af-packet: Hold reference to bound network devices.

Old code was probably safe, but with this change we
can actually use the netdev object, not just compare
the pointer values.

Signed-off-by: Ben Greear <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/packet/af_packet.c

···
 		__dev_remove_pack(&po->prot_hook);
 		__sock_put(sk);
 	}
+	if (po->prot_hook.dev) {
+		dev_put(po->prot_hook.dev);
+		po->prot_hook.dev = NULL;
+	}
 	spin_unlock(&po->bind_lock);
 
 	packet_flush_mclist(sk);
···
 
 	po->num = protocol;
 	po->prot_hook.type = protocol;
+	if (po->prot_hook.dev)
+		dev_put(po->prot_hook.dev);
 	po->prot_hook.dev = dev;
 
 	po->ifindex = dev ? dev->ifindex : 0;
···
 	strlcpy(name, uaddr->sa_data, sizeof(name));
 
 	dev = dev_get_by_name(sock_net(sk), name);
-	if (dev) {
+	if (dev)
 		err = packet_do_bind(sk, dev, pkt_sk(sk)->num);
-		dev_put(dev);
-	}
 	return err;
 }
 
···
 			goto out;
 	}
 	err = packet_do_bind(sk, dev, sll->sll_protocol ? : pkt_sk(sk)->num);
-	if (dev)
-		dev_put(dev);
 
 out:
 	return err;
···
 				}
 				if (msg == NETDEV_UNREGISTER) {
 					po->ifindex = -1;
+					if (po->prot_hook.dev)
+						dev_put(po->prot_hook.dev);
 					po->prot_hook.dev = NULL;
 				}
 				spin_unlock(&po->bind_lock);