[Patch] NetworkPkg: Fix incorrect parameter check in PXE.Mtftp() function.

[Fu Siyuan <siyuan.fu@intel.com>]

According to UEFI spec, the PXE.Mtftp() should return invalid parameter if the
BufferPtr parameter was NULL and the DontUseBuffer parameter was FALSE.
The DontUseBuffer is only used when perform MTFTP/TFTP read operation.

Cc: Ye Ting <ting.ye@intel.com>
Cc: Wu Jiaxin <jiaxin.wu@intel.com>
Cc: Wang Fan <fan.wang@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Fu Siyuan <siyuan.fu@intel.com>
---
 NetworkPkg/UefiPxeBcDxe/PxeBcImpl.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/NetworkPkg/UefiPxeBcDxe/PxeBcImpl.c b/NetworkPkg/UefiPxeBcDxe/PxeBcImpl.c
index 93f3bfa5ba..9068e0686c 100644
--- a/NetworkPkg/UefiPxeBcDxe/PxeBcImpl.c
+++ b/NetworkPkg/UefiPxeBcDxe/PxeBcImpl.c
@@ -855,11 +855,19 @@ EfiPxeBcMtftp (
       (Filename == NULL) ||
       (BufferSize == NULL) ||
       (ServerIp == NULL) ||
-      ((BufferPtr == NULL) && DontUseBuffer) ||
       ((BlockSize != NULL) && (*BlockSize < PXE_MTFTP_DEFAULT_BLOCK_SIZE))) {
     return EFI_INVALID_PARAMETER;
   }
 
+  if (Operation == EFI_PXE_BASE_CODE_TFTP_READ_FILE ||
+      Operation == EFI_PXE_BASE_CODE_TFTP_READ_DIRECTORY ||
+      Operation == EFI_PXE_BASE_CODE_MTFTP_READ_FILE ||
+      Operation == EFI_PXE_BASE_CODE_MTFTP_READ_DIRECTORY) {
+    if (BufferPtr == NULL && !DontUseBuffer) {
+      return EFI_INVALID_PARAMETER;
+    }
+  }
+
   Config    = NULL;
   Status    = EFI_DEVICE_ERROR;
   Private   = PXEBC_PRIVATE_DATA_FROM_PXEBC (This);
-- 
2.13.0.windows.1