src/core/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 "fs-util.h"
  13 #include "id128-util.h"
  14 #include "io-util.h"
  15 #include "log.h"
  16 #include "machine-id-setup.h"
  17 #include "macro.h"
  18 #include "mkdir.h"
  19 #include "mount-util.h"
  20 #include "mountpoint-util.h"
  21 #include "namespace-util.h"
  22 #include "path-util.h"
  23 #include "process-util.h"
  24 #include "stat-util.h"
  25 #include "string-util.h"
  26 #include "umask-util.h"
  27 #include "util.h"
  28 #include "virt.h"
  29
  30 static int generate_machine_id(const char *root, sd_id128_t *ret) {
  31         const char *dbus_machine_id;
  32         _cleanup_close_ int fd = -1;
  33         int r;
  34
  35         assert(ret);
  36
  37         /* First, try reading the D-Bus machine id, unless it is a symlink */
  38         dbus_machine_id = prefix_roota(root, "/var/lib/dbus/machine-id");
  39         fd = open(dbus_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW);
  40         if (fd >= 0) {
  41                 if (id128_read_fd(fd, ID128_PLAIN, ret) >= 0) {
  42                         log_info("Initializing machine ID from D-Bus machine ID.");
  43                         return 0;
  44                 }
  45
  46                 fd = safe_close(fd);
  47         }
  48
  49         if (isempty(root) && running_in_chroot() <= 0) {
  50                 /* If that didn't work, see if we are running in a container,
  51                  * and a machine ID was passed in via $container_uuid the way
  52                  * libvirt/LXC does it */
  53
  54                 if (detect_container() > 0) {
  55                         _cleanup_free_ char *e = NULL;
  56
  57                         if (getenv_for_pid(1, "container_uuid", &e) > 0 &&
  58                             sd_id128_from_string(e, ret) >= 0) {
  59                                 log_info("Initializing machine ID from container UUID.");
  60                                 return 0;
  61                         }
  62
  63                 } else if (detect_vm() == VIRTUALIZATION_KVM) {
  64
  65                         /* If we are not running in a container, see if we are
  66                          * running in qemu/kvm and a machine ID was passed in
  67                          * via -uuid on the qemu/kvm command line */
  68
  69                         if (id128_read("/sys/class/dmi/id/product_uuid", ID128_UUID, ret) >= 0) {
  70                                 log_info("Initializing machine ID from KVM UUID.");
  71                                 return 0;
  72                         }
  73                         /* on POWER, it's exported here instead */
  74                         if (id128_read("/sys/firmware/devicetree/base/vm,uuid", ID128_UUID, ret) >= 0) {
  75                                 log_info("Initializing machine ID from KVM UUID.");
  76                                 return 0;
  77                         }
  78                 }
  79         }
  80
  81         /* If that didn't work, generate a random machine id */
  82         r = sd_id128_randomize(ret);
  83         if (r < 0)
  84                 return log_error_errno(r, "Failed to generate randomized machine ID: %m");
  85
  86         log_info("Initializing machine ID from random generator.");
  87         return 0;
  88 }
  89
  90 int machine_id_setup(const char *root, bool force_transient, sd_id128_t machine_id, sd_id128_t *ret) {
  91         const char *etc_machine_id, *run_machine_id;
  92         _cleanup_close_ int fd = -1;
  93         bool writable;
  94         int r;
  95
  96         etc_machine_id = prefix_roota(root, "/etc/machine-id");
  97
  98         RUN_WITH_UMASK(0000) {
  99                 /* We create this 0444, to indicate that this isn't really
 100                  * something you should ever modify. Of course, since the file
 101                  * will be owned by root it doesn't matter much, but maybe
 102                  * people look. */
 103
 104                 (void) mkdir_parents(etc_machine_id, 0755);
 105                 fd = open(etc_machine_id, O_RDWR|O_CREAT|O_CLOEXEC|O_NOCTTY, 0444);
 106                 if (fd < 0) {
 107                         int old_errno = errno;
 108
 109                         fd = open(etc_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY);
 110                         if (fd < 0) {
 111                                 if (old_errno == EROFS && errno == ENOENT)
 112                                         return log_error_errno(errno,
