Adding upstream version 255.4.upstream/255.4

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

1 files changed, 1060 insertions, 0 deletions

diff --git a/src/basic/user-util.c b/src/basic/user-util.c
new file mode 100644
index 0000000..9e6926b
--- /dev/null
+++ b/src/basic/user-util.c
@@ -0,0 +1,1060 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/file.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <utmp.h>
+
+#include "sd-messages.h"
+
+#include "alloc-util.h"
+#include "chase.h"
+#include "errno-util.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "format-util.h"
+#include "lock-util.h"
+#include "macro.h"
+#include "mkdir.h"
+#include "parse-util.h"
+#include "path-util.h"
+#include "random-util.h"
+#include "string-util.h"
+#include "strv.h"
+#include "user-util.h"
+#include "utf8.h"
+
+bool uid_is_valid(uid_t uid) {
+
+        /* Also see POSIX IEEE Std 1003.1-2008, 2016 Edition, 3.436. */
+
+        /* Some libc APIs use UID_INVALID as special placeholder */
+        if (uid == (uid_t) UINT32_C(0xFFFFFFFF))
+                return false;
+
+        /* A long time ago UIDs where 16 bit, hence explicitly avoid the 16-bit -1 too */
+        if (uid == (uid_t) UINT32_C(0xFFFF))
+                return false;
+
+        return true;
+}
+
+int parse_uid(const char *s, uid_t *ret) {
+        uint32_t uid = 0;
+        int r;
+
+        assert(s);
+
+        assert_cc(sizeof(uid_t) == sizeof(uint32_t));
+
+        /* We are very strict when parsing UIDs, and prohibit +/- as prefix, leading zero as prefix, and
+         * whitespace. We do this, since this call is often used in a context where we parse things as UID
+         * first, and if that doesn't work we fall back to NSS. Thus we really want to make sure that UIDs
+         * are parsed as UIDs only if they really really look like UIDs. */
+        r = safe_atou32_full(s, 10
+                             | SAFE_ATO_REFUSE_PLUS_MINUS
+                             | SAFE_ATO_REFUSE_LEADING_ZERO
+                             | SAFE_ATO_REFUSE_LEADING_WHITESPACE, &uid);
+        if (r < 0)
+                return r;
+
+        if (!uid_is_valid(uid))
+                return -ENXIO; /* we return ENXIO instead of EINVAL
+                                * here, to make it easy to distinguish
+                                * invalid numeric uids from invalid
+                                * strings. */
+
+        if (ret)
+                *ret = uid;
+
+        return 0;
+}
+
+int parse_uid_range(const char *s, uid_t *ret_lower, uid_t *ret_upper) {
+        _cleanup_free_ char *word = NULL;
+        uid_t l, u;
+        int r;
+
+        assert(s);
+        assert(ret_lower);
+        assert(ret_upper);
+
+        r = extract_first_word(&s, &word, "-", EXTRACT_DONT_COALESCE_SEPARATORS);
+        if (r < 0)
+                return r;
+        if (r == 0)
+                return -EINVAL;
+
+        r = parse_uid(word, &l);
+        if (r < 0)
+                return r;
+
+        /* Check for the upper bound and extract it if needed */
+        if (!s)
+                /* Single number with no dash. */
+                u = l;
+        else if (!*s)
+                /* Trailing dash is an error. */
+                return -EINVAL;
+        else {
+                r = parse_uid(s, &u);
+                if (r < 0)
+                        return r;
+
+                if (l > u)
+                        return -EINVAL;
+        }
+
+        *ret_lower = l;
+        *ret_upper = u;
+        return 0;
+}
+
+char* getlogname_malloc(void) {
+        uid_t uid;
+        struct stat st;
+
+        if (isatty(STDIN_FILENO) && fstat(STDIN_FILENO, &st) >= 0)
+                uid = st.st_uid;
+        else
+                uid = getuid();
+
+        return uid_to_name(uid);
+}
+
+char* getusername_malloc(void) {
+        const char *e;
+
+        e = secure_getenv("USER");
+        if (e)
+                return strdup(e);
+
+        return uid_to_name(getuid());
+}
+
+bool is_nologin_shell(const char *shell) {
+        return PATH_IN_SET(shell,
+                           /* 'nologin' is the friendliest way to disable logins for a user account. It prints a nice
