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timeout(1): align execvp(3) failure statuses with GNU timeout

Align our exit statuses with those of GNU timeout in the execvp(3)
failure case.  Exit with 127 if the utility is not found.  Exit with
126 if we cannot execute the utility for any other reason.

While here, the child should _exit(2) instead of calling exit(3) via
err(3).

Update the manpage accordingly.

With input from millert@ and deraadt@.

Link: https://marc.info/?l=openbsd-tech&m=169739592322978&w=2

ok millert@

/* $OpenBSD: timeout.c,v 1.26 2023/11/03 19:16:31 cheloha Exp $ */

/*
 * Copyright (c) 2021 Job Snijders <job@openbsd.org>
 * Copyright (c) 2014 Baptiste Daroussin <bapt@FreeBSD.org>
 * Copyright (c) 2014 Vsevolod Stakhov <vsevolod@FreeBSD.org>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer
 *    in this position and unchanged.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/types.h>
#include <sys/time.h>
#include <sys/wait.h>

#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <getopt.h>
#include <limits.h>
#include <signal.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define EXIT_TIMEOUT 124

static volatile sig_atomic_t sig_chld = 0;
static volatile sig_atomic_t sig_term = 0;
static volatile sig_atomic_t sig_alrm = 0;
static volatile sig_atomic_t sig_ign = 0;

static void __dead
usage(void)
{
	fprintf(stderr,
	    "usage: timeout [-fp] [-k time] [-s signal] duration command"
	    " [arg ...]\n");
	exit(1);
}

static double
parse_duration(const char *duration)
{
	double	 ret;
	char	*suffix;

	ret = strtod(duration, &suffix);
	if (ret == 0 && suffix == duration)
		errx(1, "duration is not a number");
	if (ret < 0 || ret >= 100000000UL)
		errx(1, "duration out of range");

	if (suffix == NULL || *suffix == '\0')
		return (ret);

	if (suffix[1] != '\0')
		errx(1, "duration unit suffix too long");

	switch (*suffix) {
	case 's':
		break;
	case 'm':
		ret *= 60;
		break;
	case 'h':
		ret *= 60 * 60;
		break;
	case 'd':
		ret *= 60 * 60 * 24;
		break;
	default:
		errx(1, "duration unit suffix is invalid");
	}

	return (ret);
}

static int
parse_signal(const char *str)
{
	long long	 sig;
	const char	*errstr;

	if (isalpha((unsigned char)*str)) {
		int i;

		if (strncasecmp(str, "SIG", 3) == 0)
			str += 3;
		for (i = 1; i < NSIG; i++) {
			if (strcasecmp(str, sys_signame[i]) == 0)
				return (i);
		}
		errx(1, "invalid signal name");
	}

	sig = strtonum(str, 1, NSIG, &errstr);
	if (errstr != NULL)
		errx(1, "signal %s %s", str, errstr);

	return (int)sig;
}

static void
sig_handler(int signo)
{
	if (sig_ign != 0 && signo == sig_ign) {
		sig_ign = 0;
		return;
	}

	switch (signo) {
	case SIGINT:
	case SIGHUP:
	case SIGQUIT:
	case SIGTERM:
		sig_term = signo;
		break;
	case SIGCHLD:
		sig_chld = 1;
		break;
	case SIGALRM:
		sig_alrm = 1;
		break;
	}
}

static void
set_interval(double iv)
{
	struct itimerval tim;

	memset(&tim, 0, sizeof(tim));
	tim.it_value.tv_sec = (time_t)iv;
	iv -= (double)tim.it_value.tv_sec;
	tim.it_value.tv_usec = (suseconds_t)(iv * 1000000UL);

	if (setitimer(ITIMER_REAL, &tim, NULL) == -1)
		err(1, "setitimer");
}

int
main(int argc, char **argv)
{
	int		ch;
	unsigned long	i;
	int		foreground = 0, preserve = 0;
	int		pstat, status;
	int		killsig = SIGTERM;
	pid_t		pgid = 0, pid, cpid = 0;
	double		first_kill;
	double		second_kill = 0;
	bool		timedout = false;
	bool		do_second_kill = false;
	struct		sigaction signals;
	int		signums[] = {-1, SIGTERM, SIGINT, SIGHUP, SIGCHLD,
			    SIGALRM, SIGQUIT};

