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trap.c revision 1.41 
      1 /*	$NetBSD: trap.c,v 1.41 2017/07/05 19:47:11 kre Exp $	*/
      2 
      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  * 3. 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 #include <sys/cdefs.h>
     36 #ifndef lint
     37 #if 0
     38 static char sccsid[] = "@(#)trap.c	8.5 (Berkeley) 6/5/95";
     39 #else
     40 __RCSID("$NetBSD: trap.c,v 1.41 2017/07/05 19:47:11 kre Exp $");
     41 #endif
     42 #endif /* not lint */
     43 
     44 #include <signal.h>
     45 #include <unistd.h>
     46 #include <stdlib.h>
     47 #include <stdio.h>
     48 
     49 #include "shell.h"
     50 #include "main.h"
     51 #include "nodes.h"	/* for other headers */
     52 #include "eval.h"
     53 #include "jobs.h"
     54 #include "show.h"
     55 #include "options.h"
     56 #include "builtins.h"
     57 #include "syntax.h"
     58 #include "output.h"
     59 #include "memalloc.h"
     60 #include "error.h"
     61 #include "trap.h"
     62 #include "mystring.h"
     63 #include "var.h"
     64 
     65 
     66 /*
     67  * Sigmode records the current value of the signal handlers for the various
     68  * modes.  A value of zero means that the current handler is not known.
     69  * S_HARD_IGN indicates that the signal was ignored on entry to the shell,
     70  */
     71 
     72 #define S_DFL 1			/* default signal handling (SIG_DFL) */
     73 #define S_CATCH 2		/* signal is caught */
     74 #define S_IGN 3			/* signal is ignored (SIG_IGN) */
     75 #define S_HARD_IGN 4		/* signal is ignored permenantly */
     76 #define S_RESET 5		/* temporary - to reset a hard ignored sig */
     77 
     78 
     79 char *trap[NSIG];		/* trap handler commands */
     80 MKINIT char sigmode[NSIG];	/* current value of signal */
     81 static volatile char gotsig[NSIG];/* indicates specified signal received */
     82 volatile int pendingsigs;	/* indicates some signal received */
     83 
     84 static int getsigaction(int, sig_t *);
     85 STATIC const char *trap_signame(int);
     86 
     87 /*
     88  * return the signal number described by `p' (as a number or a name)
     89  * or -1 if it isn't one
     90  */
     91 
     92 static int
     93 signame_to_signum(const char *p)
     94 {
     95 	int i;
     96 
     97 	if (is_number(p))
     98 		return number(p);
     99 
    100 	if (strcasecmp(p, "exit") == 0 )
    101 		return 0;
    102 
    103 	if (strncasecmp(p, "sig", 3) == 0)
    104 		p += 3;
    105 
    106 	for (i = 0; i < NSIG; ++i)
    107 		if (strcasecmp (p, sys_signame[i]) == 0)
    108 			return i;
    109 	return -1;
    110 }
    111 
    112 /*
    113  * return the name of a signal used by the "trap" command
    114  */
    115 STATIC const char *
    116 trap_signame(int signo)
    117 {
    118 	static char nbuf[12];
    119 	const char *p = NULL;
    120 
    121 	if (signo == 0)
    122 		return "EXIT";
    123 	if (signo > 0 && signo < NSIG)
    124 		p = sys_signame[signo];
    125 	if (p != NULL)
    126 		return p;
    127 	(void)snprintf(nbuf, sizeof nbuf, "%d", signo);
    128 	return nbuf;
    129 }
    130 
    131 /*
    132  * Print a list of valid signal names
    133  */
    134 static void
    135 printsignals(void)
    136 {
    137 	int n;
    138 
    139 	out1str("EXIT ");
    140 
    141 	for (n = 1; n < NSIG; n++) {
    142 		out1fmt("%s", trap_signame(n));
    143 		if ((n == NSIG/2) ||  n == (NSIG - 1))
    144 			out1str("\n");
    145 		else
    146 			out1c(' ');
    147 	}
    148 }
    149 
    150 /*
    151  * The trap builtin.
