src/shared/machine-id-setup.c

   1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
   2
   3 #include <fcntl.h>
   4 #include <sched.h>
   5 #include <sys/mount.h>
   6 #include <unistd.h>
   7
   8 #include "sd-daemon.h"
   9 #include "sd-id128.h"
  10
  11 #include "alloc-util.h"
  12 #include "chase.h"
  13 #include "creds-util.h"
  14 #include "fd-util.h"
  15 #include "id128-util.h"
  16 #include "initrd-util.h"
  17 #include "io-util.h"
  18 #include "log.h"
  19 #include "machine-id-setup.h"
  20 #include "macro.h"
  21 #include "mkdir.h"
  22 #include "mount-util.h"
  23 #include "mountpoint-util.h"
  24 #include "namespace-util.h"
  25 #include "path-util.h"
  26 #include "process-util.h"
  27 #include "stat-util.h"
  28 #include "string-util.h"
  29 #include "sync-util.h"
  30 #include "umask-util.h"
  31 #include "virt.h"
  32
  33 static int acquire_machine_id_from_credential(sd_id128_t *ret) {
  34         _cleanup_free_ char *buf = NULL;
  35         int r;
  36
  37         r = read_credential_with_decryption("system.machine_id", (void**) &buf, /* ret_size= */ NULL);
  38         if (r < 0)
  39                 return log_warning_errno(r, "Failed to read system.machine_id credential, ignoring: %m");
  40         if (r == 0) /* not found */
  41                 return -ENXIO;
  42
  43         r = sd_id128_from_string(buf, ret);
  44         if (r < 0)
  45                 return log_warning_errno(r, "Failed to parse system.machine_id credential, ignoring: %m");
  46
  47         log_info("Initializing machine ID from credential.");
  48         return 0;
  49 }
  50
  51 static int acquire_machine_id(const char *root, sd_id128_t *ret) {
  52         _cleanup_close_ int fd = -EBADF;
  53         int r;
  54
  55         assert(ret);
  56
  57         /* First, try reading the machine ID from /run/machine-id, which may not be mounted on
  58          * /etc/machine-id yet. This is important on switching root especially on soft-reboot, Otherwise,
  59          * machine ID may be changed after the transition. */
  60         if (isempty(root) && running_in_chroot() <= 0 &&
  61             id128_read("/run/machine-id", ID128_FORMAT_PLAIN, ret) >= 0) {
  62                 log_info("Reusing machine ID stored in /run/machine-id.");
  63                 return 1; /* Indicate that the machine ID is reused. */
  64         }
  65
  66         /* Then, try reading the D-Bus machine id, unless it is a symlink */
  67         fd = chase_and_open("/var/lib/dbus/machine-id", root, CHASE_PREFIX_ROOT | CHASE_NOFOLLOW, O_RDONLY|O_CLOEXEC|O_NOCTTY, NULL);
  68         if (fd >= 0 && id128_read_fd(fd, ID128_FORMAT_PLAIN | ID128_REFUSE_NULL, ret) >= 0) {
  69                 log_info("Initializing machine ID from D-Bus machine ID.");
  70                 return 0;
  71         }
  72
  73         if (isempty(root) && running_in_chroot() <= 0) {
  74                 /* Let's use a system credential for the machine ID if we can */
  75                 if (acquire_machine_id_from_credential(ret) >= 0)
  76                         return 0;
  77
  78                 /* If that didn't work, see if we are running in a container,
  79                  * and a machine ID was passed in via $container_uuid the way
  80                  * libvirt/LXC does it */
  81
  82                 if (detect_container() > 0) {
  83                         _cleanup_free_ char *e = NULL;
  84
  85                         if (getenv_for_pid(1, "container_uuid", &e) > 0 &&
  86                             sd_id128_from_string(e, ret) >= 0) {
  87                                 log_info("Initializing machine ID from container UUID.");
  88                                 return 0;
  89                         }
  90
  91                 } else if (IN_SET(detect_vm(), VIRTUALIZATION_KVM, VIRTUALIZATION_AMAZON, VIRTUALIZATION_QEMU, VIRTUALIZATION_XEN)) {
  92
  93                         /* If we are not running in a container, see if we are running in a VM that provides
  94                          * a system UUID via the SMBIOS/DMI interfaces.  Such environments include QEMU/KVM
  95                          * with the -uuid on the qemu command line or the Amazon EC2 Nitro hypervisor. */
  96
  97                         if (id128_get_product(ret) >= 0) {
  98                                 log_info("Initializing machine ID from VM UUID.");
  99                                 return 0;
 100                         }
 101                 }
 102         }
 103
 104         /* If that didn't work, generate a random machine id */
 105         r = sd_id128_randomize(ret);
 106         if (r < 0)
 107                 return log_error_errno(r, "Failed to generate randomized machine ID: %m");
 108
 109         log_info("Initializing machine ID from random generator.");
 110         return 0;
 111 }
 112
 113 int machine_id_setup(const char *root, bool force_transient, sd_id128_t machine_id, sd_id128_t *ret) {
 114         const char *etc_machine_id, *run_machine_id;
 115         _cleanup_close_ int fd = -EBADF;
 116         bool writable, write_run_machine_id = true;
 117         int r;
 118
 119         etc_machine_id = prefix_roota(root, "/etc/machine-id");
 120
 121         WITH_UMASK(0000) {
 122                 /* We create this 0444, to indicate that this isn't really
 123                  * something you should ever modify. Of course, since the file
 124                  * will be owned by root it doesn't matter much, but maybe
