net: ena: fix race condition between device reset and link up setup

In rare cases, ena driver would reset and re-start the device,
for example, in case of misbehaving application that causes
transmit timeout

The first step in the reset procedure is to stop the Tx traffic by
calling ena_carrier_off().

After the driver have just started the device reset procedure, device
happens to send an asynchronous notification (via AENQ) to the driver
than there was a link change (to link-up state).
This link change is mapped to a call to netif_carrier_on() which
re-activates the Tx queues, violating the assumption of no tx traffic
until device reset is completed, as the reset task might still be in
the process of queues initialization, leading to an access to
uninitialized memory.
Signed-off-by: Netanel Belgazal <netanel@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/amazon/ena/ena_netdev.c

@@ -2579,6 +2579,7 @@ static int ena_restore_device(struct ena_adapter *adapter)
 	bool wd_state;
 	int rc;
 
+	set_bit(ENA_FLAG_ONGOING_RESET, &adapter->flags);
 	rc = ena_device_init(ena_dev, adapter->pdev, &get_feat_ctx, &wd_state);
 	if (rc) {
 		dev_err(&pdev->dev, "Can not initialize device\n");
@@ -2592,6 +2593,11 @@ static int ena_restore_device(struct ena_adapter *adapter)
 		goto err_device_destroy;
 	}
 
+	clear_bit(ENA_FLAG_ONGOING_RESET, &adapter->flags);
+	/* Make sure we don't have a race with AENQ Links state handler */
+	if (test_bit(ENA_FLAG_LINK_UP, &adapter->flags))
+		netif_carrier_on(adapter->netdev);
+
 	rc = ena_enable_msix_and_set_admin_interrupts(adapter,
 						      adapter->num_queues);
 	if (rc) {
@@ -2618,7 +2624,7 @@ static int ena_restore_device(struct ena_adapter *adapter)
 	ena_com_admin_destroy(ena_dev);
 err:
 	clear_bit(ENA_FLAG_DEVICE_RUNNING, &adapter->flags);
-
+	clear_bit(ENA_FLAG_ONGOING_RESET, &adapter->flags);
 	dev_err(&pdev->dev,
 		"Reset attempt failed. Can not reset the device\n");
 
@@ -3495,6 +3501,7 @@ static void ena_update_on_link_change(void *adapter_data,
 	if (status) {
 		netdev_dbg(adapter->netdev, "%s\n", __func__);
 		set_bit(ENA_FLAG_LINK_UP, &adapter->flags);
+		if (!test_bit(ENA_FLAG_ONGOING_RESET, &adapter->flags))
 			netif_carrier_on(adapter->netdev);
 	} else {
 		clear_bit(ENA_FLAG_LINK_UP, &adapter->flags);

drivers/net/ethernet/amazon/ena/ena_netdev.h

@@ -272,7 +272,8 @@ enum ena_flags_t {
 	ENA_FLAG_DEV_UP,
 	ENA_FLAG_LINK_UP,
 	ENA_FLAG_MSIX_ENABLED,
-	ENA_FLAG_TRIGGER_RESET
+	ENA_FLAG_TRIGGER_RESET,
+	ENA_FLAG_ONGOING_RESET
 };
 
 /* adapter specific private data structure */