Adding upstream version 252.22.upstream/252.22

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

1 files changed, 1161 insertions, 0 deletions

diff --git a/src/shared/mount-util.c b/src/shared/mount-util.c
new file mode 100644
index 0000000..dd3fd79
--- /dev/null
+++ b/src/shared/mount-util.c
@@ -0,0 +1,1161 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <stdlib.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/statvfs.h>
+#include <unistd.h>
+#include <linux/loop.h>
+#if WANT_LINUX_FS_H
+#include <linux/fs.h>
+#endif
+
+#include "alloc-util.h"
+#include "chase-symlinks.h"
+#include "dissect-image.h"
+#include "exec-util.h"
+#include "extract-word.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "fs-util.h"
+#include "glyph-util.h"
+#include "hashmap.h"
+#include "label.h"
+#include "libmount-util.h"
+#include "missing_mount.h"
+#include "missing_syscall.h"
+#include "mkdir-label.h"
+#include "mount-util.h"
+#include "mountpoint-util.h"
+#include "namespace-util.h"
+#include "parse-util.h"
+#include "path-util.h"
+#include "process-util.h"
+#include "set.h"
+#include "stat-util.h"
+#include "stdio-util.h"
+#include "string-util.h"
+#include "strv.h"
+#include "tmpfile-util.h"
+#include "user-util.h"
+
+int mount_fd(const char *source,
+             int target_fd,
+             const char *filesystemtype,
+             unsigned long mountflags,
+             const void *data) {
+
+        if (mount(source, FORMAT_PROC_FD_PATH(target_fd), filesystemtype, mountflags, data) < 0) {
+                if (errno != ENOENT)
+                        return -errno;
+
+                /* ENOENT can mean two things: either that the source is missing, or that /proc/ isn't
+                 * mounted. Check for the latter to generate better error messages. */
+                if (proc_mounted() == 0)
+                        return -ENOSYS;
+
+                return -ENOENT;
+        }
+
+        return 0;
+}
+
+int mount_nofollow(
+                const char *source,
+                const char *target,
+                const char *filesystemtype,
+                unsigned long mountflags,
+                const void *data) {
+
+        _cleanup_close_ int fd = -1;
+
+        /* In almost all cases we want to manipulate the mount table without following symlinks, hence
+         * mount_nofollow() is usually the way to go. The only exceptions are environments where /proc/ is
+         * not available yet, since we need /proc/self/fd/ for this logic to work. i.e. during the early
+         * initialization of namespacing/container stuff where /proc is not yet mounted (and maybe even the
+         * fs to mount) we can only use traditional mount() directly.
+         *
+         * Note that this disables following only for the final component of the target, i.e symlinks within
+         * the path of the target are honoured, as are symlinks in the source path everywhere. */
+
+        fd = open(target, O_PATH|O_CLOEXEC|O_NOFOLLOW);
+        if (fd < 0)
+                return -errno;
+
+        return mount_fd(source, fd, filesystemtype, mountflags, data);
+}
+
+int umount_recursive(const char *prefix, int flags) {
+        int n = 0, r;
+        bool again;
+
+        /* Try to umount everything recursively below a directory. Also, take care of stacked mounts, and
+         * keep unmounting them until they are gone. */
+
+        do {
+                _cleanup_(mnt_free_tablep) struct libmnt_table *table = NULL;
+                _cleanup_(mnt_free_iterp) struct libmnt_iter *iter = NULL;
+
+                again = false;
+
+                r = libmount_parse("/proc/self/mountinfo", NULL, &table, &iter);
+                if (r < 0)
+                        return log_debug_errno(r, "Failed to parse /proc/self/mountinfo: %m");
+
+                for (;;) {
+                        struct libmnt_fs *fs;
+                        const char *path;
+
+                        r = mnt_table_next_fs(table, iter, &fs);
+                        if (r == 1)
+                                break;
+                        if (r < 0)
+                                return log_debug_errno(r, "Failed to get next entry from /proc/self/mountinfo: %m");
+
+                        path = mnt_fs_get_target(fs);
+                        if (!path)
+                                continue;
+
+                        if (!path_startswith(path, prefix))
+                                continue;
+
+                        if (umount2(path, flags | UMOUNT_NOFOLLOW) < 0) {
+                                log_debug_errno(errno, "Failed to umount %s, ignoring: %m", path);
+                                continue;
+                        }
+
+                        log_trace("Successfully unmounted %s", path);
+
+                        again = true;
+                        n++;
+
+                        break;
+                }
+        } while (again);
+
+        return n;
+}
+
+#define MS_CONVERTIBLE_FLAGS (MS_RDONLY|MS_NOSUID|MS_NODEV|MS_NOEXEC|MS_NOSYMFOLLOW)
+
+static uint64_t ms_flags_to_mount_attr(unsigned long a) {
+        uint64_t f = 0;
+
+        if (FLAGS_SET(a, MS_RDONLY))
+                f |= MOUNT_ATTR_RDONLY;
+
+        if (FLAGS_SET(a, MS_NOSUID))
+                f |= MOUNT_ATTR_NOSUID;
+
+        if (FLAGS_SET(a, MS_NODEV))
+                f |= MOUNT_ATTR_NODEV;
+
+        if (FLAGS_SET(a, MS_NOEXEC))
+                f |= MOUNT_ATTR_NOEXEC;
+
+        if (FLAGS_SET(a, MS_NOSYMFOLLOW))
+                f |= MOUNT_ATTR_NOSYMFOLLOW;
+
+        return f;
+}
+
+static bool skip_mount_set_attr = false;
+
+/* Use this function only if you do not have direct access to /proc/self/mountinfo but the caller can open it
+ * for you. This is the case when /proc is masked or not mounted. Otherwise, use bind_remount_recursive. */
+int bind_remount_recursive_with_mountinfo(
+                const char *prefix,
+                unsigned long new_flags,
+                unsigned long flags_mask,
+                char **deny_list,
+                FILE *proc_self_mountinfo) {
+
+        _cleanup_fclose_ FILE *proc_self_mountinfo_opened = NULL;
+        _cleanup_set_free_ Set *done = NULL;
+        unsigned n_tries = 0;
+        int r;
+
+        assert(prefix);
+
+        if ((flags_mask & ~MS_CONVERTIBLE_FLAGS) == 0 && strv_isempty(deny_list) && !skip_mount_set_attr) {
+                /* Let's take a shortcut for all the flags we know how to convert into mount_setattr() flags */
