src/core/machine-id-setup.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 /***
   3   This file is part of systemd.
   4
   5   Copyright 2010 Lennart Poettering
   6 ***/
   7
   8 #include <fcntl.h>
   9 #include <sched.h>
  10 #include <sys/mount.h>
  11 #include <unistd.h>
  12
  13 #include "sd-id128.h"
  14
  15 #include "alloc-util.h"
  16 #include "fd-util.h"
  17 #include "fs-util.h"
  18 #include "id128-util.h"
  19 #include "log.h"
  20 #include "machine-id-setup.h"
  21 #include "macro.h"
  22 #include "mkdir.h"
  23 #include "mount-util.h"
  24 #include "path-util.h"
  25 #include "process-util.h"
  26 #include "stat-util.h"
  27 #include "string-util.h"
  28 #include "umask-util.h"
  29 #include "util.h"
  30 #include "virt.h"
  31
  32 static int generate_machine_id(const char *root, sd_id128_t *ret) {
  33         const char *dbus_machine_id;
  34         _cleanup_close_ int fd = -1;
  35         int r;
  36
  37         assert(ret);
  38
  39         /* First, try reading the D-Bus machine id, unless it is a symlink */
  40         dbus_machine_id = prefix_roota(root, "/var/lib/dbus/machine-id");
  41         fd = open(dbus_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW);
  42         if (fd >= 0) {
  43                 if (id128_read_fd(fd, ID128_PLAIN, ret) >= 0) {
  44                         log_info("Initializing machine ID from D-Bus machine ID.");
  45                         return 0;
  46                 }
  47
  48                 fd = safe_close(fd);
  49         }
  50
  51         if (isempty(root)) {
  52                 /* If that didn't work, see if we are running in a container,
  53                  * and a machine ID was passed in via $container_uuid the way
  54                  * libvirt/LXC does it */
  55
  56                 if (detect_container() > 0) {
  57                         _cleanup_free_ char *e = NULL;
  58
  59                         if (getenv_for_pid(1, "container_uuid", &e) > 0 &&
  60                             sd_id128_from_string(e, ret) >= 0) {
  61                                 log_info("Initializing machine ID from container UUID.");
  62                                 return 0;
  63                         }
  64
  65                 } else if (detect_vm() == VIRTUALIZATION_KVM) {
  66
  67                         /* If we are not running in a container, see if we are
  68                          * running in qemu/kvm and a machine ID was passed in
  69                          * via -uuid on the qemu/kvm command line */
  70
  71                         if (id128_read("/sys/class/dmi/id/product_uuid", ID128_UUID, ret) >= 0) {
  72                                 log_info("Initializing machine ID from KVM UUID.");
  73                                 return 0;
  74                         }
  75                 }
  76         }
  77
  78         /* If that didn't work, generate a random machine id */
  79         r = sd_id128_randomize(ret);
  80         if (r < 0)
  81                 return log_error_errno(r, "Failed to generate randomized : %m");
  82
  83         log_info("Initializing machine ID from random generator.");
  84         return 0;
  85 }
  86
  87 int machine_id_setup(const char *root, sd_id128_t machine_id, sd_id128_t *ret) {
  88         const char *etc_machine_id, *run_machine_id;
  89         _cleanup_close_ int fd = -1;
  90         bool writable;
  91         int r;
  92
  93         etc_machine_id = prefix_roota(root, "/etc/machine-id");
  94
  95         RUN_WITH_UMASK(0000) {
  96                 /* We create this 0444, to indicate that this isn't really
  97                  * something you should ever modify. Of course, since the file
  98                  * will be owned by root it doesn't matter much, but maybe
  99                  * people look. */
 100
 101                 (void) mkdir_parents(etc_machine_id, 0755);
 102                 fd = open(etc_machine_id, O_RDWR|O_CREAT|O_CLOEXEC|O_NOCTTY, 0444);
 103                 if (fd < 0) {
 104                         int old_errno = errno;
 105
 106                         fd = open(etc_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY);
 107                         if (fd < 0) {
 108                                 if (old_errno == EROFS && errno == ENOENT)
 109                                         return log_error_errno(errno,
 110                                                   "System cannot boot: Missing /etc/machine-id and /etc is mounted read-only.\n"
 111                                                   "Booting up is supported only when:\n"
 112                                                   "1) /etc/machine-id exists and is populated.\n"
 113                                                   "2) /etc/machine-id exists and is empty.\n"
 114                                                   "3) /etc/machine-id is missing and /etc is writable.\n");
 115                                 else
 116                                         return log_error_errno(errno,
 117                                                                "Cannot open %s: %m", etc_machine_id);
 118                         }
 119
 120                         writable = false;
 121                 } else
 122                         writable = true;
 123         }
 124
 125         /* A we got a valid machine ID argument, that's what counts */
 126         if (sd_id128_is_null(machine_id)) {
 127
 128                 /* Try to read any existing machine ID */
 129                 if (id128_read_fd(fd, ID128_PLAIN, ret) >= 0)
 130                         return 0;
 131