+                            * message and exits. Different distributions place the binary at different places though,
+                            * hence let's list them all. */
+                           "/bin/nologin",
+                           "/sbin/nologin",
+                           "/usr/bin/nologin",
+                           "/usr/sbin/nologin",
+                           /* 'true' and 'false' work too for the same purpose, but are less friendly as they don't do
+                            * any message printing. Different distributions place the binary at various places but at
+                            * least not in the 'sbin' directory. */
+                           "/bin/false",
+                           "/usr/bin/false",
+                           "/bin/true",
+                           "/usr/bin/true");
+}
+
+const char* default_root_shell_at(int rfd) {
+        /* We want to use the preferred shell, i.e. DEFAULT_USER_SHELL, which usually
+         * will be /bin/bash. Fall back to /bin/sh if DEFAULT_USER_SHELL is not found,
+         * or any access errors. */
+
+        assert(rfd >= 0 || rfd == AT_FDCWD);
+
+        int r = chaseat(rfd, DEFAULT_USER_SHELL, CHASE_AT_RESOLVE_IN_ROOT, NULL, NULL);
+        if (r < 0 && r != -ENOENT)
+                log_debug_errno(r, "Failed to look up shell '%s': %m", DEFAULT_USER_SHELL);
+        if (r > 0)
+                return DEFAULT_USER_SHELL;
+
+        return "/bin/sh";
+}
+
+const char* default_root_shell(const char *root) {
+        _cleanup_close_ int rfd = -EBADF;
+
+        rfd = open(empty_to_root(root), O_CLOEXEC | O_DIRECTORY | O_PATH);
+        if (rfd < 0)
+                return "/bin/sh";
+
+        return default_root_shell_at(rfd);
+}
+
+static int synthesize_user_creds(
+                const char **username,
+                uid_t *uid, gid_t *gid,
+                const char **home,
+                const char **shell,
+                UserCredsFlags flags) {
+
+        /* We enforce some special rules for uid=0 and uid=65534: in order to avoid NSS lookups for root we hardcode
+         * their user record data. */
+
+        if (STR_IN_SET(*username, "root", "0")) {
+                *username = "root";
+
+                if (uid)
+                        *uid = 0;
+                if (gid)
+                        *gid = 0;
+
+                if (home)
+                        *home = "/root";
+
+                if (shell)
+                        *shell = default_root_shell(NULL);
+
+                return 0;
+        }
+
+        if (STR_IN_SET(*username, NOBODY_USER_NAME, "65534") &&
+            synthesize_nobody()) {
+                *username = NOBODY_USER_NAME;
+
+                if (uid)
+                        *uid = UID_NOBODY;
+                if (gid)
+                        *gid = GID_NOBODY;
+
+                if (home)
+                        *home = FLAGS_SET(flags, USER_CREDS_CLEAN) ? NULL : "/";
+
+                if (shell)
+                        *shell = FLAGS_SET(flags, USER_CREDS_CLEAN) ? NULL : NOLOGIN;
+
+                return 0;
+        }
+
+        return -ENOMEDIUM;
+}
+
+int get_user_creds(
+                const char **username,
+                uid_t *uid, gid_t *gid,
+                const char **home,
+                const char **shell,
+                UserCredsFlags flags) {
+
+        uid_t u = UID_INVALID;
+        struct passwd *p;
+        int r;
+
+        assert(username);
+        assert(*username);
+
+        if (!FLAGS_SET(flags, USER_CREDS_PREFER_NSS) ||
+            (!home && !shell)) {
+
+                /* So here's the deal: normally, we'll try to synthesize all records we can synthesize, and override
+                 * the user database with that. However, if the user specifies USER_CREDS_PREFER_NSS then the
+                 * user database will override the synthetic records instead — except if the user is only interested in
+                 * the UID and/or GID (but not the home directory, or the shell), in which case we'll always override
+                 * the user database (i.e. the USER_CREDS_PREFER_NSS flag has no effect in this case). Why?