 113                                                   "System cannot boot: Missing /etc/machine-id and /etc is mounted read-only.\n"
 114                                                   "Booting up is supported only when:\n"
 115                                                   "1) /etc/machine-id exists and is populated.\n"
 116                                                   "2) /etc/machine-id exists and is empty.\n"
 117                                                   "3) /etc/machine-id is missing and /etc is writable.\n");
 118                                 else
 119                                         return log_error_errno(errno, "Cannot open %s: %m", etc_machine_id);
 120                         }
 121
 122                         writable = false;
 123                 } else
 124                         writable = true;
 125         }
 126
 127         /* A we got a valid machine ID argument, that's what counts */
 128         if (sd_id128_is_null(machine_id)) {
 129
 130                 /* Try to read any existing machine ID */
 131                 if (id128_read_fd(fd, ID128_PLAIN, ret) >= 0)
 132                         return 0;
 133
 134                 /* Hmm, so, the id currently stored is not useful, then let's generate one */
 135                 r = generate_machine_id(root, &machine_id);
 136                 if (r < 0)
 137                         return r;
 138         }
 139
 140         if (writable) {
 141                 if (lseek(fd, 0, SEEK_SET) == (off_t) -1)
 142                         return log_error_errno(errno, "Failed to seek %s: %m", etc_machine_id);
 143
 144                 if (ftruncate(fd, 0) < 0)
 145                         return log_error_errno(errno, "Failed to truncate %s: %m", etc_machine_id);
 146
 147                 /* If the caller requested a transient machine-id, write the string "uninitialized\n" to
 148                  * disk and overmount it with a transient file.
 149                  *
 150                  * Otherwise write the machine-id directly to disk. */
 151                 if (force_transient) {
 152                         r = loop_write(fd, "uninitialized\n", strlen("uninitialized\n"), false);
 153                         if (r < 0)
 154                                 return log_error_errno(r, "Failed to write uninitialized %s: %m", etc_machine_id);
 155
 156                         r = fsync_full(fd);
 157                         if (r < 0)
 158                                 return log_error_errno(r, "Failed to sync %s: %m", etc_machine_id);
 159                 } else {
 160                         r = id128_write_fd(fd, ID128_PLAIN, machine_id, true);
 161                         if (r < 0)
 162                                 return log_error_errno(r, "Failed to write %s: %m", etc_machine_id);
 163                         else
 164                                 goto finish;
 165                 }
 166         }
 167
 168         fd = safe_close(fd);
 169
 170         /* Hmm, we couldn't or shouldn't write the machine-id to /etc?
 171          * So let's write it to /run/machine-id as a replacement */
 172
 173         run_machine_id = prefix_roota(root, "/run/machine-id");
 174
 175         RUN_WITH_UMASK(0022)
 176                 r = id128_write(run_machine_id, ID128_PLAIN, machine_id, false);
 177         if (r < 0) {
 178                 (void) unlink(run_machine_id);
 179                 return log_error_errno(r, "Cannot write %s: %m", run_machine_id);
 180         }
 181
 182         /* And now, let's mount it over */
 183         r = mount_follow_verbose(LOG_ERR, run_machine_id, etc_machine_id, NULL, MS_BIND, NULL);
 184         if (r < 0) {
 185                 (void) unlink(run_machine_id);
 186                 return r;
 187         }
 188
 189         log_full(force_transient ? LOG_DEBUG : LOG_INFO, "Installed transient %s file.", etc_machine_id);
 190
 191         /* Mark the mount read-only */
 192         r = mount_follow_verbose(LOG_WARNING, NULL, etc_machine_id, NULL, MS_BIND|MS_RDONLY|MS_REMOUNT, NULL);
 193         if (r < 0)
 194                 return r;
 195
 196 finish:
 197         if (ret)
 198                 *ret = machine_id;
 199
 200         return 0;
 201 }
 202
 203 int machine_id_commit(const char *root) {
 204         _cleanup_close_ int fd = -1, initial_mntns_fd = -1;
 205         const char *etc_machine_id, *sync_path;
 206         sd_id128_t id;
 207         int r;
 208
 209         /* Before doing anything, sync everything to ensure any changes by first-boot units are persisted.