+
+                if (mount_setattr(AT_FDCWD, prefix, AT_SYMLINK_NOFOLLOW|AT_RECURSIVE,
+                                  &(struct mount_attr) {
+                                          .attr_set = ms_flags_to_mount_attr(new_flags & flags_mask),
+                                          .attr_clr = ms_flags_to_mount_attr(~new_flags & flags_mask),
+                                  }, MOUNT_ATTR_SIZE_VER0) < 0) {
+
+                        log_debug_errno(errno, "mount_setattr() failed, falling back to classic remounting: %m");
+
+                        /* We fall through to classic behaviour if not supported (i.e. kernel < 5.12). We
+                         * also do this for all other kinds of errors since they are so many different, and
+                         * mount_setattr() has no graceful mode where it continues despite seeing errors one
+                         * some mounts, but we want that. Moreover mount_setattr() only works on the mount
+                         * point inode itself, not a non-mount point inode, and we want to support arbitrary
+                         * prefixes here. */
+
+                        if (ERRNO_IS_NOT_SUPPORTED(errno)) /* if not supported, then don't bother at all anymore */
+                                skip_mount_set_attr = true;
+                } else
+                        return 0; /* Nice, this worked! */
+        }
+
+        if (!proc_self_mountinfo) {
+                r = fopen_unlocked("/proc/self/mountinfo", "re", &proc_self_mountinfo_opened);
+                if (r < 0)
+                        return r;
+
+                proc_self_mountinfo = proc_self_mountinfo_opened;
+        }
+
+        /* Recursively remount a directory (and all its submounts) with desired flags (MS_READONLY,
+         * MS_NOSUID, MS_NOEXEC). If the directory is already mounted, we reuse the mount and simply mark it
+         * MS_BIND|MS_RDONLY (or remove the MS_RDONLY for read-write operation), ditto for other flags. If it
+         * isn't we first make it one. Afterwards we apply (or remove) the flags to all submounts we can
+         * access, too. When mounts are stacked on the same mount point we only care for each individual
+         * "top-level" mount on each point, as we cannot influence/access the underlying mounts anyway. We do
+         * not have any effect on future submounts that might get propagated, they might be writable
+         * etc. This includes future submounts that have been triggered via autofs. Also note that we can't
+         * operate atomically here. Mounts established while we process the tree might or might not get
+         * noticed and thus might or might not be covered.
+         *
+         * If the "deny_list" parameter is specified it may contain a list of subtrees to exclude from the
+         * remount operation. Note that we'll ignore the deny list for the top-level path. */
+
+        for (;;) {
+                _cleanup_(mnt_free_tablep) struct libmnt_table *table = NULL;
+                _cleanup_(mnt_free_iterp) struct libmnt_iter *iter = NULL;
+                _cleanup_hashmap_free_ Hashmap *todo = NULL;
+                bool top_autofs = false;
+
+                if (n_tries++ >= 32) /* Let's not retry this loop forever */
+                        return -EBUSY;
+
+                rewind(proc_self_mountinfo);
+
+                r = libmount_parse("/proc/self/mountinfo", proc_self_mountinfo, &table, &iter);
+                if (r < 0)
+                        return log_debug_errno(r, "Failed to parse /proc/self/mountinfo: %m");
+
+                for (;;) {
+                        _cleanup_free_ char *d = NULL;
+                        const char *path, *type, *opts;
+                        unsigned long flags = 0;
+                        struct libmnt_fs *fs;
+
+                        r = mnt_table_next_fs(table, iter, &fs);
+                        if (r == 1) /* EOF */
+                                break;
+                        if (r < 0)
+                                return log_debug_errno(r, "Failed to get next entry from /proc/self/mountinfo: %m");
+
+                        path = mnt_fs_get_target(fs);
+                        if (!path)
+                                continue;
+
+                        if (!path_startswith(path, prefix))
+                                continue;
+
+                        type = mnt_fs_get_fstype(fs);
+                        if (!type)
+                                continue;
+
+                        /* Let's ignore autofs mounts. If they aren't triggered yet, we want to avoid
+                         * triggering them, as we don't make any guarantees for future submounts anyway. If
+                         * they are already triggered, then we will find another entry for this. */
+                        if (streq(type, "autofs")) {
+                                top_autofs = top_autofs || path_equal(path, prefix);
+                                continue;
+                        }
+
+                        if (set_contains(done, path))
+                                continue;
+
+                        /* Ignore this mount if it is deny-listed, but only if it isn't the top-level mount
+                         * we shall operate on. */
+                        if (!path_equal(path, prefix)) {
+                                bool deny_listed = false;
+
+                                STRV_FOREACH(i, deny_list) {
+                                        if (path_equal(*i, prefix))
+                                                continue;
+
+                                        if (!path_startswith(*i, prefix))
+                                                continue;
+
+                                        if (path_startswith(path, *i)) {
+                                                deny_listed = true;
+                                                log_trace("Not remounting %s deny-listed by %s, called for %s", path, *i, prefix);
+                                                break;
+                                        }
+                                }
+
+                                if (deny_listed)
+                                        continue;
+                        }
+
+                        opts = mnt_fs_get_vfs_options(fs);
+                        if (opts) {