+                 * Simply because there are valid usecase where the user might change the home directory or the shell
+                 * of the relevant users, but changing the UID/GID mappings for them is something we explicitly don't
+                 * support. */
+
+                r = synthesize_user_creds(username, uid, gid, home, shell, flags);
+                if (r >= 0)
+                        return 0;
+                if (r != -ENOMEDIUM) /* not a username we can synthesize */
+                        return r;
+        }
+
+        if (parse_uid(*username, &u) >= 0) {
+                errno = 0;
+                p = getpwuid(u);
+
+                /* If there are multiple users with the same id, make sure to leave $USER to the configured value
+                 * instead of the first occurrence in the database. However if the uid was configured by a numeric uid,
+                 * then let's pick the real username from /etc/passwd. */
+                if (p)
+                        *username = p->pw_name;
+                else if (FLAGS_SET(flags, USER_CREDS_ALLOW_MISSING) && !gid && !home && !shell) {
+
+                        /* If the specified user is a numeric UID and it isn't in the user database, and the caller
+                         * passed USER_CREDS_ALLOW_MISSING and was only interested in the UID, then just return that
+                         * and don't complain. */
+
+                        if (uid)
+                                *uid = u;
+
+                        return 0;
+                }
+        } else {
+                errno = 0;
+                p = getpwnam(*username);
+        }
+        if (!p) {
+                /* getpwnam() may fail with ENOENT if /etc/passwd is missing.
+                 * For us that is equivalent to the name not being defined. */
+                r = IN_SET(errno, 0, ENOENT) ? -ESRCH : -errno;
+
+                /* If the user requested that we only synthesize as fallback, do so now */
+                if (FLAGS_SET(flags, USER_CREDS_PREFER_NSS)) {
+                        if (synthesize_user_creds(username, uid, gid, home, shell, flags) >= 0)
+                                return 0;
+                }
+
+                return r;
+        }
+
+        if (uid) {
+                if (!uid_is_valid(p->pw_uid))
+                        return -EBADMSG;
+
+                *uid = p->pw_uid;
+        }
+
+        if (gid) {
+                if (!gid_is_valid(p->pw_gid))
+                        return -EBADMSG;
+
+                *gid = p->pw_gid;
+        }
+
+        if (home) {
+                if (FLAGS_SET(flags, USER_CREDS_CLEAN) &&
+                    (empty_or_root(p->pw_dir) ||
+                     !path_is_valid(p->pw_dir) ||
+                     !path_is_absolute(p->pw_dir)))
+                        *home = NULL; /* Note: we don't insist on normalized paths, since there are setups that have /./ in the path */
+                else
+                        *home = p->pw_dir;
+        }
+
+        if (shell) {
+                if (FLAGS_SET(flags, USER_CREDS_CLEAN) &&
+                    (isempty(p->pw_shell) ||
+                     !path_is_valid(p->pw_shell) ||
+                     !path_is_absolute(p->pw_shell) ||
+                     is_nologin_shell(p->pw_shell)))
+                        *shell = NULL;
+                else
+                        *shell = p->pw_shell;
+        }
+
+        return 0;
+}
+
+int get_group_creds(const char **groupname, gid_t *gid, UserCredsFlags flags) {
+        struct group *g;
+        gid_t id;
+
+        assert(groupname);
+
+        /* We enforce some special rules for gid=0: in order to avoid NSS lookups for root we hardcode its data. */
+
+        if (STR_IN_SET(*groupname, "root", "0")) {
+                *groupname = "root";
+
+                if (gid)
+                        *gid = 0;
+
+                return 0;
+        }
+
+        if (STR_IN_SET(*groupname, NOBODY_GROUP_NAME, "65534") &&
+            synthesize_nobody()) {
+                *groupname = NOBODY_GROUP_NAME;
+
+                if (gid)
+                        *gid = GID_NOBODY;
+
+                return 0;
+        }
+
+        if (parse_gid(*groupname, &id) >= 0) {
+                errno = 0;
+                g = getgrgid(id);
+
+                if (g)
+                        *groupname = g->gr_name;
+                else if (FLAGS_SET(flags, USER_CREDS_ALLOW_MISSING)) {
+                        if (gid)
+                                *gid = id;
+
+                        return 0;
+                }
+        } else {
+                errno = 0;
+                g = getgrnam(*groupname);
+        }
+
+        if (!g)
+                /* getgrnam() may fail with ENOENT if /etc/group is missing.
