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Revision: 1.4
Committed: Thu Feb 25 20:21:49 2016 UTC (8 years, 4 months ago) by root
Branch: MAIN
CVS Tags: rel-1_8, rxvt-unicode-rel-9_26, rxvt-unicode-rel-9_25, rxvt-unicode-rel-9_22
Changes since 1.3: +44 -23 lines
Log Message:
1.8

File Contents

# Content
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135 .IX Title "libptytty 3"
136 .TH libptytty 3 "2016-02-25" "1.8" "LIBPTYTTY"
137 .\" For nroff, turn off justification. Always turn off hyphenation; it makes
138 .\" way too many mistakes in technical documents.
139 .if n .ad l
140 .nh
141 .SH "NAME"
142 libptytty \- OS independent and secure pty/tty and utmp/wtmp/lastlog handling
143 .SH "SYNOPSIS"
144 .IX Header "SYNOPSIS"
145 .Vb 1
146 \& cc ... \-lptytty
147 \&
148 \& #include <libptytty.h>
149 \&
150 \&
151 \& // C++
152 \& ptytty *pty = ptytty::create ();
153 \&
154 \& if (!pty\->get ())
155 \& // error allocating pty
156 \&
157 \& if (we want utmp)
158 \& pty\->login (process_pid, 0, "remote.host");
159 \& else if (we want utmp AND wtmp/lastlog)
160 \& pty\->login (process_pid, 1, "remote.host");
161 \&
162 \& // we are done with it
163 \& delete pty;
164 \&
165 \&
166 \& // C
167 \& PTYTTY pty = ptytty_create ();
168 \&
169 \& if (!ptytty_get (pty))
170 \& // error allocating pty
171 \&
172 \& if (we want utmp)
173 \& ptytty_login (pty, process_pid, 0, "remote.host");
174 \& else if (we want utmp AND wtmp/lastlog)
175 \& ptytty_login (pty, process_pid, 1, "remote.host");
176 \&
177 \& // we are done with it
178 \& ptytty_delete (pty);
179 .Ve
180 .PP
181 See also the \fIeg/\fR directory, which currently contains the \fIc\-sample.c\fR
182 file that spawns a login shell from C using libptytty.
183 .SH "DESCRIPTION"
184 .IX Header "DESCRIPTION"
185 Libptytty is a small library that offers pseudo-tty management in an
186 OS-independent way. It was created out of frustration over the many
187 differences of pty/tty handling in different operating systems for the use
188 inside \f(CW\*(C`rxvt\-unicode\*(C'\fR.
189 .PP
190 In addition to offering mere pty/tty management, it also offers session
191 database support (utmp and optional wtmp/lastlog updates for login
192 shells).
193 .PP
194 It also supports fork'ing after startup and dropping privileges in the
195 calling process, so in case the calling process gets compromised by the
196 user starting the program there is less to gain, as only the helper
197 process runs with privileges (e.g. setuid/setgid), which reduces the area
198 of attack immensely.
199 .PP
200 Libptytty is written in \*(C+, but it also offers a C\-only \s-1API.\s0
201 .SH "SECURITY CONSIDERATIONS"
202 .IX Header "SECURITY CONSIDERATIONS"
203 \&\fI\f(BIIt is of paramount importance that you at least read the following
204 paragraph!\fI\fR
205 .PP
206 If you write a typical terminal-like program that just wants one or more
207 ptys, you should call the \f(CW\*(C`ptytty::init ()\*(C'\fR method (C: \f(CW\*(C`ptytty_init ()\*(C'\fR
208 function) as the very first thing in your program:
209 .PP
210 .Vb 5
211 \& int main (int argc, char *argv[])
212 \& {
213 \& // do nothing here
214 \& ptytty::init ();
215 \& // in C: ptytty_init ();
216 \&
217 \& // initialise, parse arguments, etc.
218 \& }
219 .Ve
220 .PP
221 This checks whether the program runs setuid or setgid. If yes then it will
222 fork a helper process and drop privileges.
223 .PP
224 Some programs need finer control over if and when this helper process
225 is started, and if and how to drop privileges. For those programs, the
226 methods \f(CW\*(C`ptytty::use_helper\*(C'\fR and \f(CW\*(C`ptytty::drop_privileges\*(C'\fR (and possibly
227 \&\f(CW\*(C`ptytty::sanitise_stdfd\*(C'\fR) are more useful.
228 .SH "\*(C+ INTERFACE: THE ptytty CLASS"
229 .IX Header " INTERFACE: THE ptytty CLASS"
230 .SS "\s-1STATIC METHODS\s0"
231 .IX Subsection "STATIC METHODS"
232 .IP "ptytty::init ()" 4
233 .IX Item "ptytty::init ()"
234 The default way to initialise libptytty. Must be called immediately as
235 the first thing in the \f(CW\*(C`main\*(C'\fR function, or earlier e.g. during static
236 construction time. The earlier, the better.
