[Patch 1/4] MdePkg DevicePathLib: Rollback former change.

[Eric Dong <eric.dong@intel.com>]

Former patch still has some bugs, so rollback it and
enhance the original code.

Cc: Ruiyu NI <ruiyu.ni@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Eric Dong <eric.dong@intel.com>
---
 .../UefiDevicePathLib.c                            | 22 ++++++----------------
 1 file changed, 6 insertions(+), 16 deletions(-)

diff --git a/MdePkg/Library/UefiDevicePathLibDevicePathProtocol/UefiDevicePathLib.c b/MdePkg/Library/UefiDevicePathLibDevicePathProtocol/UefiDevicePathLib.c
index 4872416..a514f1b 100644
--- a/MdePkg/Library/UefiDevicePathLibDevicePathProtocol/UefiDevicePathLib.c
+++ b/MdePkg/Library/UefiDevicePathLibDevicePathProtocol/UefiDevicePathLib.c
@@ -103,35 +103,25 @@ IsDevicePathValid (
 
   ASSERT (DevicePath != NULL);
 
-  if (MaxSize == 0){
-    MaxSize = MAX_UINTN;
-  }
-
-  Size = 0;
-  Count = 0;
-
-  while (MaxSize >= sizeof (EFI_DEVICE_PATH_PROTOCOL) &&
-        (MaxSize - sizeof (EFI_DEVICE_PATH_PROTOCOL) >= Size) &&
-        !IsDevicePathEnd (DevicePath)) {
+  for (Count = 0, Size = 0; !IsDevicePathEnd (DevicePath); DevicePath = NextDevicePathNode (DevicePath)) {
     NodeLength = DevicePathNodeLength (DevicePath);
     if (NodeLength < sizeof (EFI_DEVICE_PATH_PROTOCOL)) {
       return FALSE;
     }
 
-    if (NodeLength > MAX_UINTN - Size) {
-      return FALSE;
+    if (MaxSize > 0) {
+      Size += NodeLength;
+      if (Size + END_DEVICE_PATH_LENGTH > MaxSize) {
+        return FALSE;
+      }
     }
 
-    Size += NodeLength;
-
     if (PcdGet32 (PcdMaximumDevicePathNodeCount) > 0) {
       Count++;
       if (Count >= PcdGet32 (PcdMaximumDevicePathNodeCount)) {
         return FALSE;
       }
     }
-
-    DevicePath = NextDevicePathNode (DevicePath);
   }
 
   //
-- 
2.6.4.windows.1