Adding upstream version 255.4.upstream/255.4

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 591 insertions, 0 deletions

diff --git a/src/shared/mount-setup.c b/src/shared/mount-setup.c
new file mode 100644
index 0000000..1226ca1
--- /dev/null
+++ b/src/shared/mount-setup.c
@@ -0,0 +1,591 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <stdlib.h>
+#include <sys/mount.h>
+#include <sys/statvfs.h>
+#include <unistd.h>
+
+#include "alloc-util.h"
+#include "bus-util.h"
+#include "cgroup-setup.h"
+#include "cgroup-util.h"
+#include "conf-files.h"
+#include "dev-setup.h"
+#include "dirent-util.h"
+#include "efi-loader.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "fs-util.h"
+#include "label-util.h"
+#include "log.h"
+#include "macro.h"
+#include "mkdir-label.h"
+#include "mount-setup.h"
+#include "mount-util.h"
+#include "mountpoint-util.h"
+#include "nulstr-util.h"
+#include "path-util.h"
+#include "recurse-dir.h"
+#include "set.h"
+#include "smack-util.h"
+#include "strv.h"
+#include "user-util.h"
+#include "virt.h"
+
+typedef enum MountMode {
+        MNT_NONE           = 0,
+        MNT_FATAL          = 1 << 0,
+        MNT_IN_CONTAINER   = 1 << 1,
+        MNT_CHECK_WRITABLE = 1 << 2,
+        MNT_FOLLOW_SYMLINK = 1 << 3,
+} MountMode;
+
+typedef struct MountPoint {
+        const char *what;
+        const char *where;
+        const char *type;
+        const char *options;
+        unsigned long flags;
+        bool (*condition_fn)(void);
+        MountMode mode;
+} MountPoint;
+
+/* The first three entries we might need before SELinux is up. The
+ * fourth (securityfs) is needed by IMA to load a custom policy. The
+ * other ones we can delay until SELinux and IMA are loaded. When
+ * SMACK is enabled we need smackfs, too, so it's a fifth one. */
+#if ENABLE_SMACK
+#define N_EARLY_MOUNT 5
+#else
+#define N_EARLY_MOUNT 4
+#endif
+
+static bool check_recursiveprot_supported(void) {
+        int r;
+
+        if (!cg_is_unified_wanted())
+                return false;
+
+        r = mount_option_supported("cgroup2", "memory_recursiveprot", NULL);
+        if (r < 0)
+                log_debug_errno(r, "Failed to determiner whether the 'memory_recursiveprot' mount option is supported, assuming not: %m");
+        else if (r == 0)
+                log_debug("This kernel version does not support 'memory_recursiveprot', not using mount option.");
+
+        return r > 0;
+}
+
+static const MountPoint mount_table[] = {
+        { "proc",        "/proc",                     "proc",       NULL,                                       MS_NOSUID|MS_NOEXEC|MS_NODEV,
+          NULL,          MNT_FATAL|MNT_IN_CONTAINER|MNT_FOLLOW_SYMLINK },
+        { "sysfs",       "/sys",                      "sysfs",      NULL,                                       MS_NOSUID|MS_NOEXEC|MS_NODEV,
+          NULL,          MNT_FATAL|MNT_IN_CONTAINER },
+        { "devtmpfs",    "/dev",                      "devtmpfs",   "mode=0755" TMPFS_LIMITS_DEV,               MS_NOSUID|MS_STRICTATIME,
+          NULL,          MNT_FATAL|MNT_IN_CONTAINER },
+        { "securityfs",  "/sys/kernel/security",      "securityfs", NULL,                                       MS_NOSUID|MS_NOEXEC|MS_NODEV,
+          NULL,          MNT_NONE                   },
+#if ENABLE_SMACK
+        { "smackfs",     "/sys/fs/smackfs",           "smackfs",    "smackfsdef=*",                             MS_NOSUID|MS_NOEXEC|MS_NODEV,
+          mac_smack_use, MNT_FATAL                  },
+        { "tmpfs",       "/dev/shm",                  "tmpfs",      "mode=01777,smackfsroot=*",                 MS_NOSUID|MS_NODEV|MS_STRICTATIME,
+          mac_smack_use, MNT_FATAL                  },
+#endif
+        { "tmpfs",       "/dev/shm",                  "tmpfs",      "mode=01777",                               MS_NOSUID|MS_NODEV|MS_STRICTATIME,
+          NULL,          MNT_FATAL|MNT_IN_CONTAINER },
+        { "devpts",      "/dev/pts",                  "devpts",     "mode=0620,gid=" STRINGIFY(TTY_GID),        MS_NOSUID|MS_NOEXEC,
+          NULL,          MNT_IN_CONTAINER           },
+#if ENABLE_SMACK
+        { "tmpfs",       "/run",                      "tmpfs",      "mode=0755,smackfsroot=*" TMPFS_LIMITS_RUN, MS_NOSUID|MS_NODEV|MS_STRICTATIME,
