libptytty - OS independent and secure pty/tty and utmp/wtmp/lastlog handling
cc ... -lptytty
#include <libptytty.h>
// C++ ptytty *pty = ptytty::create ();
if (!pty->get ())
// error allocating pty
if (we want utmp)
pty->login (process_pid, 0, "remote.host");
else if (we want utmp AND wtmp/lastlog)
pty->login (process_pid, 1, "remote.host");
// we are done with it delete pty;
// C PTYTTY pty = ptytty_create ();
if (!ptytty_get (pty))
// error allocating pty
if (we want utmp)
ptytty_login (pty, process_pid, 0, "remote.host");
else if (we want utmp AND wtmp/lastlog)
ptytty_login (pty, process_pid, 1, "remote.host");
// we are done with it ptytty_delete (pty);
See also the eg/ directory, which currently contains the c-sample.c file that spawns a loginshell from C using libptytty.
Libptytty is a small library that offers pseudo-tty management in an
OS-independent way. It was created out of frustration over the many
differences of pty/tty handling in different operating systems for the use
inside rxvt-unicode.
In addition to offering mere pty/tty management, it also offers session database support (utmp and optional wtmp/lastlog updates for login shells).
It also supports fork'ing after startup and dropping privileges in the calling process, so in case the calling process gets compromised by the user starting the program there is less to gain, as only the helper process runs with privileges (e.g. setuid/setgid), which reduces the area of attack immensely.
Libptytty is written in C++, but it also offers a C-only API.
It is of paramount importance that you at least read the following paragraph! >
If you are a typical terminal-like program that just wants one or more
ptys, you should call the ptytty::init () method (C: ptytty_init ()
function) as the very first thing in your program:
int main (int argc, char *argv[])
{
// do nothing here
ptytty::init ();
// in C: ptytty_init ();
// initialise, parse arguments, etc.
}
This checks wether the program runs setuid or setgid. If yes then it will fork a helper process and drop privileges.
Some programs need finer control over if and when this helper process
is started, and if and how to drop privileges. For those programs, the
methods ptytty::use_helper and ptytty::drop_privileges are more
useful.
The default way to initialise libptytty. Must be called imemdiately as
the first thing in the main function, or earlier e.g. during static
construction time. The earlier, the better.
This method checks wether the program runs with setuid/setgid permissions and, if yes, spawns a helper process for pty/tty management. It then drops the privileges completely, so the actual program runs without setuid/setgid privileges.
Tries to start a helper process that retains privileges even when the
calling process does not. This is usually called from ptytty::init when
it detects that the program is running setuid or setgid, but can be called
manually if it is inconvinient to drop privileges at startup, or when
you are not running setuid/setgid but want to drop privileges (e.g. when
running as a root-started daemon).
This method will try not to start more than one helper process. The same helper process can usually be used both from the process starting it and all its fork'ed (not exec'ed) children.
Drops privileges completely, i.e. sets real, effective and saved user id to the real user id. Also aborts if this cannot be achieved. Useful to make sure that the process doesn't run with special privileges.
Utility method to send a file descriptor over a unix domain socket. Returns true if successful, false otherwise. This method is only exposed for your convinience and is not required for normal operation.
Utility method to receive a file descriptor over a unix domain
socket. Returns the fd if sucecssful and -1 otherwise. This method
is only exposed for your convinience and is not required for normal
operation.
Creates new ptytty object. Creation does not yet do anything besides allocating the structure.
A static method is used because the actual ptytty implementation can differ at runtime, so you need a dynamic object creation facility.
These members contain the pty and tty file descriptors, respectively. They
initially contain -1 until a successful to ptytty::get.
Tries to find, allocate and initialise a new pty/tty pair. Returns true
when successful.
Creates an entry in the systems session database(s) (utmp, wtmp, lastlog).
cmd_pid must be the pid of the process representing the session
(such as the login shell), login_shell defines wether the session is
associated with a login, which influences wether wtmp and lastlog entries
are created, and hostname should identify the ``hostname'' the user logs
in from, which often is the value of the DISPLAY variable or tty line
in case of local logins.
Calling this method is optional. A session starts at the time of the login call and extends until the ptytty object is destroyed.
Closes the tty. Useful after forking in the parent/pty process.
Tries to make the pty/tty pair the controlling terminal of the current process. Useful after forking in the child/tty process.
On systems supporting special UTF-8 line disciplines (e.g. Linux), this tries to enable this discipline for the given pty. Can be called at any time to change the mode.
See ptytty::init ().
=item PTYTTY ptytty_create ()
Creates a new opaque PTYTTY object and returns it. Do not try to access it
in any way except by testing it for truthness (e.g. if (pty) ....). See
ptytty::create ().
Return the pty file descriptor. See pty->pty.
=item int ptytty_tty (PTYTTY ptytty)
Return the tty file descriptor. See pty->tty.
=item void ptytty_delete (PTYTTY ptytty)
Destroys the PTYTTY object, freeing the pty/tty pair and cleaning up the
utmp/wtmp/lastlog databases, if initialised/used. Same as delete pty in
C++.
See pty->get, returns 0 in case of an error, non-zero otherwise.
See pty->login.
See pty->close_tty.
=item int ptytty_make_controlling_tty (PTYTTY ptytty)
=item void ptytty_set_utf8_mode (PTYTTY ptytty, int on)
See pty->set_utf8_mode.
See ptytty::drop_privileges.
=item void ptytty_use_helper ()
See ptytty::use_helper.
You kiddin'?