[PATCH] MdeModulePkg/PciBus: Avoid hang when BUS pad resource is not in top

[Ruiyu Ni <ruiyu.ni@intel.com>]

PciScanBus() assumes the GetResourcePadding() puts BUS descriptor
in the very beginning, if it's not, the Descriptors will be updated
to point to middle of the pool buffer, which can cause
FreePool(Descriptors) hang in DEBUG image.
No functionality impact to RELEASE image.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
---
 MdeModulePkg/Bus/Pci/PciBusDxe/PciLib.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/MdeModulePkg/Bus/Pci/PciBusDxe/PciLib.c b/MdeModulePkg/Bus/Pci/PciBusDxe/PciLib.c
index e1d62e8c21..8b076e8791 100644
--- a/MdeModulePkg/Bus/Pci/PciBusDxe/PciLib.c
+++ b/MdeModulePkg/Bus/Pci/PciBusDxe/PciLib.c
@@ -1,7 +1,7 @@
 /** @file
   Internal library implementation for PCI Bus module.
 
-Copyright (c) 2006 - 2016, Intel Corporation. All rights reserved.<BR>
+Copyright (c) 2006 - 2017, Intel Corporation. All rights reserved.<BR>
 (C) Copyright 2015 Hewlett Packard Enterprise Development LP<BR>
 This program and the accompanying materials
 are licensed and made available under the terms and conditions of the BSD License
@@ -986,6 +986,7 @@ PciScanBus (
   UINT64                            PciAddress;
   EFI_HPC_PADDING_ATTRIBUTES        Attributes;
   EFI_ACPI_ADDRESS_SPACE_DESCRIPTOR *Descriptors;
+  EFI_ACPI_ADDRESS_SPACE_DESCRIPTOR *NextDescriptors;
   UINT16                            BusRange;
   EFI_PCI_ROOT_BRIDGE_IO_PROTOCOL   *PciRootBridgeIo;
   BOOLEAN                           BusPadding;
@@ -1143,8 +1144,9 @@ PciScanBus (
               }
 
               BusRange = 0;
+              NextDescriptors = Descriptors;
               Status = PciGetBusRange (
-                        &Descriptors,
+                        &NextDescriptors,
                         NULL,
                         NULL,
                         &BusRange
-- 
2.12.2.windows.2