ixgbe: fix use of list_for_each in ixgbe_enumerate_functions

Fix a bug in the misuse of the list_for_each macro to loop over every
entry in the bus_list. Instead of attempting to loop over the list from
a random entry point, go up to the bus and use the real list_head entry
point. This prevents the possible read or write of unallocated or
incorrectly addressed memory.
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -7973,23 +7973,20 @@ static const struct net_device_ops ixgbe_netdev_ops = {
  **/
 static inline int ixgbe_enumerate_functions(struct ixgbe_adapter *adapter)
 {
-	struct list_head *entry;
+	struct pci_dev *entry;
 	int physfns = 0;
 
 	/* Some cards can not use the generic count PCIe functions method,
 	 * because they are behind a parent switch, so we hardcode these with
 	 * the correct number of functions.
 	 */
-	if (ixgbe_pcie_from_parent(&adapter->hw)) {
+	if (ixgbe_pcie_from_parent(&adapter->hw))
 		physfns = 4;
-	} else {
-		list_for_each(entry, &adapter->pdev->bus_list) {
-			struct pci_dev *pdev =
-				list_entry(entry, struct pci_dev, bus_list);
-			/* don't count virtual functions */
-			if (!pdev->is_virtfn)
-				physfns++;
-		}
+
+	list_for_each_entry(entry, &adapter->pdev->bus->devices, bus_list) {
+		/* don't count virtual functions */
+		if (!entry->is_virtfn)
+			physfns++;
 	}
 
 	return physfns;