Re: rm patch suggestion

[Marcus Brinkmann]

On Tue, May 07, 2002 at 10:50:13PM +0200, Oystein Viggen wrote:
> It seems that even if you open() a directory when it is not a
> translator, and then fchdir() into it, you will still end up inside any
> translator that is placed there in the meantime.  (I would expect to end
> up within the underlying directory, but no such luck.)

Oh, darn, from the source (man, read the source, man!):

int
_hurd_change_directory_port_from_fd (struct hurd_port *portcell, int fd)
{
  int ret;
  struct hurd_fd *d = _hurd_fd_get (fd);

  if (!d)
    return __hurd_fail (EBADF);

  HURD_CRITICAL_BEGIN;

  ret = HURD_PORT_USE (&d->port,
                       ({
                         int ret;
                         file_t dir = __file_name_lookup_under (port, ".",
                                                                0, 0);
                         if (dir == MACH_PORT_NULL)
                           ret = -1;
                         else
                           {
                             _hurd_port_set (portcell, dir);
                             ret = 0;
                           }
                         ret;
                       }));

  HURD_CRITICAL_END;

  return ret;
}

and:

int
__fchdir (fd)
     int fd;
{
  return _hurd_change_directory_port_from_fd (&_hurd_ports[INIT_PORT_CWDIR],
                                              fd);
}

So, it does indeed look up "." before it makes it the current directory.
(port cell would be CWDIR).

Just use setcwdir() from hurd.h, this should work.  I didn't find it
initially, because I stopped looking when I found the above function
(without looking at the implementation).

> This means that I can think of no safe way of changing into a directory
> owned by an untrusted user involving only "Unix space".  (Is this even
> desirable, or should we just accept it as a fact that traditional Unix
> features are unable to deal with Hurd specific features?)

Well, as Unix doesn't know about translators, it is not so important to find
a solution using only Unix interfaces.  The setcwdir() function should work
fine, it bypasses all checks and simply makes the file port your current
directory port.

Thanks,
Marcus

-- 
`Rhubarb is no Egyptian god.' Debian http://www.debian.org brinkmd@debian.org
Marcus Brinkmann              GNU    http://www.gnu.org    marcus@gnu.org
Marcus.Brinkmann@ruhr-uni-bochum.de
http://www.marcus-brinkmann.de