ptylogin(n)                                           ptylogin(n)



NAME
       ptylogin  - replacement  for  mgetty's login.config rlogin
       hack fixing security and denial of service  problems  with
       ownership of tty.

SYNOPSIS
       ptylogin login-name

DESCRIPTION
       This manual page documents ptylogin.  ptylogin is launched
       from mgetty's login.config configuration  file  with  root
       priviledges.  It  opens a pty slave/master pair, and forks
       /bin/login.  It ensures data stream is 8 bit.  This  means
       that  the  user which logs in will not be connected to the
       tty of the modem, but to a pty.  The  pty  slave  will  be
       owned  (because  of /bin/login) by the logged-on user. The
       modem tty will be owned by root, and permissions  will  be
       rw  access  for  root  only. That tty doesn't need, by the
       way, to be logged-in. When the modem disconnects, the mas-
       ter pty is closed and a SIGHUP is transmitted to the other
       side. The worse that the user can then do is  leave  their
       process on if they disabled the SIGHUP. However they can't
       access the modem device nor reopen it.

       For enhanced security we assume the escape sequence of the
       modem  is  disabled, and that a modem hangup from the user
       calling our local modem causes a SIGHUP  to  the  ptylogin
       process.

       Please look at the Paranoid Secure Port Implementation RCS
       revision SPEC,v 1.6 1999/01/05 08:41:46 or later  for  all
       details of the problem ptylogin fixes (it's quite tricky).


   OPTIONS
       in-name This must be a 8 char maximum login name to launch
       login  into,  must exist, and may not contain - or spaces.
       As /bin/login is not launched through system() but instead
       with exec(), common attacks like semicolons or other sepa-
       rators cannot happen.


EXAMPLES
       The login.config could be configured like this:

       *       root  dialin  /usr/bin/ptylogin @

       Note that if you specify users which bypass this  default,
       for  example  for  PPP, FTN or UUCP, you would enter some-
       thing like

       uu*     -       -       /bin/login.one @

       WARNING: You must use a login program which doesn't  allow
       more than one retry. Else interactive users can bypass the
       default ptylogin restricted login.


AUTHOR
       Marc SCHAEFER <schaefer@alphanet.ch>


VERSION
       Manual version 1.0 PV001 documents ptylogin version 1.0


NOTES
BUGS
       Please look at the source.


TODO
BASED-ON
       - An idea to simplify rlogin and still  fix  the  problems
       from
            Theodore Y. Ts'o <tytso@MIT.EDU>

       - rlogind and rlogin code from Linux NetKit-0.09

       -    virtual_connection   from   Marc   SCHAEFER   <schae-
       fer@alphanet.ch>


HISTORY
COPYRIGHT
       This work is (C) Marc SCHAEFER 1999 and has been  done  in
       my free time. However, it is placed under the GPL and thus
       any use is authorized as long as you do not prevent others
       from  using  it  and accessing the original source code or
       your extensions.


DISCLAIMER
       The author hereby disclaims any warranty, either expressed
       or implied, regarding this software and documentation. The
       fact that this software attempts to fix a security vulner-
       ability  doesn't mean that it doesn't have any vulnerabil-
       ity, some which could be more  serious  than  the  one  it
       tries to fix.



                         10 january 1999              ptylogin(n)