Don't log to an invalid file

[smashery]

This fixes a bug in the debug logging behaviour in C Meterp on Windows. When MeterpreterDebugBuild was set to true, but no MeterpreterDebugLogging value was set, the call to init_logging would fail. A bug existed in the handling of this. The log_to_file method expected the global value hFile to be NULL when there was no logging; however CreateFileW returns INVALID_HANDLE_VALUE. As a result, all future calls to dprintf tried to write to an invalid file handle.

This was creating issues when GetLastError() was called after dprintf - the last error value was polluted. One way of reproducing this is to run the execute_dotnet_assembly module (misdiagnosed in #746).

• Run with no debugging stuff should suceed.
• Run with MeterpreterDebugBuild=true will fail (the handle is invalid).
• Run with MeterpreterDebugBuild=true and also MeterpreterDebugLogging set to a valid value should succeed.

This resolves the issue by correctly setting hFile.

There's probably more work to be done to make sure that any GetLastError is called before any dprintf, since theoretically it is possible for that to change GetLastError (e.g. failed file write).

[smcintyre-r7]

Thanks for your work tracking this down and fixing it!

Alright I was able to reproduce the original issue and verify this fixes it. Going to combine some steps for reproducing it here for posterity.

1. Obtain a x86 Meterpreter session on a 64-bit host
2. Background the session and use the post/windows/manage/execute_dotnet_assembly module
3. Set the SESSION and DOTNET_EXE datastore options
4. Run the module with run technique=SPAWN_AND_INJECT process=c:\\windows\\sysnative\\notepad.exe verbose=true

Either see a failure, or see that the executable ran correctly. I use Rubeus.exe as my executable, so a successful run was just the help menu.