[Bug 37834] New: RtlSetCurrentDirectory_U prepends "UNC\" for network paths; the resulting path is invalid

https://bugs.winehq.org/show_bug.cgi?id=37834

Bug ID: 37834
           Summary: RtlSetCurrentDirectory_U prepends "UNC" for network
                    paths; the resulting path is invalid
           Product: Wine
           Version: 1.7.33
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: minor
          Priority: P2
         Component: ntdll
          Assignee: [e-mail]
          Reporter: [e-mail]
      Distribution: ---

Created attachment 50382
  --> https://bugs.winehq.org/attachment.cgi?id=50382
cmd.exe output showing how UNC\ gets prepended when running cd \server\share

Calling RtlSetCurrentDirectory_U with a network share argument like
"\server\share" sets the current directory to "UNC\server\share". Subsequent
calls to GetCurrentDirectory will return the modified path.
The resulting path is invalid and unusable: attempting to read the directory or
writing a file to it results in ERROR_PATH_NOT_FOUND.
The bug can be reproduced using the internal command prompt, as seen in the
attachment.
> From what I've gathered from the source code, RtlSetCurrentDirectory_U calls

RtlDosPathNameToNtPathName_U, which prepends UncPfxW to the supplied path. The
last edits to dlls/ntdll/path.c were made in 2003-2004.

I stumbled across this behavior while investigating why Total Commander cannot
copy files to network shares. The sequence of calls in Total Commander is:
SetCurrentDirectory to the network path, then GetCurrentDirectory (which
returns the modified path in the form "UNC\server\share") and then it builds
the destination parameter by concatenating this path with the destination file
name. This gets passed to CopyFileEx, which fails with ERROR_PATH_NOT_FOUND
because of the "UNC" prefix.