+                                r = mnt_optstr_get_flags(opts, &flags, mnt_get_builtin_optmap(MNT_LINUX_MAP));
+                                if (r < 0)
+                                        log_debug_errno(r, "Could not get flags for '%s', ignoring: %m", path);
+                        }
+
+                        d = strdup(path);
+                        if (!d)
+                                return -ENOMEM;
+
+                        r = hashmap_ensure_put(&todo, &path_hash_ops_free, d, ULONG_TO_PTR(flags));
+                        if (r == -EEXIST)
+                                /* If the same path was recorded, but with different mount flags, update it:
+                                 * it means a mount point is overmounted, and libmount returns the "bottom" (or
+                                 * older one) first, but we want to reapply the flags from the "top" (or newer
+                                 * one). See: https://github.com/systemd/systemd/issues/20032
+                                 * Note that this shouldn't really fail, as we were just told that the key
+                                 * exists, and it's an update so we want 'd' to be freed immediately. */
+                                r = hashmap_update(todo, d, ULONG_TO_PTR(flags));
+                        if (r < 0)
+                                return r;
+                        if (r > 0)
+                                TAKE_PTR(d);
+                }
+
+                /* Check if the top-level directory was among what we have seen so far. For that check both
+                 * 'done' and 'todo'. Also check 'top_autofs' because if the top-level dir is an autofs we'll
+                 * not include it in either set but will set this bool. */
+                if (!set_contains(done, prefix) &&
+                    !(top_autofs || hashmap_contains(todo, prefix))) {
+
+                        /* The prefix directory itself is not yet a mount, make it one. */
+                        r = mount_nofollow(prefix, prefix, NULL, MS_BIND|MS_REC, NULL);
+                        if (r < 0)
+                                return r;
+
+                        /* Immediately rescan, so that we pick up the new mount's flags */
+                        continue;
+                }
+
+                /* If we have no submounts to process anymore, we are done */
+                if (hashmap_isempty(todo))
+                        return 0;
+
+                for (;;) {
+                        unsigned long flags;
+                        char *x = NULL;
+
+                        /* Take the first mount from our list of mounts to still process */
+                        flags = PTR_TO_ULONG(hashmap_steal_first_key_and_value(todo, (void**) &x));
+                        if (!x)
+                                break;
+
+                        r = set_ensure_consume(&done, &path_hash_ops_free, x);
+                        if (IN_SET(r, 0, -EEXIST))
+                                continue; /* Already done */
+                        if (r < 0)
+                                return r;
+
+                        /* Now, remount this with the new flags set, but exclude MS_RELATIME from it. (It's
+                         * the default anyway, thus redundant, and in userns we'll get an error if we try to
+                         * explicitly enable it) */
+                        r = mount_nofollow(NULL, x, NULL, ((flags & ~flags_mask)|MS_BIND|MS_REMOUNT|new_flags) & ~MS_RELATIME, NULL);
+                        if (r < 0) {
+                                int q;
+
+                                /* OK, so the remount of this entry failed. We'll ultimately ignore this in
+                                 * almost all cases (there are simply so many reasons why this can fail,
+                                 * think autofs, NFS, FUSE, …), but let's generate useful debug messages at
+                                 * the very least. */
+
+                                q = path_is_mount_point(x, NULL, 0);
+                                if (IN_SET(q, 0, -ENOENT)) {
+                                        /* Hmm, whaaaa? The mount point is not actually a mount point? Then
+                                         * it is either obstructed by a later mount or somebody has been
+                                         * racing against us and removed it. Either way the mount point
+                                         * doesn't matter to us, let's ignore it hence. */
+                                        log_debug_errno(r, "Mount point '%s' to remount is not a mount point anymore, ignoring remount failure: %m", x);
+                                        continue;
+                                }
+                                if (q < 0) /* Any other error on this? Just log and continue */
+                                        log_debug_errno(q, "Failed to determine whether '%s' is a mount point or not, ignoring: %m", x);
+
+                                if (((flags ^ new_flags) & flags_mask & ~MS_RELATIME) == 0) { /* ignore MS_RELATIME while comparing */
+                                        log_debug_errno(r, "Couldn't remount '%s', but the flags already match what we want, hence ignoring: %m", x);
+                                        continue;
+                                }
+
+                                /* Make this fatal if this is the top-level mount */
+                                if (path_equal(x, prefix))
+                                        return r;
+
+                                /* If this is not the top-level mount, then handle this gracefully: log but
+                                 * otherwise ignore. With NFS, FUSE, autofs there are just too many reasons
+                                 * this might fail without a chance for us to do anything about it, let's
+                                 * hence be strict on the top-level mount and lenient on the inner ones. */
+                                log_debug_errno(r, "Couldn't remount submount '%s' for unexpected reason, ignoring: %m", x);
+                                continue;
+                        }
+
+                        log_trace("Remounted %s.", x);
+                }
+        }
+}
+
+int bind_remount_one_with_mountinfo(
+                const char *path,
+                unsigned long new_flags,
+                unsigned long flags_mask,
+                FILE *proc_self_mountinfo) {
