[ViewVC] Contents of: cvs/libptytty/README

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

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 eg/ directory, which currently contains the c-sample.c file
    that spawns a login shell from C using libptytty.

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 "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.

SECURITY CONSIDERATIONS
    *It is of paramount importance that you at least read the following
    paragraph!*

    If you write 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 whether 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" (and possibly
    "ptytty::sanitise_stdfd") are more useful.

C++ INTERFACE: THE ptytty CLASS
  STATIC METHODS
    ptytty::init ()
        The default way to initialise libptytty. Must be called immediately
        as the first thing in the "main" function, or earlier e.g. during
        static construction time. The earlier, the better.

        This method calls "sanitise_stdfd" and then checks whether 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 inconvenient 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.

    ptytty::drop_privileges ()
        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.

    ptytty::sanitise_stdfd ()
        Checks whether file descriptors 0, 1 and 2 (stdin, stdout and
        stderr) are valid (open) and, if not, connects them to /dev/tty or
        /dev/null if possible (and aborts otherwise). This is necessary
        because libptytty might want to output error messages to those
        descriptors, which at the time of outputting the error message,
        might be connected to something unsuitable opened by the
        unsuspecting program itself (this can be a security issue).

    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 convenience 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 successful and -1 otherwise. This method
        is only exposed for your convenience 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 whether the
        session is associated with a login, which influences whether 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),
        this tries to enable this discipline 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 ()".

    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 ()".

    int ptytty_pty (PTYTTY ptytty)
        Return the pty file descriptor. See "pty->pty".

    int ptytty_tty (PTYTTY ptytty)
        Return the tty file descriptor. See "pty->tty".

    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".

    int ptytty_make_controlling_tty (PTYTTY ptytty)
        See "pty->make_controlling_tty".

    void ptytty_set_utf8_mode (PTYTTY ptytty, int on)
        See "pty->set_utf8_mode".

    void ptytty_drop_privileges ()
        See "ptytty::drop_privileges".

    void ptytty_use_helper ()
        See "ptytty::use_helper".

BUGS
    You kiddin'?

AUTHORS
    Emanuele Giaquinta <e.giaquinta@glauco.it>, Marc Alexander Lehmann
    <rxvt-unicode@schmorp.de>.

