NAME

libptytty - OS independent and secure pty/tty and utmp/wtmp/lastlog handling

SYNOPSIS

   -lptytty

DESCRIPTION

TODO

SECURITY CONSIDERATIONS

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.

C++ INTERFACE: THE ptytty CLASS

STATIC METHODS

ptytty::init (): 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.
ptytty::use_helper (): 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 cna usually be used form the process starting it an all its fork'ed (not exec'ed) children
ptytty::drop_privileges (): Drops privileges completely, i.e. sets real, effective and saved user id to the real user id. Also aborts if this cnanot be achieved. Useful to make sure that the process doesn't run with special privileges.
bool success = ptytty::send_fd (int socket, int fd): 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.
int fd = ptytty::recv_fd (int socket): 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.
ptytty *pty = ptytty::create (): 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.

DYNAMIC/SESSION-RELATED DATA MEMBERS AND METHODS

int pty_fd = pty->pty
int tty_fd = pty->tty: These members contain the pty and tty file descriptors, respectively. They initially contain -1 until a successful to ptytty::get.
bool success = pty->get (): Tries to find, allocate and initialise a new pty/tty pair. Returns true when successful.
pty->login (int cmd_pid, bool login_shell, const char *hostname): 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.
pty->close_tty (): Closes the tty. Useful after forking in the parent/pty process.
bool success = pty->make_controlling_tty (): Tries to make the pty/tty pair the controlling terminal of the current process. Useful after forking in the child/tty process.
pty->set_utf8_mode (bool on): On systems supporting special UTF-8 line disciplines (e.g. Linux), tries to enable it for the given pty. Can be called at any time to change the mode.

C INTERFACE: THE ptytty FAMILY OF FUNCTIONS

ptytty_init ()

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 excecp by testing it for truthness (e.g. if (pty) ....). See ptytty::create ().

int ptytty_pty (PTYTTY ptytty)

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++.

int ptytty_get (PTYTTY ptytty)

See pty->get, returns 0 in case of an error, non-zero otherwise.

void ptytty_login (PTYTTY ptytty, int cmd_pid, bool login_shell, const char *hostname)

See pty->login.

void ptytty_close_tty (PTYTTY ptytty)

See pty->close_tty.


=item int ptytty_make_controlling_tty (PTYTTY ptytty)

See pty->make_controlling_tty.


=item void ptytty_set_utf8_mode (PTYTTY ptytty, int on)

See pty->set_utf8_mode.

void ptytty_drop_privileges ()

See ptytty::drop_privileges.


=item void ptytty_use_helper ()

See ptytty::use_helper.

BUGS

You kiddin'?

AUTHORS

Emanuele Giaquinta >, Marc Alexander Lehmann >.