src/core/machine-id-setup.c

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