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.\" ======================================================================== |
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.\" |
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.IX Title "libptytty 3" |
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.TH libptytty 3 "2007-12-12" "" "LIBPTYTTY" |
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes |
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.\" way too many mistakes in technical documents. |
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.if n .ad l |
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.nh |
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.SH "NAME" |
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libptytty \- OS independent and secure pty/tty and utmp/wtmp/lastlog handling |
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.SH "SYNOPSIS" |
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.IX Header "SYNOPSIS" |
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.Vb 1 |
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\& cc ... \-lptytty |
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\& |
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\& #include <libptytty.h> |
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\& |
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\& |
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\& // C++ |
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\& ptytty *pty = ptytty::create (); |
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\& |
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\& if (!pty\->get ()) |
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\& // error allocating pty |
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\& |
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\& if (we want utmp) |
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\& pty\->login (process_pid, 0, "remote.host"); |
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\& else if (we want utmp AND wtmp/lastlog) |
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\& pty\->login (process_pid, 1, "remote.host"); |
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\& |
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\& // we are done with it |
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\& delete pty; |
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\& |
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\& |
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\& // C |
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\& PTYTTY pty = ptytty_create (); |
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\& |
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\& if (!ptytty_get (pty)) |
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\& // error allocating pty |
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\& |
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\& if (we want utmp) |
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\& ptytty_login (pty, process_pid, 0, "remote.host"); |
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\& else if (we want utmp AND wtmp/lastlog) |
| 166 |
\& ptytty_login (pty, process_pid, 1, "remote.host"); |
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\& |
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\& // we are done with it |
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\& ptytty_delete (pty); |
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.Ve |
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.PP |
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See also the \fIeg/\fR directory, which currently contains the \fIc\-sample.c\fR |
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file that spawns a loginshell from C using libptytty. |
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.SH "DESCRIPTION" |
