Adding upstream version 241.upstream/241upstream

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

1 files changed, 1358 insertions, 0 deletions

diff --git a/src/basic/fs-util.c b/src/basic/fs-util.c
new file mode 100644
index 0000000..f25bf2c
--- /dev/null
+++ b/src/basic/fs-util.c
@@ -0,0 +1,1358 @@
+/* SPDX-License-Identifier: LGPL-2.1+ */
+
+#include <errno.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <linux/magic.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "alloc-util.h"
+#include "dirent-util.h"
+#include "fd-util.h"
+#include "fs-util.h"
+#include "locale-util.h"
+#include "log.h"
+#include "macro.h"
+#include "missing.h"
+#include "mkdir.h"
+#include "parse-util.h"
+#include "path-util.h"
+#include "process-util.h"
+#include "stat-util.h"
+#include "stdio-util.h"
+#include "string-util.h"
+#include "strv.h"
+#include "time-util.h"
+#include "tmpfile-util.h"
+#include "user-util.h"
+#include "util.h"
+
+int unlink_noerrno(const char *path) {
+        PROTECT_ERRNO;
+        int r;
+
+        r = unlink(path);
+        if (r < 0)
+                return -errno;
+
+        return 0;
+}
+
+int rmdir_parents(const char *path, const char *stop) {
+        size_t l;
+        int r = 0;
+
+        assert(path);
+        assert(stop);
+
+        l = strlen(path);
+
+        /* Skip trailing slashes */
+        while (l > 0 && path[l-1] == '/')
+                l--;
+
+        while (l > 0) {
+                char *t;
+
+                /* Skip last component */
+                while (l > 0 && path[l-1] != '/')
+                        l--;
+
+                /* Skip trailing slashes */
+                while (l > 0 && path[l-1] == '/')
+                        l--;
+
+                if (l <= 0)
+                        break;
+
+                t = strndup(path, l);
+                if (!t)
+                        return -ENOMEM;
+
+                if (path_startswith(stop, t)) {
+                        free(t);
+                        return 0;
+                }
+
+                r = rmdir(t);
+                free(t);
+
+                if (r < 0)
+                        if (errno != ENOENT)
+                                return -errno;
+        }
+
+        return 0;
+}
+
+int rename_noreplace(int olddirfd, const char *oldpath, int newdirfd, const char *newpath) {
+        int r;
+
+        /* Try the ideal approach first */
+        if (renameat2(olddirfd, oldpath, newdirfd, newpath, RENAME_NOREPLACE) >= 0)
+                return 0;
+
+        /* renameat2() exists since Linux 3.15, btrfs and FAT added support for it later. If it is not implemented,
+         * fall back to a different method. */
+        if (!IN_SET(errno, EINVAL, ENOSYS, ENOTTY))
+                return -errno;
+
+        /* Let's try to use linkat()+unlinkat() as fallback. This doesn't work on directories and on some file systems
+         * that do not support hard links (such as FAT, most prominently), but for files it's pretty close to what we
+         * want — though not atomic (i.e. for a short period both the new and the old filename will exist). */
+        if (linkat(olddirfd, oldpath, newdirfd, newpath, 0) >= 0) {
+
+                if (unlinkat(olddirfd, oldpath, 0) < 0) {
+                        r = -errno; /* Backup errno before the following unlinkat() alters it */
+                        (void) unlinkat(newdirfd, newpath, 0);
+                        return r;
+                }
+
+                return 0;
+        }
+
+        if (!IN_SET(errno, EINVAL, ENOSYS, ENOTTY, EPERM)) /* FAT returns EPERM on link()… */
+                return -errno;
+
+        /* OK, neither RENAME_NOREPLACE nor linkat()+unlinkat() worked. Let's then fallback to the racy TOCTOU
+         * vulnerable accessat(F_OK) check followed by classic, replacing renameat(), we have nothing better. */
+
+        if (faccessat(newdirfd, newpath, F_OK, AT_SYMLINK_NOFOLLOW) >= 0)
+                return -EEXIST;
+        if (errno != ENOENT)
+                return -errno;
+
+        if (renameat(olddirfd, oldpath, newdirfd, newpath) < 0)
+                return -errno;
+
+        return 0;
+}
+
+int readlinkat_malloc(int fd, const char *p, char **ret) {
+        size_t l = FILENAME_MAX+1;
+        int r;
+
+        assert(p);
+        assert(ret);
+
+        for (;;) {
+                char *c;
+                ssize_t n;
+
+                c = new(char, l);
+                if (!c)
+                        return -ENOMEM;
+
+                n = readlinkat(fd, p, c, l-1);
+                if (n < 0) {
+                        r = -errno;
+                        free(c);
+                        return r;
+                }
+
+                if ((size_t) n < l-1) {
+                        c[n] = 0;
+                        *ret = c;
+                        return 0;
+                }
+
+                free(c);
+                l *= 2;
+        }
+}
+
+int readlink_malloc(const char *p, char **ret) {
+        return readlinkat_malloc(AT_FDCWD, p, ret);
+}
+
+int readlink_value(const char *p, char **ret) {
+        _cleanup_free_ char *link = NULL;
+        char *value;
+        int r;
+
+        r = readlink_malloc(p, &link);
+        if (r < 0)
+                return r;
+
+        value = basename(link);
+        if (!value)
+                return -ENOENT;
+
+        value = strdup(value);
+        if (!value)
+                return -ENOMEM;
+
+        *ret = value;
+
+        return 0;
+}
+
+int readlink_and_make_absolute(const char *p, char **r) {
+        _cleanup_free_ char *target = NULL;
+        char *k;
+        int j;
+
+        assert(p);
+        assert(r);
+
+        j = readlink_malloc(p, &target);
+        if (j < 0)
