src/core/machine-id-setup.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 /***
   3   Copyright 2010 Lennart Poettering
   4 ***/
   5
   6 #include <fcntl.h>
   7 #include <sched.h>
   8 #include <sys/mount.h>
   9 #include <unistd.h>
  10
  11 #include "sd-id128.h"
  12
  13 #include "alloc-util.h"
  14 #include "fd-util.h"
  15 #include "fs-util.h"
  16 #include "id128-util.h"
  17 #include "log.h"
  18 #include "machine-id-setup.h"
  19 #include "macro.h"
  20 #include "mkdir.h"
  21 #include "mount-util.h"
  22 #include "path-util.h"
  23 #include "process-util.h"
  24 #include "stat-util.h"
  25 #include "string-util.h"
  26 #include "umask-util.h"
  27 #include "util.h"
  28 #include "virt.h"
  29
  30 static int generate_machine_id(const char *root, sd_id128_t *ret) {
  31         const char *dbus_machine_id;
  32         _cleanup_close_ int fd = -1;
  33         int r;
  34
  35         assert(ret);
  36
  37         /* First, try reading the D-Bus machine id, unless it is a symlink */
  38         dbus_machine_id = prefix_roota(root, "/var/lib/dbus/machine-id");
  39         fd = open(dbus_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW);
  40         if (fd >= 0) {
  41                 if (id128_read_fd(fd, ID128_PLAIN, ret) >= 0) {
  42                         log_info("Initializing machine ID from D-Bus machine ID.");
  43                         return 0;
  44                 }
  45
  46                 fd = safe_close(fd);
  47         }
  48
  49         if (isempty(root)) {
  50                 /* If that didn't work, see if we are running in a container,
  51                  * and a machine ID was passed in via $container_uuid the way
  52                  * libvirt/LXC does it */
  53
  54                 if (detect_container() > 0) {
  55                         _cleanup_free_ char *e = NULL;
  56
  57                         if (getenv_for_pid(1, "container_uuid", &e) > 0 &&
  58                             sd_id128_from_string(e, ret) >= 0) {
  59                                 log_info("Initializing machine ID from container UUID.");
  60                                 return 0;
  61                         }
  62
  63                 } else if (detect_vm() == VIRTUALIZATION_KVM) {
  64
  65                         /* If we are not running in a container, see if we are
  66                          * running in qemu/kvm and a machine ID was passed in
  67                          * via -uuid on the qemu/kvm command line */
  68
  69                         if (id128_read("/sys/class/dmi/id/product_uuid", ID128_UUID, ret) >= 0) {
  70                                 log_info("Initializing machine ID from KVM UUID.");
  71                                 return 0;
  72                         }
  73                 }
  74         }
  75
  76         /* If that didn't work, generate a random machine id */
  77         r = sd_id128_randomize(ret);
  78         if (r < 0)
  79                 return log_error_errno(r, "Failed to generate randomized : %m");
  80
  81         log_info("Initializing machine ID from random generator.");
  82         return 0;
  83 }
  84
  85 int machine_id_setup(const char *root, sd_id128_t machine_id, sd_id128_t *ret) {
  86         const char *etc_machine_id, *run_machine_id;
  87         _cleanup_close_ int fd = -1;
  88         bool writable;
  89         int r;
  90
  91         etc_machine_id = prefix_roota(root, "/etc/machine-id");
  92
  93         RUN_WITH_UMASK(0000) {
  94                 /* We create this 0444, to indicate that this isn't really
  95                  * something you should ever modify. Of course, since the file
  96                  * will be owned by root it doesn't matter much, but maybe
  97                  * people look. */
  98
  99                 (void) mkdir_parents(etc_machine_id, 0755);
 100                 fd = open(etc_machine_id, O_RDWR|O_CREAT|O_CLOEXEC|O_NOCTTY, 0444);
 101                 if (fd < 0) {
 102                         int old_errno = errno;
 103
 104                         fd = open(etc_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY);
 105                         if (fd < 0) {
 106                                 if (old_errno == EROFS && errno == ENOENT)
 107                                         return log_error_errno(errno,
 108                                                   "System cannot boot: Missing /etc/machine-id and /etc is mounted read-only.\n"
 109                                                   "Booting up is supported only when:\n"
 110                                                   "1) /etc/machine-id exists and is populated.\n"
 111                                                   "2) /etc/machine-id exists and is empty.\n"
 112                                                   "3) /etc/machine-id is missing and /etc is writable.\n");
 113                                 else
 114                                         return log_error_errno(errno,
 115                                                                "Cannot open %s: %m", etc_machine_id);
 116                         }
 117
 118                         writable = false;
 119                 } else
 120                         writable = true;
 121         }
 122
 123         /* A we got a valid machine ID argument, that's what counts */
 124         if (sd_id128_is_null(machine_id)) {
 125
 126                 /* Try to read any existing machine ID */
 127                 if (id128_read_fd(fd, ID128_PLAIN, ret) >= 0)
 128                         return 0;