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.IX Header "DESCRIPTION" |
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Libptytty is a small library that offers pseudo-tty management in an |
| 177 |
OS-independent way. It was created out of frustration over the many |
| 178 |
differences of pty/tty handling in different operating systems for the use |
| 179 |
inside \f(CW\*(C`rxvt\-unicode\*(C'\fR. |
| 180 |
.PP |
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In addition to offering mere pty/tty management, it also offers session |
| 182 |
database support (utmp and optional wtmp/lastlog updates for login |
| 183 |
shells). |
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.PP |
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It also supports fork'ing after startup and dropping privileges in the |
| 186 |
calling process, so in case the calling process gets compromised by the |
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user starting the program there is less to gain, as only the helper |
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process runs with privileges (e.g. setuid/setgid), which reduces the area |
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of attack immensely. |
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.PP |
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Libptytty is written in \*(C+, but it also offers a C\-only \s-1API\s0. |
| 192 |
.SH "SECURITY CONSIDERATIONS" |
| 193 |
.IX Header "SECURITY CONSIDERATIONS" |
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\&\fI\f(BIIt is of paramount importance that you at least read the following |
| 195 |
paragraph!\fI\fR |
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.PP |
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If you write a typical terminal-like program that just wants one or more |
| 198 |
ptys, you should call the \f(CW\*(C`ptytty::init ()\*(C'\fR method (C: \f(CW\*(C`ptytty_init ()\*(C'\fR |
| 199 |
function) as the very first thing in your program: |
| 200 |
.PP |
| 201 |
.Vb 5 |
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\& int main (int argc, char *argv[]) |
| 203 |
\& { |
| 204 |
\& // do nothing here |
| 205 |
\& ptytty::init (); |
| 206 |
\& // in C: ptytty_init (); |
| 207 |
\& |
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\& // initialise, parse arguments, etc. |
| 209 |
\& } |
| 210 |
.Ve |
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.PP |
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This checks wether the program runs setuid or setgid. If yes then it will |
| 213 |
fork a helper process and drop privileges. |
| 214 |
.PP |
| 215 |
Some programs need finer control over if and when this helper process |
| 216 |
is started, and if and how to drop privileges. For those programs, the |
| 217 |
methods \f(CW\*(C`ptytty::use_helper\*(C'\fR and \f(CW\*(C`ptytty::drop_privileges\*(C'\fR (and possibly |
| 218 |
\&\f(CW\*(C`ptytty::sanitise_stdfd\*(C'\fR) are more useful. |
| 219 |
.SH "\*(C+ INTERFACE: THE ptytty CLASS" |
| 220 |
.IX Header " INTERFACE: THE ptytty CLASS" |
| 221 |
.Sh "\s-1STATIC\s0 \s-1METHODS\s0" |
| 222 |
.IX Subsection "STATIC METHODS" |
| 223 |
.IP "ptytty::init ()" 4 |
| 224 |
.IX Item "ptytty::init ()" |
| 225 |
The default way to initialise libptytty. Must be called immediately as |
| 226 |
the first thing in the \f(CW\*(C`main\*(C'\fR function, or earlier e.g. during static |
| 227 |
construction time. The earlier, the better. |
| 228 |
.Sp |
| 229 |
This method calls \f(CW\*(C`sanitise_stdf\*(C'\fR and then checks wether the program runs |
| 230 |
with setuid/setgid permissions and, if yes, spawns a helper process for |
| 231 |
pty/tty management. It then drops the privileges completely, so the actual |
| 232 |
program runs without setuid/setgid privileges. |
| 233 |
.IP "ptytty::use_helper ()" 4 |
| 234 |
.IX Item "ptytty::use_helper ()" |
| 235 |
Tries to start a helper process that retains privileges even when the |
| 236 |