 125                  * people look. */
 126
 127                 (void) mkdir_parents(etc_machine_id, 0755);
 128                 fd = open(etc_machine_id, O_RDWR|O_CREAT|O_CLOEXEC|O_NOCTTY, 0444);
 129                 if (fd < 0) {
 130                         int old_errno = errno;
 131
 132                         fd = open(etc_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY);
 133                         if (fd < 0) {
 134                                 if (old_errno == EROFS && errno == ENOENT)
 135                                         return log_error_errno(errno,
 136                                                   "System cannot boot: Missing /etc/machine-id and /etc is mounted read-only.\n"
 137                                                   "Booting up is supported only when:\n"
 138                                                   "1) /etc/machine-id exists and is populated.\n"
 139                                                   "2) /etc/machine-id exists and is empty.\n"
 140                                                   "3) /etc/machine-id is missing and /etc is writable.\n");
 141                                 else
 142                                         return log_error_errno(errno, "Cannot open %s: %m", etc_machine_id);
 143                         }
 144
 145                         writable = false;
 146                 } else
 147                         writable = true;
 148         }
 149
 150         /* A we got a valid machine ID argument, that's what counts */
 151         if (sd_id128_is_null(machine_id)) {
 152
 153                 /* Try to read any existing machine ID */
 154                 if (id128_read_fd(fd, ID128_FORMAT_PLAIN, &machine_id) >= 0)
 155                         goto finish;
 156
 157                 /* Hmm, so, the id currently stored is not useful, then let's acquire one. */
 158                 r = acquire_machine_id(root, &machine_id);
 159                 if (r < 0)
 160                         return r;
 161                 write_run_machine_id = !r;
 162         }
 163
 164         if (writable) {
 165                 if (lseek(fd, 0, SEEK_SET) < 0)
 166                         return log_error_errno(errno, "Failed to seek %s: %m", etc_machine_id);
 167
 168                 if (ftruncate(fd, 0) < 0)
 169                         return log_error_errno(errno, "Failed to truncate %s: %m", etc_machine_id);
 170
 171                 /* If the caller requested a transient machine-id, write the string "uninitialized\n" to
 172                  * disk and overmount it with a transient file.
 173                  *
 174                  * Otherwise write the machine-id directly to disk. */
 175                 if (force_transient) {
 176                         r = loop_write(fd, "uninitialized\n", SIZE_MAX);
 177                         if (r < 0)
 178                                 return log_error_errno(r, "Failed to write uninitialized %s: %m", etc_machine_id);
 179
 180                         r = fsync_full(fd);
 181                         if (r < 0)
 182                                 return log_error_errno(r, "Failed to sync %s: %m", etc_machine_id);
 183                 } else {
 184                         r = id128_write_fd(fd, ID128_FORMAT_PLAIN | ID128_SYNC_ON_WRITE, machine_id);
 185                         if (r < 0)
 186                                 return log_error_errno(r, "Failed to write %s: %m", etc_machine_id);
 187                         else
 188                                 goto finish;
 189                 }
 190         }
 191
 192         fd = safe_close(fd);
 193
 194         /* Hmm, we couldn't or shouldn't write the machine-id to /etc?
 195          * So let's write it to /run/machine-id as a replacement */
 196
 197         run_machine_id = prefix_roota(root, "/run/machine-id");
 198
 199         if (write_run_machine_id) {
 200                 WITH_UMASK(0022)
 201                         r = id128_write(run_machine_id, ID128_FORMAT_PLAIN, machine_id);
 202                 if (r < 0) {
 203                         (void) unlink(run_machine_id);
 204                         return log_error_errno(r, "Cannot write %s: %m", run_machine_id);
 205                 }
 206         }
 207
 208         /* And now, let's mount it over */
 209         r = mount_follow_verbose(LOG_ERR, run_machine_id, etc_machine_id, NULL, MS_BIND, NULL);
 210         if (r < 0) {
 211                 (void) unlink(run_machine_id);
 212                 return r;
 213         }
 214
 215         log_full(force_transient ? LOG_DEBUG : LOG_INFO, "Installed transient %s file.", etc_machine_id);
 216
 217         /* Mark the mount read-only */
 218         r = mount_follow_verbose(LOG_WARNING, NULL, etc_machine_id, NULL, MS_BIND|MS_RDONLY|MS_REMOUNT, NULL);
 219         if (r < 0)
 220                 return r;
 221
 222 finish:
 223         if (!in_initrd())
 224                 (void) sd_notifyf(/* unset_environment= */ false, "X_SYSTEMD_MACHINE_ID=" SD_ID128_FORMAT_STR, SD_ID128_FORMAT_VAL(machine_id));
 225
 226         if (ret)
 227                 *ret = machine_id;
 228
 229         return 0;
 230 }
 231
 232 int machine_id_commit(const char *root) {
 233         _cleanup_close_ int fd = -EBADF, initial_mntns_fd = -EBADF;
 234         const char *etc_machine_id;
 235         sd_id128_t id;
 236         int r;
 237
 238         /* Before doing anything, sync everything to ensure any changes by first-boot units are persisted.
