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