+                return j;
+
+        k = file_in_same_dir(p, target);
+        if (!k)
+                return -ENOMEM;
+
+        *r = k;
+        return 0;
+}
+
+int chmod_and_chown(const char *path, mode_t mode, uid_t uid, gid_t gid) {
+        char fd_path[STRLEN("/proc/self/fd/") + DECIMAL_STR_MAX(int) + 1];
+        _cleanup_close_ int fd = -1;
+        assert(path);
+
+        /* Under the assumption that we are running privileged we first change the access mode and only then hand out
+         * ownership to avoid a window where access is too open. */
+
+        fd = open(path, O_PATH|O_CLOEXEC|O_NOFOLLOW); /* Let's acquire an O_PATH fd, as precaution to change mode/owner
+                                                       * on the same file */
+        if (fd < 0)
+                return -errno;
+
+        xsprintf(fd_path, "/proc/self/fd/%i", fd);
+
+        if (mode != MODE_INVALID) {
+
+                if ((mode & S_IFMT) != 0) {
+                        struct stat st;
+
+                        if (stat(fd_path, &st) < 0)
+                                return -errno;
+
+                        if ((mode & S_IFMT) != (st.st_mode & S_IFMT))
+                                return -EINVAL;
+                }
+
+                if (chmod(fd_path, mode & 07777) < 0)
+                        return -errno;
+        }
+
+        if (uid != UID_INVALID || gid != GID_INVALID)
+                if (chown(fd_path, uid, gid) < 0)
+                        return -errno;
+
+        return 0;
+}
+
+int fchmod_and_chown(int fd, mode_t mode, uid_t uid, gid_t gid) {
+        /* Under the assumption that we are running privileged we first change the access mode and only then hand out
+         * ownership to avoid a window where access is too open. */
+
+        if (mode != MODE_INVALID) {
+
+                if ((mode & S_IFMT) != 0) {
+                        struct stat st;
+
+                        if (fstat(fd, &st) < 0)
+                                return -errno;
+
+                        if ((mode & S_IFMT) != (st.st_mode & S_IFMT))
+                                return -EINVAL;
+                }
+
+                if (fchmod(fd, mode & 0777) < 0)
+                        return -errno;
+        }
+
+        if (uid != UID_INVALID || gid != GID_INVALID)
+                if (fchown(fd, uid, gid) < 0)
+                        return -errno;
+
+        return 0;
+}
+
+int fchmod_umask(int fd, mode_t m) {
+        mode_t u;
+        int r;
+
+        u = umask(0777);
+        r = fchmod(fd, m & (~u)) < 0 ? -errno : 0;
+        umask(u);
+
+        return r;
+}
+
+int fchmod_opath(int fd, mode_t m) {
+        char procfs_path[STRLEN("/proc/self/fd/") + DECIMAL_STR_MAX(int)];
+
+        /* This function operates also on fd that might have been opened with
+         * O_PATH. Indeed fchmodat() doesn't have the AT_EMPTY_PATH flag like
+         * fchownat() does. */
+
+        xsprintf(procfs_path, "/proc/self/fd/%i", fd);
+        if (chmod(procfs_path, m) < 0)
+                return -errno;
+
+        return 0;
+}
+
+int fd_warn_permissions(const char *path, int fd) {
+        struct stat st;
+
+        if (fstat(fd, &st) < 0)
+                return -errno;
+
+        if (st.st_mode & 0111)
+                log_warning("Configuration file %s is marked executable. Please remove executable permission bits. Proceeding anyway.", path);
+
+        if (st.st_mode & 0002)
+                log_warning("Configuration file %s is marked world-writable. Please remove world writability permission bits. Proceeding anyway.", path);
+
+        if (getpid_cached() == 1 && (st.st_mode & 0044) != 0044)
+                log_warning("Configuration file %s is marked world-inaccessible. This has no effect as configuration data is accessible via APIs without restrictions. Proceeding anyway.", path);
+
+        return 0;
+}
+
+int touch_file(const char *path, bool parents, usec_t stamp, uid_t uid, gid_t gid, mode_t mode) {
+        char fdpath[STRLEN("/proc/self/fd/") + DECIMAL_STR_MAX(int)];
+        _cleanup_close_ int fd = -1;
+        int r, ret = 0;
+
+        assert(path);
+
+        /* Note that touch_file() does not follow symlinks: if invoked on an existing symlink, then it is the symlink
+         * itself which is updated, not its target
+         *
+         * Returns the first error we encounter, but tries to apply as much as possible. */
+
+        if (parents)
+                (void) mkdir_parents(path, 0755);
+
+        /* Initially, we try to open the node with O_PATH, so that we get a reference to the node. This is useful in
+         * case the path refers to an existing device or socket node, as we can open it successfully in all cases, and
+         * won't trigger any driver magic or so. */
+        fd = open(path, O_PATH|O_CLOEXEC|O_NOFOLLOW);
+        if (fd < 0) {
+                if (errno != ENOENT)
+                        return -errno;
+
+                /* if the node doesn't exist yet, we create it, but with O_EXCL, so that we only create a regular file
+                 * here, and nothing else */
+                fd = open(path, O_WRONLY|O_CREAT|O_EXCL|O_CLOEXEC, IN_SET(mode, 0, MODE_INVALID) ? 0644 : mode);
+                if (fd < 0)
+                        return -errno;
+        }
+
+        /* Let's make a path from the fd, and operate on that. With this logic, we can adjust the access mode,
+         * ownership and time of the file node in all cases, even if the fd refers to an O_PATH object — which is
+         * something fchown(), fchmod(), futimensat() don't allow. */
+        xsprintf(fdpath, "/proc/self/fd/%i", fd);
+
+        if (mode != MODE_INVALID)