+
+        _cleanup_(mnt_free_tablep) struct libmnt_table *table = NULL;
+        unsigned long flags = 0;
+        struct libmnt_fs *fs;
+        const char *opts;
+        int r;
+
+        assert(path);
+        assert(proc_self_mountinfo);
+
+        if ((flags_mask & ~MS_CONVERTIBLE_FLAGS) == 0 && !skip_mount_set_attr) {
+                /* Let's take a shortcut for all the flags we know how to convert into mount_setattr() flags */
+
+                if (mount_setattr(AT_FDCWD, path, AT_SYMLINK_NOFOLLOW,
+                                  &(struct mount_attr) {
+                                          .attr_set = ms_flags_to_mount_attr(new_flags & flags_mask),
+                                          .attr_clr = ms_flags_to_mount_attr(~new_flags & flags_mask),
+                                  }, MOUNT_ATTR_SIZE_VER0) < 0) {
+
+                        log_debug_errno(errno, "mount_setattr() didn't work, falling back to classic remounting: %m");
+
+                        if (ERRNO_IS_NOT_SUPPORTED(errno)) /* if not supported, then don't bother at all anymore */
+                                skip_mount_set_attr = true;
+                } else
+                        return 0; /* Nice, this worked! */
+        }
+
+        rewind(proc_self_mountinfo);
+
+        table = mnt_new_table();
+        if (!table)
+                return -ENOMEM;
+
+        r = mnt_table_parse_stream(table, proc_self_mountinfo, "/proc/self/mountinfo");
+        if (r < 0)
+                return r;
+
+        fs = mnt_table_find_target(table, path, MNT_ITER_FORWARD);
+        if (!fs) {
+                if (laccess(path, F_OK) < 0) /* Hmm, it's not in the mount table, but does it exist at all? */
+                        return -errno;
+
+                return -EINVAL; /* Not a mount point we recognize */
+        }
+
+        opts = mnt_fs_get_vfs_options(fs);
+        if (opts) {
+                r = mnt_optstr_get_flags(opts, &flags, mnt_get_builtin_optmap(MNT_LINUX_MAP));
+                if (r < 0)
+                        log_debug_errno(r, "Could not get flags for '%s', ignoring: %m", path);
+        }
+
+        r = mount_nofollow(NULL, path, NULL, ((flags & ~flags_mask)|MS_BIND|MS_REMOUNT|new_flags) & ~MS_RELATIME, NULL);
+        if (r < 0) {
+                if (((flags ^ new_flags) & flags_mask & ~MS_RELATIME) != 0) /* Ignore MS_RELATIME again,
+                                                                             * since kernel adds it in
+                                                                             * everywhere, because it's the
+                                                                             * default. */
+                        return r;
+
+                /* Let's handle redundant remounts gracefully */
+                log_debug_errno(r, "Failed to remount '%s' but flags already match what we want, ignoring: %m", path);
+        }
+
+        return 0;
+}
+
+int mount_move_root(const char *path) {
+        assert(path);
+
+        if (chdir(path) < 0)
+                return -errno;
+
+        if (mount(path, "/", NULL, MS_MOVE, NULL) < 0)
+                return -errno;
+
+        if (chroot(".") < 0)
+                return -errno;
+
+        return RET_NERRNO(chdir("/"));
+}
+
+int repeat_unmount(const char *path, int flags) {
+        bool done = false;
+
+        assert(path);
+
+        /* If there are multiple mounts on a mount point, this
+         * removes them all */
+
+        for (;;) {
+                if (umount2(path, flags) < 0) {
+
+                        if (errno == EINVAL)
+                                return done;
+
+                        return -errno;
+                }
+
+                done = true;
+        }
+}
+
+int mode_to_inaccessible_node(
+                const char *runtime_dir,
+                mode_t mode,
+                char **ret) {
+
+        /* This function maps a node type to a corresponding inaccessible file node. These nodes are created
+         * during early boot by PID 1. In some cases we lacked the privs to create the character and block
+         * devices (maybe because we run in an userns environment, or miss CAP_SYS_MKNOD, or run with a
+         * devices policy that excludes device nodes with major and minor of 0), but that's fine, in that
+         * case we use an AF_UNIX file node instead, which is not the same, but close enough for most
+         * uses. And most importantly, the kernel allows bind mounts from socket nodes to any non-directory
+         * file nodes, and that's the most important thing that matters.
+         *
+         * Note that the runtime directory argument shall be the top-level runtime directory, i.e. /run/ if
+         * we operate in system context and $XDG_RUNTIME_DIR if we operate in user context. */
+
+        _cleanup_free_ char *d = NULL;
+        const char *node = NULL;
+
+        assert(ret);
+
+        if (!runtime_dir)
+                runtime_dir = "/run";
+
+        switch (mode & S_IFMT) {
+                case S_IFREG:
+                        node = "/systemd/inaccessible/reg";
+                        break;
+
+                case S_IFDIR:
+                        node = "/systemd/inaccessible/dir";
+                        break;
+
+                case S_IFCHR:
+                        node = "/systemd/inaccessible/chr";
+                        break;
+
+                case S_IFBLK:
+                        node = "/systemd/inaccessible/blk";
+                        break;
+
+                case S_IFIFO:
+                        node = "/systemd/inaccessible/fifo";
+                        break;
+
+                case S_IFSOCK:
+                        node = "/systemd/inaccessible/sock";
+                        break;
+        }
+        if (!node)
+                return -EINVAL;
+
+        d = path_join(runtime_dir, node);
+        if (!d)
+                return -ENOMEM;
+
+        /* On new kernels unprivileged users are permitted to create 0:0 char device nodes (because they also
+         * act as whiteout inode for overlayfs), but no other char or block device nodes. On old kernels no
+         * device node whatsoever may be created by unprivileged processes. Hence, if the caller asks for the
+         * inaccessible block device node let's see if the block device node actually exists, and if not,
+         * fall back to the character device node. From there fall back to the socket device node. This means