+          mac_smack_use, MNT_FATAL                  },
+#endif
+        { "tmpfs",       "/run",                      "tmpfs",      "mode=0755" TMPFS_LIMITS_RUN,               MS_NOSUID|MS_NODEV|MS_STRICTATIME,
+          NULL,          MNT_FATAL|MNT_IN_CONTAINER },
+        { "cgroup2",     "/sys/fs/cgroup",            "cgroup2",    "nsdelegate,memory_recursiveprot",          MS_NOSUID|MS_NOEXEC|MS_NODEV,
+          check_recursiveprot_supported, MNT_IN_CONTAINER|MNT_CHECK_WRITABLE },
+        { "cgroup2",     "/sys/fs/cgroup",            "cgroup2",    "nsdelegate",                               MS_NOSUID|MS_NOEXEC|MS_NODEV,
+          cg_is_unified_wanted, MNT_IN_CONTAINER|MNT_CHECK_WRITABLE },
+        { "cgroup2",     "/sys/fs/cgroup",            "cgroup2",    NULL,                                       MS_NOSUID|MS_NOEXEC|MS_NODEV,
+          cg_is_unified_wanted, MNT_IN_CONTAINER|MNT_CHECK_WRITABLE },
+        { "tmpfs",       "/sys/fs/cgroup",            "tmpfs",      "mode=0755" TMPFS_LIMITS_SYS_FS_CGROUP,     MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_STRICTATIME,
+          cg_is_legacy_wanted, MNT_FATAL|MNT_IN_CONTAINER },
+        { "cgroup2",     "/sys/fs/cgroup/unified",    "cgroup2",    "nsdelegate",                               MS_NOSUID|MS_NOEXEC|MS_NODEV,
+          cg_is_hybrid_wanted, MNT_IN_CONTAINER|MNT_CHECK_WRITABLE },
+        { "cgroup2",     "/sys/fs/cgroup/unified",    "cgroup2",    NULL,                                       MS_NOSUID|MS_NOEXEC|MS_NODEV,
+          cg_is_hybrid_wanted, MNT_IN_CONTAINER|MNT_CHECK_WRITABLE },
+        { "cgroup",      "/sys/fs/cgroup/systemd",    "cgroup",     "none,name=systemd,xattr",                  MS_NOSUID|MS_NOEXEC|MS_NODEV,
+          cg_is_legacy_wanted, MNT_IN_CONTAINER     },
+        { "cgroup",      "/sys/fs/cgroup/systemd",    "cgroup",     "none,name=systemd",                        MS_NOSUID|MS_NOEXEC|MS_NODEV,
+          cg_is_legacy_wanted, MNT_FATAL|MNT_IN_CONTAINER },
+#if ENABLE_PSTORE
+        { "pstore",      "/sys/fs/pstore",            "pstore",     NULL,                                       MS_NOSUID|MS_NOEXEC|MS_NODEV,
+          NULL,          MNT_NONE                   },
+#endif
+#if ENABLE_EFI
+        { "efivarfs",    "/sys/firmware/efi/efivars", "efivarfs",   NULL,                                       MS_NOSUID|MS_NOEXEC|MS_NODEV,
+          is_efi_boot,   MNT_NONE                   },
+#endif
+        { "bpf",         "/sys/fs/bpf",               "bpf",        "mode=0700",                                MS_NOSUID|MS_NOEXEC|MS_NODEV,
+          NULL,          MNT_NONE,                  },
+};
+
+assert_cc(N_EARLY_MOUNT <= ELEMENTSOF(mount_table));
+
+bool mount_point_is_api(const char *path) {
+        /* Checks if this mount point is considered "API", and hence
+         * should be ignored */
+
+        for (size_t i = 0; i < ELEMENTSOF(mount_table); i ++)
+                if (path_equal(path, mount_table[i].where))
+                        return true;
+
+        return path_startswith(path, "/sys/fs/cgroup/");
+}
+
+bool mount_point_ignore(const char *path) {
+        /* These are API file systems that might be mounted by other software, we just list them here so that
+         * we know that we should ignore them. */
+        FOREACH_STRING(i,
+                       /* SELinux file systems */
+                       "/sys/fs/selinux",
+                       /* Container bind mounts */
+                       "/dev/console",
+                       "/proc/kmsg",
+                       "/proc/sys",
+                       "/proc/sys/kernel/random/boot_id")
+                if (path_equal(path, i))
+                        return true;
+
+        if (path_startswith(path, "/run/host")) /* All mounts passed in from the container manager are
+                                                 * something we better ignore. */
+                return true;
+
+        return false;
+}
+
+static int mount_one(const MountPoint *p, bool relabel) {
+        int r, priority;
+
+        assert(p);
+
+        priority = (p->mode & MNT_FATAL) ? LOG_ERR : LOG_DEBUG;
+
+        if (p->condition_fn && !p->condition_fn())
+                return 0;
+
+        /* Relabel first, just in case */
+        if (relabel)
