src/core/machine-id-setup.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright 2010 Lennart Poettering
   5
   6   systemd is free software; you can redistribute it and/or modify it
   7   under the terms of the GNU Lesser General Public License as published by
   8   the Free Software Foundation; either version 2.1 of the License, or
   9   (at your option) any later version.
  10
  11   systemd is distributed in the hope that it will be useful, but
  12   WITHOUT ANY WARRANTY; without even the implied warranty of
  13   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  14   Lesser General Public License for more details.
  15
  16   You should have received a copy of the GNU Lesser General Public License
  17   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  18 ***/
  19
  20 #include <errno.h>
  21 #include <fcntl.h>
  22 #include <sched.h>
  23 #include <stdio.h>
  24 #include <string.h>
  25 #include <sys/mount.h>
  26 #include <unistd.h>
  27
  28 #include "sd-id128.h"
  29
  30 #include "alloc-util.h"
  31 #include "fd-util.h"
  32 #include "fileio.h"
  33 #include "fs-util.h"
  34 #include "hexdecoct.h"
  35 #include "io-util.h"
  36 #include "log.h"
  37 #include "machine-id-setup.h"
  38 #include "macro.h"
  39 #include "mkdir.h"
  40 #include "mount-util.h"
  41 #include "path-util.h"
  42 #include "process-util.h"
  43 #include "stat-util.h"
  44 #include "string-util.h"
  45 #include "umask-util.h"
  46 #include "util.h"
  47 #include "virt.h"
  48
  49 static int shorten_uuid(char destination[34], const char source[36]) {
  50         unsigned i, j;
  51
  52         assert(destination);
  53         assert(source);
  54
  55         /* Converts a UUID into a machine ID, by lowercasing it and
  56          * removing dashes. Validates everything. */
  57
  58         for (i = 0, j = 0; i < 36 && j < 32; i++) {
  59                 int t;
  60
  61                 t = unhexchar(source[i]);
  62                 if (t < 0)
  63                         continue;
  64
  65                 destination[j++] = hexchar(t);
  66         }
  67
  68         if (i != 36 || j != 32)
  69                 return -EINVAL;
  70
  71         destination[32] = '\n';
  72         destination[33] = 0;
  73         return 0;
  74 }
  75
  76 static int read_machine_id(int fd, char id[34]) {
  77         char id_to_validate[34];
  78         int r;
  79
  80         assert(fd >= 0);
  81         assert(id);
  82
  83         /* Reads a machine ID from a file, validates it, and returns
  84          * it. The returned ID ends in a newline. */
  85
  86         r = loop_read_exact(fd, id_to_validate, 33, false);
  87         if (r < 0)
  88                 return r;
  89
  90         if (id_to_validate[32] != '\n')
  91                 return -EINVAL;
  92
  93         id_to_validate[32] = 0;
  94
  95         if (!id128_is_valid(id_to_validate))
  96                 return -EINVAL;
  97
  98         memcpy(id, id_to_validate, 32);
  99         id[32] = '\n';
 100         id[33] = 0;
 101         return 0;
 102 }
 103
 104 static int write_machine_id(int fd, const char id[34]) {
 105         int r;
 106
 107         assert(fd >= 0);
 108         assert(id);
 109
 110         if (lseek(fd, 0, SEEK_SET) < 0)
 111                 return -errno;
 112
 113         r = loop_write(fd, id, 33, false);
 114         if (r < 0)
 115                 return r;
 116
 117         if (fsync(fd) < 0)
 118                 return -errno;
 119
 120         return 0;
 121 }
 122
 123 static int generate_machine_id(char id[34], const char *root) {
 124         int fd, r;
 125         unsigned char *p;
 126         sd_id128_t buf;
 127         char  *q;
 128         const char *dbus_machine_id;
 129
 130         assert(id);
 131
 132         dbus_machine_id = prefix_roota(root, "/var/lib/dbus/machine-id");
 133
 134         /* First, try reading the D-Bus machine id, unless it is a symlink */
 135         fd = open(dbus_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW);
 136         if (fd >= 0) {
 137                 r = read_machine_id(fd, id);
 138                 safe_close(fd);
 139
 140                 if (r >= 0) {
 141                         log_info("Initializing machine ID from D-Bus machine ID.");
 142                         return 0;
 143                 }
 144         }
 145
 146         if (isempty(root)) {
 147                 /* If that didn't work, see if we are running in a container,
 148                  * and a machine ID was passed in via $container_uuid the way
 149                  * libvirt/LXC does it */
 150
 151                 if (detect_container() > 0) {
 152                         _cleanup_free_ char *e = NULL;
 153
 154                         r = getenv_for_pid(1, "container_uuid", &e);
 155                         if (r > 0) {
