systemd/src/shared/machine-id-setup.c

/* SPDX-License-Identifier: LGPL-2.1-or-later */

#include <fcntl.h>
#include <sched.h>
#include <sys/mount.h>
#include <unistd.h>

#include "sd-daemon.h"
#include "sd-id128.h"

#include "alloc-util.h"
#include "chase.h"
#include "creds-util.h"
#include "fd-util.h"
#include "id128-util.h"
#include "initrd-util.h"
#include "io-util.h"
#include "log.h"
#include "machine-id-setup.h"
#include "macro.h"
#include "mkdir.h"
#include "mount-util.h"
#include "mountpoint-util.h"
#include "namespace-util.h"
#include "path-util.h"
#include "process-util.h"
#include "stat-util.h"
#include "string-util.h"
#include "sync-util.h"
#include "umask-util.h"
#include "virt.h"

static int acquire_machine_id_from_credential(sd_id128_t *ret_machine_id) {
        _cleanup_free_ char *buf = NULL;
        int r;

        assert(ret_machine_id);

        r = read_credential_with_decryption("system.machine_id", (void**) &buf, /* ret_size= */ NULL);
        if (r < 0)
                return log_warning_errno(r, "Failed to read system.machine_id credential, ignoring: %m");
        if (r == 0) {
                /* not found */
                *ret_machine_id = SD_ID128_NULL;
                return 0;
        }

        if (streq(buf, "firmware")) {
                *ret_machine_id = SD_ID128_NULL;
                return 1;
        }

        r = sd_id128_from_string(buf, ret_machine_id);
        if (r < 0)
                return log_warning_errno(r, "Failed to parse system.machine_id credential, ignoring: %m");

        log_info("Initializing machine ID from credential.");
        return 1;
}

static int acquire_machine_id(const char *root, bool machine_id_from_firmware, sd_id128_t *ret) {
        _cleanup_close_ int fd = -EBADF;
        int r;

        assert(ret);

        /* First, try reading the machine ID from /run/machine-id, which may not be mounted on
         * /etc/machine-id yet. This is important on switching root especially on soft-reboot, Otherwise,
         * machine ID may be changed after the transition. */
        if (isempty(root) && running_in_chroot() <= 0 &&
            id128_read("/run/machine-id", ID128_FORMAT_PLAIN, ret) >= 0) {
                log_info("Reusing machine ID stored in /run/machine-id.");
                return 1; /* Indicate that the machine ID is reused. */
        }

        /* Then, try reading the D-Bus machine ID, unless it is a symlink */
        fd = chase_and_open("/var/lib/dbus/machine-id", root, CHASE_PREFIX_ROOT|CHASE_NOFOLLOW|CHASE_MUST_BE_REGULAR, O_RDONLY|O_CLOEXEC|O_NOCTTY, NULL);
        if (fd >= 0 && id128_read_fd(fd, ID128_FORMAT_PLAIN | ID128_REFUSE_NULL, ret) >= 0) {
                log_info("Initializing machine ID from D-Bus machine ID.");
                return 0;
        }

        if (isempty(root) && running_in_chroot() <= 0) {
                /* Let's use a system credential for the machine ID if we can */
                sd_id128_t from_credential;
                r = acquire_machine_id_from_credential(&from_credential);
                if (r > 0) {
                        if (!sd_id128_is_null(from_credential)) {
                                /* got a valid machine id from creds */
                                *ret = from_credential;
                                return 0;
                        }

                        /* We got a credential, and it was set to "firmware", hence definitely try that */
                        machine_id_from_firmware = true;
                }

                /* If that didn't work, see if we are running in a container,
                 * and a machine ID was passed in via $container_uuid the way
                 * libvirt/LXC does it */

                if (detect_container() > 0) {
                        _cleanup_free_ char *e = NULL;

                        if (getenv_for_pid(1, "container_uuid", &e) > 0 &&
                            sd_id128_from_string(e, ret) >= 0) {
                                log_info("Initializing machine ID from container UUID.");
                                return 0;
                        }

                } else if (IN_SET(detect_vm(), VIRTUALIZATION_KVM, VIRTUALIZATION_AMAZON, VIRTUALIZATION_QEMU, VIRTUALIZATION_XEN) || machine_id_from_firmware) {

                        /* If we are not running in a container, see if we are running in a VM that provides
                         * a system UUID via the SMBIOS/DMI interfaces.  Such environments include QEMU/KVM
                         * with the -uuid on the qemu command line or the Amazon EC2 Nitro hypervisor. */

