).  It will jump over the
zero case, and there's a return in the default case, so I'm having
trouble seeing the danger.

What exactly is Coverity saying?  That would be interesting to know.

-- 
  Ed L Cashin <ecashin@coraid.com>

Re: [2.6.19 patch] drivers/block/aoe/aoedev.c: fix NULL dereference

[Adrian Bunk]

On Wed, Nov 01, 2006 at 11:36:28AM -0500, Ed L. Cashin wrote:
> On Wed, Nov 01, 2006 at 01:40:25AM +0100, Adrian Bunk wrote:
> > This patch fixes a NULL dereference introduced by
> > commit e407a7f6cd143b3ab4eb3d7e1cf882e96b710eb5:
> > 
> > This quite unusual error handling through a switch introduces NULL 
> > dereferences if exactly one of the two k{c,z}alloc's failed.
> 
> Hmm.  If exactly one of the two fails, then the value of the switch
> conditional is 1 (well, certainly not zero).  It will jump over the
> zero case, and there's a return in the default case, so I'm having
> trouble seeing the danger.
> 
> What exactly is Coverity saying?  That would be interesting to know.

The Coverity checker was wrong in this case, and I didn't spot it when 
checking since the code is really confusing.

>   Ed L Cashin <ecashin@coraid.com>

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed