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