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);

See also the F<eg/> directory, which currently contains the F<c-sample.c>
file that spawns a loginshell from C using libptytty.

=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:	1.12
Committed:	Wed Jan 25 11:14:26 2006 UTC (20 years, 7 months ago) by root
Branch:	MAIN
CVS Tags:	rel-0_1, rel-0_2
Changes since 1.11:	+2 -1 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	1.11	cc ... -lptytty
8	root	1.9
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	root	1.12	See also the F<eg/> directory, which currently contains the F<c-sample.c>
42			file that spawns a loginshell from C using libptytty.
43	root	1.1
44			=head1 DESCRIPTION
45
46	root	1.9	Libptytty is a small library that offers pseudo-tty management in an
47			OS-independent way. It was created out of frustration over the many
48			differences of pty/tty handling in different operating systems for the use
49			inside C<rxvt-unicode>.
50
51			In addition to offering mere pty/tty management, it also offers session
52			database support (utmp and optional wtmp/lastlog updates for login
53			shells).
54
55			It also supports fork'ing after startup and dropping privileges in the
56			calling process, so in case the calling process gets compromised by the
57			user starting the program there is less to gain, as only the helper
58			process runs with privileges (e.g. setuid/setgid), which reduces the area
59			of attack immensely.
60
61			Libptytty is written in C++, but it also offers a C-only API.
62	root	1.6
63	root	1.4	=head1 SECURITY CONSIDERATIONS
64	root	1.3
65	ayin	1.5	I<< B<It is of paramount importance that you at least read the following
66	root	1.4	paragraph!> >>
67
68			If you are a typical terminal-like program that just wants one or more
69	root	1.8	ptys, you should call the C<ptytty::init ()> method (C: C<ptytty_init ()>
70	root	1.7	function) as the very first thing in your program:
71	root	1.4
72			int main (int argc, char *argv[])
73			{
74			// do nothing here
75			ptytty::init ();
76	root	1.7	// in C: ptytty_init ();
77	root	1.4
78			// initialise, parse arguments, etc.
79			}
80
81			This checks wether the program runs setuid or setgid. If yes then it will
82			fork a helper process and drop privileges.
83
84	root	1.6	Some programs need finer control over if and when this helper process
85			is started, and if and how to drop privileges. For those programs, the
86			methods C<ptytty::use_helper> and C<ptytty::drop_privileges> are more
87			useful.
88
89	root	1.7	=head1 C++ INTERFACE: THE ptytty CLASS
90	root	1.6
91			=head2 STATIC METHODS
92
93			=over 4
94
95			=item ptytty::init ()
96
97			The default way to initialise libptytty. Must be called imemdiately as
98			the first thing in the C<main> function, or earlier e.g. during static
99			construction time. The earlier, the better.
100
101			This method checks wether the program runs with setuid/setgid permissions
102			and, if yes, spawns a helper process for pty/tty management. IT then
103			drops the privileges completely, so the actual program runs without
104			setuid/setgid privileges.
105
106			=item ptytty::use_helper ()
107
108	root	1.7	Tries to start a helper process that retains privileges even when the
109			calling process does not. This is usually called from C<ptytty::init> when
110			it detects that the program is running setuid or setgid, but can be called
111			manually if it is inconvinient to drop privileges at startup, or when
112			you are not running setuid/setgid but want to drop privileges (e.g. when
113			running as a root-started daemon).
114
115			This method will try not to start more than one helper process. The same
116			helper process cna usually be used form the process starting it an all its
117			fork'ed (not exec'ed) children
118	root	1.6
119			=item ptytty::drop_privileges ()
120
121			Drops privileges completely, i.e. sets real, effective and saved user id
122			to the real user id. Also aborts if this cnanot be achieved. Useful to
123			make sure that the process doesn't run with special privileges.
124
125			=item bool success = ptytty::send_fd (int socket, int fd)
126
127			Utility method to send a file descriptor over a unix domain
128			socket. Returns true if successful, false otherwise. This method is only
129			exposed for your convinience and is not required for normal operation.
130
131			=item int fd = ptytty::recv_fd (int socket)
132
133			Utility method to receive a file descriptor over a unix domain
134			socket. Returns the fd if sucecssful and C<-1> otherwise. This method
135			is only exposed for your convinience and is not required for normal
136			operation.