237 .Sp
238 This method calls \f(CW\*(C`sanitise_stdfd\*(C'\fR and then checks whether the program runs
239 with setuid/setgid permissions and, if yes, spawns a helper process for
240 pty/tty management. It then drops the privileges completely, so the actual
241 program runs without setuid/setgid privileges.
242 .Sp
243 On failure, this method terminates the process.
244 .IP "ptytty::use_helper ()" 4
245 .IX Item "ptytty::use_helper ()"
246 Tries to start a helper process that retains privileges even when the
247 calling process does not. This is usually called from \f(CW\*(C`ptytty::init\*(C'\fR when
248 it detects that the program is running setuid or setgid, but can be called
249 manually if it is inconvenient to drop privileges at startup, or when
250 you are not running setuid/setgid but want to drop privileges (e.g. when
251 running as a root-started daemon).
252 .Sp
253 This method will try not to start more than one helper process. The same
254 helper process can usually be used both from the process starting it and
255 all its fork'ed (not exec'ed) children.
256 .Sp
257 On failure, this method terminates the process.
258 .IP "ptytty::drop_privileges ()" 4
259 .IX Item "ptytty::drop_privileges ()"
260 Drops privileges completely, i.e. sets real, effective and saved user
261 id to the real user id. Useful to make sure that the process doesn't
262 run with special privileges.
263 .Sp
264 On failure, this method terminates the process.
265 .IP "ptytty::sanitise_stdfd ()" 4
266 .IX Item "ptytty::sanitise_stdfd ()"
267 Checks whether file descriptors 0, 1 and 2 (stdin, stdout and stderr)
268 are valid (open) and, if not, connects them to \fI/dev/tty\fR or
269 \&\fI/dev/null\fR if possible. This is necessary because libptytty might
270 want to output error messages to those descriptors, which at the time
271 of outputting the error message, might be connected to something
272 unsuitable opened by the unsuspecting program itself (this can be a
273 security issue).
274 .Sp
275 On failure, this method terminates the process.
276 .IP "bool success = ptytty::send_fd (int socket, int fd)" 4
277 .IX Item "bool success = ptytty::send_fd (int socket, int fd)"
278 Utility method to send a file descriptor over a unix domain
279 socket. Returns true if successful, false otherwise. This method is only
280 exposed for your convenience and is not required for normal operation.
281 .IP "int fd = ptytty::recv_fd (int socket)" 4
282 .IX Item "int fd = ptytty::recv_fd (int socket)"
283 Utility method to receive a file descriptor over a unix domain
284 socket. Returns the fd if successful and \f(CW\*(C`\-1\*(C'\fR otherwise. This method
285 is only exposed for your convenience and is not required for normal
286 operation.
287 .IP "ptytty *pty = ptytty::create ()" 4
288 .IX Item "ptytty *pty = ptytty::create ()"
289 Creates new ptytty object. Creation does not yet do anything besides
290 allocating the structure.
291 .Sp
292 A static method is used because the actual ptytty implementation can
293 differ at runtime, so you need a dynamic object creation facility.
294 .SS "\s-1DYNAMIC/SESSION\-RELATED DATA MEMBERS AND METHODS\s0"
295 .IX Subsection "DYNAMIC/SESSION-RELATED DATA MEMBERS AND METHODS"
296 .IP "int pty_fd = pty\->pty" 4
297 .IX Item "int pty_fd = pty->pty"
298 .PD 0
299 .IP "int tty_fd = pty\->tty" 4
300 .IX Item "int tty_fd = pty->tty"
301 .PD
302 These members contain the pty and tty file descriptors, respectively. They
303 initially contain \f(CW\*(C`\-1\*(C'\fR until a successful call to \f(CW\*(C`ptytty::get\*(C'\fR.
304 .IP "bool success = pty\->get ()" 4
305 .IX Item "bool success = pty->get ()"
306 Tries to find, allocate and initialise a new pty/tty pair. Returns \f(CW\*(C`true\*(C'\fR
307 when successful.
308 .Sp
309 If the helper process is running and there is a protocol error, this
310 method terminates the process.
311 .IP "pty\->login (int cmd_pid, bool login_shell, const char *hostname)" 4
312 .IX Item "pty->login (int cmd_pid, bool login_shell, const char *hostname)"
313 Creates an entry in the systems session database(s) (utmp, wtmp, lastlog).
314 \&\f(CW\*(C`cmd_pid\*(C'\fR must be the pid of the process representing the session
315 (such as the login shell), \f(CW\*(C`login_shell\*(C'\fR defines whether the session is
316 associated with a login, which influences whether wtmp and lastlog entries
317 are created, and \f(CW\*(C`hostname\*(C'\fR should identify the \*(L"hostname\*(R" the user logs
318 in from, which often is the value of the \f(CW\*(C`DISPLAY\*(C'\fR variable or tty line
319 in case of local logins.
