[PATCH 2/2] MdeModulePkg Variable: Update GetNextVariableName to follow UEFI 2.7

[Star Zeng <star.zeng@intel.com>]

"The size must be large enough to fit input string supplied in
VariableName buffer" is added in the description for VariableNameSize.
And two cases of EFI_INVALID_PARAMETER are added.
1. The input values of VariableName and VendorGuid are not a name and
   GUID of an existing variable.
2. Null-terminator is not found in the first VariableNameSize bytes of
   the input VariableName buffer.

This patch is to update code to follow them.

Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
---
 MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c b/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c
index 0a325de1659d..d8f41d799238 100644
--- a/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c
+++ b/MdeModulePkg/Universal/Variable/RuntimeDxe/Variable.c
@@ -2926,6 +2926,12 @@ VariableServiceGetNextVariableInternal (
 
   Status = FindVariable (VariableName, VendorGuid, &Variable, &mVariableModuleGlobal->VariableGlobal, FALSE);
   if (Variable.CurrPtr == NULL || EFI_ERROR (Status)) {
+    if (VariableName[0] != 0) {
+      //
+      // The input values of VariableName and VendorGuid are not a name and GUID of an existing variable.
+      //
+      Status = EFI_INVALID_PARAMETER;
+    }
     goto Done;
   }
 
@@ -3065,6 +3071,7 @@ VariableServiceGetNextVariableName (
   )
 {
   EFI_STATUS              Status;
+  UINTN                   MaxLen;
   UINTN                   VarNameSize;
   VARIABLE_HEADER         *VariablePtr;
 
@@ -3072,6 +3079,18 @@ VariableServiceGetNextVariableName (
     return EFI_INVALID_PARAMETER;
   }
 
+  //
+  // Calculate the possible maximum length of name string, including the Null terminator.
+  //
+  MaxLen = *VariableNameSize / sizeof (CHAR16);
+  if ((MaxLen == 0) ||
+      ((VariableName[MaxLen - 1] != 0) && (StrnLenS (VariableName, MaxLen) >= MaxLen))) {
+    //
+    // Null-terminator is not found in the first VariableNameSize bytes of the input VariableName buffer.
+    //
+    return EFI_INVALID_PARAMETER;
+  }
+
   AcquireLockOnlyAtBootTime(&mVariableModuleGlobal->VariableGlobal.VariableServicesLock);
 
   Status = VariableServiceGetNextVariableInternal (VariableName, VendorGuid, &VariablePtr);
-- 
2.7.0.windows.1