1 /* $OpenBSD: lib_tstp.c,v 1.12 2023/10/17 09:52:09 nicm Exp $ */
2
3 /****************************************************************************
4 * Copyright 2020-2021,2022 Thomas E. Dickey *
5 * Copyright 1998-2014,2017 Free Software Foundation, Inc. *
6 * *
7 * Permission is hereby granted, free of charge, to any person obtaining a *
8 * copy of this software and associated documentation files (the *
9 * "Software"), to deal in the Software without restriction, including *
10 * without limitation the rights to use, copy, modify, merge, publish, *
11 * distribute, distribute with modifications, sublicense, and/or sell *
12 * copies of the Software, and to permit persons to whom the Software is *
13 * furnished to do so, subject to the following conditions: *
14 * *
15 * The above copyright notice and this permission notice shall be included *
16 * in all copies or substantial portions of the Software. *
17 * *
18 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS *
19 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF *
20 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. *
21 * IN NO EVENT SHALL THE ABOVE COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, *
22 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR *
23 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR *
24 * THE USE OR OTHER DEALINGS IN THE SOFTWARE. *
25 * *
26 * Except as contained in this notice, the name(s) of the above copyright *
27 * holders shall not be used in advertising or otherwise to promote the *
28 * sale, use or other dealings in this Software without prior written *
29 * authorization. *
30 ****************************************************************************/
31
32 /****************************************************************************
33 * Author: Zeyd M. Ben-Halim <zmbenhal@netcom.com> 1992,1995 *
34 * and: Eric S. Raymond <esr@snark.thyrsus.com> *
35 * and: Thomas E. Dickey 1995-on *
36 ****************************************************************************/
37
38 /*
39 ** lib_tstp.c
40 **
41 ** The routine _nc_signal_handler().
42 **
43 */
44 #include <curses.priv.h>
45
46 #include <SigAction.h>
47
48 MODULE_ID("$Id: lib_tstp.c,v 1.12 2023/10/17 09:52:09 nicm Exp $")
49
50 #if defined(SIGTSTP) && (HAVE_SIGACTION || HAVE_SIGVEC)
51 #define USE_SIGTSTP 1
52 #else
53 #define USE_SIGTSTP 0
54 #endif
55
56 #ifdef TRACE
57 static const char *
signal_name(int sig)58 signal_name(int sig)
59 {
60 switch (sig) {
61 #ifdef SIGALRM
62 case SIGALRM:
63 return "SIGALRM";
64 #endif
65 #ifdef SIGCONT
66 case SIGCONT:
67 return "SIGCONT";
68 #endif
69 case SIGINT:
70 return "SIGINT";
71 #ifdef SIGQUIT
72 case SIGQUIT:
73 return "SIGQUIT";
74 #endif
75 case SIGTERM:
76 return "SIGTERM";
77 #ifdef SIGTSTP
78 case SIGTSTP:
79 return "SIGTSTP";
80 #endif
81 #ifdef SIGTTOU
82 case SIGTTOU:
83 return "SIGTTOU";
84 #endif
85 #ifdef SIGWINCH
86 case SIGWINCH:
87 return "SIGWINCH";
88 #endif
89 default:
90 return "unknown signal";
91 }
92 }
93 #endif
94
95 /*
96 * Note: This code is fragile! Its problem is that different OSs
97 * handle restart of system calls interrupted by signals differently.
98 * The ncurses code needs signal-call restart to happen -- otherwise,
99 * interrupted wgetch() calls will return FAIL, probably making the
100 * application think the input stream has ended and it should
101 * terminate. In particular, you know you have this problem if, when
102 * you suspend an ncurses-using lynx with ^Z and resume, it dies
103 * immediately.
104 *
105 * Default behavior of POSIX sigaction(2) is not to restart
106 * interrupted system calls, but Linux's sigaction does it anyway (at
107 * least, on and after the 1.1.47 I (esr) use). Thus this code works
108 * OK under Linux. The 4.4BSD sigaction(2) supports a (non-portable)
109 * SA_RESTART flag that forces the right behavior. Thus, this code
110 * should work OK under BSD/OS, NetBSD, and FreeBSD (let us know if it
111 * does not).
