s3: smbd: Inside filename_convert_dirfsp_nosymlink() ensure the returned smb_fname...

s3: smbd: Inside filename_convert_dirfsp_nosymlink() ensure the returned smb_fname is always allocated off mem_ctx.

Without this, if we just return smb_fname_rel->fsp->fsp_name as the smb_fname
then we return something allocated off fsp (which itself is allocated off
the conn struct), not the passed in talloc_ctx.

Do this for both non-stream and stream returns.

This matters for two reasons.

1). If we error out after calling filename_convert_dirfsp()
but before getting to the code inside create_file_unixpath()
that takes ownership of the passed in smb_fname->fsp we will
leak the fsp as the destructor for smb_fname that closes the
fsp will never fire on return to the client, as smb_fname is
owned by smb_fname->fsp, not the talloc_tos() context.

2). Some uses of filename_convert() expect to be able
to TALLOC_FREE the returned smb_fname once they've successfully
called SMB_VFS_CREATE_FILE() as they consider the passed in smb_fname
no longer used. It would be nice to be able to just change
filename_convert() -> filename_convert_dirfsp() without
having to change the lifetime handling of smb_fname.

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>