.TH ptylogin 1 "10 january 1999"
.IX ptylogin
.SH NAME
ptylogin \-\ replacement for mgetty's login.config rlogin hack fixing
security and denial of service problems with ownership of tty.
.SH SYNOPSIS
.B ptylogin
login-name
.SH DESCRIPTION
This manual page documents
.BR ptylogin .
.B 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 master 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
.B 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).

.SS OPTIONS

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

.SH EXAMPLES

The login.config could be configured like this:

.I "*       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 something like

.I "uu*     \-       \-       /bin/login.one @"

.B 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.

.SH AUTHOR
Marc SCHAEFER <schaefer@alphanet.ch>

.SH VERSION
Manual version 1.0 PV001 documents ptylogin version 1.0

.SH NOTES

.SH BUGS
Please look at the source.

.SH TODO

.SH 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 <schaefer@alphanet.ch>

.SH HISTORY

.SH 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.

.SH 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 vulnerability doesn't mean
that it doesn't have any vulnerability, some which could be more
serious than the one it tries to fix.