 210          *
 211          * First, explicitly sync the file systems we care about and check if it worked. */
 212         FOREACH_STRING(sync_path, "/etc/", "/var/") {
 213                 r = syncfs_path(AT_FDCWD, sync_path);
 214                 if (r < 0)
 215                         return log_error_errno(r, "Cannot sync %s: %m", sync_path);
 216         }
 217
 218         /* Afterwards, sync() the rest too, but we can't check the return value for these. */
 219         sync();
 220
 221         /* Replaces a tmpfs bind mount of /etc/machine-id by a proper file, atomically. For this, the umount is removed
 222          * in a mount namespace, a new file is created at the right place. Afterwards the mount is also removed in the
 223          * original mount namespace, thus revealing the file that was just created. */
 224
 225         etc_machine_id = prefix_roota(root, "/etc/machine-id");
 226
 227         r = path_is_mount_point(etc_machine_id, NULL, 0);
 228         if (r < 0)
 229                 return log_error_errno(r, "Failed to determine whether %s is a mount point: %m", etc_machine_id);
 230         if (r == 0) {
 231                 log_debug("%s is not a mount point. Nothing to do.", etc_machine_id);
 232                 return 0;
 233         }
 234
 235         /* Read existing machine-id */
 236         fd = open(etc_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY);
 237         if (fd < 0)
 238                 return log_error_errno(errno, "Cannot open %s: %m", etc_machine_id);
 239
 240         r = fd_is_temporary_fs(fd);
 241         if (r < 0)
 242                 return log_error_errno(r, "Failed to determine whether %s is on a temporary file system: %m", etc_machine_id);
 243         if (r == 0)
 244                 return log_error_errno(SYNTHETIC_ERRNO(EROFS),
 245                                        "%s is not on a temporary file system.",
 246                                        etc_machine_id);
 247
 248         r = id128_read_fd(fd, ID128_PLAIN, &id);
 249         if (r < 0)
 250                 return log_error_errno(r, "We didn't find a valid machine ID in %s: %m", etc_machine_id);
 251
 252         fd = safe_close(fd);
 253
 254         /* Store current mount namespace */
 255         r = namespace_open(0, NULL, &initial_mntns_fd, NULL, NULL, NULL);
 256         if (r < 0)
 257                 return log_error_errno(r, "Can't fetch current mount namespace: %m");
 258
 259         /* Switch to a new mount namespace, isolate ourself and unmount etc_machine_id in our new namespace */
 260         r = detach_mount_namespace();
 261         if (r < 0)
 262                 return log_error_errno(r, "Failed to set up new mount namespace: %m");
 263
 264         r = umount_verbose(LOG_ERR, etc_machine_id, 0);
 265         if (r < 0)
 266                 return r;
 267
 268         /* Update a persistent version of etc_machine_id */
 269         r = id128_write(etc_machine_id, ID128_PLAIN, id, true);
 270         if (r < 0)
 271                 return log_error_errno(r, "Cannot write %s. This is mandatory to get a persistent machine ID: %m", etc_machine_id);
 272
 273         /* Return to initial namespace and proceed a lazy tmpfs unmount */
 274         r = namespace_enter(-1, initial_mntns_fd, -1, -1, -1);
 275         if (r < 0)
 276                 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);
 277
 278         if (umount2(etc_machine_id, MNT_DETACH) < 0)
 279                 return log_warning_errno(errno, "Failed to unmount transient %s file: %m.\nWe keep that mount until next reboot.", etc_machine_id);
 280
 281         return 0;
 282 }