src/libsystemd/sd-bus/bus-container.c

/* SPDX-License-Identifier: LGPL-2.1+ */
/***
  This file is part of systemd.

  Copyright 2013 Lennart Poettering

  systemd 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.

  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
  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 <fcntl.h>
#include <unistd.h>

#include "bus-container.h"
#include "bus-internal.h"
#include "bus-socket.h"
#include "fd-util.h"
#include "process-util.h"
#include "util.h"

int bus_container_connect_socket(sd_bus *b) {
        _cleanup_close_pair_ int pair[2] = { -1, -1 };
        _cleanup_close_ int pidnsfd = -1, mntnsfd = -1, usernsfd = -1, rootfd = -1;
        int r, error_buf = 0;
        pid_t child;
        ssize_t n;

        assert(b);
        assert(b->input_fd < 0);
        assert(b->output_fd < 0);
        assert(b->nspid > 0 || b->machine);

        if (b->nspid <= 0) {
                r = container_get_leader(b->machine, &b->nspid);
                if (r < 0)
                        return r;
        }

        r = namespace_open(b->nspid, &pidnsfd, &mntnsfd, NULL, &usernsfd, &rootfd);
        if (r < 0)
                return r;

        b->input_fd = socket(b->sockaddr.sa.sa_family, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0);
        if (b->input_fd < 0)
                return -errno;

        b->output_fd = b->input_fd;

        bus_socket_setup(b);

        if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, pair) < 0)
                return -errno;

        r = safe_fork("(sd-buscntr)", FORK_RESET_SIGNALS|FORK_DEATHSIG, &child);
        if (r < 0)
                return r;
        if (r == 0) {
                pid_t grandchild;

                pair[0] = safe_close(pair[0]);

                r = namespace_enter(pidnsfd, mntnsfd, -1, usernsfd, rootfd);
                if (r < 0)
                        _exit(EXIT_FAILURE);

                /* We just changed PID namespace, however it will only
                 * take effect on the children we now fork. Hence,
                 * let's fork another time, and connect from this
                 * grandchild, so that SO_PEERCRED of our connection
                 * comes from a process from within the container, and
                 * not outside of it */

                r = safe_fork("(sd-buscntr2)", FORK_RESET_SIGNALS|FORK_DEATHSIG, &grandchild);
                if (r < 0)
                        _exit(EXIT_FAILURE);
                if (r == 0) {

                        r = connect(b->input_fd, &b->sockaddr.sa, b->sockaddr_size);
                        if (r < 0) {
                                /* Try to send error up */
                                error_buf = errno;
                                (void) write(pair[1], &error_buf, sizeof(error_buf));
                                _exit(EXIT_FAILURE);
                        }

                        _exit(EXIT_SUCCESS);
                }

                r = wait_for_terminate_and_check("(sd-buscntr2)", grandchild, 0);
                if (r < 0)
                        _exit(EXIT_FAILURE);

                _exit(r);
        }

        pair[1] = safe_close(pair[1]);

        r = wait_for_terminate_and_check("(sd-buscntr)", child, 0);
        if (r < 0)
                return r;
        if (r != EXIT_SUCCESS)
                return -EPROTO;

        n = read(pair[0], &error_buf, sizeof(error_buf));
        if (n < 0)
                return -errno;

        if (n > 0) {
                if (n != sizeof(error_buf))
                        return -EIO;

                if (error_buf < 0)
                        return -EIO;

                if (error_buf == EINPROGRESS)
                        return 1;

                if (error_buf > 0)
                        return -error_buf;
        }

        return bus_socket_start_auth(b);
}