+                if (chmod(fdpath, mode) < 0)
+                        ret = -errno;
+
+        if (uid_is_valid(uid) || gid_is_valid(gid))
+                if (chown(fdpath, uid, gid) < 0 && ret >= 0)
+                        ret = -errno;
+
+        if (stamp != USEC_INFINITY) {
+                struct timespec ts[2];
+
+                timespec_store(&ts[0], stamp);
+                ts[1] = ts[0];
+                r = utimensat(AT_FDCWD, fdpath, ts, 0);
+        } else
+                r = utimensat(AT_FDCWD, fdpath, NULL, 0);
+        if (r < 0 && ret >= 0)
+                return -errno;
+
+        return ret;
+}
+
+int touch(const char *path) {
+        return touch_file(path, false, USEC_INFINITY, UID_INVALID, GID_INVALID, MODE_INVALID);
+}
+
+int symlink_idempotent(const char *from, const char *to, bool make_relative) {
+        _cleanup_free_ char *relpath = NULL;
+        int r;
+
+        assert(from);
+        assert(to);
+
+        if (make_relative) {
+                _cleanup_free_ char *parent = NULL;
+
+                parent = dirname_malloc(to);
+                if (!parent)
+                        return -ENOMEM;
+
+                r = path_make_relative(parent, from, &relpath);
+                if (r < 0)
+                        return r;
+
+                from = relpath;
+        }
+
+        if (symlink(from, to) < 0) {
+                _cleanup_free_ char *p = NULL;
+
+                if (errno != EEXIST)
+                        return -errno;
+
+                r = readlink_malloc(to, &p);
+                if (r == -EINVAL) /* Not a symlink? In that case return the original error we encountered: -EEXIST */
+                        return -EEXIST;
+                if (r < 0) /* Any other error? In that case propagate it as is */
+                        return r;
+
+                if (!streq(p, from)) /* Not the symlink we want it to be? In that case, propagate the original -EEXIST */
+                        return -EEXIST;
+        }
+
+        return 0;
+}
+
+int symlink_atomic(const char *from, const char *to) {
+        _cleanup_free_ char *t = NULL;
+        int r;
+
+        assert(from);
+        assert(to);
+
+        r = tempfn_random(to, NULL, &t);
+        if (r < 0)
+                return r;
+
+        if (symlink(from, t) < 0)
+                return -errno;
+
+        if (rename(t, to) < 0) {
+                unlink_noerrno(t);
+                return -errno;
+        }
+
+        return 0;
+}
+
+int mknod_atomic(const char *path, mode_t mode, dev_t dev) {
+        _cleanup_free_ char *t = NULL;
+        int r;
+
+        assert(path);
+
+        r = tempfn_random(path, NULL, &t);
+        if (r < 0)
+                return r;
+
+        if (mknod(t, mode, dev) < 0)
+                return -errno;
+
+        if (rename(t, path) < 0) {
+                unlink_noerrno(t);
+                return -errno;
+        }
+
+        return 0;
+}
+
+int mkfifo_atomic(const char *path, mode_t mode) {
+        _cleanup_free_ char *t = NULL;
+        int r;
+
+        assert(path);
+
+        r = tempfn_random(path, NULL, &t);
+        if (r < 0)
+                return r;
+
+        if (mkfifo(t, mode) < 0)
+                return -errno;
+
+        if (rename(t, path) < 0) {
+                unlink_noerrno(t);
+                return -errno;
+        }
+
+        return 0;
+}
+
+int mkfifoat_atomic(int dirfd, const char *path, mode_t mode) {
+        _cleanup_free_ char *t = NULL;
+        int r;
+
+        assert(path);
+
+        if (path_is_absolute(path))
+                return mkfifo_atomic(path, mode);
+
+        /* We're only interested in the (random) filename.  */
+        r = tempfn_random_child("", NULL, &t);
+        if (r < 0)
+                return r;
+
+        if (mkfifoat(dirfd, t, mode) < 0)
+                return -errno;
+
+        if (renameat(dirfd, t, dirfd, path) < 0) {
+                unlink_noerrno(t);
+                return -errno;
+        }
+
+        return 0;
+}
+
+int get_files_in_directory(const char *path, char ***list) {
+        _cleanup_closedir_ DIR *d = NULL;
+        struct dirent *de;
+        size_t bufsize = 0, n = 0;
+        _cleanup_strv_free_ char **l = NULL;
+
+        assert(path);
+
+        /* Returns all files in a directory in *list, and the number
+         * of files as return value. If list is NULL returns only the
+         * number. */
+
+        d = opendir(path);
+        if (!d)
+                return -errno;
+
+        FOREACH_DIRENT_ALL(de, d, return -errno) {
+                dirent_ensure_type(d, de);
+
+                if (!dirent_is_file(de))
+                        continue;
+
+                if (list) {
+                        /* one extra slot is needed for the terminating NULL */
+                        if (!GREEDY_REALLOC(l, bufsize, n + 2))
+                                return -ENOMEM;
+
+                        l[n] = strdup(de->d_name);
+                        if (!l[n])
+                                return -ENOMEM;
+
+                        l[++n] = NULL;
+                } else
+                        n++;
+        }
+
+        if (list)
+                *list = TAKE_PTR(l);
+
+        return n;
+}
+
+static int getenv_tmp_dir(const char **ret_path) {
+        const char *n;
+        int r, ret = 0;
+
+        assert(ret_path);
+
+        /* We use the same order of environment variables python uses in tempfile.gettempdir():
+         * https://docs.python.org/3/library/tempfile.html#tempfile.gettempdir */
+        FOREACH_STRING(n, "TMPDIR", "TEMP", "TMP") {
+                const char *e;
+
+                e = secure_getenv(n);
+                if (!e)
+                        continue;
+                if (!path_is_absolute(e)) {
