1 /****************************************************************************
2 * Copyright 2020 Thomas E. Dickey *
3 * Copyright 1998-2014,2017 Free Software Foundation, Inc. *
4 * *
5 * Permission is hereby granted, free of charge, to any person obtaining a *
6 * copy of this software and associated documentation files (the *
7 * "Software"), to deal in the Software without restriction, including *
8 * without limitation the rights to use, copy, modify, merge, publish, *
9 * distribute, distribute with modifications, sublicense, and/or sell *
10 * copies of the Software, and to permit persons to whom the Software is *
11 * furnished to do so, subject to the following conditions: *
12 * *
13 * The above copyright notice and this permission notice shall be included *
14 * in all copies or substantial portions of the Software. *
15 * *
16 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS *
17 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF *
18 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. *
19 * IN NO EVENT SHALL THE ABOVE COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, *
20 * DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR *
21 * OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR *
22 * THE USE OR OTHER DEALINGS IN THE SOFTWARE. *
23 * *
24 * Except as contained in this notice, the name(s) of the above copyright *
25 * holders shall not be used in advertising or otherwise to promote the *
26 * sale, use or other dealings in this Software without prior written *
27 * authorization. *
28 ****************************************************************************/
29
30 /****************************************************************************
31 * Author: Zeyd M. Ben-Halim <zmbenhal@netcom.com> 1992,1995 *
32 * and: Eric S. Raymond <esr@snark.thyrsus.com> *
33 * and: Thomas E. Dickey 1995-on *
34 ****************************************************************************/
35
36 /*
37 ** lib_tstp.c
38 **
39 ** The routine _nc_signal_handler().
40 **
41 */
42 #include <curses.priv.h>
43
44 #include <SigAction.h>
45
46 MODULE_ID("$Id: lib_tstp.c,v 1.50 2020/02/02 23:34:34 tom Exp $")
47
48 #if defined(SIGTSTP) && (HAVE_SIGACTION || HAVE_SIGVEC)
49 #define USE_SIGTSTP 1
50 #else
51 #define USE_SIGTSTP 0
52 #endif
53
54 #ifdef TRACE
55 static const char *
signal_name(int sig)56 signal_name(int sig)
57 {
58 switch (sig) {
59 #ifdef SIGALRM
60 case SIGALRM:
61 return "SIGALRM";
62 #endif
63 #ifdef SIGCONT
64 case SIGCONT:
65 return "SIGCONT";
66 #endif
67 case SIGINT:
68 return "SIGINT";
69 #ifdef SIGQUIT
70 case SIGQUIT:
71 return "SIGQUIT";
72 #endif
73 case SIGTERM:
74 return "SIGTERM";
75 #ifdef SIGTSTP
76 case SIGTSTP:
77 return "SIGTSTP";
78 #endif
79 #ifdef SIGTTOU
80 case SIGTTOU:
81 return "SIGTTOU";
82 #endif
83 #ifdef SIGWINCH
84 case SIGWINCH:
85 return "SIGWINCH";
86 #endif
87 default:
88 return "unknown signal";
89 }
90 }
91 #endif
92
93 /*
94 * Note: This code is fragile! Its problem is that different OSs
95 * handle restart of system calls interrupted by signals differently.
96 * The ncurses code needs signal-call restart to happen -- otherwise,
97 * interrupted wgetch() calls will return FAIL, probably making the
98 * application think the input stream has ended and it should
99 * terminate. In particular, you know you have this problem if, when
100 * you suspend an ncurses-using lynx with ^Z and resume, it dies
101 * immediately.
102 *
103 * Default behavior of POSIX sigaction(2) is not to restart
104 * interrupted system calls, but Linux's sigaction does it anyway (at
105 * least, on and after the 1.1.47 I (esr) use). Thus this code works
106 * OK under Linux. The 4.4BSD sigaction(2) supports a (non-portable)
107 * SA_RESTART flag that forces the right behavior. Thus, this code
108 * should work OK under BSD/OS, NetBSD, and FreeBSD (let us know if it
109 * does not).