 156                                 r = shorten_uuid(id, e);
 157                                 if (r >= 0) {
 158                                         log_info("Initializing machine ID from container UUID.");
 159                                         return 0;
 160                                 }
 161                         }
 162
 163                 } else if (detect_vm() == VIRTUALIZATION_KVM) {
 164
 165                         /* If we are not running in a container, see if we are
 166                          * running in qemu/kvm and a machine ID was passed in
 167                          * via -uuid on the qemu/kvm command line */
 168
 169                         char uuid[36];
 170
 171                         fd = open("/sys/class/dmi/id/product_uuid", O_RDONLY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW);
 172                         if (fd >= 0) {
 173                                 r = loop_read_exact(fd, uuid, 36, false);
 174                                 safe_close(fd);
 175
 176                                 if (r >= 0) {
 177                                         r = shorten_uuid(id, uuid);
 178                                         if (r >= 0) {
 179                                                 log_info("Initializing machine ID from KVM UUID.");
 180                                                 return 0;
 181                                         }
 182                                 }
 183                         }
 184                 }
 185         }
 186
 187         /* If that didn't work, generate a random machine id */
 188         r = sd_id128_randomize(&buf);
 189         if (r < 0)
 190                 return log_error_errno(r, "Failed to open /dev/urandom: %m");
 191
 192         for (p = buf.bytes, q = id; p < buf.bytes + sizeof(buf); p++, q += 2) {
 193                 q[0] = hexchar(*p >> 4);
 194                 q[1] = hexchar(*p & 15);
 195         }
 196
 197         id[32] = '\n';
 198         id[33] = 0;
 199
 200         log_info("Initializing machine ID from random generator.");
 201
 202         return 0;
 203 }
 204
 205 int machine_id_setup(const char *root, sd_id128_t machine_id) {
 206         const char *etc_machine_id, *run_machine_id;
 207         _cleanup_close_ int fd = -1;
 208         bool writable = true;
 209         char id[34]; /* 32 + \n + \0 */
 210         int r;
 211
 212         etc_machine_id = prefix_roota(root, "/etc/machine-id");
 213         run_machine_id = prefix_roota(root, "/run/machine-id");
 214
 215         RUN_WITH_UMASK(0000) {
 216                 /* We create this 0444, to indicate that this isn't really
 217                  * something you should ever modify. Of course, since the file
 218                  * will be owned by root it doesn't matter much, but maybe
 219                  * people look. */
 220
 221                 mkdir_parents(etc_machine_id, 0755);
 222                 fd = open(etc_machine_id, O_RDWR|O_CREAT|O_CLOEXEC|O_NOCTTY, 0444);
 223                 if (fd < 0) {
 224                         int old_errno = errno;
 225
 226                         fd = open(etc_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY);
 227                         if (fd < 0) {
 228                                 if (old_errno == EROFS && errno == ENOENT)
 229                                         log_error_errno(errno,
 230                                                   "System cannot boot: Missing /etc/machine-id and /etc is mounted read-only.\n"
 231                                                   "Booting up is supported only when:\n"
 232                                                   "1) /etc/machine-id exists and is populated.\n"
 233                                                   "2) /etc/machine-id exists and is empty.\n"
 234                                                   "3) /etc/machine-id is missing and /etc is writable.\n");
 235                                 else
 236                                         log_error_errno(errno, "Cannot open %s: %m", etc_machine_id);
 237
 238                                 return -errno;
 239                         }
 240
 241                         writable = false;
 242                 }
 243         }
 244
 245         /* A machine id argument overrides all other machined-ids */
 246         if (!sd_id128_is_null(machine_id)) {
 247                 sd_id128_to_string(machine_id, id);
 248                 id[32] = '\n';
 249                 id[33] = 0;
 250         } else {
 251                 if (read_machine_id(fd, id) >= 0)
 252                         return 0;
 253
 254                 /* Hmm, so, the id currently stored is not useful, then let's
 255                  * generate one */
 256
 257                 r = generate_machine_id(id, root);
