Re: [PATCH] fix potential NULL pointer dereference in yam

Jesper Juhl
2006-05-15T20:18:45Z

On Sunday 14 May 2006 16:09, Alexey Dobriyan wrote:
> On Sun, May 14, 2006 at 03:12:50PM +0200, Jesper Juhl wrote:
> > Testing a pointer for NULL after it has already been dereferenced is not
> > very safe.
> > Patch below to rework yam_open() so that `dev' is not dereferenced until
> > after it has been tested for NULL.
>
> > Found by coverity checker as #787
>
> > --- linux-2.6.17-rc4-git2-orig/drivers/net/hamradio/yam.c
> > +++ linux-2.6.17-rc4-git2/drivers/net/hamradio/yam.c
> > @@ -845,15 +845,25 @@ static struct net_device_stats *yam_get_
> >
> > static int yam_open(struct net_device *dev)
> > {
> > - struct yam_port *yp = netdev_priv(dev);
> > + struct yam_port *yp;
> > enum uart u;
> > int i;
> > - int ret=0;
> > + int ret = 0;
>
> Please, don't make unrelated changes.
>
Sorry.

> > - printk(KERN_INFO "Trying %s at iobase 0x%lx irq %u\n", dev->name, dev->base_addr, dev->irq);
> > + if (!dev) {
> > + printk(KERN_ERR "yam_open() called without device\n");
> > + return -ENXIO;
> > + }
>
> How can it be NULL here? The whole array of valid net_devices was
> allocated at module init time.
>

It cannot. You are right, I'm wrong.
I guess removing the check makes sense then ?

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

--- linux-2.6.17-rc4-mm1-orig/drivers/net/hamradio/yam.c 2006-05-13 21:28:27.000000000 +0200
+++ linux-2.6.17-rc4-mm1/drivers/net/hamradio/yam.c 2006-05-15 22:16:32.000000000 +0200
@@ -852,7 +852,7 @@ static int yam_open(struct net_device *d

printk(KERN_INFO "Trying %s at iobase 0x%lx irq %u\n", dev->name, dev->base_addr, dev->irq);

- if (!dev || !yp->bitrate)
+ if (!yp->bitrate)
return -ENXIO;
if (!dev->base_addr || dev->base_addr > 0x1000 - YAM_EXTENT ||
dev->irq < 2 || dev->irq > 15) {