110 *
111 * Stock System Vs (and anything else using a strict-POSIX
112 * sigaction(2) without SA_RESTART) may have a problem. Possible
113 * solutions:
114 *
115 * sigvec restarts by default (SV_INTERRUPT flag to not restart)
116 * signal restarts by default in SVr4 (assuming you link with -lucb)
117 * and BSD, but not SVr3.
118 * sigset restarts, but is only available under SVr4/Solaris.
119 *
120 * The signal(3) call is mandated by the ANSI standard, and its
121 * interaction with sigaction(2) is described in the POSIX standard
122 * (3.3.4.2, page 72,line 934). According to section 8.1, page 191,
123 * however, signal(3) itself is not required by POSIX.1. And POSIX is
124 * silent on whether it is required to restart signals.
125 *
126 * So. The present situation is, we use sigaction(2) with no
127 * guarantee of restart anywhere but on Linux and BSD. We could
128 * switch to signal(3) and collar Linux, BSD, and SVr4. Any way
129 * we slice it, System V UNIXes older than SVr4 will probably lose
130 * (this may include XENIX).
131 *
132 * This implementation will probably be changed to use signal(3) in
133 * the future. If nothing else, it's simpler...
134 */
135
136 #if USE_SIGTSTP
137 static void
handle_SIGTSTP(int dummy GCC_UNUSED)138 handle_SIGTSTP(int dummy GCC_UNUSED)
139 {
140 SCREEN *sp = CURRENT_SCREEN;
141 sigset_t mask, omask;
142 sigaction_t act, oact;
143
144 #ifdef SIGTTOU
145 int sigttou_blocked;
146 #endif
147
148 _nc_globals.have_sigtstp = 1;
149 T(("handle_SIGTSTP() called"));
150
151 /*
152 * The user may have changed the prog_mode tty bits, so save them.
153 *
154 * But first try to detect whether we still are in the foreground
155 * process group - if not, an interactive shell may already have
156 * taken ownership of the tty and modified the settings when our
157 * parent was stopped before us, and we would likely pick up the
158 * settings already modified by the shell.
159 *
160 * Don't do this if we're not in curses -
161 */
162 if (sp != 0 && (sp->_endwin == ewRunning))
163 #if HAVE_TCGETPGRP
164 if (tcgetpgrp(STDIN_FILENO) == getpgrp())
165 #endif
166 NCURSES_SP_NAME(def_prog_mode) (NCURSES_SP_ARG);
167
168 /*
169 * Block window change and timer signals. The latter
170 * is because applications use timers to decide when
171 * to repaint the screen.
172 */
173 (void) sigemptyset(&mask);
174 #ifdef SIGALRM
175 (void) sigaddset(&mask, SIGALRM);
176 #endif
177 #if USE_SIGWINCH
178 (void) sigaddset(&mask, SIGWINCH);
179 #endif
180 (void) sigprocmask(SIG_BLOCK, &mask, &omask);
181
182 #ifdef SIGTTOU
183 sigttou_blocked = sigismember(&omask, SIGTTOU);
184 if (!sigttou_blocked) {
185 (void) sigemptyset(&mask);
186 (void) sigaddset(&mask, SIGTTOU);
187 (void) sigprocmask(SIG_BLOCK, &mask, NULL);
188 }
189 #endif
190
191 /*
192 * End window mode, which also resets the terminal state to the
193 * original (pre-curses) modes.