+         * in the best case we'll get the right device node type — but if not we'll hopefully at least get a
+         * device node at all. */
+
+        if (S_ISBLK(mode) &&
+            access(d, F_OK) < 0 && errno == ENOENT) {
+                free(d);
+                d = path_join(runtime_dir, "/systemd/inaccessible/chr");
+                if (!d)
+                        return -ENOMEM;
+        }
+
+        if (IN_SET(mode & S_IFMT, S_IFBLK, S_IFCHR) &&
+            access(d, F_OK) < 0 && errno == ENOENT) {
+                free(d);
+                d = path_join(runtime_dir, "/systemd/inaccessible/sock");
+                if (!d)
+                        return -ENOMEM;
+        }
+
+        *ret = TAKE_PTR(d);
+        return 0;
+}
+
+int mount_flags_to_string(unsigned long flags, char **ret) {
+        static const struct {
+                unsigned long flag;
+                const char *name;
+        } map[] = {
+                { .flag = MS_RDONLY,      .name = "MS_RDONLY",      },
+                { .flag = MS_NOSUID,      .name = "MS_NOSUID",      },
+                { .flag = MS_NODEV,       .name = "MS_NODEV",       },
+                { .flag = MS_NOEXEC,      .name = "MS_NOEXEC",      },
+                { .flag = MS_SYNCHRONOUS, .name = "MS_SYNCHRONOUS", },
+                { .flag = MS_REMOUNT,     .name = "MS_REMOUNT",     },
+                { .flag = MS_MANDLOCK,    .name = "MS_MANDLOCK",    },
+                { .flag = MS_DIRSYNC,     .name = "MS_DIRSYNC",     },
+                { .flag = MS_NOSYMFOLLOW, .name = "MS_NOSYMFOLLOW", },
+                { .flag = MS_NOATIME,     .name = "MS_NOATIME",     },
+                { .flag = MS_NODIRATIME,  .name = "MS_NODIRATIME",  },
+                { .flag = MS_BIND,        .name = "MS_BIND",        },
+                { .flag = MS_MOVE,        .name = "MS_MOVE",        },
+                { .flag = MS_REC,         .name = "MS_REC",         },
+                { .flag = MS_SILENT,      .name = "MS_SILENT",      },
+                { .flag = MS_POSIXACL,    .name = "MS_POSIXACL",    },
+                { .flag = MS_UNBINDABLE,  .name = "MS_UNBINDABLE",  },
+                { .flag = MS_PRIVATE,     .name = "MS_PRIVATE",     },
+                { .flag = MS_SLAVE,       .name = "MS_SLAVE",       },
+                { .flag = MS_SHARED,      .name = "MS_SHARED",      },
+                { .flag = MS_RELATIME,    .name = "MS_RELATIME",    },
+                { .flag = MS_KERNMOUNT,   .name = "MS_KERNMOUNT",   },
+                { .flag = MS_I_VERSION,   .name = "MS_I_VERSION",   },
+                { .flag = MS_STRICTATIME, .name = "MS_STRICTATIME", },
+                { .flag = MS_LAZYTIME,    .name = "MS_LAZYTIME",    },
+        };
+        _cleanup_free_ char *str = NULL;
+
+        assert(ret);
+
+        for (size_t i = 0; i < ELEMENTSOF(map); i++)
+                if (flags & map[i].flag) {
+                        if (!strextend_with_separator(&str, "|", map[i].name))
+                                return -ENOMEM;
+                        flags &= ~map[i].flag;
+                }
+
+        if (!str || flags != 0)
+                if (strextendf_with_separator(&str, "|", "%lx", flags) < 0)
+                        return -ENOMEM;
+
+        *ret = TAKE_PTR(str);
+        return 0;
+}
+
+int mount_verbose_full(
+                int error_log_level,
+                const char *what,
+                const char *where,
+                const char *type,
+                unsigned long flags,
+                const char *options,
+                bool follow_symlink) {
+
+        _cleanup_free_ char *fl = NULL, *o = NULL;
+        unsigned long f;
+        int r;
+
+        r = mount_option_mangle(options, flags, &f, &o);
+        if (r < 0)
+                return log_full_errno(error_log_level, r,
+                                      "Failed to mangle mount options %s: %m",
+                                      strempty(options));
+
+        (void) mount_flags_to_string(f, &fl);
+
+        if ((f & MS_REMOUNT) && !what && !type)
+                log_debug("Remounting %s (%s \"%s\")...",
+                          where, strnull(fl), strempty(o));
+        else if (!what && !type)
+                log_debug("Mounting %s (%s \"%s\")...",
+                          where, strnull(fl), strempty(o));
+        else if ((f & MS_BIND) && !type)
+                log_debug("Bind-mounting %s on %s (%s \"%s\")...",
+                          what, where, strnull(fl), strempty(o));
+        else if (f & MS_MOVE)
+                log_debug("Moving mount %s %s %s (%s \"%s\")...",
+                          what, special_glyph(SPECIAL_GLYPH_ARROW_RIGHT), where, strnull(fl), strempty(o));
+        else
+                log_debug("Mounting %s (%s) on %s (%s \"%s\")...",
+                          strna(what), strna(type), where, strnull(fl), strempty(o));
+
+        if (follow_symlink)
+                r = RET_NERRNO(mount(what, where, type, f, o));
+        else
+                r = mount_nofollow(what, where, type, f, o);
+        if (r < 0)
+                return log_full_errno(error_log_level, r,
+                                      "Failed to mount %s (type %s) on %s (%s \"%s\"): %m",
+                                      strna(what), strna(type), where, strnull(fl), strempty(o));
+        return 0;
+}
+
+int umount_verbose(
+                int error_log_level,
+                const char *what,
+                int flags) {
+
+        assert(what);
+
+        log_debug("Umounting %s...", what);
+
+        if (umount2(what, flags) < 0)
+                return log_full_errno(error_log_level, errno,
+                                      "Failed to unmount %s: %m", what);
+
+        return 0;
+}
+
+int mount_option_mangle(
+                const char *options,
+                unsigned long mount_flags,
+                unsigned long *ret_mount_flags,
+                char **ret_remaining_options) {
+
+        const struct libmnt_optmap *map;
+        _cleanup_free_ char *ret = NULL;
+        int r;
+
+        /* This extracts mount flags from the mount options, and store
+         * non-mount-flag options to '*ret_remaining_options'.
+         * E.g.,
+         * "rw,nosuid,nodev,relatime,size=1630748k,mode=700,uid=1000,gid=1000"
+         * is split to MS_NOSUID|MS_NODEV|MS_RELATIME and
+         * "size=1630748k,mode=700,uid=1000,gid=1000".
