src/core/machine-id-setup.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 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 <unistd.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/mount.h>

#include <systemd/sd-id128.h>

#include "machine-id-setup.h"
#include "macro.h"
#include "util.h"
#include "mkdir.h"
#include "log.h"
#include "virt.h"

static int shorten_uuid(char destination[36], const char *source) {
        unsigned i, j;

        for (i = 0, j = 0; i < 36 && j < 32; i++) {
                int t;

                t = unhexchar(source[i]);
                if (t < 0)
                        continue;

                destination[j++] = hexchar(t);
        }

        if (i == 36 && j == 32) {
                destination[32] = '\n';
                destination[33] = 0;
                return 0;
        }

        return -EINVAL;
}

static int generate(char id[34]) {
        int fd, r;
        unsigned char *p;
        sd_id128_t buf;
        char *q;
        ssize_t k;
        const char *vm_id;

        assert(id);

        /* First, try reading the D-Bus machine id, unless it is a symlink */
        fd = open("/var/lib/dbus/machine-id", O_RDONLY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW);
        if (fd >= 0) {

                k = loop_read(fd, id, 32, false);
                close_nointr_nofail(fd);

                if (k >= 32) {
                        id[32] = '\n';
                        id[33] = 0;

                        log_info("Initializing machine ID from D-Bus machine ID.");
                        return 0;
                }
        }

        /* If that didn't work, see if we are running in qemu/kvm and a
         * machine ID was passed in via -uuid on the qemu/kvm command
         * line */

        r = detect_vm(&vm_id);
        if (r > 0 && streq(vm_id, "kvm")) {
                char uuid[37];

                fd = open("/sys/class/dmi/id/product_uuid", O_RDONLY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW);
                if (fd >= 0) {
                        k = loop_read(fd, uuid, 36, false);
                        close_nointr_nofail(fd);

                        if (k >= 36) {
                                r = shorten_uuid(id, uuid);
                                if (r >= 0) {
                                        log_info("Initializing machine ID from KVM UUID.");
                                        return 0;
                                }
                        }
                }
        }

        /* If that didn't work either, see if we are running in a
         * container, and a machine ID was passed in via
         * $container_uuid the way libvirt/LXC does it */
        r = detect_container(NULL);
        if (r > 0) {
                char *e;

                r = getenv_for_pid(1, "container_uuid", &e);
                if (r > 0) {
                        if (strlen(e) >= 36) {
                                r = shorten_uuid(id, e);
                                if (r >= 0) {
                                        log_info("Initializing machine ID from container UUID.");
                                        free(e);
                                        return 0;
                                }
                        }

                        free(e);
                }
        }

        /* If that didn't work, generate a random machine id */
        r = sd_id128_randomize(&buf);
        if (r < 0) {
                log_error("Failed to open /dev/urandom: %s", strerror(-r));
                return r;
        }

        for (p = buf.bytes, q = id; p < buf.bytes + sizeof(buf); p++, q += 2) {
                q[0] = hexchar(*p >> 4);
                q[1] = hexchar(*p & 15);
        }

        id[32] = '\n';
        id[33] = 0;

        log_info("Initializing machine ID from random generator.");

        return 0;
}

int machine_id_setup(void) {
        int fd, r;
        bool writable;
        struct stat st;
        char id[34]; /* 32 + \n + \0 */
        mode_t m;

        m = umask(0000);

        /* We create this 0444, to indicate that this isn't really
         * something you should ever modify. Of course, since the file
         * will be owned by root it doesn't matter much, but maybe
         * people look. */

        fd = open("/etc/machine-id", O_RDWR|O_CREAT|O_CLOEXEC|O_NOCTTY, 0444);
        if (fd >= 0)
                writable = true;
        else {
                fd = open("/etc/machine-id", O_RDONLY|O_CLOEXEC|O_NOCTTY);
                if (fd < 0) {
                        umask(m);
                        log_error("Cannot open /etc/machine-id: %m");
                        return -errno;
                }

                writable = false;
        }

        umask(m);

        if (fstat(fd, &st) < 0) {
                log_error("fstat() failed: %m");
                r = -errno;
                goto finish;
        }

        if (S_ISREG(st.st_mode)) {
                if (loop_read(fd, id, 32, false) >= 32) {
                        r = 0;
                        goto finish;
                }
        }

        /* Hmm, so, the id currently stored is not useful, then let's
         * generate one */

        r = generate(id);
        if (r < 0)
                goto finish;

        if (S_ISREG(st.st_mode) && writable) {
                lseek(fd, 0, SEEK_SET);

                if (loop_write(fd, id, 33, false) == 33) {
                        r = 0;
                        goto finish;
                }
        }

        close_nointr_nofail(fd);
        fd = -1;

        /* Hmm, we couldn't write it? So let's write it to
         * /run/machine-id as a replacement */

        m = umask(0022);
        r = write_one_line_file("/run/machine-id", id);
        umask(m);

        if (r < 0) {
                log_error("Cannot write /run/machine-id: %s", strerror(-r));

                unlink("/run/machine-id");
                goto finish;
        }

        /* And now, let's mount it over */
        r = mount("/run/machine-id", "/etc/machine-id", NULL, MS_BIND, NULL) < 0 ? -errno : 0;
        if (r < 0) {
                unlink("/run/machine-id");
                log_error("Failed to mount /etc/machine-id: %s", strerror(-r));
        } else {
                log_info("Installed transient /etc/machine-id file.");

                /* Mark the mount read-only */
                mount(NULL, "/etc/machine-id", NULL, MS_BIND|MS_RDONLY|MS_REMOUNT, NULL);
        }

finish:

        if (fd >= 0)
                close_nointr_nofail(fd);

        return r;
}