194 */
195 NCURSES_SP_NAME(endwin) (NCURSES_SP_ARG);
196
197 /* Unblock SIGTSTP. */
198 (void) sigemptyset(&mask);
199 (void) sigaddset(&mask, SIGTSTP);
200 #ifdef SIGTTOU
201 if (!sigttou_blocked) {
202 /* Unblock this too if it wasn't blocked on entry */
203 (void) sigaddset(&mask, SIGTTOU);
204 }
205 #endif
206 (void) sigprocmask(SIG_UNBLOCK, &mask, NULL);
207
208 /* Now we want to resend SIGSTP to this process and suspend it */
209 act.sa_handler = SIG_DFL;
210 sigemptyset(&act.sa_mask);
211 act.sa_flags = 0;
212 #ifdef SA_RESTART
213 act.sa_flags |= SA_RESTART;
214 #endif /* SA_RESTART */
215 sigaction(SIGTSTP, &act, &oact);
216 kill(getpid(), SIGTSTP);
217
218 /* Process gets suspended...time passes...process resumes */
219
220 T(("SIGCONT received"));
221 sigaction(SIGTSTP, &oact, NULL);
222 NCURSES_SP_NAME(flushinp) (NCURSES_SP_ARG);
223
224 /*
225 * If the user modified the tty state while suspended, he wants
226 * those changes to stick. So save the new "default" terminal state.
227 */
228 NCURSES_SP_NAME(def_shell_mode) (NCURSES_SP_ARG);
229
230 /*
231 * This relies on the fact that doupdate() will restore the
232 * program-mode tty state, and issue enter_ca_mode if need be.
233 */
234 NCURSES_SP_NAME(doupdate) (NCURSES_SP_ARG);
235
236 /* Reset the signals. */
237 (void) sigprocmask(SIG_SETMASK, &omask, NULL);
238 }
239 #endif /* USE_SIGTSTP */
240
241 static void
handle_SIGINT(int sig)242 handle_SIGINT(int sig)
243 {
244 SCREEN *sp = CURRENT_SCREEN;
245
246 /*
247 * Much of this is unsafe from a signal handler. But we'll _try_ to clean
248 * up the screen and terminal settings on the way out.
249 *
250 * There are at least the following problems:
251 * 1) Walking the SCREEN list is unsafe, since all list management
252 * is done without any signal blocking.
253 * 2) On systems which have REENTRANT turned on, set_term() uses
254 * _nc_lock_global() which could deadlock or misbehave in other ways.
255 * 3) endwin() calls all sorts of stuff, many of which use stdio or
256 * other library functions which are clearly unsafe.
257 */
258 if (!_nc_globals.cleanup_nested++
259 && (sig == SIGINT || sig == SIGTERM)) {
260 #if HAVE_SIGACTION || HAVE_SIGVEC
261 sigaction_t act;
262 sigemptyset(&act.sa_mask);
263 act.sa_flags = 0;
264 act.sa_handler = SIG_IGN;
265 if (sigaction(sig, &act, NULL) == 0)
266 #else
267 if (signal(sig, SIG_IGN) != SIG_ERR)
268 #endif
269 {
270 SCREEN *scan;
271 for (each_screen(scan)) {
272 if (scan->_ofp != 0
273 && NC_ISATTY(fileno(scan->_ofp))) {
274 scan->_outch = NCURSES_SP_NAME(_nc_outch);
275 }
276 set_term(scan);
277 NCURSES_SP_NAME(endwin) (NCURSES_SP_ARG);
278 if (sp)
279 sp->_endwin = ewInitial; /* in case of reuse */
280 }
281 }
282 }
283 _exit(EXIT_FAILURE);
284 }
285
286 #if USE_SIGWINCH
287 static void
handle_SIGWINCH(int sig GCC_UNUSED)288 handle_SIGWINCH(int sig GCC_UNUSED)
289 {
290 _nc_globals.have_sigwinch = 1;
291 # if USE_PTHREADS_EINTR
292 if (_nc_globals.read_thread) {
293 if (!pthread_equal(pthread_self(), _nc_globals.read_thread))
294 pthread_kill(_nc_globals.read_thread, SIGWINCH);
295 _nc_globals.read_thread = 0;
296 }
297 # endif
298 }
299 #endif /* USE_SIGWINCH */
300
301 /*
302 * If the given signal is still in its default state, set it to the given
303 * handler.