+                 * For us that is equivalent to the name not being defined. */
+                return IN_SET(errno, 0, ENOENT) ? -ESRCH : -errno;
+
+        if (gid) {
+                if (!gid_is_valid(g->gr_gid))
+                        return -EBADMSG;
+
+                *gid = g->gr_gid;
+        }
+
+        return 0;
+}
+
+char* uid_to_name(uid_t uid) {
+        char *ret;
+        int r;
+
+        /* Shortcut things to avoid NSS lookups */
+        if (uid == 0)
+                return strdup("root");
+        if (uid == UID_NOBODY && synthesize_nobody())
+                return strdup(NOBODY_USER_NAME);
+
+        if (uid_is_valid(uid)) {
+                long bufsize;
+
+                bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
+                if (bufsize <= 0)
+                        bufsize = 4096;
+
+                for (;;) {
+                        struct passwd pwbuf, *pw = NULL;
+                        _cleanup_free_ char *buf = NULL;
+
+                        buf = malloc(bufsize);
+                        if (!buf)
+                                return NULL;
+
+                        r = getpwuid_r(uid, &pwbuf, buf, (size_t) bufsize, &pw);
+                        if (r == 0 && pw)
+                                return strdup(pw->pw_name);
+                        if (r != ERANGE)
+                                break;
+
+                        if (bufsize > LONG_MAX/2) /* overflow check */
+                                return NULL;
+
+                        bufsize *= 2;
+                }
+        }
+
+        if (asprintf(&ret, UID_FMT, uid) < 0)
+                return NULL;
+
+        return ret;
+}
+
+char* gid_to_name(gid_t gid) {
+        char *ret;
+        int r;
+
+        if (gid == 0)
+                return strdup("root");
+        if (gid == GID_NOBODY && synthesize_nobody())
+                return strdup(NOBODY_GROUP_NAME);
+
+        if (gid_is_valid(gid)) {
+                long bufsize;
+
+                bufsize = sysconf(_SC_GETGR_R_SIZE_MAX);
+                if (bufsize <= 0)
+                        bufsize = 4096;
+
+                for (;;) {
+                        struct group grbuf, *gr = NULL;
+                        _cleanup_free_ char *buf = NULL;
+
+                        buf = malloc(bufsize);
+                        if (!buf)
+                                return NULL;
+
+                        r = getgrgid_r(gid, &grbuf, buf, (size_t) bufsize, &gr);
+                        if (r == 0 && gr)
+                                return strdup(gr->gr_name);
+                        if (r != ERANGE)
+                                break;
+
+                        if (bufsize > LONG_MAX/2) /* overflow check */
+                                return NULL;
+
+                        bufsize *= 2;
+                }
+        }
+
+        if (asprintf(&ret, GID_FMT, gid) < 0)
+                return NULL;
+
+        return ret;
+}
+
+static bool gid_list_has(const gid_t *list, size_t size, gid_t val) {
+        for (size_t i = 0; i < size; i++)
+                if (list[i] == val)
+                        return true;
+        return false;
+}
+
+int in_gid(gid_t gid) {
+        _cleanup_free_ gid_t *gids = NULL;
+        int ngroups;
+
+        if (getgid() == gid)
+                return 1;
+
+        if (getegid() == gid)
+                return 1;
+
+        if (!gid_is_valid(gid))
+                return -EINVAL;
+
+        ngroups = getgroups_alloc(&gids);
+        if (ngroups < 0)
+                return ngroups;
+
+        return gid_list_has(gids, ngroups, gid);
+}
+
+int in_group(const char *name) {
+        int r;
+        gid_t gid;
+
+        r = get_group_creds(&name, &gid, 0);
+        if (r < 0)
+                return r;
+
+        return in_gid(gid);
+}
+
+int merge_gid_lists(const gid_t *list1, size_t size1, const gid_t *list2, size_t size2, gid_t **ret) {
+        size_t nresult = 0;
+        assert(ret);
+
+        if (size2 > INT_MAX - size1)
+                return -ENOBUFS;
+
+        gid_t *buf = new(gid_t, size1 + size2);
+        if (!buf)