+                        r = -ENOTDIR;
+                        goto next;
+                }
+                if (!path_is_normalized(e)) {
+                        r = -EPERM;
+                        goto next;
+                }
+
+                r = is_dir(e, true);
+                if (r < 0)
+                        goto next;
+                if (r == 0) {
+                        r = -ENOTDIR;
+                        goto next;
+                }
+
+                *ret_path = e;
+                return 1;
+
+        next:
+                /* Remember first error, to make this more debuggable */
+                if (ret >= 0)
+                        ret = r;
+        }
+
+        if (ret < 0)
+                return ret;
+
+        *ret_path = NULL;
+        return ret;
+}
+
+static int tmp_dir_internal(const char *def, const char **ret) {
+        const char *e;
+        int r, k;
+
+        assert(def);
+        assert(ret);
+
+        r = getenv_tmp_dir(&e);
+        if (r > 0) {
+                *ret = e;
+                return 0;
+        }
+
+        k = is_dir(def, true);
+        if (k == 0)
+                k = -ENOTDIR;
+        if (k < 0)
+                return r < 0 ? r : k;
+
+        *ret = def;
+        return 0;
+}
+
+int var_tmp_dir(const char **ret) {
+
+        /* Returns the location for "larger" temporary files, that is backed by physical storage if available, and thus
+         * even might survive a boot: /var/tmp. If $TMPDIR (or related environment variables) are set, its value is
+         * returned preferably however. Note that both this function and tmp_dir() below are affected by $TMPDIR,
+         * making it a variable that overrides all temporary file storage locations. */
+
+        return tmp_dir_internal("/var/tmp", ret);
+}
+
+int tmp_dir(const char **ret) {
+
+        /* Similar to var_tmp_dir() above, but returns the location for "smaller" temporary files, which is usually
+         * backed by an in-memory file system: /tmp. */
+
+        return tmp_dir_internal("/tmp", ret);
+}
+
+int unlink_or_warn(const char *filename) {
+        if (unlink(filename) < 0 && errno != ENOENT)
+                /* If the file doesn't exist and the fs simply was read-only (in which
+                 * case unlink() returns EROFS even if the file doesn't exist), don't
+                 * complain */
+                if (errno != EROFS || access(filename, F_OK) >= 0)
+                        return log_error_errno(errno, "Failed to remove \"%s\": %m", filename);
+
+        return 0;
+}
+
+int inotify_add_watch_fd(int fd, int what, uint32_t mask) {
+        char path[STRLEN("/proc/self/fd/") + DECIMAL_STR_MAX(int) + 1];
+        int r;
+
+        /* This is like inotify_add_watch(), except that the file to watch is not referenced by a path, but by an fd */
+        xsprintf(path, "/proc/self/fd/%i", what);
+
+        r = inotify_add_watch(fd, path, mask);
+        if (r < 0)
+                return -errno;
+
+        return r;
+}
+
+static bool unsafe_transition(const struct stat *a, const struct stat *b) {
+        /* Returns true if the transition from a to b is safe, i.e. that we never transition from unprivileged to
+         * privileged files or directories. Why bother? So that unprivileged code can't symlink to privileged files
+         * making us believe we read something safe even though it isn't safe in the specific context we open it in. */
+
+        if (a->st_uid == 0) /* Transitioning from privileged to unprivileged is always fine */
+                return false;
+
+        return a->st_uid != b->st_uid; /* Otherwise we need to stay within the same UID */
+}
+
+static int log_unsafe_transition(int a, int b, const char *path, unsigned flags) {
+        _cleanup_free_ char *n1 = NULL, *n2 = NULL;
+
+        if (!FLAGS_SET(flags, CHASE_WARN))
+                return -ENOLINK;
+
+        (void) fd_get_path(a, &n1);
+        (void) fd_get_path(b, &n2);
+
+        return log_warning_errno(SYNTHETIC_ERRNO(ENOLINK),
+                                 "Detected unsafe path transition %s %s %s during canonicalization of %s.",
+                                 n1, special_glyph(SPECIAL_GLYPH_ARROW), n2, path);
+}
+
+static int log_autofs_mount_point(int fd, const char *path, unsigned flags) {
+        _cleanup_free_ char *n1 = NULL;
+
+        if (!FLAGS_SET(flags, CHASE_WARN))
+                return -EREMOTE;
+
+        (void) fd_get_path(fd, &n1);
+
+        return log_warning_errno(SYNTHETIC_ERRNO(EREMOTE),
+                                 "Detected autofs mount point %s during canonicalization of %s.",
+                                 n1, path);
+}
+
+int chase_symlinks(const char *path, const char *original_root, unsigned flags, char **ret) {
+        _cleanup_free_ char *buffer = NULL, *done = NULL, *root = NULL;
+        _cleanup_close_ int fd = -1;
+        unsigned max_follow = CHASE_SYMLINKS_MAX; /* how many symlinks to follow before giving up and returning ELOOP */
+        struct stat previous_stat;
+        bool exists = true;
+        char *todo;
+        int r;
+
+        assert(path);
+
+        /* Either the file may be missing, or we return an fd to the final object, but both make no sense */
+        if (FLAGS_SET(flags, CHASE_NONEXISTENT | CHASE_OPEN))
+                return -EINVAL;
+
+        if (FLAGS_SET(flags, CHASE_STEP | CHASE_OPEN))
+                return -EINVAL;
+
+        if (isempty(path))
+                return -EINVAL;
+
+        /* This is a lot like canonicalize_file_name(), but takes an additional "root" parameter, that allows following
+         * symlinks relative to a root directory, instead of the root of the host.