+                (void) label_fix(p->where, LABEL_IGNORE_ENOENT|LABEL_IGNORE_EROFS);
+
+        r = path_is_mount_point(p->where, NULL, AT_SYMLINK_FOLLOW);
+        if (r < 0 && r != -ENOENT) {
+                log_full_errno(priority, r, "Failed to determine whether %s is a mount point: %m", p->where);
+                return (p->mode & MNT_FATAL) ? r : 0;
+        }
+        if (r > 0)
+                return 0;
+
+        /* Skip securityfs in a container */
+        if (!(p->mode & MNT_IN_CONTAINER) && detect_container() > 0)
+                return 0;
+
+        /* The access mode here doesn't really matter too much, since
+         * the mounted file system will take precedence anyway. */
+        if (relabel)
+                (void) mkdir_p_label(p->where, 0755);
+        else
+                (void) mkdir_p(p->where, 0755);
+
+        log_debug("Mounting %s to %s of type %s with options %s.",
+                  p->what,
+                  p->where,
+                  p->type,
+                  strna(p->options));
+
+        if (FLAGS_SET(p->mode, MNT_FOLLOW_SYMLINK))
+                r = mount_follow_verbose(priority, p->what, p->where, p->type, p->flags, p->options);
+        else
+                r = mount_nofollow_verbose(priority, p->what, p->where, p->type, p->flags, p->options);
+        if (r < 0)
+                return (p->mode & MNT_FATAL) ? r : 0;
+
+        /* Relabel again, since we now mounted something fresh here */
+        if (relabel)
+                (void) label_fix(p->where, 0);
+
+        if (p->mode & MNT_CHECK_WRITABLE) {
+                if (access(p->where, W_OK) < 0) {
+                        r = -errno;
+
+                        (void) umount2(p->where, UMOUNT_NOFOLLOW);
+                        (void) rmdir(p->where);
+
+                        log_full_errno(priority, r, "Mount point %s not writable after mounting, undoing: %m", p->where);
+                        return (p->mode & MNT_FATAL) ? r : 0;
+                }
+        }
+
+        return 1;
+}
+
+static int mount_points_setup(size_t n, bool loaded_policy) {
+        int ret = 0, r;
+
+        assert(n <= ELEMENTSOF(mount_table));
+
+        FOREACH_ARRAY(mp, mount_table, n) {
+                r = mount_one(mp, loaded_policy);
+                if (r != 0 && ret >= 0)
+                        ret = r;
+        }
+
+        return ret;
+}
+
+int mount_setup_early(void) {
+        /* Do a minimal mount of /proc and friends to enable the most basic stuff, such as SELinux */
+        return mount_points_setup(N_EARLY_MOUNT, /* loaded_policy= */ false);
+}
+
+static const char *join_with(const char *controller) {
+
+        static const char* const pairs[] = {
+                "cpu", "cpuacct",
+                "net_cls", "net_prio",
+                NULL
+        };
+
+        assert(controller);
+
+        /* This will lookup which controller to mount another controller with. Input is a controller name, and output
+         * is the other controller name. The function works both ways: you can input one and get the other, and input
+         * the other to get the one. */
+
+        STRV_FOREACH_PAIR(x, y, pairs) {
+                if (streq(controller, *x))
+                        return *y;
+                if (streq(controller, *y))
+                        return *x;
+        }
+
+        return NULL;
+}
+
+static int symlink_controller(const char *target, const char *alias) {
+        const char *a;
+        int r;
+
+        assert(target);
+        assert(alias);
+
+        a = strjoina("/sys/fs/cgroup/", alias);
+
+        r = symlink_idempotent(target, a, false);
+        if (r < 0)
+                return log_error_errno(r, "Failed to create symlink %s: %m", a);
+
+#if HAVE_SMACK_RUN_LABEL
+        const char *p;
+
+        p = strjoina("/sys/fs/cgroup/", target);
+
+        r = mac_smack_copy(a, p);
+        if (r < 0 && !ERRNO_IS_NOT_SUPPORTED(r))
+                return log_error_errno(r, "Failed to copy smack label from %s to %s: %m", p, a);
+#endif
+
+        return 0;
+}
+
+int mount_cgroup_controllers(void) {
+        _cleanup_set_free_ Set *controllers = NULL;
+        int r;
+
+        if (!cg_is_legacy_wanted())
+                return 0;
+
+        /* Mount all available cgroup controllers that are built into the kernel. */