    152  */
    153 
    154 int
    155 trapcmd(int argc, char **argv)
    156 {
    157 	char *action;
    158 	char **ap;
    159 	int signo;
    160 	int errs = 0;
    161 	int printonly = 0;
    162 
    163 	ap = argv + 1;
    164 
    165 	if (argc == 2 && strcmp(*ap, "-l") == 0) {
    166 		printsignals();
    167 		return 0;
    168 	}
    169 	if (argc == 2 && strcmp(*ap, "-") == 0) {
    170 		for (signo = 0; signo < NSIG; signo++) {
    171 			if (trap[signo] == NULL)
    172 				continue;
    173 			INTOFF;
    174 			ckfree(trap[signo]);
    175 			trap[signo] = NULL;
    176 			if (signo != 0)
    177 				setsignal(signo, 0);
    178 			INTON;
    179 		}
    180 		return 0;
    181 	}
    182 	if (argc >= 2 && strcmp(*ap, "-p") == 0) {
    183 		printonly = 1;
    184 		ap++;
    185 		argc--;
    186 	}
    187 
    188 	if (argc > 1 && strcmp(*ap, "--") == 0) {
    189 		argc--;
    190 		ap++;
    191 	}
    192 
    193 	if (argc <= 1) {
    194 		int count;
    195 
    196 		if (printonly) {
    197 			for (count = 0, signo = 0 ; signo < NSIG ; signo++)
    198 				if (trap[signo] == NULL) {
    199 					if (count == 0)
    200 						out1str("trap -- -");
    201 					out1fmt(" %s", trap_signame(signo));
    202 					/* oh! unlucky 13 */
    203 					if (++count >= 13) {
    204 						out1str("\n");
    205 						count = 0;
    206 					}
    207 				}
    208 			if (count)
    209 				out1str("\n");
    210 		}
    211 
    212 		for (count = 0, signo = 0 ; signo < NSIG ; signo++)
    213 			if (trap[signo] != NULL && trap[signo][0] == '\0') {
    214 				if (count == 0)
    215 					out1str("trap -- ''");
    216 				out1fmt(" %s", trap_signame(signo));
    217 				/*
    218 				 * the prefix is 10 bytes, with 4 byte
    219 				 * signal names (common) we have room in
    220 				 * the 70 bytes left on a normal line for
    221 				 * 70/(4+1) signals, that's 14, but to
    222 				 * allow for the occasional longer sig name
    223 				 * we output one less...
    224 				 */
    225 				if (++count >= 13) {
    226 					out1str("\n");
    227 					count = 0;
    228 				}
    229 			}
    230 		if (count)
    231 			out1str("\n");
    232 
    233 		for (signo = 0 ; signo < NSIG ; signo++)
    234 			if (trap[signo] != NULL && trap[signo][0] != '\0') {
    235 				out1str("trap -- ");
    236 				print_quoted(trap[signo]);
    237 				out1fmt(" %s\n", trap_signame(signo));
    238 			}
    239 
    240 		return 0;
    241 	}
    242 
    243 	action = NULL;
    244 
    245 	if (!printonly && !is_number(*ap)) {
    246 		if ((*ap)[0] == '-' && (*ap)[1] == '\0')
    247 			ap++;			/* reset to default */
    248 		else
    249 			action = *ap++;		/* can be '' for "ignore" */
    250 		argc--;
    251 	}
    252 
    253 	if (argc < 2) {		/* there must be at least 1 condition */
    254 		out2str("Usage: trap [-l]\n"
    255 			"       trap -p [condition ...]\n"
    256 			"       trap action condition ...\n"
    257 			"       trap N condition ...\n");
    258 		return 2;
    259 	}
    260 
    261 
    262 	while (*ap) {
    263 		signo = signame_to_signum(*ap);
    264 
    265 		if (signo < 0 || signo >= NSIG) {
    266 			/* This is not a fatal error, so sayeth posix */
    267 			outfmt(out2, "trap: '%s' bad condition\n", *ap);
    268 			errs = 1;
    269 			ap++;
    270 			continue;
    271 		}
    272 		ap++;
    273 
    274 		if (printonly) {
    275 			out1str("trap -- ");
    276 			if (trap[signo] == NULL)
    277 				out1str("-");
    278 			else
    279 				print_quoted(trap[signo]);
    280 			out1fmt(" %s\n", trap_signame(signo));
    281 			continue;
    282 		}
    283 
    284 		INTOFF;
    285 		if (action)
    286 			action = savestr(action);
    287 
    288 		if (trap[signo])
    289 			ckfree(trap[signo]);
    290 
    291 		trap[signo] = action;
    292 
    293 		if (signo != 0)
    294 			setsignal(signo, 0);
    295 		INTON;
    296 	}
    297 	return errs;
    298 }
    299 
    300 
    301 
    302 /*
    303  * Clear traps on a fork or vfork.
    304  * Takes one arg vfork, to tell it to not be destructive of
    305  * the parents variables.