137	root	1.4
138	root	1.6	=item ptytty *pty = ptytty::create ()
139	root	1.3
140	root	1.6	Creates new ptytty object. Creation does not yet do anything besides
141			allocating the structure.
142
143			A static method is used because the actual ptytty implementation can
144			differ at runtime, so you need a dynamic object creation facility.
145
146			=back
147
148	root	1.7
149	root	1.6	=head2 DYNAMIC/SESSION-RELATED DATA MEMBERS AND METHODS
150	root	1.1
151			=over 4
152
153	root	1.6	=item int pty_fd = pty->pty
154
155			=item int tty_fd = pty->tty
156
157			These members contain the pty and tty file descriptors, respectively. They
158			initially contain C<-1> until a successful to C<ptytty::get>.
159
160			=item bool success = pty->get ()
161
162			Tries to find, allocate and initialise a new pty/tty pair. Returns C<true>
163			when successful.
164
165			=item pty->login (int cmd_pid, bool login_shell, const char *hostname)
166
167			Creates an entry in the systems session database(s) (utmp, wtmp, lastlog).
168			C<cmd_pid> must be the pid of the process representing the session
169			(such as the login shell), C<login_shell> defines wether the session is
170			associated with a login, which influences wether wtmp and lastlog entries
171			are created, and C<hostname> should identify the "hostname" the user logs
172			in from, which often is the value of the C<DISPLAY> variable or tty line
173			in case of local logins.
174
175			Calling this method is optional. A session starts at the time of the login
176			call and extends until the ptytty object is destroyed.
177
178			=item pty->close_tty ()
179
180			Closes the tty. Useful after forking in the parent/pty process.
181
182			=item bool success = pty->make_controlling_tty ()
183
184			Tries to make the pty/tty pair the controlling terminal of the current
185			process. Useful after forking in the child/tty process.
186
187			=item pty->set_utf8_mode (bool on)
188	root	1.1
189	root	1.6	On systems supporting special UTF-8 line disciplines (e.g. Linux), tries
190			to enable it for the given pty. Can be called at any time to change the
191			mode.
192	root	1.1
193			=back
194
195	root	1.7
196			=head1 C INTERFACE: THE ptytty FAMILY OF FUNCTIONS
197
198			=over 4
199
200			=item ptytty_init ()
201
202			See C<ptytty::init ()>.
203
204			=item PTYTTY ptytty_create ()
205
206			Creates a new opaque PTYTTY object and returns it. Do not try to access it
207			in any way excecp by testing it for truthness (e.g. C<if (pty) ....>). See
208			C<ptytty::create ()>.
209
210			=item int ptytty_pty (PTYTTY ptytty)
211
212			Return the pty file descriptor. See C<< pty->pty >>.
213
214			=item int ptytty_tty (PTYTTY ptytty)
215
216			Return the tty file descriptor. See C<< pty->tty >>.
217
218			=item void ptytty_delete (PTYTTY ptytty)
219
220			Destroys the PTYTTY object, freeing the pty/tty pair and cleaning up the
221			utmp/wtmp/lastlog databases, if initialised/used. Same as C<delete pty> in
222			C++.
223
224			=item int ptytty_get (PTYTTY ptytty)
225
226			See C<< pty->get >>, returns 0 in case of an error, non-zero otherwise.
227
228			=item void ptytty_login (PTYTTY ptytty, int cmd_pid, bool login_shell, const char *hostname)
229
230			See C<< pty->login >>.
231
232			=item void ptytty_close_tty (PTYTTY ptytty)
233
234			See C<< pty->close_tty >>.
235
236			=item int ptytty_make_controlling_tty (PTYTTY ptytty)
237
238			See C<< pty->make_controlling_tty >>.
239
240			=item void ptytty_set_utf8_mode (PTYTTY ptytty, int on)
241
242			See C<< pty->set_utf8_mode >>.
243
244			=item void ptytty_drop_privileges ()
245
246			See C<< ptytty::drop_privileges >>.
247
248			=item void ptytty_use_helper ()
249
250			See C<< ptytty::use_helper >>.
251
252			=back
253
254
255	root	1.1	=head1 BUGS
256
257			You kiddin'?
258
259			=head1 AUTHORS
260
261			Emanuele Giaquinta L<< <e.giaquinta@glauco.it> >>, Marc Alexander Lehmann
262			L<< <rxvt-unicode@schmorp.de> >>.