+        r = cg_kernel_controllers(&controllers);
+        if (r < 0)
+                return log_error_errno(r, "Failed to enumerate cgroup controllers: %m");
+
+        for (;;) {
+                _cleanup_free_ char *options = NULL, *controller = NULL, *where = NULL;
+                const char *other_controller;
+                MountPoint p = {
+                        .what = "cgroup",
+                        .type = "cgroup",
+                        .flags = MS_NOSUID|MS_NOEXEC|MS_NODEV,
+                        .mode = MNT_IN_CONTAINER,
+                };
+
+                controller = set_steal_first(controllers);
+                if (!controller)
+                        break;
+
+                /* Check if we shall mount this together with another controller */
+                other_controller = join_with(controller);
+                if (other_controller) {
+                        _cleanup_free_ char *c = NULL;
+
+                        /* Check if the other controller is actually available in the kernel too */
+                        c = set_remove(controllers, other_controller);
+                        if (c) {
+
+                                /* Join the two controllers into one string, and maintain a stable ordering */
+                                if (strcmp(controller, other_controller) < 0)
+                                        options = strjoin(controller, ",", other_controller);
+                                else
+                                        options = strjoin(other_controller, ",", controller);
+                                if (!options)
+                                        return log_oom();
+                        }
+                }
+
+                /* The simple case, where there's only one controller to mount together */
+                if (!options)
+                        options = TAKE_PTR(controller);
+
+                where = path_join("/sys/fs/cgroup", options);
+                if (!where)
+                        return log_oom();
+
+                p.where = where;
+                p.options = options;
+
+                r = mount_one(&p, true);
+                if (r < 0)
+                        return r;
+
+                /* Create symlinks from the individual controller names, in case we have a joined mount */
+                if (controller)
+                        (void) symlink_controller(options, controller);
+                if (other_controller)
+                        (void) symlink_controller(options, other_controller);
+        }
+
+        /* Now that we mounted everything, let's make the tmpfs the cgroup file systems are mounted into read-only. */
+        (void) mount_nofollow("tmpfs", "/sys/fs/cgroup", "tmpfs",
+                              MS_REMOUNT|MS_NOSUID|MS_NOEXEC|MS_NODEV|MS_STRICTATIME|MS_RDONLY,
+                              "mode=0755" TMPFS_LIMITS_SYS_FS_CGROUP);
+
+        return 0;
+}
+
+#if HAVE_SELINUX || ENABLE_SMACK
+static int relabel_cb(
+                RecurseDirEvent event,
+                const char *path,
+                int dir_fd,
+                int inode_fd,
+                const struct dirent *de,
+                const struct statx *sx,
+                void *userdata) {
+
+        switch (event) {
+
+        case RECURSE_DIR_LEAVE:
+        case RECURSE_DIR_SKIP_MOUNT:
+                /* If we already saw this dirent when entering it or this is a dirent that on a different
+                 * mount, don't relabel it. */
+                return RECURSE_DIR_CONTINUE;
+
+        case RECURSE_DIR_ENTER:
+                /* /run/initramfs/ + /run/nextroot/ are static data and big, no need to dynamically relabel
+                 * its contents at boot... */
+                if (PATH_STARTSWITH_SET(path, "/run/initramfs", "/run/nextroot"))
+                        return RECURSE_DIR_SKIP_ENTRY;
+
+                _fallthrough_;
+
+        default:
+                /* Otherwise, label it, even if we had trouble stat()ing it and similar. SELinux can figure this out */
+                (void) label_fix(path, 0);
+                return RECURSE_DIR_CONTINUE;
+        }
+}
+
+static int relabel_tree(const char *path) {
+        int r;
+
