libptytty/doc/libptytty.3.pod

=head1 NAME

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

=head1 SYNOPSIS

   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);


=head1 DESCRIPTION

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 C<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.

=head1 SECURITY CONSIDERATIONS

I<< B<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 C<ptytty::init ()> method (C: 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 C<ptytty::use_helper> and C<ptytty::drop_privileges> are more
useful.

=head1 C++ INTERFACE: THE ptytty CLASS

=head2 STATIC METHODS

=over 4

=item ptytty::init ()

The default way to initialise libptytty. Must be called imemdiately as
the first thing in the C<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.

=item ptytty::use_helper ()

Tries to start a helper process that retains privileges even when the
calling process does not. This is usually called from C<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

=item 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.

=item 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.

=item 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 C<-1> otherwise. This method
is only exposed for your convinience and is not required for normal
operation.

=item 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.

=back


=head2 DYNAMIC/SESSION-RELATED DATA MEMBERS AND METHODS

=over 4

=item int pty_fd = pty->pty

=item int tty_fd = pty->tty

These members contain the pty and tty file descriptors, respectively. They
initially contain C<-1> until a successful to C<ptytty::get>.

=item bool success = pty->get ()

Tries to find, allocate and initialise a new pty/tty pair. Returns C<true>
when successful.

=item pty->login (int cmd_pid, bool login_shell, const char *hostname)

Creates an entry in the systems session database(s) (utmp, wtmp, lastlog).
C<cmd_pid> must be the pid of the process representing the session
(such as the login shell), C<login_shell> defines wether the session is
associated with a login, which influences wether wtmp and lastlog entries
are created, and C<hostname> should identify the "hostname" the user logs
in from, which often is the value of the C<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.

=item pty->close_tty ()

Closes the tty. Useful after forking in the parent/pty process.

=item 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.

=item 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.

=back


=head1 C INTERFACE: THE ptytty FAMILY OF FUNCTIONS

=over 4

=item ptytty_init ()

See C<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. C<if (pty) ....>). See
C<ptytty::create ()>.

=item int ptytty_pty (PTYTTY ptytty)

Return the pty file descriptor. See C<< pty->pty >>.
   
=item int ptytty_tty (PTYTTY ptytty)

Return the tty file descriptor. See C<< 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 C<delete pty> in
C++.

=item int ptytty_get (PTYTTY ptytty)

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

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

See C<< pty->login >>.

=item void ptytty_close_tty (PTYTTY ptytty)

See C<< pty->close_tty >>.
   
=item int ptytty_make_controlling_tty (PTYTTY ptytty)

See C<< pty->make_controlling_tty >>.
   
=item void ptytty_set_utf8_mode (PTYTTY ptytty, int on)

See C<< pty->set_utf8_mode >>.

=item void ptytty_drop_privileges ()

See C<< ptytty::drop_privileges >>.
   
=item void ptytty_use_helper ()

See C<< ptytty::use_helper >>.

=back


=head1 BUGS

You kiddin'?