                        if (id128_get_product(ret) >= 0) {
                                log_info("Initializing machine ID from SMBIOS/DMI UUID.");
                                return 0;
                        }
                }
        }

        /* If that didn't work, generate a random machine ID */
        r = sd_id128_randomize(ret);
        if (r < 0)
                return log_error_errno(r, "Failed to generate randomized machine ID: %m");

        log_info("Initializing machine ID from random generator.");
        return 0;
}

int machine_id_setup(const char *root, sd_id128_t machine_id, MachineIdSetupFlags flags, sd_id128_t *ret) {
        _cleanup_free_ char *etc_machine_id = NULL, *run_machine_id = NULL;
        bool writable, write_run_machine_id = true;
        _cleanup_close_ int fd = -EBADF, run_fd = -EBADF;
        bool unlink_run_machine_id = false;
        int r;

        WITH_UMASK(0000) {
                _cleanup_close_ int inode_fd = -EBADF;

                r = chase("/etc/machine-id", root, CHASE_PREFIX_ROOT|CHASE_MUST_BE_REGULAR, &etc_machine_id, &inode_fd);
                if (r == -ENOENT) {
                        _cleanup_close_ int etc_fd = -EBADF;
                        _cleanup_free_ char *etc = NULL;

                        r = chase("/etc/", root, CHASE_PREFIX_ROOT|CHASE_MKDIR_0755|CHASE_MUST_BE_DIRECTORY, &etc, &etc_fd);
                        if (r < 0)
                                return log_error_errno(r, "Failed to open '/etc/': %m");

                        etc_machine_id = path_join(etc, "machine-id");
                        if (!etc_machine_id)
                                return log_oom();

                        /* We create this 0444, to indicate that this isn't really something you should ever
                         * modify. Of course, since the file will be owned by root it doesn't matter much, but maybe
                         * people look. */

                        fd = openat(etc_fd, "machine-id", O_CREAT|O_EXCL|O_RDWR|O_NOFOLLOW|O_CLOEXEC, 0444);
                        if (fd < 0) {
                                if (errno == EROFS)
                                        return log_error_errno(errno,
                                                               "System cannot boot: Missing %s and %s/ is read-only.\n"
                                                               "Booting up is supported only when:\n"
                                                               "1) /etc/machine-id exists and is populated.\n"
                                                               "2) /etc/machine-id exists and is empty.\n"
                                                               "3) /etc/machine-id is missing and /etc/ is writable.",
                                                               etc_machine_id,
                                                               etc);

                                return log_error_errno(errno, "Cannot create '%s': %m", etc_machine_id);
                        }

                        log_debug("Successfully opened new '%s' file.", etc_machine_id);
                        writable = true;
                } else if (r < 0)
                        return log_error_errno(r, "Cannot open '/etc/machine-id': %m");
                else {
                        /* We pinned the inode, now try to convert it into a writable file */

                        fd = xopenat_full(inode_fd, /* path= */ NULL, O_RDWR|O_CLOEXEC, XO_REGULAR, 0444);
                        if (fd < 0) {
                                log_debug_errno(fd, "Failed to topen '%s' in writable mode, retrying in read-only mode: %m", etc_machine_id);

                                /* If that didn't work, convert it into a readable file */
                                fd = xopenat_full(inode_fd, /* path= */ NULL, O_RDONLY|O_CLOEXEC, XO_REGULAR, MODE_INVALID);
                                if (fd < 0)
                                        return log_error_errno(fd, "Cannot open '%s' in neither writable nor read-only mode: %m", etc_machine_id);

                                log_debug("Successfully opened existing '%s' file in read-only mode.", etc_machine_id);
                                writable = false;
                        } else {
                                log_debug("Successfully opened existing '%s' file in writable mode.", etc_machine_id);
                                writable = true;
                        }
                }
        }

        /* A we got a valid machine ID argument, that's what counts */
        if (sd_id128_is_null(machine_id) || FLAGS_SET(flags, MACHINE_ID_SETUP_FORCE_FIRMWARE)) {

                /* Try to read any existing machine ID */
                r = id128_read_fd(fd, ID128_FORMAT_PLAIN, &machine_id);
                if (r >= 0)
                        goto finish;

                log_debug_errno(r, "Unable to read current machine ID, acquiring new one: %m");