304 */
305 static int
CatchIfDefault(int sig,void (* handler)(int))306 CatchIfDefault(int sig, void (*handler) (int))
307 {
308 int result;
309 #if HAVE_SIGACTION || HAVE_SIGVEC
310 sigaction_t old_act;
311 sigaction_t new_act;
312
313 memset(&new_act, 0, sizeof(new_act));
314 sigemptyset(&new_act.sa_mask);
315 #ifdef SA_RESTART
316 #ifdef SIGWINCH
317 if (sig != SIGWINCH)
318 #endif
319 new_act.sa_flags |= SA_RESTART;
320 #endif /* SA_RESTART */
321 new_act.sa_handler = handler;
322
323 if (sigaction(sig, NULL, &old_act) == 0
324 && (old_act.sa_handler == SIG_DFL
325 || old_act.sa_handler == handler
326 #if USE_SIGWINCH
327 || (sig == SIGWINCH && old_act.sa_handler == SIG_IGN)
328 #endif
329 )) {
330 (void) sigaction(sig, &new_act, NULL);
331 result = TRUE;
332 } else {
333 result = FALSE;
334 }
335 #else /* !HAVE_SIGACTION */
336 void (*ohandler) (int);
337
338 ohandler = signal(sig, SIG_IGN);
339 if (ohandler == SIG_DFL
340 || ohandler == handler
341 #if USE_SIGWINCH
342 || (sig == SIGWINCH && ohandler == SIG_IGN)
343 #endif
344 ) {
345 signal(sig, handler);
346 result = TRUE;
347 } else {
348 signal(sig, ohandler);
349 result = FALSE;
350 }
351 #endif
352 T(("CatchIfDefault - will %scatch %s",
353 result ? "" : "not ", signal_name(sig)));
354 return result;
355 }
356
357 /*
358 * This is invoked once at the beginning (e.g., from 'initscr()'), to
359 * initialize the signal catchers, and thereafter when spawning a shell (and
360 * returning) to disable/enable the SIGTSTP (i.e., ^Z) catcher.
361 *
362 * If the application has already set one of the signals, we'll not modify it
363 * (during initialization).
364 *
365 * The XSI document implies that we shouldn't keep the SIGTSTP handler if
366 * the caller later changes its mind, but that doesn't seem correct.
367 */
368 NCURSES_EXPORT(void)
_nc_signal_handler(int enable)369 _nc_signal_handler(int enable)
370 {
371 T((T_CALLED("_nc_signal_handler(%d)"), enable));
372 #if USE_SIGTSTP /* Xenix 2.x doesn't have SIGTSTP, for example */
373 {
374 static bool ignore_tstp = FALSE;
375
376 if (!ignore_tstp) {
377 static sigaction_t new_sigaction, old_sigaction;
378
379 if (!enable) {
380 new_sigaction.sa_handler = SIG_IGN;
381 sigaction(SIGTSTP, &new_sigaction, &old_sigaction);
382 } else if (new_sigaction.sa_handler != SIG_DFL) {
383 sigaction(SIGTSTP, &old_sigaction, NULL);
384 } else if (sigaction(SIGTSTP, NULL, &old_sigaction) == 0
385 && (old_sigaction.sa_handler == SIG_DFL)) {
386 sigemptyset(&new_sigaction.sa_mask);
387 #ifdef SA_RESTART
388 new_sigaction.sa_flags |= SA_RESTART;
389 #endif /* SA_RESTART */
390 new_sigaction.sa_handler = handle_SIGTSTP;
391 (void) sigaction(SIGTSTP, &new_sigaction, NULL);
392 } else {
393 ignore_tstp = TRUE;
394 }
395 }
396 }
397 #endif /* !USE_SIGTSTP */
398
399 if (!_nc_globals.init_signals) {
400 if (enable) {
401 CatchIfDefault(SIGINT, handle_SIGINT);
402 CatchIfDefault(SIGTERM, handle_SIGINT);
403 #if USE_SIGWINCH
404 CatchIfDefault(SIGWINCH, handle_SIGWINCH);
405 #endif
406 _nc_globals.init_signals = TRUE;
407 }
408 }
409 returnVoid;
410 }
411