+         *
+         * Note that "root" primarily matters if we encounter an absolute symlink. It is also used when following
+         * relative symlinks to ensure they cannot be used to "escape" the root directory. The path parameter passed is
+         * assumed to be already prefixed by it, except if the CHASE_PREFIX_ROOT flag is set, in which case it is first
+         * prefixed accordingly.
+         *
+         * Algorithmically this operates on two path buffers: "done" are the components of the path we already
+         * processed and resolved symlinks, "." and ".." of. "todo" are the components of the path we still need to
+         * process. On each iteration, we move one component from "todo" to "done", processing it's special meaning
+         * each time. The "todo" path always starts with at least one slash, the "done" path always ends in no
+         * slash. We always keep an O_PATH fd to the component we are currently processing, thus keeping lookup races
+         * at a minimum.
+         *
+         * Suggested usage: whenever you want to canonicalize a path, use this function. Pass the absolute path you got
+         * as-is: fully qualified and relative to your host's root. Optionally, specify the root parameter to tell this
+         * function what to do when encountering a symlink with an absolute path as directory: prefix it by the
+         * specified path.
+         *
+         * There are three ways to invoke this function:
+         *
+         * 1. Without CHASE_STEP or CHASE_OPEN: in this case the path is resolved and the normalized path is returned
+         *    in `ret`. The return value is < 0 on error. If CHASE_NONEXISTENT is also set 0 is returned if the file
+         *    doesn't exist, > 0 otherwise. If CHASE_NONEXISTENT is not set >= 0 is returned if the destination was
+         *    found, -ENOENT if it doesn't.
+         *
+         * 2. With CHASE_OPEN: in this case the destination is opened after chasing it as O_PATH and this file
+         *    descriptor is returned as return value. This is useful to open files relative to some root
+         *    directory. Note that the returned O_PATH file descriptors must be converted into a regular one (using
+         *    fd_reopen() or such) before it can be used for reading/writing. CHASE_OPEN may not be combined with
+         *    CHASE_NONEXISTENT.
+         *
+         * 3. With CHASE_STEP: in this case only a single step of the normalization is executed, i.e. only the first
+         *    symlink or ".." component of the path is resolved, and the resulting path is returned. This is useful if
+         *    a caller wants to trace the a path through the file system verbosely. Returns < 0 on error, > 0 if the
+         *    path is fully normalized, and == 0 for each normalization step. This may be combined with
+         *    CHASE_NONEXISTENT, in which case 1 is returned when a component is not found.
+         *
+         * 4. With CHASE_SAFE: in this case the path must not contain unsafe transitions, i.e. transitions from
+         *    unprivileged to privileged files or directories. In such cases the return value is -ENOLINK. If
+         *    CHASE_WARN is also set a warning describing the unsafe transition is emitted.
+         *
+         * 5. With CHASE_NO_AUTOFS: in this case if an autofs mount point is encountered, the path normalization is
+         *    aborted and -EREMOTE is returned. If CHASE_WARN is also set a warning showing the path of the mount point
+         *    is emitted.
+         *
+         * */
+
+        /* A root directory of "/" or "" is identical to none */
+        if (empty_or_root(original_root))
+                original_root = NULL;
+
+        if (!original_root && !ret && (flags & (CHASE_NONEXISTENT|CHASE_NO_AUTOFS|CHASE_SAFE|CHASE_OPEN|CHASE_STEP)) == CHASE_OPEN) {
+                /* Shortcut the CHASE_OPEN case if the caller isn't interested in the actual path and has no root set
+                 * and doesn't care about any of the other special features we provide either. */
+                r = open(path, O_PATH|O_CLOEXEC|((flags & CHASE_NOFOLLOW) ? O_NOFOLLOW : 0));
+                if (r < 0)
+                        return -errno;
+
+                return r;
+        }
+
+        if (original_root) {
+                r = path_make_absolute_cwd(original_root, &root);
+                if (r < 0)
+                        return r;
+
+                if (flags & CHASE_PREFIX_ROOT) {
+
+                        /* We don't support relative paths in combination with a root directory */
+                        if (!path_is_absolute(path))
+                                return -EINVAL;
+
+                        path = prefix_roota(root, path);
+                }
+        }
+
+        r = path_make_absolute_cwd(path, &buffer);
+        if (r < 0)
+                return r;
+
+        fd = open("/", O_CLOEXEC|O_NOFOLLOW|O_PATH);
+        if (fd < 0)
+                return -errno;
+
+        if (flags & CHASE_SAFE) {
+                if (fstat(fd, &previous_stat) < 0)
+                        return -errno;
+        }
+
+        todo = buffer;
+        for (;;) {
+                _cleanup_free_ char *first = NULL;
+                _cleanup_close_ int child = -1;
+                struct stat st;
+                size_t n, m;
+
+                /* Determine length of first component in the path */
+                n = strspn(todo, "/");                  /* The slashes */
+                m = n + strcspn(todo + n, "/");         /* The entire length of the component */
+
+                /* Extract the first component. */
+                first = strndup(todo, m);
+                if (!first)
+                        return -ENOMEM;
+
+                todo += m;
+
+                /* Empty? Then we reached the end. */
+                if (isempty(first))
+                        break;
+
+                /* Just a single slash? Then we reached the end. */
+                if (path_equal(first, "/")) {
+                        /* Preserve the trailing slash */
+
+                        if (flags & CHASE_TRAIL_SLASH)
+                                if (!strextend(&done, "/", NULL))
+                                        return -ENOMEM;
+
+                        break;
+                }
+
+                /* Just a dot? Then let's eat this up. */
+                if (path_equal(first, "/."))