 132                 /* Hmm, so, the id currently stored is not useful, then let's generate one */
 133                 r = generate_machine_id(root, &machine_id);
 134                 if (r < 0)
 135                         return r;
 136         }
 137
 138         if (writable) {
 139                 if (lseek(fd, 0, SEEK_SET) == (off_t) -1)
 140                         return log_error_errno(errno, "Failed to seek %s: %m", etc_machine_id);
 141
 142                 if (ftruncate(fd, 0) < 0)
 143                         return log_error_errno(errno, "Failed to truncate %s: %m", etc_machine_id);
 144
 145                 if (id128_write_fd(fd, ID128_PLAIN, machine_id, true) >= 0)
 146                         goto finish;
 147         }
 148
 149         fd = safe_close(fd);
 150
 151         /* Hmm, we couldn't write it? So let's write it to /run/machine-id as a replacement */
 152
 153         run_machine_id = prefix_roota(root, "/run/machine-id");
 154
 155         RUN_WITH_UMASK(0022)
 156                 r = id128_write(run_machine_id, ID128_PLAIN, machine_id, false);
 157         if (r < 0) {
 158                 (void) unlink(run_machine_id);
 159                 return log_error_errno(r, "Cannot write %s: %m", run_machine_id);
 160         }
 161
 162         /* And now, let's mount it over */
 163         if (mount(run_machine_id, etc_machine_id, NULL, MS_BIND, NULL) < 0) {
 164                 (void) unlink_noerrno(run_machine_id);
 165                 return log_error_errno(errno, "Failed to mount %s: %m", etc_machine_id);
 166         }
 167
 168         log_info("Installed transient %s file.", etc_machine_id);
 169
 170         /* Mark the mount read-only */
 171         if (mount(NULL, etc_machine_id, NULL, MS_BIND|MS_RDONLY|MS_REMOUNT, NULL) < 0)
 172                 log_warning_errno(errno, "Failed to make transient %s read-only, ignoring: %m", etc_machine_id);
 173
 174 finish:
 175         if (ret)
 176                 *ret = machine_id;
 177
 178         return 0;
 179 }
 180
 181 int machine_id_commit(const char *root) {
 182         _cleanup_close_ int fd = -1, initial_mntns_fd = -1;
 183         const char *etc_machine_id;
 184         sd_id128_t id;
 185         int r;
 186
 187         /* Replaces a tmpfs bind mount of /etc/machine-id by a proper file, atomically. For this, the umount is removed
 188          * in a mount namespace, a new file is created at the right place. Afterwards the mount is also removed in the
 189          * original mount namespace, thus revealing the file that was just created. */
 190
 191         etc_machine_id = prefix_roota(root, "/etc/machine-id");
 192
 193         r = path_is_mount_point(etc_machine_id, NULL, 0);
 194         if (r < 0)
 195                 return log_error_errno(r, "Failed to determine whether %s is a mount point: %m", etc_machine_id);
 196         if (r == 0) {
 197                 log_debug("%s is not a mount point. Nothing to do.", etc_machine_id);
 198                 return 0;
 199         }
 200
 201         /* Read existing machine-id */
 202         fd = open(etc_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY);
 203         if (fd < 0)
 204                 return log_error_errno(errno, "Cannot open %s: %m", etc_machine_id);
 205
 206         r = fd_is_temporary_fs(fd);
 207         if (r < 0)
 208                 return log_error_errno(r, "Failed to determine whether %s is on a temporary file system: %m", etc_machine_id);
 209         if (r == 0) {
 210                 log_error("%s is not on a temporary file system.", etc_machine_id);
 211                 return -EROFS;
 212         }
 213
 214         r = id128_read_fd(fd, ID128_PLAIN, &id);
 215         if (r < 0)
 216                 return log_error_errno(r, "We didn't find a valid machine ID in %s.", etc_machine_id);
 217
 218         fd = safe_close(fd);
 219
 220         /* Store current mount namespace */
 221         r = namespace_open(0, NULL, &initial_mntns_fd, NULL, NULL, NULL);
 222         if (r < 0)
 223                 return log_error_errno(r, "Can't fetch current mount namespace: %m");
 224
 225         /* Switch to a new mount namespace, isolate ourself and unmount etc_machine_id in our new namespace */
 226         if (unshare(CLONE_NEWNS) < 0)
 227                 return log_error_errno(errno, "Failed to enter new namespace: %m");
 228
 229         if (mount(NULL, "/", NULL, MS_SLAVE | MS_REC, NULL) < 0)
 230                 return log_error_errno(errno, "Couldn't make-rslave / mountpoint in our private namespace: %m");
 231
 232         if (umount(etc_machine_id) < 0)
 233                 return log_error_errno(errno, "Failed to unmount transient %s file in our private namespace: %m", etc_machine_id);
 234
 235         /* Update a persistent version of etc_machine_id */
 236         r = id128_write(etc_machine_id, ID128_PLAIN, id, true);
 237         if (r < 0)
 238                 return log_error_errno(r, "Cannot write %s. This is mandatory to get a persistent machine ID: %m", etc_machine_id);
 239
 240         /* Return to initial namespace and proceed a lazy tmpfs unmount */
 241         r = namespace_enter(-1, initial_mntns_fd, -1, -1, -1);
 242         if (r < 0)
 243                 return log_warning_errno(r, "Failed to switch back to initial mount namespace: %m.\nWe'll keep transient %s file until next reboot.", etc_machine_id);
 244
 245         if (umount2(etc_machine_id, MNT_DETACH) < 0)
 246                 return log_warning_errno(errno, "Failed to unmount transient %s file: %m.\nWe keep that mount until next reboot.", etc_machine_id);
 247
 248         return 0;
 249 }