From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [i4l] stop address leakage when shutting down an i4l ppp
 interface
Date: Wed, 14 Jan 2009 14:50:35 -0800 (PST)
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To: pebolle@tiscali.nl
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From: Paul Bolle <pebolle@tiscali.nl>
Date: Mon, 12 Jan 2009 13:54:49 +0100

> @@ -1336,6 +1336,13 @@ isdn_net_close(struct net_device *dev)
>  	}
>  	isdn_net_hangup(dev);
>  	isdn_unlock_drivers();
> +#ifdef CONFIG_ISDN_PPP
> +	/* make sure arp_mc_map() handles this device properly */
> +	if (dev->type == ARPHRD_PPP) {
> +		dev->type = ARPHRD_ETHER;
> +		dev->addr_len = ETH_ALEN;
> +	}
> +#endif
>  	return 0;
>  }

Just like the CONFIG_ISDN_PPP case, this code also changes the
p->dev->type and clears p->dev->addr_len for CONFIG_ISDN_X25

So at a minimum you'd need to add a case for that here as well.

I think it's pretty much illegal to change the device type after the
device has been registered.  Probably a lot of surgery is needed
here to correct this.

Althought what might work is to unregister then re-register the
device when the device type needs to be changed.  That should
work as long as it doesn't cause other undesirable side effects.