	const struct option longopts[] = {
		{ "preserve-status", no_argument,       NULL,        'p'},
		{ "foreground",      no_argument,       NULL,        'f'},
		{ "kill-after",      required_argument, NULL,        'k'},
		{ "signal",          required_argument, NULL,        's'},
		{ "help",            no_argument,       NULL,        'h'},
		{ NULL,              0,                 NULL,         0 }
	};

	if (pledge("stdio proc exec", NULL) == -1)
		err(1, "pledge");

	while ((ch = getopt_long(argc, argv, "+fk:ps:h", longopts, NULL))
	    != -1) {
		switch (ch) {
		case 'f':
			foreground = 1;
			break;
		case 'k':
			do_second_kill = true;
			second_kill = parse_duration(optarg);
			break;
		case 'p':
			preserve = 1;
			break;
		case 's':
			killsig = parse_signal(optarg);
			break;
		case 0:
			break;
		default:
			usage();
			break;
		}
	}

	argc -= optind;
	argv += optind;

	if (argc < 2)
		usage();

	first_kill = parse_duration(argv[0]);
	argc--;
	argv++;

	if (!foreground) {
		pgid = setpgid(0, 0);

		if (pgid == -1)
			err(1, "setpgid");
	}

	memset(&signals, 0, sizeof(signals));
	sigemptyset(&signals.sa_mask);

	if (killsig != SIGKILL && killsig != SIGSTOP)
		signums[0] = killsig;

	for (i = 0; i < sizeof(signums) / sizeof(signums[0]); i++)
		sigaddset(&signals.sa_mask, signums[i]);

	signals.sa_handler = sig_handler;
	signals.sa_flags = SA_RESTART;

	for (i = 0; i < sizeof(signums) / sizeof(signums[0]); i++) {
		if (signums[i] != -1 && signums[i] != 0 &&
		    sigaction(signums[i], &signals, NULL) == -1)
			err(1, "sigaction");
	}

	signal(SIGTTIN, SIG_IGN);
	signal(SIGTTOU, SIG_IGN);

	pid = fork();
	if (pid == -1)
		err(1, "fork");
	else if (pid == 0) {
		/* child process */
		signal(SIGTTIN, SIG_DFL);
		signal(SIGTTOU, SIG_DFL);

		execvp(argv[0], argv);
		warn("%s", argv[0]);
		_exit(errno == ENOENT ? 127 : 126);
	}

	/* parent continues here */

	if (pledge("stdio proc", NULL) == -1)
		err(1, "pledge");

	if (sigprocmask(SIG_BLOCK, &signals.sa_mask, NULL) == -1)
		err(1, "sigprocmask");

	set_interval(first_kill);

	for (;;) {
		sigemptyset(&signals.sa_mask);
		sigsuspend(&signals.sa_mask);

		if (sig_chld) {
			sig_chld = 0;
			while (((cpid = wait(&status)) < 0) && errno == EINTR)
				continue;

			if (cpid == pid) {
				pstat = status;
				break;
			}
		} else if (sig_alrm) {
			sig_alrm = 0;

			timedout = true;
			if (!foreground)
				killpg(pgid, killsig);
			else
				kill(pid, killsig);

			if (do_second_kill) {
				set_interval(second_kill);
				second_kill = 0;
				sig_ign = killsig;
				killsig = SIGKILL;
			} else
				break;

		} else if (sig_term) {
			if (!foreground)
				killpg(pgid, killsig);
			else
				kill(pid, (int)sig_term);

			if (do_second_kill) {
				set_interval(second_kill);
				second_kill = 0;
				sig_ign = killsig;
				killsig = SIGKILL;
			} else
				break;
		}
	}

	while (cpid != pid && wait(&pstat) == -1) {
		if (errno != EINTR)
			err(1, "wait");
	}

	if (WEXITSTATUS(pstat))
		pstat = WEXITSTATUS(pstat);
	else if (WIFSIGNALED(pstat))
		pstat = 128 + WTERMSIG(pstat);

	if (timedout && !preserve)
		pstat = EXIT_TIMEOUT;

	return (pstat);
}