Avoid Invalid Memory Object error #13677

tpowell-progress · 2023-04-10T12:46:50Z

Description

Windows runs of Chef get intermittent ArgumentErrors for "Invalid Memory Object". This is due to an attempt to compare a legitimate Windows HANDLE retrieved from GetCurrentProcess with an FFI::Pointer. The "Invalid Memory Object" error itself comes from trying to compare a memory object (FFI::Pointer with the return value from GetCurrentProcess(), a HANDLE from Windows)

Windows data types

These errors do not result in breakage because of their happening in a finalizer, but

Error example

C:/opscode/chef/embedded/lib/ruby/gems/3.1.0/gems/chef-18.2.9-x64-mingw-ucrt/lib/chef/win32/handle.rb:45:in `==': Invalid Memory object (ArgumentError)
	from C:/opscode/chef/embedded/lib/ruby/gems/3.1.0/gems/chef-18.2.9-x64-mingw-ucrt/lib/chef/win32/handle.rb:45:in `close_handle'
	from C:/opscode/chef/embedded/lib/ruby/gems/3.1.0/gems/chef-18.2.9-x64-mingw-ucrt/lib/chef/win32/handle.rb:37:in `block in close_handle_finalizer'
	from C:/opscode/chef/embedded/lib/ruby/gems/3.1.0/gems/ffi-win32-extensions-1.0.4/lib/ffi/win32/extensions.rb:60:in `read_utf16string'
	from C:/opscode/chef/embedded/lib/ruby/gems/3.1.0/gems/chef-powershell-18.0.1/lib/chef-powershell/powershell.rb:120:in `exec'
	from C:/opscode/chef/embedded/lib/ruby/gems/3.1.0/gems/chef-powershell-18.0.1/lib/chef-powershell/powershell.rb:45:in `initialize'
	from C:/opscode/chef/embedded/lib/ruby/gems/3.1.0/gems/chef-powershell-18.0.1/lib/chef-powershell/powershell_exec.rb:116:in `new'

Analysis

Chef::ReservedNames::Win32::Security.open_process_token passes a unsigned long and Chef::ReservedNames::Win32::Process.get_current_process the actual HANDLE from GetCurrentProcess()... these finalize properly, because they are compared as numerical values in handle == GetCurrentProcess().

Chef::ReservedNames::Win32::Security.logon_user passes the result of FFI::Buffer#read_pointer to Handle.new instead, which results in an FFI::Pointer being stored as the handle.

Prior to Ruby 3.1/Chef 18/UCRT, this mismatch was at least not as noisy as it is in the current versions of everything.

Solution

Use FFI::Buffer#read_ulong to prevent the 8-byte value from being interpreted as a Ruby memory object so that Ruby will assume it's comparing a primitive 8-byte value to the return value of GetCurrentProcess(). While HANDLE is a void * in Windows, Ruby has no type information or heap access to know what to do with the memory.

Related Issue

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)
Chore (non-breaking change that does not add functionality or fix an issue)