+                return -ENOMEM;
+
+        /* Duplicates need to be skipped on merging, otherwise they'll be passed on and stored in the kernel. */
+        for (size_t i = 0; i < size1; i++)
+                if (!gid_list_has(buf, nresult, list1[i]))
+                        buf[nresult++] = list1[i];
+        for (size_t i = 0; i < size2; i++)
+                if (!gid_list_has(buf, nresult, list2[i]))
+                        buf[nresult++] = list2[i];
+        *ret = buf;
+        return (int)nresult;
+}
+
+int getgroups_alloc(gid_t** gids) {
+        gid_t *allocated;
+        _cleanup_free_  gid_t *p = NULL;
+        int ngroups = 8;
+        unsigned attempt = 0;
+
+        allocated = new(gid_t, ngroups);
+        if (!allocated)
+                return -ENOMEM;
+        p = allocated;
+
+        for (;;) {
+                ngroups = getgroups(ngroups, p);
+                if (ngroups >= 0)
+                        break;
+                if (errno != EINVAL)
+                        return -errno;
+
+                /* Give up eventually */
+                if (attempt++ > 10)
+                        return -EINVAL;
+
+                /* Get actual size needed, and size the array explicitly. Note that this is potentially racy
+                 * to use (in multi-threaded programs), hence let's call this in a loop. */
+                ngroups = getgroups(0, NULL);
+                if (ngroups < 0)
+                        return -errno;
+                if (ngroups == 0)
+                        return false;
+
+                free(allocated);
+
+                p = allocated = new(gid_t, ngroups);
+                if (!allocated)
+                        return -ENOMEM;
+        }
+
+        *gids = TAKE_PTR(p);
+        return ngroups;
+}
+
+int get_home_dir(char **ret) {
+        struct passwd *p;
+        const char *e;
+        uid_t u;
+
+        assert(ret);
+
+        /* Take the user specified one */
+        e = secure_getenv("HOME");
+        if (e && path_is_valid(e) && path_is_absolute(e))
+                goto found;
+
+        /* Hardcode home directory for root and nobody to avoid NSS */
+        u = getuid();
+        if (u == 0) {
+                e = "/root";
+                goto found;
+        }
+
+        if (u == UID_NOBODY && synthesize_nobody()) {
+                e = "/";
+                goto found;
+        }
+
+        /* Check the database... */
+        errno = 0;
+        p = getpwuid(u);
+        if (!p)
+                return errno_or_else(ESRCH);
+        e = p->pw_dir;
+
+        if (!path_is_valid(e) || !path_is_absolute(e))
+                return -EINVAL;
+
+ found:
+        return path_simplify_alloc(e, ret);
+}
+
+int get_shell(char **ret) {
+        struct passwd *p;
+        const char *e;
+        uid_t u;
+
+        assert(ret);
+
+        /* Take the user specified one */
+        e = secure_getenv("SHELL");
+        if (e && path_is_valid(e) && path_is_absolute(e))
+                goto found;
+
+        /* Hardcode shell for root and nobody to avoid NSS */
+        u = getuid();
+        if (u == 0) {
+                e = default_root_shell(NULL);
+                goto found;
+        }
+        if (u == UID_NOBODY && synthesize_nobody()) {
+                e = NOLOGIN;
+                goto found;
+        }
+
+        /* Check the database... */
+        errno = 0;
+        p = getpwuid(u);
+        if (!p)
+                return errno_or_else(ESRCH);
+        e = p->pw_shell;
+
+        if (!path_is_valid(e) || !path_is_absolute(e))
+                return -EINVAL;
+
+ found:
+        return path_simplify_alloc(e, ret);
+}
+
+int reset_uid_gid(void) {
+        int r;
+
+        r = maybe_setgroups(0, NULL);
+        if (r < 0)
+                return r;
+
+        if (setresgid(0, 0, 0) < 0)
+                return -errno;
+
+        return RET_NERRNO(setresuid(0, 0, 0));
+}
+
+int take_etc_passwd_lock(const char *root) {
+        int r;
+
+        /* This is roughly the same as lckpwdf(), but not as awful. We don't want to use alarm() and signals,
+         * hence we implement our own trivial version of this.
