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 "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 "umask-util.h"
  26 #include "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_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 (detect_vm() == VIRTUALIZATION_KVM) {
  63
  64                         /* If we are not running in a container, see if we are
  65                          * running in qemu/kvm and a machine ID was passed in
  66                          * via -uuid on the qemu/kvm command line */
  67
  68                         if (id128_read("/sys/class/dmi/id/product_uuid", ID128_UUID, ret) >= 0) {
  69                                 log_info("Initializing machine ID from KVM UUID.");
  70                                 return 0;
  71                         }
  72                         /* on POWER, it's exported here instead */
  73                         if (id128_read("/sys/firmware/devicetree/base/vm,uuid", ID128_UUID, ret) >= 0) {
  74                                 log_info("Initializing machine ID from KVM UUID.");
  75                                 return 0;
  76                         }
  77                 }
  78         }
  79
  80         /* If that didn't work, generate a random machine id */
  81         r = sd_id128_randomize(ret);
  82         if (r < 0)
  83                 return log_error_errno(r, "Failed to generate randomized machine ID: %m");
  84
  85         log_info("Initializing machine ID from random generator.");
  86         return 0;
  87 }
  88
  89 int machine_id_setup(const char *root, sd_id128_t machine_id, sd_id128_t *ret) {
  90         const char *etc_machine_id, *run_machine_id;
  91         _cleanup_close_ int fd = -1;
  92         bool writable;
  93         int r;
  94
  95         etc_machine_id = prefix_roota(root, "/etc/machine-id");
  96
  97         RUN_WITH_UMASK(0000) {
  98                 /* We create this 0444, to indicate that this isn't really
  99                  * something you should ever modify. Of course, since the file
 100                  * will be owned by root it doesn't matter much, but maybe
 101                  * people look. */
 102
 103                 (void) mkdir_parents(etc_machine_id, 0755);
 104                 fd = open(etc_machine_id, O_RDWR|O_CREAT|O_CLOEXEC|O_NOCTTY, 0444);
 105                 if (fd < 0) {
 106                         int old_errno = errno;
 107
 108                         fd = open(etc_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY);
 109                         if (fd < 0) {
 110                                 if (old_errno == EROFS && errno == ENOENT)
 111                                         return log_error_errno(errno,
 112                                                   "System cannot boot: Missing /etc/machine-id and /etc is mounted read-only.\n"
 113                                                   "Booting up is supported only when:\n"
 114                                                   "1) /etc/machine-id exists and is populated.\n"
 115                                                   "2) /etc/machine-id exists and is empty.\n"
 116                                                   "3) /etc/machine-id is missing and /etc is writable.\n");
 117                                 else
 118                                         return log_error_errno(errno, "Cannot open %s: %m", etc_machine_id);
 119                         }
 120
 121                         writable = false;
 122                 } else
 123                         writable = true;
 124         }
 125
 126         /* A we got a valid machine ID argument, that's what counts */
 127         if (sd_id128_is_null(machine_id)) {
 128
 129                 /* Try to read any existing machine ID */
 130                 if (id128_read_fd(fd, ID128_PLAIN, ret) >= 0)
 131                         return 0;
 132
 133                 /* Hmm, so, the id currently stored is not useful, then let's generate one */
 134                 r = generate_machine_id(root, &machine_id);
 135                 if (r < 0)
 136                         return r;
 137         }
 138
 139         if (writable) {
 140                 if (lseek(fd, 0, SEEK_SET) == (off_t) -1)
 141                         return log_error_errno(errno, "Failed to seek %s: %m", etc_machine_id);
 142
 143                 if (ftruncate(fd, 0) < 0)
 144                         return log_error_errno(errno, "Failed to truncate %s: %m", etc_machine_id);
 145
 146                 if (id128_write_fd(fd, ID128_PLAIN, machine_id, true) >= 0)
 147                         goto finish;