+         * See more examples in test-mount-utils.c.
+         *
+         * Note that if 'options' does not contain any non-mount-flag options,
+         * then '*ret_remaining_options' is set to NULL instead of empty string.
+         * Note that this does not check validity of options stored in
+         * '*ret_remaining_options'.
+         * Note that if 'options' is NULL, then this just copies 'mount_flags'
+         * to '*ret_mount_flags'. */
+
+        assert(ret_mount_flags);
+        assert(ret_remaining_options);
+
+        map = mnt_get_builtin_optmap(MNT_LINUX_MAP);
+        if (!map)
+                return -EINVAL;
+
+        for (const char *p = options;;) {
+                _cleanup_free_ char *word = NULL;
+                const struct libmnt_optmap *ent;
+
+                r = extract_first_word(&p, &word, ",", EXTRACT_KEEP_QUOTE);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+
+                for (ent = map; ent->name; ent++) {
+                        /* All entries in MNT_LINUX_MAP do not take any argument.
+                         * Thus, ent->name does not contain "=" or "[=]". */
+                        if (!streq(word, ent->name))
+                                continue;
+
+                        if (!(ent->mask & MNT_INVERT))
+                                mount_flags |= ent->id;
+                        else if (mount_flags & ent->id)
+                                mount_flags ^= ent->id;
+
+                        break;
+                }
+
+                /* If 'word' is not a mount flag, then store it in '*ret_remaining_options'. */
+                if (!ent->name &&
+                    !startswith_no_case(word, "x-") &&
+                    !strextend_with_separator(&ret, ",", word))
+                        return -ENOMEM;
+        }
+
+        *ret_mount_flags = mount_flags;
+        *ret_remaining_options = TAKE_PTR(ret);
+
+        return 0;
+}
+
+static int mount_in_namespace(
+                pid_t target,
+                const char *propagate_path,
+                const char *incoming_path,
+                const char *src,
+                const char *dest,
+                bool read_only,
+                bool make_file_or_directory,
+                const MountOptions *options,
+                bool is_image) {
+
+        _cleanup_close_pair_ int errno_pipe_fd[2] = { -1, -1 };
+        _cleanup_close_ int mntns_fd = -1, root_fd = -1, pidns_fd = -1, chased_src_fd = -1;
+        char mount_slave[] = "/tmp/propagate.XXXXXX", *mount_tmp, *mount_outside, *p;
+        bool mount_slave_created = false, mount_slave_mounted = false,
+                mount_tmp_created = false, mount_tmp_mounted = false,
+                mount_outside_created = false, mount_outside_mounted = false;
+        _cleanup_free_ char *chased_src_path = NULL;
+        struct stat st;
+        pid_t child;
+        int r;
+
+        assert(target > 0);
+        assert(propagate_path);
+        assert(incoming_path);
+        assert(src);
+        assert(dest);
+        assert(!options || is_image);
+
+        r = namespace_open(target, &pidns_fd, &mntns_fd, NULL, NULL, &root_fd);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to retrieve FDs of the target process' namespace: %m");
+
+        r = in_same_namespace(target, 0, NAMESPACE_MOUNT);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to determine if mount namespaces are equal: %m");
+        /* We can't add new mounts at runtime if the process wasn't started in a namespace */
+        if (r > 0)
+                return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), "Failed to activate bind mount in target, not running in a mount namespace");
+
+        /* One day, when bind mounting /proc/self/fd/n works across namespace boundaries we should rework
+         * this logic to make use of it... */
+
+        p = strjoina(propagate_path, "/");
+        r = laccess(p, F_OK);
+        if (r < 0)
+                return log_debug_errno(r == -ENOENT ? SYNTHETIC_ERRNO(EOPNOTSUPP) : r, "Target does not allow propagation of mount points");
+
+        r = chase_symlinks(src, NULL, 0, &chased_src_path, &chased_src_fd);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to resolve source path of %s: %m", src);
+        log_debug("Chased source path of %s to %s", src, chased_src_path);
+
+        if (fstat(chased_src_fd, &st) < 0)
+                return log_debug_errno(errno, "Failed to stat() resolved source path %s: %m", src);
+        if (S_ISLNK(st.st_mode)) /* This shouldn't really happen, given that we just chased the symlinks above, but let's better be safe… */
+                return log_debug_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "Source directory %s can't be a symbolic link", src);
+
+        /* Our goal is to install a new bind mount into the container,
+           possibly read-only. This is irritatingly complex
+           unfortunately, currently.
