trap.c revision 330897 
1/*-
2 * SPDX-License-Identifier: BSD-3-Clause
3 *
4 * Copyright (c) 1991, 1993
5 *	The Regents of the University of California.  All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * Kenneth Almquist.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 *    notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 *    notice, this list of conditions and the following disclaimer in the
17 *    documentation and/or other materials provided with the distribution.
18 * 4. Neither the name of the University nor the names of its contributors
19 *    may be used to endorse or promote products derived from this software
20 *    without specific prior written permission.
21 *
22 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34
35#ifndef lint
36#if 0
37static char sccsid[] = "@(#)trap.c	8.5 (Berkeley) 6/5/95";
38#endif
39#endif /* not lint */
40#include <sys/cdefs.h>
41__FBSDID("$FreeBSD: stable/11/bin/sh/trap.c 330897 2018-03-14 03:19:51Z eadler $");
42
43#include <signal.h>
44#include <unistd.h>
45#include <stdlib.h>
46
47#include "shell.h"
48#include "main.h"
49#include "nodes.h"	/* for other headers */
50#include "eval.h"
51#include "jobs.h"
52#include "show.h"
53#include "options.h"
54#include "syntax.h"
55#include "output.h"
56#include "memalloc.h"
57#include "error.h"
58#include "trap.h"
59#include "mystring.h"
60#include "builtins.h"
61#include "myhistedit.h"
62
63
64/*
65 * Sigmode records the current value of the signal handlers for the various
66 * modes.  A value of zero means that the current handler is not known.
67 * S_HARD_IGN indicates that the signal was ignored on entry to the shell,
68 */
69
70#define S_DFL 1			/* default signal handling (SIG_DFL) */
71#define S_CATCH 2		/* signal is caught */
72#define S_IGN 3			/* signal is ignored (SIG_IGN) */
73#define S_HARD_IGN 4		/* signal is ignored permanently */
74#define S_RESET 5		/* temporary - to reset a hard ignored sig */
75
76
77static char sigmode[NSIG];	/* current value of signal */
78volatile sig_atomic_t pendingsig;	/* indicates some signal received */
79volatile sig_atomic_t pendingsig_waitcmd;	/* indicates wait builtin should be interrupted */
80static int in_dotrap;			/* do we execute in a trap handler? */
81static char *volatile trap[NSIG];	/* trap handler commands */
82static volatile sig_atomic_t gotsig[NSIG];
83				/* indicates specified signal received */
84static int ignore_sigchld;	/* Used while handling SIGCHLD traps. */
85static int last_trapsig;
86
87static int exiting;		/* exitshell() has been called */
88static int exiting_exitstatus;	/* value passed to exitshell() */
89
90static int getsigaction(int, sig_t *);
91
92
93/*
94 * Map a string to a signal number.
95 *
96 * Note: the signal number may exceed NSIG.
97 */
98static int
99sigstring_to_signum(char *sig)
100{
101
102	if (is_number(sig)) {
103		int signo;
104
105		signo = atoi(sig);
106		return ((signo >= 0 && signo < NSIG) ? signo : (-1));
107	} else if (strcasecmp(sig, "EXIT") == 0) {
108		return (0);
109	} else {
110		int n;
111
112		if (strncasecmp(sig, "SIG", 3) == 0)
113			sig += 3;
114		for (n = 1; n < sys_nsig; n++)
115			if (sys_signame[n] &&
116			    strcasecmp(sys_signame[n], sig) == 0)
117				return (n);
118	}
119	return (-1);
120}
121
122
123/*
124 * Print a list of valid signal names.
125 */
126static void
127printsignals(void)
128{
129	int n, outlen;
130
131	outlen = 0;
132	for (n = 1; n < sys_nsig; n++) {
133		if (sys_signame[n]) {
134			out1fmt("%s", sys_signame[n]);
135			outlen += strlen(sys_signame[n]);
136		} else {
137			out1fmt("%d", n);
138			outlen += 3;	/* good enough */
139		}
140		++outlen;
141		if (outlen > 71 || n == sys_nsig - 1) {
142			out1str("\n");
143			outlen = 0;
144		} else {
145			out1c(' ');
146		}
147	}
148}
149
150
151/*
152 * The trap builtin.