=head1 AUTHORS

Emanuele Giaquinta L<< <e.giaquinta@glauco.it> >>, Marc Alexander Lehmann
L<< <rxvt-unicode@schmorp.de> >>.
Revision:	1.9
Committed:	Mon Jan 23 12:37:09 2006 UTC (20 years, 7 months ago) by root
Branch:	MAIN
Changes since 1.8:	+51 -2 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3	root	1.2	libptytty - OS independent and secure pty/tty and utmp/wtmp/lastlog handling
4	root	1.1
5			=head1 SYNOPSIS
6
7	root	1.9	cc ... -lptytty
8
9			#include <libptytty.h>
10
11
12			// C++
13			ptytty *pty = ptytty::create ();
14
15			if (!pty->get ())
16			// error allocating pty
17
18			if (we want utmp)
19			pty->login (process_pid, 0, "remote.host");
20			else if (we want utmp AND wtmp/lastlog)
21			pty->login (process_pid, 1, "remote.host");
22
23			// we are done with it
24			delete pty;
25
26
27			// C
28			PTYTTY pty = ptytty_create ();
29
30			if (!ptytty_get (pty))
31			// error allocating pty
32
33			if (we want utmp)
34			ptytty_login (pty, process_pid, 0, "remote.host");
35			else if (we want utmp AND wtmp/lastlog)
36			ptytty_login (pty, process_pid, 1, "remote.host");
37
38			// we are done with it
39			ptytty_delete (pty);
40
41
42	root	1.1
43			=head1 DESCRIPTION
44
45	root	1.9	Libptytty is a small library that offers pseudo-tty management in an
46			OS-independent way. It was created out of frustration over the many
47			differences of pty/tty handling in different operating systems for the use
48			inside C<rxvt-unicode>.
49
50			In addition to offering mere pty/tty management, it also offers session
51			database support (utmp and optional wtmp/lastlog updates for login
52			shells).
53
54			It also supports fork'ing after startup and dropping privileges in the
55			calling process, so in case the calling process gets compromised by the
56			user starting the program there is less to gain, as only the helper
57			process runs with privileges (e.g. setuid/setgid), which reduces the area
58			of attack immensely.
59
60			Libptytty is written in C++, but it also offers a C-only API.
61	root	1.6
62	root	1.4	=head1 SECURITY CONSIDERATIONS
63	root	1.3
64	ayin	1.5	I<< B<It is of paramount importance that you at least read the following
65	root	1.4	paragraph!> >>
66
67			If you are a typical terminal-like program that just wants one or more
68	root	1.8	ptys, you should call the C<ptytty::init ()> method (C: C<ptytty_init ()>
69	root	1.7	function) as the very first thing in your program:
70	root	1.4
71			int main (int argc, char *argv[])
72			{
73			// do nothing here
74			ptytty::init ();
75	root	1.7	// in C: ptytty_init ();
76	root	1.4
77			// initialise, parse arguments, etc.
78			}
79
80			This checks wether the program runs setuid or setgid. If yes then it will
81			fork a helper process and drop privileges.
82
83	root	1.6	Some programs need finer control over if and when this helper process
84			is started, and if and how to drop privileges. For those programs, the
85			methods C<ptytty::use_helper> and C<ptytty::drop_privileges> are more
86			useful.
87
88	root	1.7	=head1 C++ INTERFACE: THE ptytty CLASS
89	root	1.6
90			=head2 STATIC METHODS
91
92			=over 4
93
94			=item ptytty::init ()
95
96			The default way to initialise libptytty. Must be called imemdiately as
97			the first thing in the C<main> function, or earlier e.g. during static
98			construction time. The earlier, the better.
99
100			This method checks wether the program runs with setuid/setgid permissions
101			and, if yes, spawns a helper process for pty/tty management. IT then
102			drops the privileges completely, so the actual program runs without
103			setuid/setgid privileges.
104
105			=item ptytty::use_helper ()
106
107	root	1.7	Tries to start a helper process that retains privileges even when the
108			calling process does not. This is usually called from C<ptytty::init> when
109			it detects that the program is running setuid or setgid, but can be called
110			manually if it is inconvinient to drop privileges at startup, or when
111			you are not running setuid/setgid but want to drop privileges (e.g. when
112			running as a root-started daemon).
113
114			This method will try not to start more than one helper process. The same
115			helper process cna usually be used form the process starting it an all its
116			fork'ed (not exec'ed) children
117	root	1.6
118			=item ptytty::drop_privileges ()
119
120			Drops privileges completely, i.e. sets real, effective and saved user id
121			to the real user id. Also aborts if this cnanot be achieved. Useful to
122			make sure that the process doesn't run with special privileges.