+
+           First, we start by creating a private playground in /tmp,
+           that we can mount MS_SLAVE. (Which is necessary, since
+           MS_MOVE cannot be applied to mounts with MS_SHARED parent
+           mounts.) */
+
+        if (!mkdtemp(mount_slave))
+                return log_debug_errno(errno, "Failed to create playground %s: %m", mount_slave);
+
+        mount_slave_created = true;
+
+        r = mount_nofollow_verbose(LOG_DEBUG, mount_slave, mount_slave, NULL, MS_BIND, NULL);
+        if (r < 0)
+                goto finish;
+
+        mount_slave_mounted = true;
+
+        r = mount_nofollow_verbose(LOG_DEBUG, NULL, mount_slave, NULL, MS_SLAVE, NULL);
+        if (r < 0)
+                goto finish;
+
+        /* Second, we mount the source file or directory to a directory inside of our MS_SLAVE playground. */
+        mount_tmp = strjoina(mount_slave, "/mount");
+        if (is_image)
+                r = mkdir_p(mount_tmp, 0700);
+        else
+                r = make_mount_point_inode_from_stat(&st, mount_tmp, 0700);
+        if (r < 0) {
+                log_debug_errno(r, "Failed to create temporary mount point %s: %m", mount_tmp);
+                goto finish;
+        }
+
+        mount_tmp_created = true;
+
+        if (is_image)
+                r = verity_dissect_and_mount(chased_src_fd, chased_src_path, mount_tmp, options, NULL, NULL, NULL, NULL);
+        else
+                r = mount_follow_verbose(LOG_DEBUG, FORMAT_PROC_FD_PATH(chased_src_fd), mount_tmp, NULL, MS_BIND, NULL);
+        if (r < 0)
+                goto finish;
+
+        mount_tmp_mounted = true;
+
+        /* Third, we remount the new bind mount read-only if requested. */
+        if (read_only) {
+                r = mount_nofollow_verbose(LOG_DEBUG, NULL, mount_tmp, NULL, MS_BIND|MS_REMOUNT|MS_RDONLY, NULL);
+                if (r < 0)
+                        goto finish;
+        }
+
+        /* Fourth, we move the new bind mount into the propagation directory. This way it will appear there read-only
+         * right-away. */
+
+        mount_outside = strjoina(propagate_path, "/XXXXXX");
+        if (is_image || S_ISDIR(st.st_mode))
+                r = mkdtemp(mount_outside) ? 0 : -errno;
+        else {
+                r = mkostemp_safe(mount_outside);
+                safe_close(r);
+        }
+        if (r < 0) {
+                log_debug_errno(r, "Cannot create propagation file or directory %s: %m", mount_outside);
+                goto finish;
+        }
+
+        mount_outside_created = true;
+
+        r = mount_nofollow_verbose(LOG_DEBUG, mount_tmp, mount_outside, NULL, MS_MOVE, NULL);
+        if (r < 0)
+                goto finish;
+
+        mount_outside_mounted = true;
+        mount_tmp_mounted = false;
+
+        if (is_image || S_ISDIR(st.st_mode))
+                (void) rmdir(mount_tmp);
+        else
+                (void) unlink(mount_tmp);
+        mount_tmp_created = false;
+
+        (void) umount_verbose(LOG_DEBUG, mount_slave, UMOUNT_NOFOLLOW);
+        mount_slave_mounted = false;
+
+        (void) rmdir(mount_slave);
+        mount_slave_created = false;
+
+        if (pipe2(errno_pipe_fd, O_CLOEXEC|O_NONBLOCK) < 0) {
+                log_debug_errno(errno, "Failed to create pipe: %m");
+                goto finish;
+        }
+
+        r = namespace_fork("(sd-bindmnt)", "(sd-bindmnt-inner)", NULL, 0, FORK_RESET_SIGNALS|FORK_DEATHSIG,
+                           pidns_fd, mntns_fd, -1, -1, root_fd, &child);
+        if (r < 0)
+                goto finish;
+        if (r == 0) {
+                const char *mount_inside;
+
+                errno_pipe_fd[0] = safe_close(errno_pipe_fd[0]);
+
+                if (make_file_or_directory) {
+                        if (!is_image) {
+                                (void) mkdir_parents(dest, 0755);
+                                (void) make_mount_point_inode_from_stat(&st, dest, 0700);
+                        } else
+                                (void) mkdir_p(dest, 0755);
+                }
+
+                /* Fifth, move the mount to the right place inside */
+                mount_inside = strjoina(incoming_path, basename(mount_outside));
+                r = mount_nofollow_verbose(LOG_ERR, mount_inside, dest, NULL, MS_MOVE, NULL);
+                if (r < 0)
+                        goto child_fail;
+
+                _exit(EXIT_SUCCESS);
+
+        child_fail:
+                (void) write(errno_pipe_fd[1], &r, sizeof(r));
+                errno_pipe_fd[1] = safe_close(errno_pipe_fd[1]);
+
+                _exit(EXIT_FAILURE);
+        }
+
+        errno_pipe_fd[1] = safe_close(errno_pipe_fd[1]);
+
+        r = wait_for_terminate_and_check("(sd-bindmnt)", child, 0);
+        if (r < 0) {
+                log_debug_errno(r, "Failed to wait for child: %m");
+                goto finish;
+        }
+        if (r != EXIT_SUCCESS) {
+                if (read(errno_pipe_fd[0], &r, sizeof(r)) == sizeof(r))
+                        log_debug_errno(r, "Failed to mount: %m");
+                else
+                        log_debug("Child failed.");
+                goto finish;
+        }
+
+finish:
+        if (mount_outside_mounted)
+                (void) umount_verbose(LOG_DEBUG, mount_outside, UMOUNT_NOFOLLOW);
+        if (mount_outside_created) {
+                if (is_image || S_ISDIR(st.st_mode))
+                        (void) rmdir(mount_outside);
+                else
+                        (void) unlink(mount_outside);
+        }
+
+        if (mount_tmp_mounted)
+                (void) umount_verbose(LOG_DEBUG, mount_tmp, UMOUNT_NOFOLLOW);
+        if (mount_tmp_created) {
+                if (is_image || S_ISDIR(st.st_mode))
+                        (void) rmdir(mount_tmp);
+                else
+                        (void) unlink(mount_tmp);
+        }
+
+        if (mount_slave_mounted)
+                (void) umount_verbose(LOG_DEBUG, mount_slave, UMOUNT_NOFOLLOW);
+        if (mount_slave_created)
+                (void) rmdir(mount_slave);
+
+        return r;
+}
+
+int bind_mount_in_namespace(
+                pid_t target,
+                const char *propagate_path,
+                const char *incoming_path,
+                const char *src,
+                const char *dest,
+                bool read_only,
+                bool make_file_or_directory) {
+
