Fix pointer dereference before call to pcie_bus_configure_settings

Commit b03e7495a8 ("PCI: Set PCI-E Max Payload Size on fabric")
introduced a potential NULL pointer dereference in calls to
pcie_bus_configure_settings due to attempts to access pci_bus self
variables when the self pointer is NULL.

To correct this, verify that the self pointer in pci_bus is non-NULL
before dereferencing it.

Reported-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Shyam Iyer <shyam_iyer@dell.com>
Signed-off-by: Jon Mason <mason@myri.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/pci/acpi.c

@@ -365,8 +365,13 @@ struct pci_bus * __devinit pci_acpi_scan_root(struct acpi_pci_root *root)
 	 */
 	if (bus) {
 		struct pci_bus *child;
-		list_for_each_entry(child, &bus->children, node)
-			pcie_bus_configure_settings(child, child->self->pcie_mpss);
+		list_for_each_entry(child, &bus->children, node) {
+			struct pci_dev *self = child->self;
+			if (!self)
+				continue;
+
+			pcie_bus_configure_settings(child, self->pcie_mpss);
+		}
 	}
 
 	if (!bus)

drivers/pci/hotplug/pcihp_slot.c

@@ -169,7 +169,9 @@ void pci_configure_slot(struct pci_dev *dev)
 			(dev->class >> 8) == PCI_CLASS_BRIDGE_PCI)))
 		return;
 
-	pcie_bus_configure_settings(dev->bus, dev->bus->self->pcie_mpss);
+	if (dev->bus && dev->bus->self)
+		pcie_bus_configure_settings(dev->bus,
+					    dev->bus->self->pcie_mpss);
 
 	memset(&hpp, 0, sizeof(hpp));
 	ret = pci_get_hp_params(dev, &hpp);

drivers/pci/probe.c

@@ -1456,9 +1456,6 @@ void pcie_bus_configure_settings(struct pci_bus *bus, u8 mpss)
 {
 	u8 smpss = mpss;
 
-	if (!bus->self)
-		return;
-
 	if (!pci_is_pcie(bus->self))
 		return;