320 .Sp
321 Calling this method is optional. A session starts at the time of the login
322 call and extends until the ptytty object is destroyed.
323 .IP "pty\->close_tty ()" 4
324 .IX Item "pty->close_tty ()"
325 Closes the tty. Useful after forking in the parent/pty process.
326 .IP "bool success = pty\->make_controlling_tty ()" 4
327 .IX Item "bool success = pty->make_controlling_tty ()"
328 Tries to make the pty/tty pair the controlling terminal of the current
329 process. Useful after forking in the child/tty process.
330 .IP "pty\->set_utf8_mode (bool on)" 4
331 .IX Item "pty->set_utf8_mode (bool on)"
332 On systems supporting special \s-1UTF\-8\s0 line disciplines (e.g. Linux), this
333 tries to enable this discipline for the given pty. Can be called at any
334 time to change the mode.
335 .SH "C INTERFACE: THE ptytty FAMILY OF FUNCTIONS"
336 .IX Header "C INTERFACE: THE ptytty FAMILY OF FUNCTIONS"
337 .IP "ptytty_init ()" 4
338 .IX Item "ptytty_init ()"
339 See \f(CW\*(C`ptytty::init ()\*(C'\fR.
340 .IP "\s-1PTYTTY\s0 ptytty_create ()" 4
341 .IX Item "PTYTTY ptytty_create ()"
342 Creates a new opaque \s-1PTYTTY\s0 object and returns it. Do not try to access it
343 in any way except by testing it for truthness (e.g. \f(CW\*(C`if (pty) ....\*(C'\fR). See
344 \&\f(CW\*(C`ptytty::create ()\*(C'\fR.
345 .IP "int ptytty_pty (\s-1PTYTTY\s0 ptytty)" 4
346 .IX Item "int ptytty_pty (PTYTTY ptytty)"
347 Return the pty file descriptor. See \f(CW\*(C`pty\->pty\*(C'\fR.
348 .IP "int ptytty_tty (\s-1PTYTTY\s0 ptytty)" 4
349 .IX Item "int ptytty_tty (PTYTTY ptytty)"
350 Return the tty file descriptor. See \f(CW\*(C`pty\->tty\*(C'\fR.
351 .IP "void ptytty_delete (\s-1PTYTTY\s0 ptytty)" 4
352 .IX Item "void ptytty_delete (PTYTTY ptytty)"
353 Destroys the \s-1PTYTTY\s0 object, freeing the pty/tty pair and cleaning up the
354 utmp/wtmp/lastlog databases, if initialised/used. Same as \f(CW\*(C`delete pty\*(C'\fR in
355 \&\*(C+.
356 .IP "int ptytty_get (\s-1PTYTTY\s0 ptytty)" 4
357 .IX Item "int ptytty_get (PTYTTY ptytty)"
358 See \f(CW\*(C`pty\->get\*(C'\fR, returns 0 in case of an error, non-zero otherwise.
359 .IP "void ptytty_login (\s-1PTYTTY\s0 ptytty, int cmd_pid, bool login_shell, const char *hostname)" 4
360 .IX Item "void ptytty_login (PTYTTY ptytty, int cmd_pid, bool login_shell, const char *hostname)"
361 See \f(CW\*(C`pty\->login\*(C'\fR.
362 .IP "void ptytty_close_tty (\s-1PTYTTY\s0 ptytty)" 4
363 .IX Item "void ptytty_close_tty (PTYTTY ptytty)"
364 See \f(CW\*(C`pty\->close_tty\*(C'\fR.
365 .IP "int ptytty_make_controlling_tty (\s-1PTYTTY\s0 ptytty)" 4
366 .IX Item "int ptytty_make_controlling_tty (PTYTTY ptytty)"
367 See \f(CW\*(C`pty\->make_controlling_tty\*(C'\fR.
368 .IP "void ptytty_set_utf8_mode (\s-1PTYTTY\s0 ptytty, int on)" 4
369 .IX Item "void ptytty_set_utf8_mode (PTYTTY ptytty, int on)"
370 See \f(CW\*(C`pty\->set_utf8_mode\*(C'\fR.
371 .IP "void ptytty_drop_privileges ()" 4
372 .IX Item "void ptytty_drop_privileges ()"
373 See \f(CW\*(C`ptytty::drop_privileges\*(C'\fR.
374 .IP "void ptytty_use_helper ()" 4
375 .IX Item "void ptytty_use_helper ()"
376 See \f(CW\*(C`ptytty::use_helper\*(C'\fR.
377 .SH "BUGS"
378 .IX Header "BUGS"
379 You kiddin'?
380 .SH "AUTHORS"
381 .IX Header "AUTHORS"
382 Emanuele Giaquinta <e.giaquinta@glauco.it>, Marc Alexander Lehmann
383 <rxvt\-unicode@schmorp.de>.