systemd/src/dbus-common.c

/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/

/***
  This file is part of systemd.

  Copyright 2010 Lennart Poettering

  systemd is free software; you can redistribute it and/or modify it
  under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2 of the License, or
  (at your option) any later version.

  systemd 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
  General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/

#include <assert.h>
#include <sys/socket.h>
#include <errno.h>
#include <unistd.h>
#include <dbus/dbus.h>

#include "log.h"
#include "dbus-common.h"
#include "util.h"

int bus_check_peercred(DBusConnection *c) {
        int fd;
        struct ucred ucred;
        socklen_t l;

        assert(c);

        assert_se(dbus_connection_get_unix_fd(c, &fd));

        l = sizeof(struct ucred);
        if (getsockopt(fd, SOL_SOCKET, SO_PEERCRED, &ucred, &l) < 0) {
                log_error("SO_PEERCRED failed: %m");
                return -errno;
        }

        if (l != sizeof(struct ucred)) {
                log_error("SO_PEERCRED returned wrong size.");
                return -E2BIG;
        }

        if (ucred.uid != 0)
                return -EPERM;

        return 1;
}

int bus_connect(DBusBusType t, DBusConnection **_bus, bool *private, DBusError *error) {
        DBusConnection *bus;

        assert(_bus);

#define TIMEOUT_USEC (60*USEC_PER_SEC)

        /* If we are root, then let's not go via the bus */
        if (geteuid() == 0 && t == DBUS_BUS_SYSTEM) {
                usec_t begin, tstamp;

                if (!(bus = dbus_connection_open_private("unix:abstract=/org/freedesktop/systemd1/private", error)))
                        return -EIO;

                if (bus_check_peercred(bus) < 0) {
                        dbus_connection_close(bus);
                        dbus_connection_unref(bus);

                        dbus_set_error_const(error, DBUS_ERROR_ACCESS_DENIED, "Failed to verify owner of bus.");
                        return -EACCES;
                }

                /* This complexity should probably move into D-Bus itself:
                 *
                 * https://bugs.freedesktop.org/show_bug.cgi?id=35189 */
                begin = tstamp = now(CLOCK_MONOTONIC);
                for (;;) {

                        if (tstamp > begin + TIMEOUT_USEC)
                                break;

                        if (dbus_connection_get_is_authenticated(bus))
                                break;

                        if (!dbus_connection_read_write_dispatch(bus, ((begin + TIMEOUT_USEC - tstamp) + USEC_PER_MSEC - 1) / USEC_PER_MSEC))
                                break;

                        tstamp = now(CLOCK_MONOTONIC);
                }

                if (!dbus_connection_get_is_connected(bus)) {
                        dbus_connection_close(bus);
                        dbus_connection_unref(bus);

                        dbus_set_error_const(error, DBUS_ERROR_NO_SERVER, "Connection terminated during authentication.");
                        return -ECONNREFUSED;
                }

                if (!dbus_connection_get_is_authenticated(bus)) {
                        dbus_connection_close(bus);
                        dbus_connection_unref(bus);

                        dbus_set_error_const(error, DBUS_ERROR_TIMEOUT, "Failed to authenticate in time.");
                        return -EACCES;
                }

                if (private)
                        *private = true;

        } else {
                if (!(bus = dbus_bus_get_private(t, error)))
                        return -EIO;

                if (private)
                        *private = false;
        }

        dbus_connection_set_exit_on_disconnect(bus, FALSE);

        *_bus = bus;
        return 0;
}

const char *bus_error_message(const DBusError *error) {
        assert(error);

        /* Sometimes the D-Bus server is a little bit too verbose with
         * its error messages, so let's override them here */
        if (dbus_error_has_name(error, DBUS_ERROR_ACCESS_DENIED))
                return "Access denied";

        return error->message;
}