bin/sh/trap.c

   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  * 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 #ifndef lint
  36 #if 0
  37 static char sccsid[] = "@(#)trap.c      8.5 (Berkeley) 6/5/95";
  38 #endif
  39 #endif /* not lint */
  40 #include <sys/cdefs.h>
  41 __FBSDID("$FreeBSD: head/bin/sh/trap.c 364919 2020-08-28 15:35:45Z jilles $");
  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 #ifndef NO_HISTORY
  62 #include "myhistedit.h"
  63 #endif
  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 permanently */
  76 #define S_RESET 5               /* temporary - to reset a hard ignored sig */
  77
  78
  79 static char sigmode[NSIG];      /* current value of signal */
  80 volatile sig_atomic_t pendingsig;       /* indicates some signal received */
  81 volatile sig_atomic_t pendingsig_waitcmd;       /* indicates wait builtin should be interrupted */
  82 static int in_dotrap;                   /* do we execute in a trap handler? */
  83 static char *volatile trap[NSIG];       /* trap handler commands */
  84 static volatile sig_atomic_t gotsig[NSIG];
  85                                 /* indicates specified signal received */
  86 static int ignore_sigchld;      /* Used while handling SIGCHLD traps. */
  87 static int last_trapsig;
  88
  89 static int exiting;             /* exitshell() has been called */
  90 static int exiting_exitstatus;  /* value passed to exitshell() */
  91
  92 static int getsigaction(int, sig_t *);
  93
  94
  95 /*
  96  * Map a string to a signal number.
  97  *
  98  * Note: the signal number may exceed NSIG.
  99  */
 100 static int
 101 sigstring_to_signum(char *sig)
 102 {
 103
 104         if (is_number(sig)) {
 105                 int signo;
 106
 107                 signo = atoi(sig);
 108                 return ((signo >= 0 && signo < NSIG) ? signo : (-1));
 109         } else if (strcasecmp(sig, "EXIT") == 0) {
 110                 return (0);
 111         } else {
 112                 int n;
 113
 114                 if (strncasecmp(sig, "SIG", 3) == 0)
 115                         sig += 3;
 116                 for (n = 1; n < sys_nsig; n++)
 117                         if (sys_signame[n] &&
 118                             strcasecmp(sys_signame[n], sig) == 0)
 119                                 return (n);
 120         }
 121         return (-1);
 122 }
 123
 124
 125 /*
 126  * Print a list of valid signal names.
 127  */
 128 static void
 129 printsignals(void)
 130 {
 131         int n, outlen;
 132
 133         outlen = 0;
 134         for (n = 1; n < sys_nsig; n++) {
 135                 if (sys_signame[n]) {
 136                         out1fmt("%s", sys_signame[n]);
 137                         outlen += strlen(sys_signame[n]);
 138                 } else {
 139                         out1fmt("%d", n);
 140                         outlen += 3;    /* good enough */
 141                 }
 142                 ++outlen;
 143                 if (outlen > 71 || n == sys_nsig - 1) {
 144                         out1str("\n");
 145                         outlen = 0;
 146                 } else {
 147                         out1c(' ');
 148                 }
 149         }
 150 }
 151
 152
 153 /*
 154  * The trap builtin.
 155  */
 156 int
 157 trapcmd(int argc __unused, char **argv)
 158 {
 159         char *action;
 160         int signo;
 161         int errors = 0;
 162         int i;
 163
 164         while ((i = nextopt("l")) != '\0') {
 165                 switch (i) {
 166                 case 'l':
 167                         printsignals();
 168                         return (0);
 169                 }
 170         }
 171         argv = argptr;
 172
 173         if (*argv == NULL) {
 174                 for (signo = 0 ; signo < sys_nsig ; signo++) {
 175                         if (signo < NSIG && trap[signo] != NULL) {
 176                                 out1str("trap -- ");
 177                                 out1qstr(trap[signo]);
 178                                 if (signo == 0) {
 179                                         out1str(" EXIT\n");
 180                                 } else if (sys_signame[signo]) {
 181                                         out1fmt(" %s\n", sys_signame[signo]);
 182                                 } else {
 183                                         out1fmt(" %d\n", signo);
 184                                 }
 185                         }
 186                 }
 187                 return 0;
 188         }
 189         action = NULL;
 190         if (*argv && !is_number(*argv)) {
 191                 if (strcmp(*argv, "-") == 0)
 192                         argv++;
 193                 else {
 194                         action = *argv;
 195                         argv++;
 196                 }
 197         }
 198         for (; *argv; argv++) {
 199                 if ((signo = sigstring_to_signum(*argv)) == -1) {
 200                         warning("bad signal %s", *argv);
 201                         errors = 1;
 202                         continue;
 203                 }
 204                 INTOFF;
 205                 if (action)
 206                         action = savestr(action);
 207                 if (trap[signo])
 208                         ckfree(trap[signo]);
 209                 trap[signo] = action;
 210                 if (signo != 0)
 211                         setsignal(signo);
 212                 INTON;
 213         }
 214         return errors;
 215 }
 216
 217
 218 /*
 219  * Clear traps on a fork.