                /* Hmm, so, the id currently stored is not useful, then let's acquire one. */
                r = acquire_machine_id(root, FLAGS_SET(flags, MACHINE_ID_SETUP_FORCE_FIRMWARE), &machine_id);
                if (r < 0)
                        return r;

                write_run_machine_id = !r; /* acquire_machine_id() returns 1 in case we read this machine ID
                                            * from /run/machine-id */
        }

        if (writable) {
                if (lseek(fd, 0, SEEK_SET) < 0)
                        return log_error_errno(errno, "Failed to seek %s: %m", etc_machine_id);

                if (ftruncate(fd, 0) < 0)
                        return log_error_errno(errno, "Failed to truncate %s: %m", etc_machine_id);

                /* If the caller requested a transient machine-id, write the string "uninitialized\n" to
                 * disk and overmount it with a transient file.
                 *
                 * Otherwise write the machine-id directly to disk. */
                if (FLAGS_SET(flags, MACHINE_ID_SETUP_FORCE_TRANSIENT)) {
                        r = loop_write(fd, "uninitialized\n", SIZE_MAX);
                        if (r < 0)
                                return log_error_errno(r, "Failed to write uninitialized %s: %m", etc_machine_id);

                        r = fsync_full(fd);
                        if (r < 0)
                                return log_error_errno(r, "Failed to sync %s: %m", etc_machine_id);
                } else {
                        r = id128_write_fd(fd, ID128_FORMAT_PLAIN | ID128_SYNC_ON_WRITE, machine_id);
                        if (r < 0)
                                return log_error_errno(r, "Failed to write %s: %m", etc_machine_id);

                        goto finish;
                }
        }

        /* Hmm, we couldn't or shouldn't write the machine-id to /etc/? So let's write it to /run/machine-id
         * as a replacement */

        if (write_run_machine_id) {
                _cleanup_free_ char *run = NULL;

                r = chase("/run/", root, CHASE_PREFIX_ROOT|CHASE_MKDIR_0755|CHASE_MUST_BE_DIRECTORY, &run, &run_fd);
                if (r < 0)
                        return log_error_errno(r, "Failed to open '/run/': %m");

                run_machine_id = path_join(run, "machine-id");
                if (!run_machine_id)
                        return log_oom();

                WITH_UMASK(0022) {
                        r = id128_write_at(run_fd, "machine-id", ID128_FORMAT_PLAIN, machine_id);
                        if (r < 0)
                                return log_error_errno(r, "Cannot write '%s': %m", run_machine_id);
                }

                unlink_run_machine_id = true;
        } else {
                r = chase("/run/machine-id", root, CHASE_PREFIX_ROOT|CHASE_MUST_BE_REGULAR, &run_machine_id, /* ret_inode_fd= */ NULL);
                if (r < 0)
                        return log_error_errno(r, "Failed to open '/run/machine-id': %m");
        }

        /* And now, let's mount it over */
        r = mount_follow_verbose(LOG_ERR, run_machine_id, FORMAT_PROC_FD_PATH(fd), /* fstype= */ NULL, MS_BIND, /* options= */ NULL);
        if (r < 0)
                return r;

        log_full(FLAGS_SET(flags, MACHINE_ID_SETUP_FORCE_TRANSIENT) ? LOG_DEBUG : LOG_INFO, "Installed transient '%s' file.", etc_machine_id);

        unlink_run_machine_id = false;

        /* Mark the mount read-only (note: we are not going via FORMAT_PROC_FD_PATH() here because that fd is not updated to our new bind mount) */
        (void) mount_follow_verbose(LOG_WARNING, /* source= */ NULL, etc_machine_id, /* fstype= */ NULL, MS_BIND|MS_RDONLY|MS_REMOUNT, /* options= */ NULL);

finish:
        if (unlink_run_machine_id)
                (void) unlinkat(ASSERT_FD(run_fd), "machine-id", /* flags= */ 0);

        if (!in_initrd())
                (void) sd_notifyf(/* unset_environment= */ false, "X_SYSTEMD_MACHINE_ID=" SD_ID128_FORMAT_STR, SD_ID128_FORMAT_VAL(machine_id));

        if (ret)
                *ret = machine_id;

        return 0;
}

int machine_id_commit(const char *root) {
        sd_id128_t id;
        int r;

        if (empty_or_root(root)) {
                /* Before doing anything, sync everything to ensure any changes by first-boot units are
                 * persisted.
                 *
                 * First, explicitly sync the file systems we care about and check if it worked. */
                FOREACH_STRING(sync_path, "/etc/", "/var/") {
                        r = syncfs_path(AT_FDCWD, sync_path);
                        if (r < 0)
                                return log_error_errno(r, "Cannot sync %s: %m", sync_path);
                }