 258                 if (r < 0)
 259                         return r;
 260         }
 261
 262         if (writable)
 263                 if (write_machine_id(fd, id) >= 0)
 264                         return 0;
 265
 266         fd = safe_close(fd);
 267
 268         /* Hmm, we couldn't write it? So let's write it to
 269          * /run/machine-id as a replacement */
 270
 271         RUN_WITH_UMASK(0022) {
 272                 r = write_string_file(run_machine_id, id, WRITE_STRING_FILE_CREATE);
 273                 if (r < 0) {
 274                         (void) unlink(run_machine_id);
 275                         return log_error_errno(r, "Cannot write %s: %m", run_machine_id);
 276                 }
 277         }
 278
 279         /* And now, let's mount it over */
 280         if (mount(run_machine_id, etc_machine_id, NULL, MS_BIND, NULL) < 0) {
 281                 (void) unlink_noerrno(run_machine_id);
 282                 return log_error_errno(errno, "Failed to mount %s: %m", etc_machine_id);
 283         }
 284
 285         log_info("Installed transient %s file.", etc_machine_id);
 286
 287         /* Mark the mount read-only */
 288         if (mount(NULL, etc_machine_id, NULL, MS_BIND|MS_RDONLY|MS_REMOUNT, NULL) < 0)
 289                 log_warning_errno(errno, "Failed to make transient %s read-only: %m", etc_machine_id);
 290
 291         return 0;
 292 }
 293
 294 int machine_id_commit(const char *root) {
 295         _cleanup_close_ int fd = -1, initial_mntns_fd = -1;
 296         const char *etc_machine_id;
 297         char id[34]; /* 32 + \n + \0 */
 298         int r;
 299
 300         etc_machine_id = prefix_roota(root, "/etc/machine-id");
 301
 302         r = path_is_mount_point(etc_machine_id, 0);
 303         if (r < 0)
 304                 return log_error_errno(r, "Failed to determine whether %s is a mount point: %m", etc_machine_id);
 305         if (r == 0) {
 306                 log_debug("%s is is not a mount point. Nothing to do.", etc_machine_id);
 307                 return 0;
 308         }
 309
 310         /* Read existing machine-id */
 311         fd = open(etc_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY);
 312         if (fd < 0)
 313                 return log_error_errno(errno, "Cannot open %s: %m", etc_machine_id);
 314
 315         r = read_machine_id(fd, id);
 316         if (r < 0)
 317                 return log_error_errno(r, "We didn't find a valid machine ID in %s.", etc_machine_id);
 318
 319         r = fd_is_temporary_fs(fd);
 320         if (r < 0)
 321                 return log_error_errno(r, "Failed to determine whether %s is on a temporary file system: %m", etc_machine_id);
 322         if (r == 0) {
 323                 log_error("%s is not on a temporary file system.", etc_machine_id);
 324                 return -EROFS;
 325         }
 326
 327         fd = safe_close(fd);
 328
 329         /* Store current mount namespace */
 330         r = namespace_open(0, NULL, &initial_mntns_fd, NULL, NULL, NULL);
 331         if (r < 0)
 332                 return log_error_errno(r, "Can't fetch current mount namespace: %m");
 333
 334         /* Switch to a new mount namespace, isolate ourself and unmount etc_machine_id in our new namespace */
 335         if (unshare(CLONE_NEWNS) < 0)
 336                 return log_error_errno(errno, "Failed to enter new namespace: %m");
 337
 338         if (mount(NULL, "/", NULL, MS_SLAVE | MS_REC, NULL) < 0)
 339                 return log_error_errno(errno, "Couldn't make-rslave / mountpoint in our private namespace: %m");
 340
 341         if (umount(etc_machine_id) < 0)
 342                 return log_error_errno(errno, "Failed to unmount transient %s file in our private namespace: %m", etc_machine_id);
 343
 344         /* Update a persistent version of etc_machine_id */
 345         fd = open(etc_machine_id, O_RDWR|O_CREAT|O_CLOEXEC|O_NOCTTY, 0444);
 346         if (fd < 0)
 347                 return log_error_errno(errno, "Cannot open for writing %s. This is mandatory to get a persistent machine-id: %m", etc_machine_id);
 348
 349         r = write_machine_id(fd, id);
 350         if (r < 0)
 351                 return log_error_errno(r, "Cannot write %s: %m", etc_machine_id);
 352
 353         fd = safe_close(fd);
 354
 355         /* Return to initial namespace and proceed a lazy tmpfs unmount */
 356         r = namespace_enter(-1, initial_mntns_fd, -1, -1, -1);
 357         if (r < 0)
 358                 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);
 359
 360         if (umount2(etc_machine_id, MNT_DETACH) < 0)
 361                 return log_warning_errno(errno, "Failed to unmount transient %s file: %m.\nWe keep that mount until next reboot.", etc_machine_id);
 362
 363         return 0;
 364 }