+                        continue;
+
+                /* Two dots? Then chop off the last bit of what we already found out. */
+                if (path_equal(first, "/..")) {
+                        _cleanup_free_ char *parent = NULL;
+                        _cleanup_close_ int fd_parent = -1;
+
+                        /* If we already are at the top, then going up will not change anything. This is in-line with
+                         * how the kernel handles this. */
+                        if (empty_or_root(done))
+                                continue;
+
+                        parent = dirname_malloc(done);
+                        if (!parent)
+                                return -ENOMEM;
+
+                        /* Don't allow this to leave the root dir.  */
+                        if (root &&
+                            path_startswith(done, root) &&
+                            !path_startswith(parent, root))
+                                continue;
+
+                        free_and_replace(done, parent);
+
+                        if (flags & CHASE_STEP)
+                                goto chased_one;
+
+                        fd_parent = openat(fd, "..", O_CLOEXEC|O_NOFOLLOW|O_PATH);
+                        if (fd_parent < 0)
+                                return -errno;
+
+                        if (flags & CHASE_SAFE) {
+                                if (fstat(fd_parent, &st) < 0)
+                                        return -errno;
+
+                                if (unsafe_transition(&previous_stat, &st))
+                                        return log_unsafe_transition(fd, fd_parent, path, flags);
+
+                                previous_stat = st;
+                        }
+
+                        safe_close(fd);
+                        fd = TAKE_FD(fd_parent);
+
+                        continue;
+                }
+
+                /* Otherwise let's see what this is. */
+                child = openat(fd, first + n, O_CLOEXEC|O_NOFOLLOW|O_PATH);
+                if (child < 0) {
+
+                        if (errno == ENOENT &&
+                            (flags & CHASE_NONEXISTENT) &&
+                            (isempty(todo) || path_is_normalized(todo))) {
+
+                                /* If CHASE_NONEXISTENT is set, and the path does not exist, then that's OK, return
+                                 * what we got so far. But don't allow this if the remaining path contains "../ or "./"
+                                 * or something else weird. */
+
+                                /* If done is "/", as first also contains slash at the head, then remove this redundant slash. */
+                                if (streq_ptr(done, "/"))
+                                        *done = '\0';
+
+                                if (!strextend(&done, first, todo, NULL))
+                                        return -ENOMEM;
+
+                                exists = false;
+                                break;
+                        }
+
+                        return -errno;
+                }
+
+                if (fstat(child, &st) < 0)
+                        return -errno;
+                if ((flags & CHASE_SAFE) &&
+                    unsafe_transition(&previous_stat, &st))
+                        return log_unsafe_transition(fd, child, path, flags);
+
+                previous_stat = st;
+
+                if ((flags & CHASE_NO_AUTOFS) &&
+                    fd_is_fs_type(child, AUTOFS_SUPER_MAGIC) > 0)
+                        return log_autofs_mount_point(child, path, flags);
+
+                if (S_ISLNK(st.st_mode) && !((flags & CHASE_NOFOLLOW) && isempty(todo))) {
+                        char *joined;
+
+                        _cleanup_free_ char *destination = NULL;
+
+                        /* This is a symlink, in this case read the destination. But let's make sure we don't follow
+                         * symlinks without bounds. */
+                        if (--max_follow <= 0)
+                                return -ELOOP;
+
+                        r = readlinkat_malloc(fd, first + n, &destination);
+                        if (r < 0)
+                                return r;
+                        if (isempty(destination))
+                                return -EINVAL;
+
+                        if (path_is_absolute(destination)) {
+
+                                /* An absolute destination. Start the loop from the beginning, but use the root
+                                 * directory as base. */
+
+                                safe_close(fd);
+                                fd = open(root ?: "/", O_CLOEXEC|O_NOFOLLOW|O_PATH);
+                                if (fd < 0)
+                                        return -errno;
+
+                                if (flags & CHASE_SAFE) {
+                                        if (fstat(fd, &st) < 0)
+                                                return -errno;
+
+                                        if (unsafe_transition(&previous_stat, &st))
+                                                return log_unsafe_transition(child, fd, path, flags);
+
+                                        previous_stat = st;
+                                }
+
+                                free(done);
+
+                                /* Note that we do not revalidate the root, we take it as is. */
+                                if (isempty(root))
+                                        done = NULL;
+                                else {
+                                        done = strdup(root);
+                                        if (!done)
+                                                return -ENOMEM;
+                                }
+
+                                /* Prefix what's left to do with what we just read, and start the loop again, but
+                                 * remain in the current directory. */
+                                joined = strjoin(destination, todo);
+                        } else
+                                joined = strjoin("/", destination, todo);
+                        if (!joined)
+                                return -ENOMEM;
+
+                        free(buffer);
+                        todo = buffer = joined;
+
+                        if (flags & CHASE_STEP)
+                                goto chased_one;
+
+                        continue;
+                }
+
+                /* If this is not a symlink, then let's just add the name we read to what we already verified. */