123
124			=item bool success = ptytty::send_fd (int socket, int fd)
125
126			Utility method to send a file descriptor over a unix domain
127			socket. Returns true if successful, false otherwise. This method is only
128			exposed for your convinience and is not required for normal operation.
129
130			=item int fd = ptytty::recv_fd (int socket)
131
132			Utility method to receive a file descriptor over a unix domain
133			socket. Returns the fd if sucecssful and C<-1> otherwise. This method
134			is only exposed for your convinience and is not required for normal
135			operation.
136	root	1.4
137	root	1.6	=item ptytty *pty = ptytty::create ()
138	root	1.3
139	root	1.6	Creates new ptytty object. Creation does not yet do anything besides
140			allocating the structure.
141
142			A static method is used because the actual ptytty implementation can
143			differ at runtime, so you need a dynamic object creation facility.
144
145			=back
146
147	root	1.7
148	root	1.6	=head2 DYNAMIC/SESSION-RELATED DATA MEMBERS AND METHODS
149	root	1.1
150			=over 4
151
152	root	1.6	=item int pty_fd = pty->pty
153
154			=item int tty_fd = pty->tty
155
156			These members contain the pty and tty file descriptors, respectively. They
157			initially contain C<-1> until a successful to C<ptytty::get>.
158
159			=item bool success = pty->get ()
160
161			Tries to find, allocate and initialise a new pty/tty pair. Returns C<true>
162			when successful.
163
164			=item pty->login (int cmd_pid, bool login_shell, const char *hostname)
165
166			Creates an entry in the systems session database(s) (utmp, wtmp, lastlog).
167			C<cmd_pid> must be the pid of the process representing the session
168			(such as the login shell), C<login_shell> defines wether the session is
169			associated with a login, which influences wether wtmp and lastlog entries
170			are created, and C<hostname> should identify the "hostname" the user logs
171			in from, which often is the value of the C<DISPLAY> variable or tty line
172			in case of local logins.
173
174			Calling this method is optional. A session starts at the time of the login
175			call and extends until the ptytty object is destroyed.
176
177			=item pty->close_tty ()
178
179			Closes the tty. Useful after forking in the parent/pty process.
180
181			=item bool success = pty->make_controlling_tty ()
182
183			Tries to make the pty/tty pair the controlling terminal of the current
184			process. Useful after forking in the child/tty process.
185
186			=item pty->set_utf8_mode (bool on)
187	root	1.1
188	root	1.6	On systems supporting special UTF-8 line disciplines (e.g. Linux), tries
189			to enable it for the given pty. Can be called at any time to change the
190			mode.
191	root	1.1
192			=back
193
194	root	1.7
195			=head1 C INTERFACE: THE ptytty FAMILY OF FUNCTIONS
196
197			=over 4
198
199			=item ptytty_init ()
200
201			See C<ptytty::init ()>.
202
203			=item PTYTTY ptytty_create ()
204
205			Creates a new opaque PTYTTY object and returns it. Do not try to access it
206			in any way excecp by testing it for truthness (e.g. C<if (pty) ....>). See
207			C<ptytty::create ()>.
208
209			=item int ptytty_pty (PTYTTY ptytty)
210
211			Return the pty file descriptor. See C<< pty->pty >>.
212
213			=item int ptytty_tty (PTYTTY ptytty)
214
215			Return the tty file descriptor. See C<< pty->tty >>.
216
217			=item void ptytty_delete (PTYTTY ptytty)
218
219			Destroys the PTYTTY object, freeing the pty/tty pair and cleaning up the
220			utmp/wtmp/lastlog databases, if initialised/used. Same as C<delete pty> in
221			C++.
222
223			=item int ptytty_get (PTYTTY ptytty)
224
225			See C<< pty->get >>, returns 0 in case of an error, non-zero otherwise.
226
227			=item void ptytty_login (PTYTTY ptytty, int cmd_pid, bool login_shell, const char *hostname)
228
229			See C<< pty->login >>.
230
231			=item void ptytty_close_tty (PTYTTY ptytty)
232
233			See C<< pty->close_tty >>.
234
235			=item int ptytty_make_controlling_tty (PTYTTY ptytty)
236
237			See C<< pty->make_controlling_tty >>.
238
239			=item void ptytty_set_utf8_mode (PTYTTY ptytty, int on)
240
241			See C<< pty->set_utf8_mode >>.
242
243			=item void ptytty_drop_privileges ()
244
245			See C<< ptytty::drop_privileges >>.
246
247			=item void ptytty_use_helper ()
248
249			See C<< ptytty::use_helper >>.
250
251			=back
252
253
254	root	1.1	=head1 BUGS
255
256			You kiddin'?
257
258			=head1 AUTHORS
259
260			Emanuele Giaquinta L<< <e.giaquinta@glauco.it> >>, Marc Alexander Lehmann
261			L<< <rxvt-unicode@schmorp.de> >>.