    306  */
    307 
    308 void
    309 clear_traps(int vforked)
    310 {
    311 	char **tp;
    312 
    313 	for (tp = trap ; tp < &trap[NSIG] ; tp++) {
    314 		if (*tp && **tp) {	/* trap not NULL or SIG_IGN */
    315 			INTOFF;
    316 			if (!vforked) {
    317 				ckfree(*tp);
    318 				*tp = NULL;
    319 			}
    320 			if (tp != &trap[0])
    321 				setsignal(tp - trap, vforked);
    322 			INTON;
    323 		}
    324 	}
    325 }
    326 
    327 
    328 
    329 /*
    330  * Set the signal handler for the specified signal.  The routine figures
    331  * out what it should be set to.
    332  */
    333 
    334 sig_t
    335 setsignal(int signo, int vforked)
    336 {
    337 	int action;
    338 	sig_t sigact = SIG_DFL, sig;
    339 	char *t, tsig;
    340 
    341 	if ((t = trap[signo]) == NULL)
    342 		action = S_DFL;
    343 	else if (*t != '\0')
    344 		action = S_CATCH;
    345 	else
    346 		action = S_IGN;
    347 	if (rootshell && !vforked && action == S_DFL) {
    348 		switch (signo) {
    349 		case SIGINT:
    350 			if (iflag || minusc || sflag == 0)
    351 				action = S_CATCH;
    352 			break;
    353 		case SIGQUIT:
    354 #ifdef DEBUG
    355 			if (debug)
    356 				break;
    357 #endif
    358 			/* FALLTHROUGH */
    359 		case SIGTERM:
    360 			if (iflag)
    361 				action = S_IGN;
    362 			break;
    363 #if JOBS
    364 		case SIGTSTP:
    365 		case SIGTTOU:
    366 			if (mflag)
    367 				action = S_IGN;
    368 			break;
    369 #endif
    370 		}
    371 	}
    372 
    373 	t = &sigmode[signo - 1];
    374 	tsig = *t;
    375 	if (tsig == 0) {
    376 		/*
    377 		 * current setting unknown
    378 		 */
    379 		if (!getsigaction(signo, &sigact)) {
    380 			/*
    381 			 * Pretend it worked; maybe we should give a warning
    382 			 * here, but other shells don't. We don't alter
    383 			 * sigmode, so that we retry every time.
    384 			 */
    385 			return 0;
    386 		}
    387 		if (sigact == SIG_IGN) {
    388 			/*
    389 			 * POSIX 3.14.13 states that non-interactive shells
    390 			 * should ignore trap commands for signals that were
    391 			 * ignored upon entry, and leaves the behavior
    392 			 * unspecified for interactive shells. On interactive
    393 			 * shells, or if job control is on, and we have a job
    394 			 * control related signal, we allow the trap to work.
    395 			 *
    396 			 * This change allows us to be POSIX compliant, and
    397 			 * at the same time override the default behavior if
    398 			 * we need to by setting the interactive flag.
    399 			 */
    400 			if ((mflag && (signo == SIGTSTP ||
    401 			     signo == SIGTTIN || signo == SIGTTOU)) || iflag) {
    402 				tsig = S_IGN;
    403 			} else
    404 				tsig = S_HARD_IGN;
    405 		} else {
    406 			tsig = S_RESET;	/* force to be set */
    407 		}
    408 	}
    409 	if (tsig == S_HARD_IGN || tsig == action)
    410 		return 0;
    411 	switch (action) {
    412 		case S_DFL:	sigact = SIG_DFL;	break;
    413 		case S_CATCH:  	sigact = onsig;		break;
    414 		case S_IGN:	sigact = SIG_IGN;	break;
    415 	}
    416 	sig = signal(signo, sigact);
    417 	if (sig != SIG_ERR) {
    418 		sigset_t ss;
    419 		if (!vforked)
    420 			*t = action;
    421 		if (action == S_CATCH)
    422 			(void)siginterrupt(signo, 1);
    423 		/*
    424 		 * If our parent accidentally blocked signals for
    425 		 * us make sure we unblock them
    426 		 */
    427 		(void)sigemptyset(&ss);
    428 		(void)sigaddset(&ss, signo);
    429 		(void)sigprocmask(SIG_UNBLOCK, &ss, NULL);
    430 	}
    431 	return sig;
    432 }
    433 
    434 /*
    435  * Return the current setting for sig w/o changing it.
    436  */
    437 static int
    438 getsigaction(int signo, sig_t *sigact)
    439 {
    440 	struct sigaction sa;
    441 
    442 	if (sigaction(signo, (struct sigaction *)0, &sa) == -1)
    443 		return 0;
    444 	*sigact = (sig_t) sa.sa_handler;
    445 	return 1;
    446 }
    447 
    448 /*
    449  * Ignore a signal.
