From c0cba3d5ddec83e2bf09deb01a25140a71f8b7e6 Mon Sep 17 00:00:00 2001
From: Eric Dong <eric.dong@intel.com>
Date: Thu, 27 Oct 2016 11:08:37 +0800
Subject: [PATCH] MdePkg DevicePathLib: Validate before touch input buffer.

Current code not validate the input buffer before touch.
it may touch the buffer outside the validate scope. This
patch validate the input size big enough to touch the
first node.

Cc: Ruiyu NI <ruiyu.ni@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Eric Dong <eric.dong@intel.com>
---
 .../UefiDevicePathLib.c                       | 26 +++++++++++++++----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/MdePkg/Library/UefiDevicePathLibDevicePathProtocol/UefiDevicePathLib.c b/MdePkg/Library/UefiDevicePathLibDevicePathProtocol/UefiDevicePathLib.c
index a514f1b6f9..2252d186cb 100644
--- a/MdePkg/Library/UefiDevicePathLibDevicePathProtocol/UefiDevicePathLib.c
+++ b/MdePkg/Library/UefiDevicePathLibDevicePathProtocol/UefiDevicePathLib.c
@@ -103,17 +103,33 @@ IsDevicePathValid (
 
   ASSERT (DevicePath != NULL);
 
+  if (MaxSize == 0) {
+    MaxSize = MAX_UINTN;
+  }
+
+  //
+  // Validate the input size big enough to touch the first node.
+  //
+  if (MaxSize < sizeof (EFI_DEVICE_PATH_PROTOCOL)) {
+    return FALSE;
+  }
+
   for (Count = 0, Size = 0; !IsDevicePathEnd (DevicePath); DevicePath = NextDevicePathNode (DevicePath)) {
     NodeLength = DevicePathNodeLength (DevicePath);
     if (NodeLength < sizeof (EFI_DEVICE_PATH_PROTOCOL)) {
       return FALSE;
     }
 
-    if (MaxSize > 0) {
-      Size += NodeLength;
-      if (Size + END_DEVICE_PATH_LENGTH > MaxSize) {
-        return FALSE;
-      }
+    if (NodeLength > MAX_UINTN - Size) {
+      return FALSE;
+    }
+    Size += NodeLength;
+
+    //
+    // Validate next node before touch it.
+    //
+    if (Size > MaxSize - END_DEVICE_PATH_LENGTH ) {
+      return FALSE;
     }
 
     if (PcdGet32 (PcdMaximumDevicePathNodeCount) > 0) {