153 */
154int
155trapcmd(int argc __unused, char **argv)
156{
157	char *action;
158	int signo;
159	int errors = 0;
160	int i;
161
162	while ((i = nextopt("l")) != '\0') {
163		switch (i) {
164		case 'l':
165			printsignals();
166			return (0);
167		}
168	}
169	argv = argptr;
170
171	if (*argv == NULL) {
172		for (signo = 0 ; signo < sys_nsig ; signo++) {
173			if (signo < NSIG && trap[signo] != NULL) {
174				out1str("trap -- ");
175				out1qstr(trap[signo]);
176				if (signo == 0) {
177					out1str(" EXIT\n");
178				} else if (sys_signame[signo]) {
179					out1fmt(" %s\n", sys_signame[signo]);
180				} else {
181					out1fmt(" %d\n", signo);
182				}
183			}
184		}
185		return 0;
186	}
187	action = NULL;
188	if (*argv && !is_number(*argv)) {
189		if (strcmp(*argv, "-") == 0)
190			argv++;
191		else {
192			action = *argv;
193			argv++;
194		}
195	}
196	for (; *argv; argv++) {
197		if ((signo = sigstring_to_signum(*argv)) == -1) {
198			warning("bad signal %s", *argv);
199			errors = 1;
200			continue;
201		}
202		INTOFF;
203		if (action)
204			action = savestr(action);
205		if (trap[signo])
206			ckfree(trap[signo]);
207		trap[signo] = action;
208		if (signo != 0)
209			setsignal(signo);
210		INTON;
211	}
212	return errors;
213}
214
215
216/*
217 * Clear traps on a fork.
218 */
219void
220clear_traps(void)
221{
222	char *volatile *tp;
223
224	for (tp = trap ; tp <= &trap[NSIG - 1] ; tp++) {
225		if (*tp && **tp) {	/* trap not NULL or SIG_IGN */
226			INTOFF;
227			ckfree(*tp);
228			*tp = NULL;
229			if (tp != &trap[0])
230				setsignal(tp - trap);
231			INTON;
232		}
233	}
234}
235
236
237/*
238 * Check if we have any traps enabled.
239 */
240int
241have_traps(void)
242{
243	char *volatile *tp;
244
245	for (tp = trap ; tp <= &trap[NSIG - 1] ; tp++) {
246		if (*tp && **tp)	/* trap not NULL or SIG_IGN */
247			return 1;
248	}
249	return 0;
250}
251
252/*
253 * Set the signal handler for the specified signal.  The routine figures
254 * out what it should be set to.
255 */
256void
257setsignal(int signo)
258{
259	int action;
260	sig_t sigact = SIG_DFL;
261	struct sigaction sa;
262	char *t;
263
264	if ((t = trap[signo]) == NULL)
265		action = S_DFL;
266	else if (*t != '\0')
267		action = S_CATCH;
268	else
269		action = S_IGN;
270	if (action == S_DFL) {
271		switch (signo) {
272		case SIGINT:
273			action = S_CATCH;
274			break;
275		case SIGQUIT:
276#ifdef DEBUG
277			{
278			extern int debug;
279
280			if (debug)
281				break;
282			}
283#endif
284			action = S_CATCH;
285			break;
286		case SIGTERM:
287			if (rootshell && iflag)
288				action = S_IGN;
289			break;
290#if JOBS
291		case SIGTSTP:
292		case SIGTTOU:
293			if (rootshell && mflag)
294				action = S_IGN;
295			break;
296#endif
297		}
298	}
299
300	t = &sigmode[signo];
301	if (*t == 0) {
302		/*
303		 * current setting unknown
304		 */
305		if (!getsigaction(signo, &sigact)) {
306			/*
307			 * Pretend it worked; maybe we should give a warning
308			 * here, but other shells don't. We don't alter
309			 * sigmode, so that we retry every time.
310			 */
311			return;
312		}
313		if (sigact == SIG_IGN) {
314			if (mflag && (signo == SIGTSTP ||
315			     signo == SIGTTIN || signo == SIGTTOU)) {
316				*t = S_IGN;	/* don't hard ignore these */
317			} else
318				*t = S_HARD_IGN;
319		} else {
320			*t = S_RESET;	/* force to be set */
321		}
322	}
323	if (*t == S_HARD_IGN || *t == action)
324		return;
325	switch (action) {
326		case S_DFL:	sigact = SIG_DFL;	break;
327		case S_CATCH:  	sigact = onsig;		break;
328		case S_IGN:	sigact = SIG_IGN;	break;
329	}
330	*t = action;
331	sa.sa_handler = sigact;
332	sa.sa_flags = 0;
333	sigemptyset(&sa.sa_mask);
334	sigaction(signo, &sa, NULL);
335}
336
337
338/*
339 * Return the current setting for sig w/o changing it.
340 */
341static int
342getsigaction(int signo, sig_t *sigact)
343{
344	struct sigaction sa;
345
346	if (sigaction(signo, (struct sigaction *)0, &sa) == -1)
347		return 0;
348	*sigact = (sig_t) sa.sa_handler;
349	return 1;
350}
351
352
353/*
354 * Ignore a signal.
355 */
356void
357ignoresig(int signo)
358{
359
360	if (sigmode[signo] == 0)
361		setsignal(signo);
362	if (sigmode[signo] != S_IGN && sigmode[signo] != S_HARD_IGN) {
363		signal(signo, SIG_IGN);
364		sigmode[signo] = S_IGN;
365	}
366}
367
368
369int
370issigchldtrapped(void)
371{
372
373	return (trap[SIGCHLD] != NULL && *trap[SIGCHLD] != '\0');
374}
375
376
377/*
378 * Signal handler.
