powerpc/PCI: Fix NULL dereference in sys_pciconfig_iobase() list traversal

3bc955987fb3 ("powerpc/PCI: Use list_for_each_entry() for bus traversal")
caused a NULL pointer dereference because the loop body set the iterator to
NULL:

  Unable to handle kernel paging request for data at address 0x00000000
  Faulting instruction address: 0xc000000000041d78
  Oops: Kernel access of bad area, sig: 11 [#1]
  ...
  NIP [c000000000041d78] .sys_pciconfig_iobase+0x68/0x1f0
  LR [c000000000041e0c] .sys_pciconfig_iobase+0xfc/0x1f0
  Call Trace:
  [c0000003b4787db0] [c000000000041e0c] .sys_pciconfig_iobase+0xfc/0x1f0 (unreliable)
  [c0000003b4787e30] [c000000000009ed8] syscall_exit+0x0/0x98

Fix it by using a temporary variable for the iterator.

[bhelgaas: changelog, drop tmp_bus initialization]
Fixes: 3bc955987fb3 powerpc/PCI: Use list_for_each_entry() for bus traversal
Signed-off-by: Mike Qiu <qiudayu@linux.vnet.ibm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

1 files changed, 6 insertions, 4 deletions

diff --git a/arch/powerpc/kernel/pci_64.c b/arch/powerpc/kernel/pci_64.c
index 2a4779091a58..155013da27e0 100644
--- a/arch/powerpc/kernel/pci_64.c
+++ b/arch/powerpc/kernel/pci_64.c
@@ -208,7 +208,7 @@ long sys_pciconfig_iobase(long which, unsigned long in_bus,
                           unsigned long in_devfn)
 {
         struct pci_controller* hose;
-        struct pci_bus *bus = NULL;
+        struct pci_bus *tmp_bus, *bus = NULL;
         struct device_node *hose_node;
 
         /* Argh ! Please forgive me for that hack, but that's the
@@ -229,10 +229,12 @@ long sys_pciconfig_iobase(long which, unsigned long in_bus,
          * used on pre-domains setup. We return the first match
          */
 
-        list_for_each_entry(bus, &pci_root_buses, node) {
-                if (in_bus >= bus->number && in_bus <= bus->busn_res.end)
+        list_for_each_entry(tmp_bus, &pci_root_buses, node) {
+                if (in_bus >= tmp_bus->number &&
+                    in_bus <= tmp_bus->busn_res.end) {
+                        bus = tmp_bus;
                         break;
-                bus = NULL;
+                }
         }
         if (bus == NULL || bus->dev.of_node == NULL)
                 return -ENODEV;