[Patch 1/2] MdeModulePkg/Ip4Dxe: Fix the potential NULL pointer free

[Jiaxin Wu <jiaxin.wu@intel.com>]

Ip4Config2SetDnsServer may cause ASSERT if the invalid DNS
server address received. The issue is triggered by the NULL
pointer(Tmp) free.

Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
---
 MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Config2Impl.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Config2Impl.c b/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Config2Impl.c
index 88ead9d..131b03f 100644
--- a/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Config2Impl.c
+++ b/MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Config2Impl.c
@@ -1,9 +1,9 @@
 /** @file
   The implementation of EFI IPv4 Configuration II Protocol.
 
-  Copyright (c) 2015 - 2016, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2015 - 2017, Intel Corporation. All rights reserved.<BR>
   (C) Copyright 2015-2016 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
   which accompanies this distribution.  The full text of the license may be found at
@@ -739,17 +739,21 @@ Ip4Config2SetDnsServerWorker (
     CopyMem (&DnsAddress, NewDns + NewIndex, sizeof (IP4_ADDR));
     if (IP4_IS_UNSPECIFIED (NTOHL (DnsAddress)) || IP4_IS_LOCAL_BROADCAST (NTOHL (DnsAddress))) {
       //
       // The dns server address must be unicast.
       //
-      FreePool (Tmp);
+      if (Tmp != NULL) {
+        FreePool (Tmp);
+      }
       return EFI_INVALID_PARAMETER;
     }
 
     for (Index1 = NewIndex + 1; Index1 < NewDnsCount; Index1++) {
       if (EFI_IP4_EQUAL (NewDns + NewIndex, NewDns + Index1)) {
-        FreePool (Tmp);
+        if (Tmp != NULL) {
+          FreePool (Tmp);
+        }
         return EFI_INVALID_PARAMETER;
       }
     }
 
     if (OneAdded) {
-- 
1.9.5.msysgit.1