 129
 130                 /* Hmm, so, the id currently stored is not useful, then let's generate one */
 131                 r = generate_machine_id(root, &machine_id);
 132                 if (r < 0)
 133                         return r;
 134         }
 135
 136         if (writable) {
 137                 if (lseek(fd, 0, SEEK_SET) == (off_t) -1)
 138                         return log_error_errno(errno, "Failed to seek %s: %m", etc_machine_id);
 139
 140                 if (ftruncate(fd, 0) < 0)
 141                         return log_error_errno(errno, "Failed to truncate %s: %m", etc_machine_id);
 142
 143                 if (id128_write_fd(fd, ID128_PLAIN, machine_id, true) >= 0)
 144                         goto finish;
 145         }
 146
 147         fd = safe_close(fd);
 148
 149         /* Hmm, we couldn't write it? So let's write it to /run/machine-id as a replacement */
 150
 151         run_machine_id = prefix_roota(root, "/run/machine-id");
 152
 153         RUN_WITH_UMASK(0022)
 154                 r = id128_write(run_machine_id, ID128_PLAIN, machine_id, false);
 155         if (r < 0) {
 156                 (void) unlink(run_machine_id);
 157                 return log_error_errno(r, "Cannot write %s: %m", run_machine_id);
 158         }
 159
 160         /* And now, let's mount it over */
 161         if (mount(run_machine_id, etc_machine_id, NULL, MS_BIND, NULL) < 0) {
 162                 (void) unlink_noerrno(run_machine_id);
 163                 return log_error_errno(errno, "Failed to mount %s: %m", etc_machine_id);
 164         }
 165
 166         log_info("Installed transient %s file.", etc_machine_id);
 167
 168         /* Mark the mount read-only */
 169         if (mount(NULL, etc_machine_id, NULL, MS_BIND|MS_RDONLY|MS_REMOUNT, NULL) < 0)
 170                 log_warning_errno(errno, "Failed to make transient %s read-only, ignoring: %m", etc_machine_id);
 171
 172 finish:
 173         if (ret)
 174                 *ret = machine_id;
 175
 176         return 0;
 177 }
 178
 179 int machine_id_commit(const char *root) {
 180         _cleanup_close_ int fd = -1, initial_mntns_fd = -1;
 181         const char *etc_machine_id;
 182         sd_id128_t id;
 183         int r;
 184
 185         /* Replaces a tmpfs bind mount of /etc/machine-id by a proper file, atomically. For this, the umount is removed
 186          * in a mount namespace, a new file is created at the right place. Afterwards the mount is also removed in the
 187          * original mount namespace, thus revealing the file that was just created. */
 188
 189         etc_machine_id = prefix_roota(root, "/etc/machine-id");
 190
 191         r = path_is_mount_point(etc_machine_id, NULL, 0);
 192         if (r < 0)
 193                 return log_error_errno(r, "Failed to determine whether %s is a mount point: %m", etc_machine_id);
 194         if (r == 0) {
 195                 log_debug("%s is not a mount point. Nothing to do.", etc_machine_id);
 196                 return 0;
 197         }
 198
 199         /* Read existing machine-id */
 200         fd = open(etc_machine_id, O_RDONLY|O_CLOEXEC|O_NOCTTY);
 201         if (fd < 0)
 202                 return log_error_errno(errno, "Cannot open %s: %m", etc_machine_id);
 203
 204         r = fd_is_temporary_fs(fd);
 205         if (r < 0)
 206                 return log_error_errno(r, "Failed to determine whether %s is on a temporary file system: %m", etc_machine_id);
 207         if (r == 0) {
 208                 log_error("%s is not on a temporary file system.", etc_machine_id);
 209                 return -EROFS;
 210         }
 211
 212         r = id128_read_fd(fd, ID128_PLAIN, &id);
 213         if (r < 0)
 214                 return log_error_errno(r, "We didn't find a valid machine ID in %s.", etc_machine_id);
 215
 216         fd = safe_close(fd);
 217
 218         /* Store current mount namespace */
 219         r = namespace_open(0, NULL, &initial_mntns_fd, NULL, NULL, NULL);
 220         if (r < 0)
 221                 return log_error_errno(r, "Can't fetch current mount namespace: %m");
 222
 223         /* Switch to a new mount namespace, isolate ourself and unmount etc_machine_id in our new namespace */
 224         if (unshare(CLONE_NEWNS) < 0)
 225                 return log_error_errno(errno, "Failed to enter new namespace: %m");
 226
 227         if (mount(NULL, "/", NULL, MS_SLAVE | MS_REC, NULL) < 0)
 228                 return log_error_errno(errno, "Couldn't make-rslave / mountpoint in our private namespace: %m");
 229
 230         if (umount(etc_machine_id) < 0)
 231                 return log_error_errno(errno, "Failed to unmount transient %s file in our private namespace: %m", etc_machine_id);
 232
 233         /* Update a persistent version of etc_machine_id */
 234         r = id128_write(etc_machine_id, ID128_PLAIN, id, true);
 235         if (r < 0)
 236                 return log_error_errno(r, "Cannot write %s. This is mandatory to get a persistent machine ID: %m", etc_machine_id);
 237
 238         /* Return to initial namespace and proceed a lazy tmpfs unmount */
 239         r = namespace_enter(-1, initial_mntns_fd, -1, -1, -1);
 240         if (r < 0)
 241                 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);
 242
 243         if (umount2(etc_machine_id, MNT_DETACH) < 0)
 244                 return log_warning_errno(errno, "Failed to unmount transient %s file: %m.\nWe keep that mount until next reboot.", etc_machine_id);
 245
 246         return 0;
 247 }