calling process does not. This is usually called from \f(CW\*(C`ptytty::init\*(C'\fR when |
| 237 |
it detects that the program is running setuid or setgid, but can be called |
| 238 |
manually if it is inconvinient to drop privileges at startup, or when |
| 239 |
you are not running setuid/setgid but want to drop privileges (e.g. when |
| 240 |
running as a root-started daemon). |
| 241 |
.Sp |
| 242 |
This method will try not to start more than one helper process. The same |
| 243 |
helper process can usually be used both from the process starting it and |
| 244 |
all its fork'ed (not exec'ed) children. |
| 245 |
.IP "ptytty::drop_privileges ()" 4 |
| 246 |
.IX Item "ptytty::drop_privileges ()" |
| 247 |
Drops privileges completely, i.e. sets real, effective and saved user id |
| 248 |
to the real user id. Also aborts if this cannot be achieved. Useful to |
| 249 |
make sure that the process doesn't run with special privileges. |
| 250 |
.IP "ptytty::sanitise_stdfd ()" 4 |
| 251 |
.IX Item "ptytty::sanitise_stdfd ()" |
| 252 |
Checks wether file descriptors 0, 1 and 2 (stdin, stdout and stderr) are |
| 253 |
valid (open) and, if not, connects them to \fI/dev/tty\fR or \fI/dev/null\fR if |
| 254 |
possible (and aborts otherwise). This is necessary because libptytty might |
| 255 |
want to output error messages to those descriptors, which at the time of |
| 256 |
outputting the error message, might be connected to something unsuitable |
| 257 |
opened by the unsuspecting program itself (this can be a security issue). |
| 258 |
.IP "bool success = ptytty::send_fd (int socket, int fd)" 4 |
| 259 |
.IX Item "bool success = ptytty::send_fd (int socket, int fd)" |
| 260 |
Utility method to send a file descriptor over a unix domain |
| 261 |
socket. Returns true if successful, false otherwise. This method is only |
| 262 |
exposed for your convinience and is not required for normal operation. |
| 263 |
.IP "int fd = ptytty::recv_fd (int socket)" 4 |
| 264 |
.IX Item "int fd = ptytty::recv_fd (int socket)" |
| 265 |
Utility method to receive a file descriptor over a unix domain |
| 266 |
socket. Returns the fd if sucecssful and \f(CW\*(C`\-1\*(C'\fR otherwise. This method |
| 267 |
is only exposed for your convinience and is not required for normal |
| 268 |
operation. |
| 269 |
.IP "ptytty *pty = ptytty::create ()" 4 |
| 270 |
.IX Item "ptytty *pty = ptytty::create ()" |
| 271 |
Creates new ptytty object. Creation does not yet do anything besides |
| 272 |
allocating the structure. |
| 273 |
.Sp |
| 274 |
A static method is used because the actual ptytty implementation can |
| 275 |
differ at runtime, so you need a dynamic object creation facility. |
| 276 |
.Sh "\s-1DYNAMIC/SESSION\-RELATED\s0 \s-1DATA\s0 \s-1MEMBERS\s0 \s-1AND\s0 \s-1METHODS\s0" |
| 277 |
.IX Subsection "DYNAMIC/SESSION-RELATED DATA MEMBERS AND METHODS" |
| 278 |
.IP "int pty_fd = pty\->pty" 4 |
| 279 |
.IX Item "int pty_fd = pty->pty" |
| 280 |
.PD 0 |
| 281 |
.IP "int tty_fd = pty\->tty" 4 |
| 282 |
.IX Item "int tty_fd = pty->tty" |
| 283 |
.PD |
| 284 |
These members contain the pty and tty file descriptors, respectively. They |
| 285 |
initially contain \f(CW\*(C`\-1\*(C'\fR until a successful to \f(CW\*(C`ptytty::get\*(C'\fR. |
| 286 |
.IP "bool success = pty\->get ()" 4 |
| 287 |
.IX Item "bool success = pty->get ()" |
| 288 |
Tries to find, allocate and initialise a new pty/tty pair. Returns \f(CW\*(C`true\*(C'\fR |
| 289 |
when successful. |
| 290 |
.IP "pty\->login (int cmd_pid, bool login_shell, const char *hostname)" 4 |
| 291 |
.IX Item "pty->login (int cmd_pid, bool login_shell, const char *hostname)" |
| 292 |
Creates an entry in the systems session database(s) (utmp, wtmp, lastlog). |
| 293 |
\&\f(CW\*(C`cmd_pid\*(C'\fR must be the pid of the process representing the session |
| 294 |
(such as the login shell), \f(CW\*(C`login_shell\*(C'\fR defines wether the session is |
| 295 |
associated with a login, which influences wether wtmp and lastlog entries |
