linux-kernel - Re: [PATCH] Fix a potential NULL pointer dereference in uli526x_interrupt() in drivers/net/tulip/uli526x.c

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Message-ID: <alpine.LFD.0.999.0709041418400.13651@enigma.security.iitk.ac.in>
Date:	Tue, 4 Sep 2007 14:20:21 +0530 (IST)
From:	Satyam Sharma <satyam@...radead.org>
To:	Micah Gruber <micah.gruber@...il.com>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Netdev Mailing List <netdev@...r.kernel.org>,
	jgarzik@...ox.com
Subject: Re: [PATCH] Fix a potential NULL pointer dereference in uli526x_interrupt()
 in drivers/net/tulip/uli526x.c



On Tue, 4 Sep 2007, Satyam Sharma wrote:

> Hi Micah,
> 
> 
> On Tue, 4 Sep 2007, Micah Gruber wrote:
> 
> > This patch fixes a potential null dereference bug where we dereference
> > dev before a null check. This patch simply moves the dereferencing after
> > the null check.
> > 
> > Signed-off-by: Micah Gruber <micah.gruber@...il.com>
> > ---
> > 
> > --- a/drivers/net/tulip/uli526x.c
> > +++ b/drivers/net/tulip/uli526x.c
> > @@ -663,7 +663,7 @@
> >  {
> >  	struct net_device *dev = dev_id;
> >  	struct uli526x_board_info *db = netdev_priv(dev);
> > -	unsigned long ioaddr;
> > +	unsigned long ioaddr = dev->base_addr;
> >  	unsigned long flags;
> >  
> >  	if (!dev) {
> > @@ -671,8 +671,6 @@
> >  		return IRQ_NONE;
> >  	}
> >  
> > -	ioaddr = dev->base_addr;
> > -
> >  	spin_lock_irqsave(&db->lock, flags);
> >  	outl(0, ioaddr + DCR7);
> 
> 
> [The patch is reversed.]
> 
> But it is also complete -- you've left out the "netdev_priv(dev)"
                 ^^^^^^^^
I meant:       incomplete

> statement _just_ before the dereference that you've pushed down.
> Coverity wasn't smart enough to tell, but that's actually a dev->priv,
> so we'll _still_ be dereferencing dev before checking it for NULL below.
> And lastly, the patch isn't quite correct. It is the (!dev) check that
> is redundant and must be removed instead :-)
> 
> I bet more such pointless checks exist all over. It makes more sense to
> remove them than unnecessarily try to solve "potential" NULL dereferences,
> that we (naturally) never saw earlier, because they're impossible. ISTR
> pointing out two similar patches a month or so back when Jeff pushed net
> driver patches upstream, IIRC ... ]
> 
> 
> Satyam
-
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