[PATCH v2 2/2] MdePkg/UefiDevicePathLib: Add a checking step

[Shenglei Zhang <shenglei.zhang@intel.com>]

Add a checking step in DevicePathUtilities.c to verify the DevicePath.
https://bugzilla.tianocore.org/show_bug.cgi?id=1372

v2: Remove ASSERT() and the redundant checking step. 
    Update related description in DevicePathLib.h

Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Shenglei Zhang <shenglei.zhang@intel.com>
---
 MdePkg/Include/Library/DevicePathLib.h             |  2 +-
 .../UefiDevicePathLib/DevicePathUtilities.c        | 14 ++++++--------
 2 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/MdePkg/Include/Library/DevicePathLib.h b/MdePkg/Include/Library/DevicePathLib.h
index 959299704a..717d4db42f 100644
--- a/MdePkg/Include/Library/DevicePathLib.h
+++ b/MdePkg/Include/Library/DevicePathLib.h
@@ -22,7 +22,7 @@ WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
 
 /**
   Determine whether a given device path is valid.
-  If DevicePath is NULL, then ASSERT().
+  If DevicePath is NULL or the size is not suitable, then return false.
 
   @param  DevicePath  A pointer to a device path data structure.
   @param  MaxSize     The maximum size of the device path data structure.
diff --git a/MdePkg/Library/UefiDevicePathLib/DevicePathUtilities.c b/MdePkg/Library/UefiDevicePathLib/DevicePathUtilities.c
index 665e5a4adc..05f82c1313 100644
--- a/MdePkg/Library/UefiDevicePathLib/DevicePathUtilities.c
+++ b/MdePkg/Library/UefiDevicePathLib/DevicePathUtilities.c
@@ -59,19 +59,17 @@ IsDevicePathValid (
   UINTN Size;
   UINTN NodeLength;
 
-  ASSERT (DevicePath != NULL);
-
-  if (MaxSize == 0) {
-    MaxSize = MAX_UINTN;
-  }
-
   //
-  // Validate the input size big enough to touch the first node.
+  //Validate the input whether exists and its size big enough to touch the first node
   //
-  if (MaxSize < sizeof (EFI_DEVICE_PATH_PROTOCOL)) {
+  if (DevicePath == NULL || (MaxSize > 0 && MaxSize < END_DEVICE_PATH_LENGTH)) {
     return FALSE;
   }
 
+  if (MaxSize == 0) {
+    MaxSize = MAX_UINTN;
+  }
+
   for (Count = 0, Size = 0; !IsDevicePathEnd (DevicePath); DevicePath = NextDevicePathNode (DevicePath)) {
     NodeLength = DevicePathNodeLength (DevicePath);
     if (NodeLength < sizeof (EFI_DEVICE_PATH_PROTOCOL)) {
-- 
2.18.0.windows.1