| 296 |
are created, and \f(CW\*(C`hostname\*(C'\fR should identify the \*(L"hostname\*(R" the user logs |
| 297 |
in from, which often is the value of the \f(CW\*(C`DISPLAY\*(C'\fR variable or tty line |
| 298 |
in case of local logins. |
| 299 |
.Sp |
| 300 |
Calling this method is optional. A session starts at the time of the login |
| 301 |
call and extends until the ptytty object is destroyed. |
| 302 |
.IP "pty\->close_tty ()" 4 |
| 303 |
.IX Item "pty->close_tty ()" |
| 304 |
Closes the tty. Useful after forking in the parent/pty process. |
| 305 |
.IP "bool success = pty\->make_controlling_tty ()" 4 |
| 306 |
.IX Item "bool success = pty->make_controlling_tty ()" |
| 307 |
Tries to make the pty/tty pair the controlling terminal of the current |
| 308 |
process. Useful after forking in the child/tty process. |
| 309 |
.IP "pty\->set_utf8_mode (bool on)" 4 |
| 310 |
.IX Item "pty->set_utf8_mode (bool on)" |
| 311 |
On systems supporting special \s-1UTF\-8\s0 line disciplines (e.g. Linux), this |
| 312 |
tries to enable this discipline for the given pty. Can be called at any |
| 313 |
time to change the mode. |
| 314 |
.SH "C INTERFACE: THE ptytty FAMILY OF FUNCTIONS" |
| 315 |
.IX Header "C INTERFACE: THE ptytty FAMILY OF FUNCTIONS" |
| 316 |
.IP "ptytty_init ()" 4 |
| 317 |
.IX Item "ptytty_init ()" |
| 318 |
See \f(CW\*(C`ptytty::init ()\*(C'\fR. |
| 319 |
.IP "\s-1PTYTTY\s0 ptytty_create ()" 4 |
| 320 |
.IX Item "PTYTTY ptytty_create ()" |
| 321 |
Creates a new opaque \s-1PTYTTY\s0 object and returns it. Do not try to access it |
| 322 |
in any way except by testing it for truthness (e.g. \f(CW\*(C`if (pty) ....\*(C'\fR). See |
| 323 |
\&\f(CW\*(C`ptytty::create ()\*(C'\fR. |
| 324 |
.IP "int ptytty_pty (\s-1PTYTTY\s0 ptytty)" 4 |
| 325 |
.IX Item "int ptytty_pty (PTYTTY ptytty)" |
| 326 |
Return the pty file descriptor. See \f(CW\*(C`pty\->pty\*(C'\fR. |
| 327 |
.IP "int ptytty_tty (\s-1PTYTTY\s0 ptytty)" 4 |
| 328 |
.IX Item "int ptytty_tty (PTYTTY ptytty)" |
| 329 |
Return the tty file descriptor. See \f(CW\*(C`pty\->tty\*(C'\fR. |
| 330 |
.IP "void ptytty_delete (\s-1PTYTTY\s0 ptytty)" 4 |
| 331 |
.IX Item "void ptytty_delete (PTYTTY ptytty)" |
| 332 |
Destroys the \s-1PTYTTY\s0 object, freeing the pty/tty pair and cleaning up the |
| 333 |
utmp/wtmp/lastlog databases, if initialised/used. Same as \f(CW\*(C`delete pty\*(C'\fR in |
| 334 |
\&\*(C+. |
| 335 |
.IP "int ptytty_get (\s-1PTYTTY\s0 ptytty)" 4 |
| 336 |
.IX Item "int ptytty_get (PTYTTY ptytty)" |
| 337 |
See \f(CW\*(C`pty\->get\*(C'\fR, returns 0 in case of an error, non-zero otherwise. |
| 338 |
.IP "void ptytty_login (\s-1PTYTTY\s0 ptytty, int cmd_pid, bool login_shell, const char *hostname)" 4 |
| 339 |
.IX Item "void ptytty_login (PTYTTY ptytty, int cmd_pid, bool login_shell, const char *hostname)" |
| 340 |
See \f(CW\*(C`pty\->login\*(C'\fR. |
| 341 |
.IP "void ptytty_close_tty (\s-1PTYTTY\s0 ptytty)" 4 |
| 342 |
.IX Item "void ptytty_close_tty (PTYTTY ptytty)" |
| 343 |
See \f(CW\*(C`pty\->close_tty\*(C'\fR. |
| 344 |
.IP "int ptytty_make_controlling_tty (\s-1PTYTTY\s0 ptytty)" 4 |
| 345 |
.IX Item "int ptytty_make_controlling_tty (PTYTTY ptytty)" |
| 346 |
See \f(CW\*(C`pty\->make_controlling_tty\*(C'\fR. |
| 347 |
.IP "void ptytty_set_utf8_mode (\s-1PTYTTY\s0 ptytty, int on)" 4 |
| 348 |
.IX Item "void ptytty_set_utf8_mode (PTYTTY ptytty, int on)" |
| 349 |
See \f(CW\*(C`pty\->set_utf8_mode\*(C'\fR. |
| 350 |
.IP "void ptytty_drop_privileges ()" 4 |
| 351 |
.IX Item "void ptytty_drop_privileges ()" |
| 352 |
See \f(CW\*(C`ptytty::drop_privileges\*(C'\fR. |
| 353 |
.IP "void ptytty_use_helper ()" 4 |
| 354 |
.IX Item "void ptytty_use_helper ()" |
| 355 |
See \f(CW\*(C`ptytty::use_helper\*(C'\fR. |
| 356 |
.SH "BUGS" |
| 357 |
.IX Header "BUGS" |
| 358 |
You kiddin'? |
| 359 |
.SH "AUTHORS" |
| 360 |
.IX Header "AUTHORS" |
| 361 |
Emanuele Giaquinta <e.giaquinta@glauco.it>, Marc Alexander Lehmann |
| 362 |
<rxvt\-unicode@schmorp.de>. |