+                if (!done)
+                        done = TAKE_PTR(first);
+                else {
+                        /* If done is "/", as first also contains slash at the head, then remove this redundant slash. */
+                        if (streq(done, "/"))
+                                *done = '\0';
+
+                        if (!strextend(&done, first, NULL))
+                                return -ENOMEM;
+                }
+
+                /* And iterate again, but go one directory further down. */
+                safe_close(fd);
+                fd = TAKE_FD(child);
+        }
+
+        if (!done) {
+                /* Special case, turn the empty string into "/", to indicate the root directory. */
+                done = strdup("/");
+                if (!done)
+                        return -ENOMEM;
+        }
+
+        if (ret)
+                *ret = TAKE_PTR(done);
+
+        if (flags & CHASE_OPEN) {
+                /* Return the O_PATH fd we currently are looking to the caller. It can translate it to a proper fd by
+                 * opening /proc/self/fd/xyz. */
+
+                assert(fd >= 0);
+                return TAKE_FD(fd);
+        }
+
+        if (flags & CHASE_STEP)
+                return 1;
+
+        return exists;
+
+chased_one:
+        if (ret) {
+                char *c;
+
+                c = strjoin(strempty(done), todo);
+                if (!c)
+                        return -ENOMEM;
+
+                *ret = c;
+        }
+
+        return 0;
+}
+
+int chase_symlinks_and_open(
+                const char *path,
+                const char *root,
+                unsigned chase_flags,
+                int open_flags,
+                char **ret_path) {
+
+        _cleanup_close_ int path_fd = -1;
+        _cleanup_free_ char *p = NULL;
+        int r;
+
+        if (chase_flags & CHASE_NONEXISTENT)
+                return -EINVAL;
+
+        if (empty_or_root(root) && !ret_path && (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE)) == 0) {
+                /* Shortcut this call if none of the special features of this call are requested */
+                r = open(path, open_flags);
+                if (r < 0)
+                        return -errno;
+
+                return r;
+        }
+
+        path_fd = chase_symlinks(path, root, chase_flags|CHASE_OPEN, ret_path ? &p : NULL);
+        if (path_fd < 0)
+                return path_fd;
+
+        r = fd_reopen(path_fd, open_flags);
+        if (r < 0)
+                return r;
+
+        if (ret_path)
+                *ret_path = TAKE_PTR(p);
+
+        return r;
+}
+
+int chase_symlinks_and_opendir(
+                const char *path,
+                const char *root,
+                unsigned chase_flags,
+                char **ret_path,
+                DIR **ret_dir) {
+
+        char procfs_path[STRLEN("/proc/self/fd/") + DECIMAL_STR_MAX(int)];
+        _cleanup_close_ int path_fd = -1;
+        _cleanup_free_ char *p = NULL;
+        DIR *d;
+
+        if (!ret_dir)
+                return -EINVAL;
+        if (chase_flags & CHASE_NONEXISTENT)
+                return -EINVAL;
+
+        if (empty_or_root(root) && !ret_path && (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE)) == 0) {
+                /* Shortcut this call if none of the special features of this call are requested */
+                d = opendir(path);
+                if (!d)
+                        return -errno;
+
+                *ret_dir = d;
+                return 0;
+        }
+
+        path_fd = chase_symlinks(path, root, chase_flags|CHASE_OPEN, ret_path ? &p : NULL);
+        if (path_fd < 0)
+                return path_fd;
+
+        xsprintf(procfs_path, "/proc/self/fd/%i", path_fd);
+        d = opendir(procfs_path);
+        if (!d)
+                return -errno;
+
+        if (ret_path)
+                *ret_path = TAKE_PTR(p);
+
+        *ret_dir = d;
+        return 0;
+}
+
+int chase_symlinks_and_stat(
+                const char *path,
+                const char *root,
+                unsigned chase_flags,
+                char **ret_path,
+                struct stat *ret_stat) {
+
+        _cleanup_close_ int path_fd = -1;
+        _cleanup_free_ char *p = NULL;
+
+        assert(path);
+        assert(ret_stat);
+
+        if (chase_flags & CHASE_NONEXISTENT)
+                return -EINVAL;
+
+        if (empty_or_root(root) && !ret_path && (chase_flags & (CHASE_NO_AUTOFS|CHASE_SAFE)) == 0) {
+                /* Shortcut this call if none of the special features of this call are requested */
+                if (stat(path, ret_stat) < 0)
+                        return -errno;
+
+                return 1;
+        }
+
+        path_fd = chase_symlinks(path, root, chase_flags|CHASE_OPEN, ret_path ? &p : NULL);
+        if (path_fd < 0)
+                return path_fd;
+
+        if (fstat(path_fd, ret_stat) < 0)
+                return -errno;
+
+        if (ret_path)
+                *ret_path = TAKE_PTR(p);
+
+        if (chase_flags & CHASE_OPEN)
+                return TAKE_FD(path_fd);
+
+        return 1;
+}
+
+int access_fd(int fd, int mode) {
+        char p[STRLEN("/proc/self/fd/") + DECIMAL_STR_MAX(fd) + 1];
+        int r;
+
+        /* Like access() but operates on an already open fd */
+
+        xsprintf(p, "/proc/self/fd/%i", fd);
+        r = access(p, mode);
+        if (r < 0)
+                return -errno;
+
+        return r;
+}
+
+void unlink_tempfilep(char (*p)[]) {
+        /* If the file is created with mkstemp(), it will (almost always)
+         * change the suffix. Treat this as a sign that the file was
+         * successfully created. We ignore both the rare case where the
+         * original suffix is used and unlink failures. */
+        if (!endswith(*p, ".XXXXXX"))
+                (void) unlink_noerrno(*p);
+}
+
+int unlinkat_deallocate(int fd, const char *name, int flags) {
+        _cleanup_close_ int truncate_fd = -1;
+        struct stat st;
+        off_t l, bs;
+
+        /* Operates like unlinkat() but also deallocates the file contents if it is a regular file and there's no other
+         * link to it. This is useful to ensure that other processes that might have the file open for reading won't be
+         * able to keep the data pinned on disk forever. This call is particular useful whenever we execute clean-up
+         * jobs ("vacuuming"), where we want to make sure the data is really gone and the disk space released and
+         * returned to the free pool.
