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Because pledge(2) does not allow us to pass directory file descriptors
around, we can't use file descriptors for the working directory because
we will be unable to pass it to a privileged process to tell it where to
read or write files or spawn children. So move tmux back to using
strings for the current working directory. We try to check it exists
with access() when it is set but ultimately fall back to ~ if it fails
at time of use (or / if that fails too).

/* $OpenBSD: job.c,v 1.38 2015/10/31 08:13:58 nicm Exp $ */

/*
 * Copyright (c) 2009 Nicholas Marriott <nicm@users.sourceforge.net>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
 * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/types.h>
#include <sys/socket.h>

#include <fcntl.h>
#include <paths.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include "tmux.h"

/*
 * Job scheduling. Run queued commands in the background and record their
 * output.
 */

void	job_callback(struct bufferevent *, short, void *);
void	job_write_callback(struct bufferevent *, void *);

/* All jobs list. */
struct joblist	all_jobs = LIST_HEAD_INITIALIZER(all_jobs);

/* Start a job running, if it isn't already. */
struct job *
job_run(const char *cmd, struct session *s, const char *cwd,
    void (*callbackfn)(struct job *), void (*freefn)(void *), void *data)
{
	struct job	*job;
	struct environ	*env;
	pid_t		 pid;
	int		 nullfd, out[2];
	const char	*home;

	if (socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC, out) != 0)
		return (NULL);

	env = environ_create();
	environ_copy(global_environ, env);
	if (s != NULL)
		environ_copy(s->environ, env);
	server_fill_environ(s, env);

	switch (pid = fork()) {
	case -1:
		environ_free(env);
		close(out[0]);
		close(out[1]);
		return (NULL);
	case 0:		/* child */
		clear_signals(1);

		if (cwd == NULL || chdir(cwd) != 0) {
			if ((home = find_home()) == NULL || chdir(home) != 0)
				chdir("/");
		}

		environ_push(env);
		environ_free(env);

		if (dup2(out[1], STDIN_FILENO) == -1)
			fatal("dup2 failed");
		if (dup2(out[1], STDOUT_FILENO) == -1)
			fatal("dup2 failed");
		if (out[1] != STDIN_FILENO && out[1] != STDOUT_FILENO)
			close(out[1]);
		close(out[0]);

		nullfd = open(_PATH_DEVNULL, O_RDWR, 0);
		if (nullfd < 0)
			fatal("open failed");
		if (dup2(nullfd, STDERR_FILENO) == -1)
			fatal("dup2 failed");
		if (nullfd != STDERR_FILENO)
			close(nullfd);

		closefrom(STDERR_FILENO + 1);

		execl(_PATH_BSHELL, "sh", "-c", cmd, (char *) NULL);
		fatal("execl failed");
	}

	/* parent */
	environ_free(env);
	close(out[1]);

	job = xmalloc(sizeof *job);
	job->state = JOB_RUNNING;

	job->cmd = xstrdup(cmd);
	job->pid = pid;
	job->status = 0;

	LIST_INSERT_HEAD(&all_jobs, job, lentry);

	job->callbackfn = callbackfn;
	job->freefn = freefn;
	job->data = data;

	job->fd = out[0];
	setblocking(job->fd, 0);

	job->event = bufferevent_new(job->fd, NULL, job_write_callback,
	    job_callback, job);
	bufferevent_enable(job->event, EV_READ|EV_WRITE);

	log_debug("run job %p: %s, pid %ld", job, job->cmd, (long) job->pid);
	return (job);
}

/* Kill and free an individual job. */
void
job_free(struct job *job)
{
	log_debug("free job %p: %s", job, job->cmd);

	LIST_REMOVE(job, lentry);
	free(job->cmd);

	if (job->freefn != NULL && job->data != NULL)
		job->freefn(job->data);

	if (job->pid != -1)
		kill(job->pid, SIGTERM);
	if (job->event != NULL)
		bufferevent_free(job->event);
	if (job->fd != -1)
		close(job->fd);

	free(job);
}

/* Called when output buffer falls below low watermark (default is 0). */
void
job_write_callback(unused struct bufferevent *bufev, void *data)
{
	struct job	*job = data;
	size_t		 len = EVBUFFER_LENGTH(EVBUFFER_OUTPUT(job->event));

	log_debug("job write %p: %s, pid %ld, output left %zu", job, job->cmd,
	    (long) job->pid, len);

	if (len == 0) {
		shutdown(job->fd, SHUT_WR);
		bufferevent_disable(job->event, EV_WRITE);
	}
}

/* Job buffer error callback. */
void
job_callback(unused struct bufferevent *bufev, unused short events, void *data)
{
	struct job	*job = data;

	log_debug("job error %p: %s, pid %ld", job, job->cmd, (long) job->pid);

	if (job->state == JOB_DEAD) {
		if (job->callbackfn != NULL)
			job->callbackfn(job);
		job_free(job);
	} else {
		bufferevent_disable(job->event, EV_READ);
		job->state = JOB_CLOSED;
	}
}

/* Job died (waitpid() returned its pid). */
void
job_died(struct job *job, int status)
{
	log_debug("job died %p: %s, pid %ld", job, job->cmd, (long) job->pid);

	job->status = status;

	if (job->state == JOB_CLOSED) {
		if (job->callbackfn != NULL)
			job->callbackfn(job);
		job_free(job);
	} else {
		job->pid = -1;
		job->state = JOB_DEAD;
	}
}