 148         }
 149
 150         fd = safe_close(fd);
 151
 152         /* Hmm, we couldn't write it? So let's write it to /run/machine-id as a replacement */
 153
 154         run_machine_id = prefix_roota(root, "/run/machine-id");
 155
 156         RUN_WITH_UMASK(0022)
 157                 r = id128_write(run_machine_id, ID128_PLAIN, machine_id, false);
 158         if (r < 0) {
 159                 (void) unlink(run_machine_id);
 160                 return log_error_errno(r, "Cannot write %s: %m", run_machine_id);
 161         }
 162
 163         /* And now, let's mount it over */
 164         r = mount_follow_verbose(LOG_ERR, run_machine_id, etc_machine_id, NULL, MS_BIND, NULL);
 165         if (r < 0) {
 166                 (void) unlink(run_machine_id);
 167                 return r;
 168         }
 169
 170         log_info("Installed transient %s file.", etc_machine_id);
 171
 172         /* Mark the mount read-only */
 173         r = mount_follow_verbose(LOG_WARNING, NULL, etc_machine_id, NULL, MS_BIND|MS_RDONLY|MS_REMOUNT, NULL);
 174         if (r < 0)
 175                 return r;
 176
 177 finish:
 178         if (ret)
 179                 *ret = machine_id;
 180
 181         return 0;
 182 }
 183
 184 int machine_id_commit(const char *root) {
 185         _cleanup_close_ int fd = -1, initial_mntns_fd = -1;
 186         const char *etc_machine_id;
 187         sd_id128_t id;
 188         int r;
 189
 190         /* Replaces a tmpfs bind mount of /etc/machine-id by a proper file, atomically. For this, the umount is removed
 191          * in a mount namespace, a new file is created at the right place. Afterwards the mount is also removed in the
 192          * original mount namespace, thus revealing the file that was just created. */
 193
 194         etc_machine_id = prefix_roota(root, "/etc/machine-id");
 195
 196         r = path_is_mount_point(etc_machine_id, NULL, 0);
 197         if (r < 0)
 198                 return log_error_errno(r, "Failed to determine whether %s is a mount point: %m", etc_machine_id);
 199         if (r == 0) {
 200                 log_debug("%s is not a mount point. Nothing to do.", etc_machine_id);
 201                 return 0;
 202         }
 203
 204         /* Read existing machine-id */
 205         fd = open(etc_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY);
 206         if (fd < 0)
 207                 return log_error_errno(errno, "Cannot open %s: %m", etc_machine_id);
 208
 209         r = fd_is_temporary_fs(fd);
 210         if (r < 0)
 211                 return log_error_errno(r, "Failed to determine whether %s is on a temporary file system: %m", etc_machine_id);
 212         if (r == 0)
 213                 return log_error_errno(SYNTHETIC_ERRNO(EROFS),
 214                                        "%s is not on a temporary file system.",
 215                                        etc_machine_id);
 216
 217         r = id128_read_fd(fd, ID128_PLAIN, &id);
 218         if (r < 0)
 219                 return log_error_errno(r, "We didn't find a valid machine ID in %s: %m", etc_machine_id);
 220
 221         fd = safe_close(fd);
 222
 223         /* Store current mount namespace */
 224         r = namespace_open(0, NULL, &initial_mntns_fd, NULL, NULL, NULL);
 225         if (r < 0)
 226                 return log_error_errno(r, "Can't fetch current mount namespace: %m");
 227
 228         /* Switch to a new mount namespace, isolate ourself and unmount etc_machine_id in our new namespace */
 229         r = detach_mount_namespace();
 230         if (r < 0)
 231                 return log_error_errno(r, "Failed to set up new mount namespace: %m");
 232
 233         r = umount_verbose(LOG_ERR, etc_machine_id, 0);
 234         if (r < 0)
 235                 return r;
 236
 237         /* Update a persistent version of etc_machine_id */
 238         r = id128_write(etc_machine_id, ID128_PLAIN, id, true);
 239         if (r < 0)
 240                 return log_error_errno(r, "Cannot write %s. This is mandatory to get a persistent machine ID: %m", etc_machine_id);
 241
 242         /* Return to initial namespace and proceed a lazy tmpfs unmount */
 243         r = namespace_enter(-1, initial_mntns_fd, -1, -1, -1);
 244         if (r < 0)
 245                 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);
 246
 247         if (umount2(etc_machine_id, MNT_DETACH) < 0)
 248                 return log_warning_errno(errno, "Failed to unmount transient %s file: %m.\nWe keep that mount until next reboot.", etc_machine_id);
 249
 250         return 0;
 251 }