112 *
113 * Stock System Vs (and anything else using a strict-POSIX
114 * sigaction(2) without SA_RESTART) may have a problem. Possible
115 * solutions:
116 *
117 * sigvec restarts by default (SV_INTERRUPT flag to not restart)
118 * signal restarts by default in SVr4 (assuming you link with -lucb)
119 * and BSD, but not SVr3.
120 * sigset restarts, but is only available under SVr4/Solaris.
121 *
122 * The signal(3) call is mandated by the ANSI standard, and its
123 * interaction with sigaction(2) is described in the POSIX standard
124 * (3.3.4.2, page 72,line 934). According to section 8.1, page 191,
125 * however, signal(3) itself is not required by POSIX.1. And POSIX is
126 * silent on whether it is required to restart signals.
127 *
128 * So. The present situation is, we use sigaction(2) with no
129 * guarantee of restart anywhere but on Linux and BSD. We could
130 * switch to signal(3) and collar Linux, BSD, and SVr4. Any way
131 * we slice it, System V UNIXes older than SVr4 will probably lose
132 * (this may include XENIX).
133 *
134 * This implementation will probably be changed to use signal(3) in
135 * the future. If nothing else, it is simpler...
136 */
137
138 #if USE_SIGTSTP
139 static void
handle_SIGTSTP(int dummy GCC_UNUSED)140 handle_SIGTSTP(int dummy GCC_UNUSED)
141 {
142 SCREEN *sp = CURRENT_SCREEN;
143 sigset_t mask, omask;
144 sigaction_t act, oact;
145
146 #ifdef SIGTTOU
147 int sigttou_blocked;
148 #endif
149
150 _nc_globals.have_sigtstp = 1;
151 T(("handle_SIGTSTP() called"));
152
153 /*
154 * The user may have changed the prog_mode tty bits, so save them.
155 *
156 * But first try to detect whether we still are in the foreground
157 * process group - if not, an interactive shell may already have
158 * taken ownership of the tty and modified the settings when our
159 * parent was stopped before us, and we would likely pick up the
160 * settings already modified by the shell.
161 *
162 * Don't do this if we're not in curses -
163 */
164 if (sp != 0 && (sp->_endwin == ewRunning))
165 #if HAVE_TCGETPGRP
166 if (tcgetpgrp(STDIN_FILENO) == getpgrp())
167 #endif
168 NCURSES_SP_NAME(def_prog_mode) (NCURSES_SP_ARG);
169
170 /*
171 * Block window change and timer signals. The latter
172 * is because applications use timers to decide when
173 * to repaint the screen.
174 */
175 (void) sigemptyset(&mask);
176 #ifdef SIGALRM
177 (void) sigaddset(&mask, SIGALRM);
178 #endif
179 #if USE_SIGWINCH
180 (void) sigaddset(&mask, SIGWINCH);
181 #endif
182 (void) sigprocmask(SIG_BLOCK, &mask, &omask);
183
184 #ifdef SIGTTOU
185 sigttou_blocked = sigismember(&omask, SIGTTOU);
186 if (!sigttou_blocked) {
187 (void) sigemptyset(&mask);
188 (void) sigaddset(&mask, SIGTTOU);
189 (void) sigprocmask(SIG_BLOCK, &mask, NULL);
190 }
191 #endif
192
193 /*
194 * End window mode, which also resets the terminal state to the
195 * original (pre-curses) modes.
196 */
197 NCURSES_SP_NAME(endwin) (NCURSES_SP_ARG);
198
199 /* Unblock SIGTSTP. */
200 (void) sigemptyset(&mask);
201 (void) sigaddset(&mask, SIGTSTP);
202 #ifdef SIGTTOU
203 if (!sigttou_blocked) {
204 /* Unblock this too if it wasn't blocked on entry */
205 (void) sigaddset(&mask, SIGTTOU);
206 }
207 #endif
208 (void) sigprocmask(SIG_UNBLOCK, &mask, NULL);
209
210 /* Now we want to resend SIGSTP to this process and suspend it */
211 act.sa_handler = SIG_DFL;
212 sigemptyset(&act.sa_mask);
213 act.sa_flags = 0;
214 #ifdef SA_RESTART
215 act.sa_flags |= SA_RESTART;
216 #endif /* SA_RESTART */
217 sigaction(SIGTSTP, &act, &oact);
218 kill(getpid(), SIGTSTP);
219
220 /* Process gets suspended...time passes...process resumes */
221
222 T(("SIGCONT received"));
223 sigaction(SIGTSTP, &oact, NULL);
224 NCURSES_SP_NAME(flushinp) (NCURSES_SP_ARG);
225
226 /*
227 * If the user modified the tty state while suspended, he wants
228 * those changes to stick. So save the new "default" terminal state.