+        return mount_in_namespace(target, propagate_path, incoming_path, src, dest, read_only, make_file_or_directory, NULL, false);
+}
+
+int mount_image_in_namespace(
+                pid_t target,
+                const char *propagate_path,
+                const char *incoming_path,
+                const char *src,
+                const char *dest,
+                bool read_only,
+                bool make_file_or_directory,
+                const MountOptions *options) {
+
+        return mount_in_namespace(target, propagate_path, incoming_path, src, dest, read_only, make_file_or_directory, options, true);
+}
+
+int make_mount_point(const char *path) {
+        int r;
+
+        assert(path);
+
+        /* If 'path' is already a mount point, does nothing and returns 0. If it is not it makes it one, and returns 1. */
+
+        r = path_is_mount_point(path, NULL, 0);
+        if (r < 0)
+                return log_debug_errno(r, "Failed to determine whether '%s' is a mount point: %m", path);
+        if (r > 0)
+                return 0;
+
+        r = mount_nofollow_verbose(LOG_DEBUG, path, path, NULL, MS_BIND|MS_REC, NULL);
+        if (r < 0)
+                return r;
+
+        return 1;
+}
+
+static int make_userns(uid_t uid_shift, uid_t uid_range, uid_t owner, RemountIdmapping idmapping) {
+        _cleanup_close_ int userns_fd = -1;
+        _cleanup_free_ char *line = NULL;
+
+        /* Allocates a userns file descriptor with the mapping we need. For this we'll fork off a child
+         * process whose only purpose is to give us a new user namespace. It's killed when we got it. */
+
+        if (IN_SET(idmapping, REMOUNT_IDMAPPING_NONE, REMOUNT_IDMAPPING_HOST_ROOT)) {
+                if (asprintf(&line, UID_FMT " " UID_FMT " " UID_FMT "\n", 0u, uid_shift, uid_range) < 0)
+                        return log_oom_debug();
+
+                /* If requested we'll include an entry in the mapping so that the host root user can make
+                 * changes to the uidmapped mount like it normally would. Specifically, we'll map the user
+                 * with UID_MAPPED_ROOT on the backing fs to UID 0. This is useful, since nspawn code wants
+                 * to create various missing inodes in the OS tree before booting into it, and this becomes
+                 * very easy and straightforward to do if it can just do it under its own regular UID. Note
+                 * that in that case the container's runtime uidmap (i.e. the one the container payload
+                 * processes run in) will leave this UID unmapped, i.e. if we accidentally leave files owned
+                 * by host root in the already uidmapped tree around they'll show up as owned by 'nobody',
+                 * which is safe. (Of course, we shouldn't leave such inodes around, but always chown() them
+                 * to the container's own UID range, but it's good to have a safety net, in case we
+                 * forget it.) */
+                if (idmapping == REMOUNT_IDMAPPING_HOST_ROOT)
+                        if (strextendf(&line,
+                                       UID_FMT " " UID_FMT " " UID_FMT "\n",
+                                       UID_MAPPED_ROOT, 0u, 1u) < 0)
+                                return log_oom_debug();
+        }
+
+        if (idmapping == REMOUNT_IDMAPPING_HOST_OWNER) {
+                /* Remap the owner of the bind mounted directory to the root user within the container. This
+                 * way every file written by root within the container to the bind-mounted directory will
+                 * be owned by the original user. All other user will remain unmapped. */
+                if (asprintf(&line, UID_FMT " " UID_FMT " " UID_FMT "\n", owner, uid_shift, 1u) < 0)
+                        return log_oom_debug();
+        }
+
+        /* We always assign the same UID and GID ranges */
+        userns_fd = userns_acquire(line, line);
+        if (userns_fd < 0)
+                return log_debug_errno(userns_fd, "Failed to acquire new userns: %m");
+
+        return TAKE_FD(userns_fd);
+}
+
+int remount_idmap(
+                const char *p,
+                uid_t uid_shift,
+                uid_t uid_range,
+                uid_t owner,
+                RemountIdmapping idmapping) {
+
+        _cleanup_close_ int mount_fd = -1, userns_fd = -1;
+        int r;
+
+        assert(p);
+
+        if (!userns_shift_range_valid(uid_shift, uid_range))
+                return -EINVAL;
+
+        /* Clone the mount point */
+        mount_fd = open_tree(-1, p, OPEN_TREE_CLONE | OPEN_TREE_CLOEXEC);
+        if (mount_fd < 0)
+                return log_debug_errno(errno, "Failed to open tree of mounted filesystem '%s': %m", p);
+
+        /* Create a user namespace mapping */
+        userns_fd = make_userns(uid_shift, uid_range, owner, idmapping);
+        if (userns_fd < 0)
+                return userns_fd;
+
+        /* Set the user namespace mapping attribute on the cloned mount point */
+        if (mount_setattr(mount_fd, "", AT_EMPTY_PATH | AT_RECURSIVE,
+                          &(struct mount_attr) {
+                                  .attr_set = MOUNT_ATTR_IDMAP,
+                                  .userns_fd = userns_fd,
+                          }, sizeof(struct mount_attr)) < 0)
+                return log_debug_errno(errno, "Failed to change bind mount attributes for '%s': %m", p);
+
+        /* Remove the old mount point */
+        r = umount_verbose(LOG_DEBUG, p, UMOUNT_NOFOLLOW);
+        if (r < 0)
+                return r;
+
+        /* And place the cloned version in its place */
+        if (move_mount(mount_fd, "", -1, p, MOVE_MOUNT_F_EMPTY_PATH) < 0)
+                return log_debug_errno(errno, "Failed to attach UID mapped mount to '%s': %m", p);
+
+        return 0;
+}
+
+int make_mount_point_inode_from_stat(const struct stat *st, const char *dest, mode_t mode) {
+        assert(st);
+        assert(dest);
+
+        if (S_ISDIR(st->st_mode))
+                return mkdir_label(dest, mode);
+        else
+                return RET_NERRNO(mknod(dest, S_IFREG|(mode & ~0111), 0));
+}
+
+int make_mount_point_inode_from_path(const char *source, const char *dest, mode_t mode) {
+        struct stat st;
+
+        assert(source);
+        assert(dest);
+
+        if (stat(source, &st) < 0)
+                return -errno;
+
+        return make_mount_point_inode_from_stat(&st, dest, mode);
+}