[Patch] ShellPkg/TftpDynamicCommand: Fix the potential assertion and memory leak issue.

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

This patch is to fix the issue reported from
https://bugzilla.tianocore.org/show_bug.cgi?id=925.

DataSize variable was not assigned the value if ShellOpenFileByName returns error.
In the such a case, it should not be used to FreePages. Instead, DataSize can be
used to record the file size once DownloadFile successfully.

Cc: Vladimir Olovyannikov <vladimir.olovyannikov@broadcom.com>
Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Jaben Carsey <jaben.carsey@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
---
 ShellPkg/DynamicCommand/TftpDynamicCommand/Tftp.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/ShellPkg/DynamicCommand/TftpDynamicCommand/Tftp.c b/ShellPkg/DynamicCommand/TftpDynamicCommand/Tftp.c
index 8569c966dd..0620aec1a7 100644
--- a/ShellPkg/DynamicCommand/TftpDynamicCommand/Tftp.c
+++ b/ShellPkg/DynamicCommand/TftpDynamicCommand/Tftp.c
@@ -1,10 +1,10 @@
 /** @file
   The implementation for the 'tftp' Shell command.
 
   Copyright (c) 2015, ARM Ltd. All rights reserved.<BR>
-  Copyright (c) 2015 - 2017, Intel Corporation. All rights reserved. <BR>
+  Copyright (c) 2015 - 2018, Intel Corporation. All rights reserved. <BR>
   (C) Copyright 2015 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
@@ -517,10 +517,12 @@ RunTftp (
         mTftpHiiHandle, RemoteFilePath, NicName, Status
       );
       goto NextHandle;
     }
 
+    DataSize = FileSize;
+
     if (!EFI_ERROR (ShellFileExists (LocalFilePath))) {
       ShellDeleteFileByName (LocalFilePath);
     }
 
     Status = ShellOpenFileByName (
@@ -537,11 +539,10 @@ RunTftp (
         mTftpHiiHandle, L"tftp", LocalFilePath
       );
       goto NextHandle;
     }
 
-    DataSize = FileSize;
     Status = ShellWriteFile (FileHandle, &FileSize, Data);
     if (!EFI_ERROR (Status)) {
       ShellStatus = SHELL_SUCCESS;
     } else {
       ShellPrintHiiEx (
-- 
2.16.2.windows.1