Revision:	1.7
Committed:	Wed Dec 21 00:48:52 2011 UTC (12 years, 4 months ago) by sf-exg
Branch:	MAIN
CVS Tags:	rxvt-unicode-rel-9_20, rxvt-unicode-rel-9_21, rel-9_14, rxvt-unicode-rel-9_19, rxvt-unicode-rel-9_18, rxvt-unicode-rel-9_17, rel-1_5, rxvt-unicode-rel-9_16, rel-1_7, rxvt-unicode-rel-9_15, rel-1_6
Changes since 1.6:	+27 -15 lines
Log Message:	Regenerate libptytty.3 and README.
#	Content
1	NAME
2	libptytty - OS independent and secure pty/tty and utmp/wtmp/lastlog
3	handling
4
5	SYNOPSIS
6	cc ... -lptytty
7
8	#include <libptytty.h>
9
10
11	// C++
12	ptytty *pty = ptytty::create ();
13
14	if (!pty->get ())
15	// error allocating pty
16
17	if (we want utmp)
18	pty->login (process_pid, 0, "remote.host");
19	else if (we want utmp AND wtmp/lastlog)
20	pty->login (process_pid, 1, "remote.host");
21
22	// we are done with it
23	delete pty;
24
25
26	// C
27	PTYTTY pty = ptytty_create ();
28
29	if (!ptytty_get (pty))
30	// error allocating pty
31
32	if (we want utmp)
33	ptytty_login (pty, process_pid, 0, "remote.host");
34	else if (we want utmp AND wtmp/lastlog)
35	ptytty_login (pty, process_pid, 1, "remote.host");
36
37	// we are done with it
38	ptytty_delete (pty);
39
40	See also the eg/ directory, which currently contains the c-sample.c file
41	that spawns a login shell from C using libptytty.
42
43	DESCRIPTION
44	Libptytty is a small library that offers pseudo-tty management in an
45	OS-independent way. It was created out of frustration over the many
46	differences of pty/tty handling in different operating systems for the
47	use inside "rxvt-unicode".
48
49	In addition to offering mere pty/tty management, it also offers session
50	database support (utmp and optional wtmp/lastlog updates for login
51	shells).
52
53	It also supports fork'ing after startup and dropping privileges in the
54	calling process, so in case the calling process gets compromised by the
55	user starting the program there is less to gain, as only the helper
56	process runs with privileges (e.g. setuid/setgid), which reduces the
57	area of attack immensely.
58
59	Libptytty is written in C++, but it also offers a C-only API.
60
61	SECURITY CONSIDERATIONS
62	*It is of paramount importance that you at least read the following
63	paragraph!*
64
65	If you write a typical terminal-like program that just wants one or more
66	ptys, you should call the "ptytty::init ()" method (C: "ptytty_init ()"
67	function) as the very first thing in your program:
68
69	int main (int argc, char *argv[])
70	{
71	// do nothing here
72	ptytty::init ();
73	// in C: ptytty_init ();
74
75	// initialise, parse arguments, etc.
76	}
77
78	This checks whether the program runs setuid or setgid. If yes then it
79	will fork a helper process and drop privileges.
80
81	Some programs need finer control over if and when this helper process is
82	started, and if and how to drop privileges. For those programs, the
83	methods "ptytty::use_helper" and "ptytty::drop_privileges" (and possibly
84	"ptytty::sanitise_stdfd") are more useful.
85
86	C++ INTERFACE: THE ptytty CLASS
87	STATIC METHODS
88	ptytty::init ()
89	The default way to initialise libptytty. Must be called immediately
90	as the first thing in the "main" function, or earlier e.g. during
91	static construction time. The earlier, the better.
92
93	This method calls "sanitise_stdfd" and then checks whether the
94	program runs with setuid/setgid permissions and, if yes, spawns a
95	helper process for pty/tty management. It then drops the privileges
96	completely, so the actual program runs without setuid/setgid
97	privileges.
98
99	ptytty::use_helper ()
100	Tries to start a helper process that retains privileges even when
101	the calling process does not. This is usually called from
102	"ptytty::init" when it detects that the program is running setuid or
103	setgid, but can be called manually if it is inconvenient to drop
104	privileges at startup, or when you are not running setuid/setgid but
105	want to drop privileges (e.g. when running as a root-started
106	daemon).
107
108	This method will try not to start more than one helper process. The
109	same helper process can usually be used both from the process
110	starting it and all its fork'ed (not exec'ed) children.
111
112	ptytty::drop_privileges ()
113	Drops privileges completely, i.e. sets real, effective and saved
114	user id to the real user id. Also aborts if this cannot be achieved.
115	Useful to make sure that the process doesn't run with special
116	privileges.
117
118	ptytty::sanitise_stdfd ()
119	Checks whether file descriptors 0, 1 and 2 (stdin, stdout and
120	stderr) are valid (open) and, if not, connects them to /dev/tty or
121	/dev/null if possible (and aborts otherwise). This is necessary
122	because libptytty might want to output error messages to those
123	descriptors, which at the time of outputting the error message,
124	might be connected to something unsuitable opened by the
125	unsuspecting program itself (this can be a security issue).
126
127	bool success = ptytty::send_fd (int socket, int fd)
128	Utility method to send a file descriptor over a unix domain socket.
129	Returns true if successful, false otherwise. This method is only
130	exposed for your convenience and is not required for normal
131	operation.
132
133	int fd = ptytty::recv_fd (int socket)
134	Utility method to receive a file descriptor over a unix domain
135	socket. Returns the fd if successful and -1 otherwise. This method
136	is only exposed for your convenience and is not required for normal
137	operation.
138
139	ptytty *pty = ptytty::create ()
140	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	DYNAMIC/SESSION-RELATED DATA MEMBERS AND METHODS
147	int pty_fd = pty->pty
148	int tty_fd = pty->tty
149	These members contain the pty and tty file descriptors,
150	respectively. They initially contain -1 until a successful to
151	"ptytty::get".
152
153	bool success = pty->get ()
154	Tries to find, allocate and initialise a new pty/tty pair. Returns
155	"true" when successful.
156
157	pty->login (int cmd_pid, bool login_shell, const char *hostname)
158	Creates an entry in the systems session database(s) (utmp, wtmp,
159	lastlog). "cmd_pid" must be the pid of the process representing the
160	session (such as the login shell), "login_shell" defines whether the
161	session is associated with a login, which influences whether wtmp
162	and lastlog entries are created, and "hostname" should identify the
163	"hostname" the user logs in from, which often is the value of the
164	"DISPLAY" variable or tty line in case of local logins.
165
166	Calling this method is optional. A session starts at the time of the
167	login call and extends until the ptytty object is destroyed.
168
169	pty->close_tty ()
170	Closes the tty. Useful after forking in the parent/pty process.
171
172	bool success = pty->make_controlling_tty ()
173	Tries to make the pty/tty pair the controlling terminal of the
174	current process. Useful after forking in the child/tty process.
175
176	pty->set_utf8_mode (bool on)
177	On systems supporting special UTF-8 line disciplines (e.g. Linux),
178	this tries to enable this discipline for the given pty. Can be
179	called at any time to change the mode.
180
181	C INTERFACE: THE ptytty FAMILY OF FUNCTIONS
182	ptytty_init ()
183	See "ptytty::init ()".
184
185	PTYTTY ptytty_create ()
186	Creates a new opaque PTYTTY object and returns it. Do not try to
187	access it in any way except by testing it for truthness (e.g. "if
188	(pty) ...."). See "ptytty::create ()".
189
190	int ptytty_pty (PTYTTY ptytty)
191	Return the pty file descriptor. See "pty->pty".
192
193	int ptytty_tty (PTYTTY ptytty)
194	Return the tty file descriptor. See "pty->tty".
195
196	void ptytty_delete (PTYTTY ptytty)
197	Destroys the PTYTTY object, freeing the pty/tty pair and cleaning up
198	the utmp/wtmp/lastlog databases, if initialised/used. Same as
199	"delete pty" in C++.
200
201	int ptytty_get (PTYTTY ptytty)
202	See "pty->get", returns 0 in case of an error, non-zero otherwise.
203
204	void ptytty_login (PTYTTY ptytty, int cmd_pid, bool login_shell, const
205	char *hostname)
206	See "pty->login".
207
208	void ptytty_close_tty (PTYTTY ptytty)
209	See "pty->close_tty".
210
211	int ptytty_make_controlling_tty (PTYTTY ptytty)
212	See "pty->make_controlling_tty".
213
214	void ptytty_set_utf8_mode (PTYTTY ptytty, int on)
215	See "pty->set_utf8_mode".
216
217	void ptytty_drop_privileges ()
218	See "ptytty::drop_privileges".
219
220	void ptytty_use_helper ()
221	See "ptytty::use_helper".
222
223	BUGS
224	You kiddin'?
225
226	AUTHORS
227	Emanuele Giaquinta <e.giaquinta@glauco.it>, Marc Alexander Lehmann
228	<rxvt-unicode@schmorp.de>.
229