SecurityPkg/DxeImageVerificationLib: plug Data leak in IsForbiddenByD…

…bx() (CVE-2019-14575)

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1608

If the second GetVariable() call for "dbx" fails, in IsForbiddenByDbx(),
we have to free Data. Jump to "Done" for that.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Chao Zhang <chao.b.zhang@intel.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>

SecurityPkg/Library/DxeImageVerificationLib/DxeImageVerificationLib.c

@@ -1274,7 +1274,7 @@ IsForbiddenByDbx (
 
   Status = gRT->GetVariable (EFI_IMAGE_SECURITY_DATABASE1, &gEfiImageSecurityDatabaseGuid, NULL, &DataSize, (VOID *) Data);
   if (EFI_ERROR (Status)) {
-    return IsForbidden;
+    goto Done;
   }
 
   //