379 */
380void
381onsig(int signo)
382{
383
384	if (signo == SIGINT && trap[SIGINT] == NULL) {
385		/*
386		 * The !in_dotrap here is safe.  The only way we can arrive
387		 * here with in_dotrap set is that a trap handler set SIGINT to
388		 * SIG_DFL and killed itself.
389		 */
390		if (suppressint && !in_dotrap)
391			SET_PENDING_INT;
392		else
393			onint();
394		return;
395	}
396
397	/* If we are currently in a wait builtin, prepare to break it */
398	if (signo == SIGINT || signo == SIGQUIT)
399		pendingsig_waitcmd = signo;
400
401	if (trap[signo] != NULL && trap[signo][0] != '\0' &&
402	    (signo != SIGCHLD || !ignore_sigchld)) {
403		gotsig[signo] = 1;
404		pendingsig = signo;
405		pendingsig_waitcmd = signo;
406	}
407}
408
409
410/*
411 * Called to execute a trap.  Perhaps we should avoid entering new trap
412 * handlers while we are executing a trap handler.
413 */
414void
415dotrap(void)
416{
417	struct stackmark smark;
418	int i;
419	int savestatus, prev_evalskip, prev_skipcount;
420
421	in_dotrap++;
422	for (;;) {
423		pendingsig = 0;
424		pendingsig_waitcmd = 0;
425		for (i = 1; i < NSIG; i++) {
426			if (gotsig[i]) {
427				gotsig[i] = 0;
428				if (trap[i]) {
429					/*
430					 * Ignore SIGCHLD to avoid infinite
431					 * recursion if the trap action does
432					 * a fork.
433					 */
434					if (i == SIGCHLD)
435						ignore_sigchld++;
436
437					/*
438					 * Backup current evalskip
439					 * state and reset it before
440					 * executing a trap, so that the
441					 * trap is not disturbed by an
442					 * ongoing break/continue/return
443					 * statement.
444					 */
445					prev_evalskip  = evalskip;
446					prev_skipcount = skipcount;
447					evalskip = 0;
448
449					last_trapsig = i;
450					savestatus = exitstatus;
451					setstackmark(&smark);
452					evalstring(stsavestr(trap[i]), 0);
453					popstackmark(&smark);
454
455					/*
456					 * If such a command was not
457					 * already in progress, allow a
458					 * break/continue/return in the
459					 * trap action to have an effect
460					 * outside of it.
461					 */
462					if (evalskip == 0 ||
463					    prev_evalskip != 0) {
464						evalskip  = prev_evalskip;
465						skipcount = prev_skipcount;
466						exitstatus = savestatus;
467					}
468
469					if (i == SIGCHLD)
470						ignore_sigchld--;
471				}
472				break;
473			}
474		}
475		if (i >= NSIG)
476			break;
477	}
478	in_dotrap--;
479}
480
481
482/*
483 * Controls whether the shell is interactive or not.
484 */
485void
486setinteractive(int on)
487{
488	static int is_interactive = -1;
489
490	if (on == is_interactive)
491		return;
492	setsignal(SIGINT);
493	setsignal(SIGQUIT);
494	setsignal(SIGTERM);
495	is_interactive = on;
496}
497
498
499/*
500 * Called to exit the shell.
501 */
502void
503exitshell(int status)
504{
505	TRACE(("exitshell(%d) pid=%d\n", status, getpid()));
506	exiting = 1;
507	exiting_exitstatus = status;
508	exitshell_savedstatus();
509}
510
511void
512exitshell_savedstatus(void)
513{
514	struct jmploc loc1, loc2;
515	char *p;
516	int sig = 0;
517	sigset_t sigs;
518
519	if (!exiting) {
520		if (in_dotrap && last_trapsig) {
521			sig = last_trapsig;
522			exiting_exitstatus = sig + 128;
523		} else
524			exiting_exitstatus = oexitstatus;
525	}
526	exitstatus = oexitstatus = exiting_exitstatus;
527	if (!setjmp(loc1.loc)) {
528		handler = &loc1;
529		if ((p = trap[0]) != NULL && *p != '\0') {
530			/*
531			 * Reset evalskip, or the trap on EXIT could be
532			 * interrupted if the last command was a "return".
533			 */
534			evalskip = 0;
535			trap[0] = NULL;
536			evalstring(p, 0);
537		}
538	}
539	if (!setjmp(loc2.loc)) {
540		handler = &loc2;		/* probably unnecessary */
541		flushall();
542#if JOBS
543		setjobctl(0);
544#endif
545	}
546	if (sig != 0 && sig != SIGSTOP && sig != SIGTSTP && sig != SIGTTIN &&
547	    sig != SIGTTOU) {
548		signal(sig, SIG_DFL);
549		sigemptyset(&sigs);
550		sigaddset(&sigs, sig);
551		sigprocmask(SIG_UNBLOCK, &sigs, NULL);
552		kill(getpid(), sig);
553		/* If the default action is to ignore, fall back to _exit(). */
554	}
555	_exit(exiting_exitstatus);
556}
557