+         *
+         * Deallocation is preferably done by FALLOC_FL_PUNCH_HOLE|FALLOC_FL_KEEP_SIZE (👊) if supported, which means
+         * the file won't change size. That's a good thing since we shouldn't needlessly trigger SIGBUS in other
+         * programs that have mmap()ed the file. (The assumption here is that changing file contents to all zeroes
+         * underneath those programs is the better choice than simply triggering SIGBUS in them which truncation does.)
+         * However if hole punching is not implemented in the kernel or file system we'll fall back to normal file
+         * truncation (🔪), as our goal of deallocating the data space trumps our goal of being nice to readers (💐).
+         *
+         * Note that we attempt deallocation, but failure to succeed with that is not considered fatal, as long as the
+         * primary job – to delete the file – is accomplished. */
+
+        if ((flags & AT_REMOVEDIR) == 0) {
+                truncate_fd = openat(fd, name, O_WRONLY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW|O_NONBLOCK);
+                if (truncate_fd < 0) {
+
+                        /* If this failed because the file doesn't exist propagate the error right-away. Also,
+                         * AT_REMOVEDIR wasn't set, and we tried to open the file for writing, which means EISDIR is
+                         * returned when this is a directory but we are not supposed to delete those, hence propagate
+                         * the error right-away too. */
+                        if (IN_SET(errno, ENOENT, EISDIR))
+                                return -errno;
+
+                        if (errno != ELOOP) /* don't complain if this is a symlink */
+                                log_debug_errno(errno, "Failed to open file '%s' for deallocation, ignoring: %m", name);
+                }
+        }
+
+        if (unlinkat(fd, name, flags) < 0)
+                return -errno;
+
+        if (truncate_fd < 0) /* Don't have a file handle, can't do more ☹️ */
+                return 0;
+
+        if (fstat(truncate_fd, &st) < 0) {
+                log_debug_errno(errno, "Failed to stat file '%s' for deallocation, ignoring: %m", name);
+                return 0;
+        }
+
+        if (!S_ISREG(st.st_mode) || st.st_blocks == 0 || st.st_nlink > 0)
+                return 0;
+
+        /* If this is a regular file, it actually took up space on disk and there are no other links it's time to
+         * punch-hole/truncate this to release the disk space. */
+
+        bs = MAX(st.st_blksize, 512);
+        l = DIV_ROUND_UP(st.st_size, bs) * bs; /* Round up to next block size */
+
+        if (fallocate(truncate_fd, FALLOC_FL_PUNCH_HOLE|FALLOC_FL_KEEP_SIZE, 0, l) >= 0)
+                return 0; /* Successfully punched a hole! 😊 */
+
+        /* Fall back to truncation */
+        if (ftruncate(truncate_fd, 0) < 0) {
+                log_debug_errno(errno, "Failed to truncate file to 0, ignoring: %m");
+                return 0;
+        }
+
+        return 0;
+}
+
+int fsync_directory_of_file(int fd) {
+        _cleanup_free_ char *path = NULL;
+        _cleanup_close_ int dfd = -1;
+        int r;
+
+        r = fd_verify_regular(fd);
+        if (r < 0)
+                return r;
+
+        r = fd_get_path(fd, &path);
+        if (r < 0) {
+                log_debug_errno(r, "Failed to query /proc/self/fd/%d%s: %m",
+                                fd,
+                                r == -EOPNOTSUPP ? ", ignoring" : "");
+
+                if (r == -EOPNOTSUPP)
+                        /* If /proc is not available, we're most likely running in some
+                         * chroot environment, and syncing the directory is not very
+                         * important in that case. Let's just silently do nothing. */
+                        return 0;
+
+                return r;
+        }
+
+        if (!path_is_absolute(path))
+                return -EINVAL;
+
+        dfd = open_parent(path, O_CLOEXEC, 0);
+        if (dfd < 0)
+                return dfd;
+
+        if (fsync(dfd) < 0)
+                return -errno;
+
+        return 0;
+}
+
+int fsync_path_at(int at_fd, const char *path) {
+        _cleanup_close_ int opened_fd = -1;
+        int fd;
+
+        if (isempty(path)) {
+                if (at_fd == AT_FDCWD) {
+                        opened_fd = open(".", O_RDONLY|O_DIRECTORY|O_CLOEXEC);
+                        if (opened_fd < 0)
+                                return -errno;
+
+                        fd = opened_fd;
+                } else
+                        fd = at_fd;
+        } else {
+
+                opened_fd = openat(at_fd, path, O_RDONLY|O_CLOEXEC);
+                if (opened_fd < 0)
+                        return -errno;
+
+                fd = opened_fd;
+        }
+
+        if (fsync(fd) < 0)
+                return -errno;
+
+        return 0;
+}
+
+int open_parent(const char *path, int flags, mode_t mode) {
+        _cleanup_free_ char *parent = NULL;
+        int fd;
+
+        if (isempty(path))
+                return -EINVAL;
+        if (path_equal(path, "/")) /* requesting the parent of the root dir is fishy, let's prohibit that */
+                return -EINVAL;
+
+        parent = dirname_malloc(path);
+        if (!parent)
+                return -ENOMEM;
+
+        /* Let's insist on O_DIRECTORY since the parent of a file or directory is a directory. Except if we open an
+         * O_TMPFILE file, because in that case we are actually create a regular file below the parent directory. */
+
+        if ((flags & O_PATH) == O_PATH)
+                flags |= O_DIRECTORY;
+        else if ((flags & O_TMPFILE) != O_TMPFILE)
+                flags |= O_DIRECTORY|O_RDONLY;
+
+        fd = open(parent, flags, mode);
+        if (fd < 0)
+                return -errno;
+
+        return fd;
+}