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