229 */
230 NCURSES_SP_NAME(def_shell_mode) (NCURSES_SP_ARG);
231
232 /*
233 * This relies on the fact that doupdate() will restore the
234 * program-mode tty state, and issue enter_ca_mode if need be.
235 */
236 NCURSES_SP_NAME(doupdate) (NCURSES_SP_ARG);
237
238 /* Reset the signals. */
239 (void) sigprocmask(SIG_SETMASK, &omask, NULL);
240 }
241 #endif /* USE_SIGTSTP */
242
243 static void
handle_SIGINT(int sig)244 handle_SIGINT(int sig)
245 {
246 SCREEN *sp = CURRENT_SCREEN;
247
248 /*
249 * Much of this is unsafe from a signal handler. But we'll _try_ to clean
250 * up the screen and terminal settings on the way out.
251 *
252 * There are at least the following problems:
253 * 1) Walking the SCREEN list is unsafe, since all list management
254 * is done without any signal blocking.
255 * 2) On systems which have REENTRANT turned on, set_term() uses
256 * _nc_lock_global() which could deadlock or misbehave in other ways.
257 * 3) endwin() calls all sorts of stuff, many of which use stdio or
258 * other library functions which are clearly unsafe.
259 */
260 if (!_nc_globals.cleanup_nested++
261 && (sig == SIGINT || sig == SIGTERM)) {
262 #if HAVE_SIGACTION || HAVE_SIGVEC
263 sigaction_t act;
264 sigemptyset(&act.sa_mask);
265 act.sa_flags = 0;
266 act.sa_handler = SIG_IGN;
267 if (sigaction(sig, &act, NULL) == 0)
268 #else
269 if (signal(sig, SIG_IGN) != SIG_ERR)
270 #endif
271 {
272 SCREEN *scan;
273 for (each_screen(scan)) {
274 if (scan->_ofp != 0
275 && NC_ISATTY(fileno(scan->_ofp))) {
276 scan->_outch = NCURSES_SP_NAME(_nc_outch);
277 }
278 set_term(scan);
279 NCURSES_SP_NAME(endwin) (NCURSES_SP_ARG);
280 if (sp)
281 sp->_endwin = ewInitial; /* in case of reuse */
282 }
283 }
284 }
285 _exit(EXIT_FAILURE);
286 }
287
288 # ifndef _nc_set_read_thread
289 NCURSES_EXPORT(void)
_nc_set_read_thread(bool enable)290 _nc_set_read_thread(bool enable)
291 {
292 _nc_lock_global(curses);
293 if (enable) {
294 # if USE_WEAK_SYMBOLS
295 if ((pthread_self) && (pthread_kill) && (pthread_equal))
296 # endif
297 _nc_globals.read_thread = pthread_self();
298 } else {
299 _nc_globals.read_thread = 0;
300 }
301 _nc_unlock_global(curses);
302 }
303 # endif
304
305 #if USE_SIGWINCH
306
307 static void
handle_SIGWINCH(int sig GCC_UNUSED)308 handle_SIGWINCH(int sig GCC_UNUSED)
309 {
310 _nc_globals.have_sigwinch = 1;
311 # if USE_PTHREADS_EINTR
312 if (_nc_globals.read_thread) {
313 if (!pthread_equal(pthread_self(), _nc_globals.read_thread))
314 pthread_kill(_nc_globals.read_thread, SIGWINCH);
315 _nc_globals.read_thread = 0;
316 }
317 # endif
318 }
319 #endif /* USE_SIGWINCH */
320
321 /*
322 * If the given signal is still in its default state, set it to the given
323 * handler.
