netvsc: fix use after free on module removal

The NAPI data structure is embedded in the netvsc_device structure
and is freed when device is closed. There is still a reference
(in NAPI list) to this which causes a crash in netif_napi_del
when device is removed. Fix by managing NAPI instances correctly.
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/netvsc.c

@@ -584,8 +584,9 @@ void netvsc_device_remove(struct hv_device *device)
 	/* Now, we can close the channel safely */
 	vmbus_close(device->channel);
 
+	/* And dissassociate NAPI context from device */
 	for (i = 0; i < net_device->num_chn; i++)
-		napi_disable(&net_device->chan_table[i].napi);
+		netif_napi_del(&net_device->chan_table[i].napi);
 
 	/* Release all resources */
 	free_netvsc_device_rcu(net_device);
@@ -1320,8 +1321,6 @@ int netvsc_device_add(struct hv_device *device,
 		struct netvsc_channel *nvchan = &net_device->chan_table[i];
 
 		nvchan->channel = device->channel;
-		netif_napi_add(ndev, &nvchan->napi,
-			       netvsc_poll, NAPI_POLL_WEIGHT);
 	}
 
 	/* Open the channel */
@@ -1339,6 +1338,8 @@ int netvsc_device_add(struct hv_device *device,
 	netdev_dbg(ndev, "hv_netvsc channel opened successfully\n");
 
 	/* Enable NAPI handler for init callbacks */
+	netif_napi_add(ndev, &net_device->chan_table[0].napi,
+		       netvsc_poll, NAPI_POLL_WEIGHT);
 	napi_enable(&net_device->chan_table[0].napi);
 
 	/* Writing nvdev pointer unlocks netvsc_send(), make sure chn_table is
@@ -1357,7 +1358,7 @@ int netvsc_device_add(struct hv_device *device,
 	return ret;
 
 close:
-	napi_disable(&net_device->chan_table[0].napi);
+	netif_napi_del(&net_device->chan_table[0].napi);
 
 	/* Now, we can close the channel safely */
 	vmbus_close(device->channel);

drivers/net/hyperv/rndis_filter.c

@@ -1009,13 +1009,16 @@ static void netvsc_sc_open(struct vmbus_channel *new_sc)
 
 	/* Set the channel before opening.*/
 	nvchan->channel = new_sc;
+	netif_napi_add(ndev, &nvchan->napi,
+		       netvsc_poll, NAPI_POLL_WEIGHT);
 
 	ret = vmbus_open(new_sc, nvscdev->ring_size * PAGE_SIZE,
 			 nvscdev->ring_size * PAGE_SIZE, NULL, 0,
 			 netvsc_channel_cb, nvchan);
-
-
+	if (ret == 0)
 		napi_enable(&nvchan->napi);
+	else
+		netdev_err(ndev, "sub channel open failed (%d)\n", ret);
 
 	if (refcount_dec_and_test(&nvscdev->sc_offered))
 		complete(&nvscdev->channel_init_wait);