 220  */
 221 void
 222 clear_traps(void)
 223 {
 224         char *volatile *tp;
 225
 226         for (tp = trap ; tp <= &trap[NSIG - 1] ; tp++) {
 227                 if (*tp && **tp) {      /* trap not NULL or SIG_IGN */
 228                         INTOFF;
 229                         ckfree(*tp);
 230                         *tp = NULL;
 231                         if (tp != &trap[0])
 232                                 setsignal(tp - trap);
 233                         INTON;
 234                 }
 235         }
 236 }
 237
 238
 239 /*
 240  * Check if we have any traps enabled.
 241  */
 242 int
 243 have_traps(void)
 244 {
 245         char *volatile *tp;
 246
 247         for (tp = trap ; tp <= &trap[NSIG - 1] ; tp++) {
 248                 if (*tp && **tp)        /* trap not NULL or SIG_IGN */
 249                         return 1;
 250         }
 251         return 0;
 252 }
 253
 254 /*
 255  * Set the signal handler for the specified signal.  The routine figures
 256  * out what it should be set to.
 257  */
 258 void
 259 setsignal(int signo)
 260 {
 261         int action;
 262         sig_t sigact = SIG_DFL;
 263         struct sigaction sa;
 264         char *t;
 265
 266         if ((t = trap[signo]) == NULL)
 267                 action = S_DFL;
 268         else if (*t != '\0')
 269                 action = S_CATCH;
 270         else
 271                 action = S_IGN;
 272         if (action == S_DFL) {
 273                 switch (signo) {
 274                 case SIGINT:
 275                         action = S_CATCH;
 276                         break;
 277                 case SIGQUIT:
 278 #ifdef DEBUG
 279                         {
 280                         extern int debug;
 281
 282                         if (debug)
 283                                 break;
 284                         }
 285 #endif
 286                         action = S_CATCH;
 287                         break;
 288                 case SIGTERM:
 289                         if (rootshell && iflag)
 290                                 action = S_IGN;
 291                         break;
 292 #if JOBS
 293                 case SIGTSTP:
 294                 case SIGTTOU:
 295                         if (rootshell && mflag)
 296                                 action = S_IGN;
 297                         break;
 298 #endif
 299                 }
 300         }
 301
 302         t = &sigmode[signo];
 303         if (*t == 0) {
 304                 /*
 305                  * current setting unknown
 306                  */
 307                 if (!getsigaction(signo, &sigact)) {
 308                         /*
 309                          * Pretend it worked; maybe we should give a warning
 310                          * here, but other shells don't. We don't alter
 311                          * sigmode, so that we retry every time.
 312                          */
 313                         return;
 314                 }
 315                 if (sigact == SIG_IGN) {
 316                         if (mflag && (signo == SIGTSTP ||
 317                              signo == SIGTTIN || signo == SIGTTOU)) {
 318                                 *t = S_IGN;     /* don't hard ignore these */
 319                         } else
 320                                 *t = S_HARD_IGN;
 321                 } else {
 322                         *t = S_RESET;   /* force to be set */
 323                 }
 324         }
 325         if (*t == S_HARD_IGN || *t == action)
 326                 return;
 327         switch (action) {
 328                 case S_DFL:     sigact = SIG_DFL;       break;
 329                 case S_CATCH:   sigact = onsig;         break;
 330                 case S_IGN:     sigact = SIG_IGN;       break;
 331         }
 332         *t = action;
 333         sa.sa_handler = sigact;
 334         sa.sa_flags = 0;
 335         sigemptyset(&sa.sa_mask);
 336         sigaction(signo, &sa, NULL);
 337 }
 338
 339
 340 /*
 341  * Return the current setting for sig w/o changing it.
 342  */
 343 static int
 344 getsigaction(int signo, sig_t *sigact)
 345 {
 346         struct sigaction sa;
 347
 348         if (sigaction(signo, (struct sigaction *)0, &sa) == -1)
 349                 return 0;
 350         *sigact = (sig_t) sa.sa_handler;
 351         return 1;
 352 }
 353
 354
 355 /*
 356  * Ignore a signal.
 357  */
 358 void
 359 ignoresig(int signo)
 360 {
 361
 362         if (sigmode[signo] == 0)
 363                 setsignal(signo);
 364         if (sigmode[signo] != S_IGN && sigmode[signo] != S_HARD_IGN) {
 365                 signal(signo, SIG_IGN);
 366                 sigmode[signo] = S_IGN;
 367         }
 368 }
 369
 370
 371 int
 372 issigchldtrapped(void)
 373 {
 374
 375         return (trap[SIGCHLD] != NULL && *trap[SIGCHLD] != '\0');
 376 }
 377
 378
 379 /*
 380  * Signal handler.