324 */
325 static int
CatchIfDefault(int sig,void (* handler)(int))326 CatchIfDefault(int sig, void (*handler) (int))
327 {
328 int result;
329 #if HAVE_SIGACTION || HAVE_SIGVEC
330 sigaction_t old_act;
331 sigaction_t new_act;
332
333 memset(&new_act, 0, sizeof(new_act));
334 sigemptyset(&new_act.sa_mask);
335 #ifdef SA_RESTART
336 #ifdef SIGWINCH
337 if (sig != SIGWINCH)
338 #endif
339 new_act.sa_flags |= SA_RESTART;
340 #endif /* SA_RESTART */
341 new_act.sa_handler = handler;
342
343 if (sigaction(sig, NULL, &old_act) == 0
344 && (old_act.sa_handler == SIG_DFL
345 || old_act.sa_handler == handler
346 #if USE_SIGWINCH
347 || (sig == SIGWINCH && old_act.sa_handler == SIG_IGN)
348 #endif
349 )) {
350 (void) sigaction(sig, &new_act, NULL);
351 result = TRUE;
352 } else {
353 result = FALSE;
354 }
355 #else /* !HAVE_SIGACTION */
356 void (*ohandler) (int);
357
358 ohandler = signal(sig, SIG_IGN);
359 if (ohandler == SIG_DFL
360 || ohandler == handler
361 #if USE_SIGWINCH
362 || (sig == SIGWINCH && ohandler == SIG_IGN)
363 #endif
364 ) {
365 signal(sig, handler);
366 result = TRUE;
367 } else {
368 signal(sig, ohandler);
369 result = FALSE;
370 }
371 #endif
372 T(("CatchIfDefault - will %scatch %s",
373 result ? "" : "not ", signal_name(sig)));
374 return result;
375 }
376
377 /*
378 * This is invoked once at the beginning (e.g., from 'initscr()'), to
379 * initialize the signal catchers, and thereafter when spawning a shell (and
380 * returning) to disable/enable the SIGTSTP (i.e., ^Z) catcher.
381 *
382 * If the application has already set one of the signals, we'll not modify it
383 * (during initialization).
384 *
385 * The XSI document implies that we shouldn't keep the SIGTSTP handler if
386 * the caller later changes its mind, but that doesn't seem correct.
387 */
388 NCURSES_EXPORT(void)
_nc_signal_handler(int enable)389 _nc_signal_handler(int enable)
390 {
391 T((T_CALLED("_nc_signal_handler(%d)"), enable));
392 #if USE_SIGTSTP /* Xenix 2.x doesn't have SIGTSTP, for example */
393 {
394 static bool ignore_tstp = FALSE;
395
396 if (!ignore_tstp) {
397 static sigaction_t new_sigaction, old_sigaction;
398
399 if (!enable) {
400 new_sigaction.sa_handler = SIG_IGN;
401 sigaction(SIGTSTP, &new_sigaction, &old_sigaction);
402 } else if (new_sigaction.sa_handler != SIG_DFL) {
403 sigaction(SIGTSTP, &old_sigaction, NULL);
404 } else if (sigaction(SIGTSTP, NULL, &old_sigaction) == 0
405 && (old_sigaction.sa_handler == SIG_DFL)) {
406 sigemptyset(&new_sigaction.sa_mask);
407 #ifdef SA_RESTART
408 new_sigaction.sa_flags |= SA_RESTART;
409 #endif /* SA_RESTART */
410 new_sigaction.sa_handler = handle_SIGTSTP;
411 (void) sigaction(SIGTSTP, &new_sigaction, NULL);
412 } else {
413 ignore_tstp = TRUE;
414 }
415 }
416 }
417 #endif /* !USE_SIGTSTP */
418
419 if (!_nc_globals.init_signals) {
420 if (enable) {
421 CatchIfDefault(SIGINT, handle_SIGINT);
422 CatchIfDefault(SIGTERM, handle_SIGINT);
423 #if USE_SIGWINCH
424 CatchIfDefault(SIGWINCH, handle_SIGWINCH);
425 #endif
426 _nc_globals.init_signals = TRUE;
427 }
428 }
429 returnVoid;
430 }
431