net: usb: fix possible use-after-free in smsc75xx_bind

The commit 46a8b29c ("net: usb: fix memory leak in smsc75xx_bind")
fails to clean up the work scheduled in smsc75xx_reset->
smsc75xx_set_multicast, which leads to use-after-free if the work is
scheduled to start after the deallocation. In addition, this patch
also removes a dangling pointer - dev->data[0].

This patch calls cancel_work_sync to cancel the scheduled work and set
the dangling pointer to NULL.

Fixes: 46a8b29c ("net: usb: fix memory leak in smsc75xx_bind")
Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/smsc75xx.c

@@ -1483,7 +1483,7 @@ static int smsc75xx_bind(struct usbnet *dev, struct usb_interface *intf)
 	ret = smsc75xx_wait_ready(dev, 0);
 	if (ret < 0) {
 		netdev_warn(dev->net, "device not ready in smsc75xx_bind\n");
-		goto err;
+		goto free_pdata;
 	}
 
 	smsc75xx_init_mac_address(dev);
@@ -1492,7 +1492,7 @@ static int smsc75xx_bind(struct usbnet *dev, struct usb_interface *intf)
 	ret = smsc75xx_reset(dev);
 	if (ret < 0) {
 		netdev_warn(dev->net, "smsc75xx_reset error %d\n", ret);
-		goto err;
+		goto cancel_work;
 	}
 
 	dev->net->netdev_ops = &smsc75xx_netdev_ops;
@@ -1503,8 +1503,11 @@ static int smsc75xx_bind(struct usbnet *dev, struct usb_interface *intf)
 	dev->net->max_mtu = MAX_SINGLE_PACKET_SIZE;
 	return 0;
 
-err:
+cancel_work:
+	cancel_work_sync(&pdata->set_multicast);
+free_pdata:
 	kfree(pdata);
+	dev->data[0] = 0;
 	return ret;
 }
 
@@ -1515,7 +1518,6 @@ static void smsc75xx_unbind(struct usbnet *dev, struct usb_interface *intf)
 		cancel_work_sync(&pdata->set_multicast);
 		netif_dbg(dev, ifdown, dev->net, "free pdata\n");
 		kfree(pdata);
-		pdata = NULL;
 		dev->data[0] = 0;
 	}
 }