Re: [PATCH v2] MdeModulePkg/UdfDxe: Additional checks for ResolveSymlink()

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

Reviewed-by: Star Zeng <star.zeng@intel.com>

-----Original Message-----
From: Wu, Hao A 
Sent: Saturday, October 27, 2018 8:28 PM
To: edk2-devel@lists.01.org
Cc: Wu, Hao A <hao.a.wu@intel.com>; Ni, Ruiyu <ruiyu.ni@intel.com>; Zeng, Star <star.zeng@intel.com>
Subject: [PATCH v2] MdeModulePkg/UdfDxe: Additional checks for ResolveSymlink()

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=1279

V2 change:

Refine type C check (refer to V1 history below) to eliminate the unnecessary CopyMem() call.

V1 history:

The commit will add 3 types of checks for function ResolveSymlink():

A. Check for the value of 'Component Type' field within a Path Component

According to the ECMA-167 standard (3rd Edition - June 1997), Section 14.16.1.1, valid values are 1 to 5. All other values will be treated as a corrupted volume.

B. Check for the content pointed by 'File'

Since content within 'File' is the output data for ResolveSymlink().
Checks is added to ensure the content in 'File' is valid. Otherwise, possible null pointer dereference issue will occur during the subsequent usage of the data returned by ResolveSymlink().

C. Check for possible memory double free/use after free case

For codes:

    if (CompareMem ((VOID *)&PreviousFile, (VOID *)Parent,
                    sizeof (UDF_FILE_INFO)) != 0) {
      CleanupFileInformation (&PreviousFile);
    }

    CopyMem ((VOID *)&PreviousFile, (VOID *)File, sizeof (UDF_FILE_INFO));

If the contents in 'PreviousFile' and 'File' are the same, call to "CleanupFileInformation (&PreviousFile);" will free the buffers in 'File'
as well. This will lead to potential memory double free/use after free issues.

Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Star Zeng <star.zeng@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>
---
 MdeModulePkg/Universal/Disk/UdfDxe/FileSystemOperations.c | 38 ++++++++++++++++++--
 1 file changed, 35 insertions(+), 3 deletions(-)

diff --git a/MdeModulePkg/Universal/Disk/UdfDxe/FileSystemOperations.c b/MdeModulePkg/Universal/Disk/UdfDxe/FileSystemOperations.c
index b9ebddfe62..971f562ae2 100644
--- a/MdeModulePkg/Universal/Disk/UdfDxe/FileSystemOperations.c
+++ b/MdeModulePkg/Universal/Disk/UdfDxe/FileSystemOperations.c
@@ -2144,6 +2144,10 @@ ResolveSymlink (
   UINTN               Index;
   UINT8               CompressionId;
   UDF_FILE_INFO       PreviousFile;
+  BOOLEAN             NotParent;
+  BOOLEAN             NotFile;
+
+  ZeroMem ((VOID *)File, sizeof (UDF_FILE_INFO));
 
   //
   // Symlink files on UDF volumes do not contain so much data other than @@ -2257,6 +2261,13 @@ ResolveSymlink (
       }
       FileName[Index] = L'\0';
       break;
+    default:
+      //
+      // Accoring to the ECMA-167 standard (3rd Edition - June 1997), Section
+      // 14.16.1.1, all other values are reserved.
+      //
+      Status = EFI_VOLUME_CORRUPTED;
+      goto Error_Find_File;
     }
 
     //
@@ -2281,12 +2292,26 @@ ResolveSymlink (
       break;
     }
 
-    if (CompareMem ((VOID *)&PreviousFile, (VOID *)Parent,
-                    sizeof (UDF_FILE_INFO)) != 0) {
+    //
+    // Check the content in the file info pointed by File.
+    //
+    if ((File->FileEntry == NULL) || (File->FileIdentifierDesc == NULL)) {
+      Status = EFI_VOLUME_CORRUPTED;
+      goto Error_Find_File;
+    }
+
+    NotParent = (CompareMem ((VOID *)&PreviousFile, (VOID *)Parent,
+                 sizeof (UDF_FILE_INFO)) != 0);
+    NotFile   = (CompareMem ((VOID *)&PreviousFile, (VOID *)File,
+                 sizeof (UDF_FILE_INFO)) != 0);
+
+    if (NotParent && NotFile) {
       CleanupFileInformation (&PreviousFile);
     }
 
-    CopyMem ((VOID *)&PreviousFile, (VOID *)File, sizeof (UDF_FILE_INFO));
+    if (NotFile) {
+      CopyMem ((VOID *)&PreviousFile, (VOID *)File, sizeof (UDF_FILE_INFO));
+    }
   }
 
   //
@@ -2294,6 +2319,13 @@ ResolveSymlink (
   //
   FreePool (ReadFileInfo.FileData);
 
+  //
+  // Check the content in the resolved file info.
+  //
+  if ((File->FileEntry == NULL) || (File->FileIdentifierDesc == NULL)) {
+    return EFI_VOLUME_CORRUPTED;
+  }
+
   return EFI_SUCCESS;
 
 Error_Find_File:
--
2.12.0.windows.1