                /* Afterwards, sync() the rest too, but we can't check the return value for these. */
                sync();
        }

        /* Replaces a tmpfs bind mount of /etc/machine-id by a proper file, atomically. For this, the umount is removed
         * in a mount namespace, a new file is created at the right place. Afterwards the mount is also removed in the
         * original mount namespace, thus revealing the file that was just created. */

        _cleanup_close_ int etc_fd = -EBADF;
        _cleanup_free_ char *etc = NULL;
        r = chase("/etc/", root, CHASE_PREFIX_ROOT|CHASE_MUST_BE_DIRECTORY, &etc, &etc_fd);
        if (r < 0)
                return log_error_errno(r, "Failed to open /etc/: %m");

        _cleanup_free_ char *etc_machine_id = path_join(etc, "machine-id");
        if (!etc_machine_id)
                return log_oom();

        r = is_mount_point_at(etc_fd, "machine-id", /* flags= */ 0);
        if (r < 0)
                return log_error_errno(r, "Failed to determine whether %s is a mount point: %m", etc_machine_id);
        if (r == 0) {
                log_debug("%s is not a mount point. Nothing to do.", etc_machine_id);
                return 0;
        }

        /* Read existing machine-id */

        _cleanup_close_ int fd = xopenat_full(etc_fd, "machine-id", O_RDONLY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW, XO_REGULAR, MODE_INVALID);
        if (fd < 0)
                return log_error_errno(fd, "Cannot open %s: %m", etc_machine_id);

        etc_fd = safe_close(etc_fd);

        r = fd_is_temporary_fs(fd);
        if (r < 0)
                return log_error_errno(r, "Failed to determine whether %s is on a temporary file system: %m", etc_machine_id);
        if (r == 0)
                return log_error_errno(SYNTHETIC_ERRNO(EROFS),
                                       "%s is not on a temporary file system.",
                                       etc_machine_id);

        r = id128_read_fd(fd, ID128_FORMAT_PLAIN, &id);
        if (r < 0)
                return log_error_errno(r, "We didn't find a valid machine ID in %s: %m", etc_machine_id);

        /* Store current mount namespace */
        _cleanup_close_ int initial_mntns_fd = namespace_open_by_type(NAMESPACE_MOUNT);
        if (initial_mntns_fd < 0)
                return log_error_errno(initial_mntns_fd, "Can't fetch current mount namespace: %m");

        /* Switch to a new mount namespace, isolate ourself and unmount etc_machine_id in our new namespace */
        r = detach_mount_namespace();
        if (r < 0)
                return log_error_errno(r, "Failed to set up new mount namespace: %m");

        /* Open /etc/ again after we transitioned into our own private mount namespace */
        _cleanup_close_ int etc_fd_again = -EBADF;
        r = chase("/etc/", root, CHASE_PREFIX_ROOT|CHASE_MUST_BE_DIRECTORY, /* ret_path= */ NULL, &etc_fd_again);
        if (r < 0)
                return log_error_errno(r, "Failed to open /etc/: %m");

        r = umountat_detach_verbose(LOG_ERR, etc_fd_again, "machine-id");
        if (r < 0)
                return r;

        /* Update a persistent version of etc_machine_id */
        r = id128_write_at(etc_fd_again, "machine-id", ID128_FORMAT_PLAIN | ID128_SYNC_ON_WRITE, id);
        if (r < 0)
                return log_error_errno(r, "Cannot write %s. This is mandatory to get a persistent machine ID: %m", etc_machine_id);

        etc_fd_again = safe_close(etc_fd_again);

        /* Return to initial namespace and proceed a lazy tmpfs unmount */
        r = namespace_enter(/* pidns_fd = */ -EBADF,
                            initial_mntns_fd,
                            /* netns_fd = */ -EBADF,
                            /* userns_fd = */ -EBADF,
                            /* root_fd = */ -EBADF);
        if (r < 0)
                return log_warning_errno(r,
                                         "Failed to switch back to initial mount namespace: %m.\n"
                                         "We'll keep transient %s file until next reboot.", etc_machine_id);

        r = umountat_detach_verbose(LOG_DEBUG, fd, /* filename= */ NULL);
        if (r < 0)
                return log_warning_errno(r,
                                         "Failed to unmount transient %s file: %m.\n"
                                         "We keep that mount until next reboot.", etc_machine_id);

        return 0;
}