src/core/machine-id-setup.c

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