+        r = recurse_dir_at(AT_FDCWD, path, 0, UINT_MAX, RECURSE_DIR_ENSURE_TYPE|RECURSE_DIR_SAME_MOUNT, relabel_cb, NULL);
+        if (r < 0)
+                log_debug_errno(r, "Failed to recursively relabel '%s': %m", path);
+
+        return r;
+}
+
+static int relabel_cgroup_filesystems(void) {
+        int r;
+        struct statfs st;
+
+        r = cg_all_unified();
+        if (r == 0) {
+                /* Temporarily remount the root cgroup filesystem to give it a proper label. Do this
+                   only when the filesystem has been already populated by a previous instance of systemd
+                   running from initrd. Otherwise don't remount anything and leave the filesystem read-write
+                   for the cgroup filesystems to be mounted inside. */
+                if (statfs("/sys/fs/cgroup", &st) < 0)
+                        return log_error_errno(errno, "Failed to determine mount flags for /sys/fs/cgroup: %m");
+
+                if (st.f_flags & ST_RDONLY)
+                        (void) mount_nofollow(NULL, "/sys/fs/cgroup", NULL, MS_REMOUNT, NULL);
+
+                (void) label_fix("/sys/fs/cgroup", 0);
+                (void) relabel_tree("/sys/fs/cgroup");
+
+                if (st.f_flags & ST_RDONLY)
+                        (void) mount_nofollow(NULL, "/sys/fs/cgroup", NULL, MS_REMOUNT|MS_RDONLY, NULL);
+
+        } else if (r < 0)
+                return log_error_errno(r, "Failed to determine whether we are in all unified mode: %m");
+
+        return 0;
+}
+
+static int relabel_extra(void) {
+        _cleanup_strv_free_ char **files = NULL;
+        int r, c = 0;
+
+        /* Support for relabelling additional files or directories after loading the policy. For this, code in the
+         * initrd simply has to drop in *.relabel files into /run/systemd/relabel-extra.d/. We'll read all such files
+         * expecting one absolute path by line and will relabel each (and everyone below that in case the path refers
+         * to a directory). These drop-in files are supposed to be absolutely minimal, and do not understand comments
+         * and such. After the operation succeeded the files are removed, and the drop-in directory as well, if
+         * possible.
+         */
+
+        r = conf_files_list(&files, ".relabel", NULL,
+                            CONF_FILES_FILTER_MASKED | CONF_FILES_REGULAR,
+                            "/run/systemd/relabel-extra.d/");
+        if (r < 0)
+                return log_error_errno(r, "Failed to enumerate /run/systemd/relabel-extra.d/, ignoring: %m");
+
+        STRV_FOREACH(file, files) {
+                _cleanup_fclose_ FILE *f = NULL;
+
+                f = fopen(*file, "re");
+                if (!f) {
+                        log_warning_errno(errno, "Failed to open %s, ignoring: %m", *file);
+                        continue;
+                }
+
+                for (;;) {
+                        _cleanup_free_ char *line = NULL;
+
+                        r = read_line(f, LONG_LINE_MAX, &line);
+                        if (r < 0) {
+                                log_warning_errno(r, "Failed to read %s, ignoring: %m", *file);
+                                break;
+                        }
+                        if (r == 0) /* EOF */
+                                break;
+
+                        path_simplify(line);
+
+                        if (!path_is_normalized(line)) {
+                                log_warning("Path to relabel is not normalized, ignoring: %s", line);
+                                continue;
+                        }
+
+                        if (!path_is_absolute(line)) {
+                                log_warning("Path to relabel is not absolute, ignoring: %s", line);
+                                continue;
+                        }
+
+                        log_debug("Relabelling additional file/directory '%s'.", line);
+                        (void) label_fix(line, 0);
+                        (void) relabel_tree(line);
+                        c++;
+                }
+
+                if (unlink(*file) < 0)
+                        log_warning_errno(errno, "Failed to remove %s, ignoring: %m", *file);
+        }
+
+        /* Remove when we complete things. */
+        if (rmdir("/run/systemd/relabel-extra.d") < 0 &&