    450  */
    451 
    452 void
    453 ignoresig(int signo, int vforked)
    454 {
    455 	if (sigmode[signo - 1] != S_IGN && sigmode[signo - 1] != S_HARD_IGN) {
    456 		signal(signo, SIG_IGN);
    457 	}
    458 	if (!vforked)
    459 		sigmode[signo - 1] = S_HARD_IGN;
    460 }
    461 
    462 
    463 #ifdef mkinit
    464 INCLUDE <signal.h>
    465 INCLUDE "trap.h"
    466 
    467 SHELLPROC {
    468 	char *sm;
    469 
    470 	clear_traps(0);
    471 	for (sm = sigmode ; sm < sigmode + NSIG ; sm++) {
    472 		if (*sm == S_IGN)
    473 			*sm = S_HARD_IGN;
    474 	}
    475 }
    476 #endif
    477 
    478 
    479 
    480 /*
    481  * Signal handler.
    482  */
    483 
    484 void
    485 onsig(int signo)
    486 {
    487 	CTRACE(DBG_SIG, ("Signal %d, had: pending %d, gotsig[%d]=%d\n",
    488 	    signo, pendingsigs, signo, gotsig[signo]));
    489 
    490 	signal(signo, onsig);
    491 	if (signo == SIGINT && trap[SIGINT] == NULL) {
    492 		onint();
    493 		return;
    494 	}
    495 	gotsig[signo] = 1;
    496 	pendingsigs++;
    497 }
    498 
    499 
    500 
    501 /*
    502  * Called to execute a trap.  Perhaps we should avoid entering new trap
    503  * handlers while we are executing a trap handler.
    504  */
    505 
    506 void
    507 dotrap(void)
    508 {
    509 	int i;
    510 	int savestatus;
    511 	char *tr;
    512 
    513 	for (;;) {
    514 		for (i = 1 ; ; i++) {
    515 			if (i >= NSIG) {
    516 				pendingsigs = 0;
    517 				return;
    518 			}
    519 			if (gotsig[i])
    520 				break;
    521 		}
    522 		gotsig[i] = 0;
    523 		savestatus=exitstatus;
    524 		CTRACE(DBG_TRAP|DBG_SIG, ("dotrap %d: \"%s\"\n", i,
    525 		    trap[i] ? trap[i] : "-NULL-"));
    526 		tr = savestr(trap[i]);		/* trap code may free trap[i] */
    527 		evalstring(tr, 0);
    528 		ckfree(tr);
    529 		exitstatus=savestatus;
    530 	}
    531 }
    532 
    533 int
    534 lastsig(void)
    535 {
    536 	int i;
    537 
    538 	for (i = NSIG; --i > 0; )
    539 		if (gotsig[i])
    540 			return i;
    541 	return SIGINT;	/* XXX */
    542 }
    543 
    544 /*
    545  * Controls whether the shell is interactive or not.
    546  */
    547 
    548 
    549 void
    550 setinteractive(int on)
    551 {
    552 	static int is_interactive;
    553 
    554 	if (on == is_interactive)
    555 		return;
    556 	setsignal(SIGINT, 0);
    557 	setsignal(SIGQUIT, 0);
    558 	setsignal(SIGTERM, 0);
    559 	is_interactive = on;
    560 }
    561 
    562 
    563 
    564 /*
    565  * Called to exit the shell.
    566  */
    567 
    568 void
    569 exitshell(int status)
    570 {
    571 	struct jmploc loc1, loc2;
    572 	char *p;
    573 
    574 	CTRACE(DBG_ERRS|DBG_PROCS|DBG_CMDS|DBG_TRAP,
    575 	    ("pid %d, exitshell(%d)\n", getpid(), status));
    576 
    577 	if (setjmp(loc1.loc)) {
    578 		goto l1;
    579 	}
    580 	if (setjmp(loc2.loc)) {
    581 		goto l2;
    582 	}
    583 	handler = &loc1;
    584 	if ((p = trap[0]) != NULL && *p != '\0') {
    585 		trap[0] = NULL;
    586 		VTRACE(DBG_TRAP, ("exit trap: \"%s\"\n", p));
    587 		evalstring(p, 0);
    588 	}
    589  l1:	handler = &loc2;			/* probably unnecessary */
    590 	flushall();
    591 #if JOBS
    592 	setjobctl(0);
    593 #endif
    594  l2:	_exit(status);
    595 	/* NOTREACHED */
    596 }
    597