From 68099b52b0fcc1d45864154954d776d91afb33e0 Mon Sep 17 00:00:00 2001
From: Hao Wu <hao.a.wu@intel.com>
Date: Tue, 16 Oct 2018 13:09:43 +0800
Subject: [PATCH] MdeModulePkg/UdfDxe: Avoid possible use of already-freed data

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=1255

For function ReadFile():

If the line

  Status = GetAedAdsData (
   ...
   );

is reached multiple times during the 'for' loop, freeing the data pointed
by variable 'Data' may potentially lead to variable 'Ad' referencing the
already-freed data.

After calling function GetAllocationDescriptor(), 'Data' and 'Ad' may
point to the same memory (with some possible offset). Hence, this commit
will move the FreePool() call backwards to ensure the data will no longer
be used.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Hao Wu <hao.a.wu@intel.com>
Reviewed-by: Paulo Alcantara <palcantara@suse.de>
Acked-by: Star Zeng <star.zeng@intel.com>
---
 .../Universal/Disk/UdfDxe/FileSystemOperations.c  | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/MdeModulePkg/Universal/Disk/UdfDxe/FileSystemOperations.c b/MdeModulePkg/Universal/Disk/UdfDxe/FileSystemOperations.c
index cabb599695..b9ebddfe62 100644
--- a/MdeModulePkg/Universal/Disk/UdfDxe/FileSystemOperations.c
+++ b/MdeModulePkg/Universal/Disk/UdfDxe/FileSystemOperations.c
@@ -1078,6 +1078,7 @@ ReadFile (
   EFI_STATUS              Status;
   UINT32                  LogicalBlockSize;
   VOID                    *Data;
+  VOID                    *DataBak;
   UINT64                  Length;
   VOID                    *Ad;
   UINT64                  AdOffset;
@@ -1218,12 +1219,7 @@ ReadFile (
       // Descriptor and its extents (ADs).
       //
       if (GET_EXTENT_FLAGS (RecordingFlags, Ad) == ExtentIsNextExtent) {
-        if (!DoFreeAed) {
-          DoFreeAed = TRUE;
-        } else {
-          FreePool (Data);
-        }
-
+        DataBak = Data;
         Status = GetAedAdsData (
           BlockIo,
           DiskIo,
@@ -1234,6 +1230,13 @@ ReadFile (
           &Data,
           &Length
           );
+
+        if (!DoFreeAed) {
+          DoFreeAed = TRUE;
+        } else {
+          FreePool (DataBak);
+        }
+
         if (EFI_ERROR (Status)) {
           goto Error_Get_Aed;
         }
-- 
2.39.2