+         *
+         * Note that shadow-utils also takes per-database locks in addition to lckpwdf(). However, we don't,
+         * given that they are redundant: they invoke lckpwdf() first and keep it during everything they do.
+         * The per-database locks are awfully racy, and thus we just won't do them. */
+
+        _cleanup_free_ char *path = path_join(root, ETC_PASSWD_LOCK_PATH);
+        if (!path)
+                return log_oom_debug();
+
+        (void) mkdir_parents(path, 0755);
+
+        _cleanup_close_ int fd = open(path, O_WRONLY|O_CREAT|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW, 0600);
+        if (fd < 0)
+                return log_debug_errno(errno, "Cannot open %s: %m", path);
+
+        r = unposix_lock(fd, LOCK_EX);
+        if (r < 0)
+                return log_debug_errno(r, "Locking %s failed: %m", path);
+
+        return TAKE_FD(fd);
+}
+
+bool valid_user_group_name(const char *u, ValidUserFlags flags) {
+        const char *i;
+
+        /* Checks if the specified name is a valid user/group name. There are two flavours of this call:
+         * strict mode is the default which is POSIX plus some extra rules; and relaxed mode where we accept
+         * pretty much everything except the really worst offending names.
+         *
+         * Whenever we synthesize users ourselves we should use the strict mode. But when we process users
+         * created by other stuff, let's be more liberal. */
+
+        if (isempty(u)) /* An empty user name is never valid */
+                return false;
+
+        if (parse_uid(u, NULL) >= 0) /* Something that parses as numeric UID string is valid exactly when the
+                                      * flag for it is set */
+                return FLAGS_SET(flags, VALID_USER_ALLOW_NUMERIC);
+
+        if (FLAGS_SET(flags, VALID_USER_RELAX)) {
+
+                /* In relaxed mode we just check very superficially. Apparently SSSD and other stuff is
+                 * extremely liberal (way too liberal if you ask me, even inserting "@" in user names, which
+                 * is bound to cause problems for example when used with an MTA), hence only filter the most
+                 * obvious cases, or where things would result in an invalid entry if such a user name would
+                 * show up in /etc/passwd (or equivalent getent output).
