linux-kernel - Re: [PATCH] sb1000: prevent a potential NULL pointer dereference in sb1000_dev

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Date:	Mon, 30 Jul 2007 00:04:46 +0530 (IST)
From:	Satyam Sharma <satyam@...radead.org>
To:	Domen Puncer <domen@...erock.org>
cc:	Jesper Juhl <jesper.juhl@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org, Steven Hirsch <shirsch@...lphia.net>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH] sb1000: prevent a potential NULL pointer dereference in
 sb1000_dev_ioctl()



> On Sun, 29 Jul 2007, Domen Puncer wrote:
> 
> > On 29/07/07 00:02 +0200, Jesper Juhl wrote:
> > > Hi,
> > > 
> > > Here's a small patch, prompted by a find by the Coverity checker, 
> > > that removes a potential NULL pointer dereference from 
> > > drivers/net/sb1000.c::sb1000_dev_ioctl().
> > > The checker spotted that we do a NULL test of 'dev', yet we 
> > > dereference the pointer prior to that check.
> > > This patch simply moves the dereference after the NULL test.
> > 
> > But... it can't be called without a valid 'dev', no?
> > A quick 'grep do_ioctl net/' confirms that all calls are in
> > the form of 'dev->do_ioctl(dev, ...'.
> 
> Yup, I think so too ...
> 
> 
> > > @@ -991,11 +991,13 @@ static int sb1000_dev_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
> > >  	short PID[4];
> > >  	int ioaddr[2], status, frequency;
> > >  	unsigned int stats[5];
> > > -	struct sb1000_private *lp = netdev_priv(dev);
> > > +	struct sb1000_private *lp;
> > >  
> > >  	if (!(dev && dev->flags & IFF_UP))
> > >  		return -ENODEV;
> 
> I think we could get rid of the !dev check itself. Actually, the IFF_UP
> check /also/ looks suspect to me for two reasons: (1) I remember Stephen
> Hemminger once telling me dev->flags is legacy and unsafe, and one of
> the netif_xxx() functions be used instead, and, (2) I wonder if we really
> require the interface to be up and *running* when we do this ioctl.

Updated patch below.

[PATCH] sb1000: Remove bogus checks

In net_device->do_ioctl() of the sb1000 driver (sb1000_dev_ioctl):

(1) !dev condition is always false -- this function cannot be called with
NULL net_device.
(2) !(dev->flags & IFF_UP) is bogus because the functions of this ioctl
can (and should) be allowed even when the interface is not up and running.

So let's remove these checks.

Signed-off-by: Satyam Sharma <satyam@...radead.org>
Cc: Jesper Juhl <jesper.juhl@...il.com>
Cc: Domen Puncer <domen@...erock.org>

---

 drivers/net/sb1000.c |    3 ---
 1 files changed, 0 insertions(+), 3 deletions(-)

diff --git a/drivers/net/sb1000.c b/drivers/net/sb1000.c
index 1de3eec..f60fe98 100644
--- a/drivers/net/sb1000.c
+++ b/drivers/net/sb1000.c
@@ -993,9 +993,6 @@ static int sb1000_dev_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
 	unsigned int stats[5];
 	struct sb1000_private *lp = netdev_priv(dev);
 
-	if (!(dev && dev->flags & IFF_UP))
-		return -ENODEV;
-
 	ioaddr[0] = dev->base_addr;
 	/* mem_start holds the second I/O address */
 	ioaddr[1] = dev->mem_start;
-
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