 381  */
 382 void
 383 onsig(int signo)
 384 {
 385
 386         if (signo == SIGINT && trap[SIGINT] == NULL) {
 387                 if (suppressint)
 388                         SET_PENDING_INT;
 389                 else
 390                         onint();
 391                 return;
 392         }
 393
 394         /* If we are currently in a wait builtin, prepare to break it */
 395         if (signo == SIGINT || signo == SIGQUIT)
 396                 pendingsig_waitcmd = signo;
 397
 398         if (trap[signo] != NULL && trap[signo][0] != '\0' &&
 399             (signo != SIGCHLD || !ignore_sigchld)) {
 400                 gotsig[signo] = 1;
 401                 pendingsig = signo;
 402                 pendingsig_waitcmd = signo;
 403         }
 404 }
 405
 406
 407 /*
 408  * Called to execute a trap.  Perhaps we should avoid entering new trap
 409  * handlers while we are executing a trap handler.
 410  */
 411 void
 412 dotrap(void)
 413 {
 414         struct stackmark smark;
 415         int i;
 416         int savestatus, prev_evalskip, prev_skipcount;
 417
 418         in_dotrap++;
 419         for (;;) {
 420                 pendingsig = 0;
 421                 pendingsig_waitcmd = 0;
 422                 for (i = 1; i < NSIG; i++) {
 423                         if (gotsig[i]) {
 424                                 gotsig[i] = 0;
 425                                 if (trap[i]) {
 426                                         /*
 427                                          * Ignore SIGCHLD to avoid infinite
 428                                          * recursion if the trap action does
 429                                          * a fork.
 430                                          */
 431                                         if (i == SIGCHLD)
 432                                                 ignore_sigchld++;
 433
 434                                         /*
 435                                          * Backup current evalskip
 436                                          * state and reset it before
 437                                          * executing a trap, so that the
 438                                          * trap is not disturbed by an
 439                                          * ongoing break/continue/return
 440                                          * statement.
 441                                          */
 442                                         prev_evalskip  = evalskip;
 443                                         prev_skipcount = skipcount;
 444                                         evalskip = 0;
 445
 446                                         last_trapsig = i;
 447                                         savestatus = exitstatus;
 448                                         setstackmark(&smark);
 449                                         evalstring(stsavestr(trap[i]), 0);
 450                                         popstackmark(&smark);
 451
 452                                         /*
 453                                          * If such a command was not
 454                                          * already in progress, allow a
 455                                          * break/continue/return in the
 456                                          * trap action to have an effect
 457                                          * outside of it.
 458                                          */
 459                                         if (evalskip == 0 ||
 460                                             prev_evalskip != 0) {
 461                                                 evalskip  = prev_evalskip;
 462                                                 skipcount = prev_skipcount;
 463                                                 exitstatus = savestatus;
 464                                         }
 465
 466                                         if (i == SIGCHLD)
 467                                                 ignore_sigchld--;
 468                                 }
 469                                 break;
 470                         }
 471                 }
 472                 if (i >= NSIG)
 473                         break;
 474         }
 475         in_dotrap--;
 476 }
 477
 478
 479 void
 480 trap_init(void)
 481 {
 482         setsignal(SIGINT);
 483         setsignal(SIGQUIT);
 484 }
 485
 486
 487 /*
 488  * Controls whether the shell is interactive or not based on iflag.
 489  */
 490 void
 491 setinteractive(void)
 492 {
 493         setsignal(SIGTERM);
 494 }
 495
 496
 497 /*
 498  * Called to exit the shell.
 499  */
 500 void
 501 exitshell(int status)
 502 {
 503         TRACE(("exitshell(%d) pid=%d\n", status, getpid()));
 504         exiting = 1;
 505         exiting_exitstatus = status;
 506         exitshell_savedstatus();
 507 }
 508
 509 void
 510 exitshell_savedstatus(void)
 511 {
 512         struct jmploc loc1, loc2;
 513         char *p;
 514         int sig = 0;
 515         sigset_t sigs;
 516
 517         if (!exiting) {
 518                 if (in_dotrap && last_trapsig) {
 519                         sig = last_trapsig;
 520                         exiting_exitstatus = sig + 128;
 521                 } else
 522                         exiting_exitstatus = oexitstatus;
 523         }
 524         exitstatus = oexitstatus = exiting_exitstatus;
 525         if (!setjmp(loc1.loc)) {
 526                 handler = &loc1;
 527                 if ((p = trap[0]) != NULL && *p != '\0') {
 528                         /*
 529                          * Reset evalskip, or the trap on EXIT could be
 530                          * interrupted if the last command was a "return".
 531                          */
 532                         evalskip = 0;
 533                         trap[0] = NULL;
 534                         FORCEINTON;
 535                         evalstring(p, 0);
 536                 }
 537         }
 538         if (!setjmp(loc2.loc)) {
 539                 handler = &loc2;                /* probably unnecessary */
 540                 FORCEINTON;
 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 }