Addendum to commit 0a392b18.
The actual problem that existed all along was that the buffers being
validated with CsrValidateMessageBuffer() were not the correct ones!
What had to be checked is the string buffer **INSIDE** the UNICODE_STRING
structures! Indeed, it is these buffers that we are allocating on client side,
see 9b421af1/dll/win32/kernel32/client/dosdev.c (L324-L336)
Dedicated to Pierre Schweitzer.