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SubjectRe: [PATCH] fix potential NULL pointer dereference in yam
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.

> - 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.

> - if (!dev || !yp->bitrate)
> + yp = netdev_priv(dev);
> + if (!yp->bitrate) {
> + printk(KERN_ERR "%s: no bitrate\n", dev->name);
> return -ENXIO;
> + }
> +
> + printk(KERN_INFO "Trying %s at iobase 0x%lx irq %u\n",
> + dev->name, dev->base_addr, dev->irq);
> +
> if (!dev->base_addr || dev->base_addr > 0x1000 - YAM_EXTENT ||
> dev->irq < 2 || dev->irq > 15) {
> return -ENXIO;

-
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