+            errno != ENOENT)
+                log_warning_errno(errno, "Failed to remove /run/systemd/relabel-extra.d/ directory: %m");
+
+        return c;
+}
+#endif
+
+int mount_setup(bool loaded_policy, bool leave_propagation) {
+        int r;
+
+        r = mount_points_setup(ELEMENTSOF(mount_table), loaded_policy);
+        if (r < 0)
+                return r;
+
+#if HAVE_SELINUX || ENABLE_SMACK
+        /* Nodes in devtmpfs and /run need to be manually updated for
+         * the appropriate labels, after mounting. The other virtual
+         * API file systems like /sys and /proc do not need that, they
+         * use the same label for all their files. */
+        if (loaded_policy) {
+                usec_t before_relabel, after_relabel;
+                int n_extra;
+
+                before_relabel = now(CLOCK_MONOTONIC);
+
+                FOREACH_STRING(i, "/dev", "/dev/shm", "/run")
+                        (void) relabel_tree(i);
+
+                (void) relabel_cgroup_filesystems();
+
+                n_extra = relabel_extra();
+
+                after_relabel = now(CLOCK_MONOTONIC);
+
+                log_info("Relabeled /dev, /dev/shm, /run, /sys/fs/cgroup%s in %s.",
+                         n_extra > 0 ? ", additional files" : "",
+                         FORMAT_TIMESPAN(after_relabel - before_relabel, 0));
+        }
+#endif
+
+        /* Create a few default symlinks, which are normally created
+         * by udevd, but some scripts might need them before we start
+         * udevd. */
+        dev_setup(NULL, UID_INVALID, GID_INVALID);
+
+        /* Mark the root directory as shared in regards to mount propagation. The kernel defaults to "private", but we
+         * think it makes more sense to have a default of "shared" so that nspawn and the container tools work out of
+         * the box. If specific setups need other settings they can reset the propagation mode to private if
+         * needed. Note that we set this only when we are invoked directly by the kernel. If we are invoked by a
+         * container manager we assume the container manager knows what it is doing (for example, because it set up
+         * some directories with different propagation modes). */
+        if (detect_container() <= 0 && !leave_propagation)
+                if (mount(NULL, "/", NULL, MS_REC|MS_SHARED, NULL) < 0)
+                        log_warning_errno(errno, "Failed to set up the root directory for shared mount propagation: %m");
+
+        /* Create a few directories we always want around, Note that sd_booted() checks for /run/systemd/system, so
+         * this mkdir really needs to stay for good, otherwise software that copied sd-daemon.c into their sources will
+         * misdetect systemd. */
+        (void) mkdir_label("/run/systemd", 0755);
+        (void) mkdir_label("/run/systemd/system", 0755);
+
+        /* Make sure there's always a place where sandboxed environments can mount root file systems they are
+         * about to move into, even when unprivileged, without having to create a temporary one in /tmp/
+         * (which they then have to keep track of and clean) */
+        (void) mkdir_label("/run/systemd/mount-rootfs", 0555);
+
+        /* Make sure we have a mount point to hide in sandboxes */
+        (void) mkdir_label("/run/credentials", 0755);
+
+        /* Also create /run/systemd/inaccessible nodes, so that we always have something to mount
+         * inaccessible nodes from. If we run in a container the host might have created these for us already
+         * in /run/host/inaccessible/. Use those if we can, since that way we likely get access to block/char
+         * device nodes that are inaccessible, and if userns is used to nodes that are on mounts owned by a
+         * userns outside the container and thus nicely read-only and not remountable. */
+        if (access("/run/host/inaccessible/", F_OK) < 0) {
+                if (errno != ENOENT)
+                        log_debug_errno(errno, "Failed to check if /run/host/inaccessible exists, ignoring: %m");
+
+                (void) make_inaccessible_nodes("/run/systemd", UID_INVALID, GID_INVALID);
+        } else
+                (void) symlink("../host/inaccessible", "/run/systemd/inaccessible");
+
+        return 0;
+}