/* -*- Mode: C; tab-width: 8; indent-tabs-mode: t; c-basic-offset: 8 -*-
 *
 * Copyright (C) 2011 Lennart Poettering <lennart@poettering.net>
 * Copyright (C) 2012 Matthias Klumpp <matthias@tenstral.net>
 *
 * Licensed under the GNU Lesser General Public License Version 2.1
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with systemd; If not, see <http://www.gnu.org/licenses/>.
 */

#include <stdio.h>
#include <sys/types.h>
#ifdef __linux__
#include <sys/prctl.h>
#endif
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <dirent.h>
#include <signal.h>
#include <fcntl.h>
#include <errno.h>
#include <inttypes.h>
#include <sys/poll.h>
#include <sys/wait.h>
#include <glib.h>

#include "pk-spawn-polkit-agent.h"

#define memzero(x,l) (memset((x), 0, (l)))
#define zero(x) (memzero(&(x), sizeof(x)))

#define POLKIT_TTY_AGENT_BINARY_PATH "/usr/bin/pkttyagent"

static pid_t agent_pid = 0;

static int
fork_agent (pid_t *pid, const char *path, ...) {
	pid_t parent_pid, n_agent_pid;
	int fd;
	gboolean stdout_is_tty, stderr_is_tty;
	unsigned n, i;
	va_list ap;
	char **l;

	g_return_val_if_fail (pid != 0, 0);
	g_assert (path);

	parent_pid = getpid ();

	/* Spawns a temporary TTY agent, making sure it goes away when
	 * we go away */

	n_agent_pid = fork ();
	if (n_agent_pid < 0)
		return -errno;

	if (n_agent_pid != 0) {
		*pid = n_agent_pid;
		return 0;
	}
#ifdef __linux__

	/* In the child:
	 *
	 * Make sure the agent goes away when the parent dies */
	if (prctl (PR_SET_PDEATHSIG, SIGTERM) < 0)
		_exit (EXIT_FAILURE);
#endif
	/* Check whether our parent died before we were able
	 * to set the death signal */
	if (getppid () != parent_pid)
		_exit (EXIT_SUCCESS);

	/* TODO: it might be more clean to close all FDs so we don't leak them to the agent */

	stdout_is_tty = isatty (STDOUT_FILENO);
	stderr_is_tty = isatty (STDERR_FILENO);

	if (!stdout_is_tty || !stderr_is_tty) {
		/* Detach from stdout/stderr. and reopen
		 * /dev/tty for them. This is important to
		 * ensure that when systemctl is started via
		 * popen() or a similar call that expects to
		 * read EOF we actually do generate EOF and
		 * not delay this indefinitely by because we
		 * keep an unused copy of stdin around. */
		fd = open("/dev/tty", O_WRONLY);
		if (fd < 0) {
			g_error ("Failed to open /dev/tty: %m");
			_exit(EXIT_FAILURE);
		}

		if (!stdout_is_tty)
			dup2(fd, STDOUT_FILENO);

		if (!stderr_is_tty)
			dup2(fd, STDERR_FILENO);

		if (fd > 2)
			close(fd);
	}

	/* Count arguments */
	va_start (ap, path);
	for (n = 0; va_arg(ap, char*); n++)
		;
	va_end(ap);

	/* Allocate strv */
	l = alloca (sizeof(char *) * (n + 1));

	/* Fill in arguments */
	va_start (ap, path);
	for (i = 0; i <= n; i++)
		l[i] = va_arg (ap, char*);
	va_end (ap);

	execv (path, l);
	_exit (EXIT_FAILURE);
}

static int
close_nointr (int fd) {
        g_assert (fd >= 0);

        for (;;) {
                int r;

                r = close (fd);
                if (r >= 0)
                        return r;

                if (errno != EINTR)
                        return -errno;
        }
}

static void
close_nointr_nofail (int fd) {
	int saved_errno = errno;

	/* cannot fail, and guarantees errno is unchanged */

	g_assert (close_nointr (fd) == 0);

	errno = saved_errno;
}

static int
fd_wait_for_event (int fd, int event, uint64_t t) {
	struct pollfd pollfd;
	int r;

	zero(pollfd);
	pollfd.fd = fd;
	pollfd.events = event;

	r = poll(&pollfd, 1, t == (uint64_t) -1 ? -1 : (int) (t / 1000));
	if (r < 0)
		return -errno;

	if (r == 0)
		return 0;

	return pollfd.revents;
}

static int
wait_for_terminate (pid_t pid) {
        int status;
	g_assert (pid >= 1);

	for (;;) {
		if (waitpid(pid, &status, 0) < 0) {
			if (errno == EINTR)
				continue;
			return -errno;
		}
		return 0;
	}
}

int
pk_polkit_agent_open (void) {
	int r;
	int pipe_fd[2];
	char notify_fd[10 + 1];

	if (agent_pid > 0)
		return 0;

	/* We check STDIN here, not STDOUT, since this is about input,
	 * not output */
	if (!isatty (STDIN_FILENO))
		return 0;

	if (pipe (pipe_fd) < 0)
		return -errno;

	snprintf (notify_fd, sizeof (notify_fd), "%i", pipe_fd[1]);
	notify_fd[sizeof (notify_fd) -1] = 0;

	r = fork_agent (&agent_pid,
		       POLKIT_TTY_AGENT_BINARY_PATH,
		       POLKIT_TTY_AGENT_BINARY_PATH, "--notify-fd", notify_fd, "--fallback", NULL);

	/* Close the writing side, because that's the one for the agent */
	close_nointr_nofail (pipe_fd[1]);

	if (r < 0)
		g_warning ("Failed to fork TTY ask password agent: %s", strerror (-r));
	else
		/* Wait until the agent closes the fd */
		fd_wait_for_event (pipe_fd[0], POLLHUP, (uint64_t) -1);

	close_nointr_nofail (pipe_fd[0]);

	return r;
}

void
pk_polkit_agent_close (void) {

	if (agent_pid <= 0)
		return;

	/* Inform agent that we are done */
	kill (agent_pid, SIGTERM);
	kill (agent_pid, SIGCONT);
	wait_for_terminate (agent_pid);
	agent_pid = 0;
}