 239          *
 240          * First, explicitly sync the file systems we care about and check if it worked. */
 241         FOREACH_STRING(sync_path, "/etc/", "/var/") {
 242                 r = syncfs_path(AT_FDCWD, sync_path);
 243                 if (r < 0)
 244                         return log_error_errno(r, "Cannot sync %s: %m", sync_path);
 245         }
 246
 247         /* Afterwards, sync() the rest too, but we can't check the return value for these. */
 248         sync();
 249
 250         /* Replaces a tmpfs bind mount of /etc/machine-id by a proper file, atomically. For this, the umount is removed
 251          * in a mount namespace, a new file is created at the right place. Afterwards the mount is also removed in the
 252          * original mount namespace, thus revealing the file that was just created. */
 253
 254         etc_machine_id = prefix_roota(root, "/etc/machine-id");
 255
 256         r = path_is_mount_point(etc_machine_id);
 257         if (r < 0)
 258                 return log_error_errno(r, "Failed to determine whether %s is a mount point: %m", etc_machine_id);
 259         if (r == 0) {
 260                 log_debug("%s is not a mount point. Nothing to do.", etc_machine_id);
 261                 return 0;
 262         }
 263
 264         /* Read existing machine-id */
 265         fd = open(etc_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY);
 266         if (fd < 0)
 267                 return log_error_errno(errno, "Cannot open %s: %m", etc_machine_id);
 268
 269         r = fd_is_temporary_fs(fd);
 270         if (r < 0)
 271                 return log_error_errno(r, "Failed to determine whether %s is on a temporary file system: %m", etc_machine_id);
 272         if (r == 0)
 273                 return log_error_errno(SYNTHETIC_ERRNO(EROFS),
 274                                        "%s is not on a temporary file system.",
 275                                        etc_machine_id);
 276
 277         r = id128_read_fd(fd, ID128_FORMAT_PLAIN, &id);
 278         if (r < 0)
 279                 return log_error_errno(r, "We didn't find a valid machine ID in %s: %m", etc_machine_id);
 280
 281         fd = safe_close(fd);
 282
 283         /* Store current mount namespace */
 284         r = namespace_open(0,
 285                            /* ret_pidns_fd = */ NULL,
 286                            &initial_mntns_fd,
 287                            /* ret_netns_fd = */ NULL,
 288                            /* ret_userns_fd = */ NULL,
 289                            /* ret_root_fd = */ NULL);
 290         if (r < 0)
 291                 return log_error_errno(r, "Can't fetch current mount namespace: %m");
 292
 293         /* Switch to a new mount namespace, isolate ourself and unmount etc_machine_id in our new namespace */
 294         r = detach_mount_namespace();
 295         if (r < 0)
 296                 return log_error_errno(r, "Failed to set up new mount namespace: %m");
 297
 298         r = umount_verbose(LOG_ERR, etc_machine_id, 0);
 299         if (r < 0)
 300                 return r;
 301
 302         /* Update a persistent version of etc_machine_id */
 303         r = id128_write(etc_machine_id, ID128_FORMAT_PLAIN | ID128_SYNC_ON_WRITE, id);
 304         if (r < 0)
 305                 return log_error_errno(r, "Cannot write %s. This is mandatory to get a persistent machine ID: %m", etc_machine_id);
 306
 307         /* Return to initial namespace and proceed a lazy tmpfs unmount */
 308         r = namespace_enter(/* pidns_fd = */ -EBADF,
 309                             initial_mntns_fd,
 310                             /* netns_fd = */ -EBADF,
 311                             /* userns_fd = */ -EBADF,
 312                             /* root_fd = */ -EBADF);
 313         if (r < 0)
 314                 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);
 315
 316         if (umount2(etc_machine_id, MNT_DETACH) < 0)
 317                 return log_warning_errno(errno, "Failed to unmount transient %s file: %m.\nWe keep that mount until next reboot.", etc_machine_id);
 318
 319         return 0;
 320 }