+                 *
+                 * Note that we stepped far out of POSIX territory here. It's not our fault though, but
+                 * SSSD's, Samba's and everybody else who ignored POSIX on this. (I mean, I am happy to step
+                 * outside of POSIX' bounds any day, but I must say in this case I probably wouldn't
+                 * have...) */
+
+                if (startswith(u, " ") || endswith(u, " ")) /* At least expect whitespace padding is removed
+                                                             * at front and back (accept in the middle, since
+                                                             * that's apparently a thing on Windows). Note
+                                                             * that this also blocks usernames consisting of
+                                                             * whitespace only. */
+                        return false;
+
+                if (!utf8_is_valid(u)) /* We want to synthesize JSON from this, hence insist on UTF-8 */
+                        return false;
+
+                if (string_has_cc(u, NULL)) /* CC characters are just dangerous (and \n in particular is the
+                                             * record separator in /etc/passwd), so we can't allow that. */
+                        return false;
+
+                if (strpbrk(u, ":/")) /* Colons are the field separator in /etc/passwd, we can't allow
+                                       * that. Slashes are special to file systems paths and user names
+                                       * typically show up in the file system as home directories, hence
+                                       * don't allow slashes. */
+                        return false;
+
+                if (in_charset(u, "0123456789")) /* Don't allow fully numeric strings, they might be confused
+                                                  * with UIDs (note that this test is more broad than
+                                                  * the parse_uid() test above, as it will cover more than
+                                                  * the 32-bit range, and it will detect 65535 (which is in
+                                                  * invalid UID, even though in the unsigned 32 bit range) */
+                        return false;
+
+                if (u[0] == '-' && in_charset(u + 1, "0123456789")) /* Don't allow negative fully numeric
+                                                                     * strings either. After all some people
+                                                                     * write 65535 as -1 (even though that's
+                                                                     * not even true on 32-bit uid_t
+                                                                     * anyway) */
+                        return false;
+
+                if (dot_or_dot_dot(u)) /* User names typically become home directory names, and these two are
+                                        * special in that context, don't allow that. */
+                        return false;
+
+                /* Compare with strict result and warn if result doesn't match */
+                if (FLAGS_SET(flags, VALID_USER_WARN) && !valid_user_group_name(u, 0))
+                        log_struct(LOG_NOTICE,
+                                   LOG_MESSAGE("Accepting user/group name '%s', which does not match strict user/group name rules.", u),
+                                   "USER_GROUP_NAME=%s", u,
+                                   "MESSAGE_ID=" SD_MESSAGE_UNSAFE_USER_NAME_STR);
+
+                /* Note that we make no restrictions on the length in relaxed mode! */
+        } else {
+                long sz;
+                size_t l;
+
+                /* Also see POSIX IEEE Std 1003.1-2008, 2016 Edition, 3.437. We are a bit stricter here
+                 * however. Specifically we deviate from POSIX rules:
+                 *
+                 * - We don't allow empty user names (see above)
+                 * - We require that names fit into the appropriate utmp field
+                 * - We don't allow any dots (this conflicts with chown syntax which permits dots as user/group name separator)
+                 * - We don't allow dashes or digit as the first character
+                 *
+                 * Note that other systems are even more restrictive, and don't permit underscores or uppercase characters.
+                 */
+
+                if (!ascii_isalpha(u[0]) &&
+                    u[0] != '_')
+                        return false;
+
+                for (i = u+1; *i; i++)
+                        if (!ascii_isalpha(*i) &&
+                            !ascii_isdigit(*i) &&
+                            !IN_SET(*i, '_', '-'))
+                                return false;
+
+                l = i - u;
+
+                sz = sysconf(_SC_LOGIN_NAME_MAX);
+                assert_se(sz > 0);
+
+                if (l > (size_t) sz)
+                        return false;
+                if (l > NAME_MAX) /* must fit in a filename */
+                        return false;
+                if (l > UT_NAMESIZE - 1)
+                        return false;
+        }
+
+        return true;
+}
+
+bool valid_gecos(const char *d) {
+
+        if (!d)
+                return false;
+
+        if (!utf8_is_valid(d))
+                return false;
+
+        if (string_has_cc(d, NULL))
+                return false;
+
+        /* Colons are used as field separators, and hence not OK */
+        if (strchr(d, ':'))
+                return false;
+
+        return true;
+}
+
+char* mangle_gecos(const char *d) {
+        char *mangled;
+
+        /* Makes sure the provided string becomes valid as a GEGOS field, by dropping bad chars. glibc's
+         * putwent() only changes \n and : to spaces. We do more: replace all CC too, and remove invalid
+         * UTF-8 */
+
+        mangled = strdup(d);
+        if (!mangled)
+                return NULL;
+
+        for (char *i = mangled; *i; i++) {
+                int len;
+
+                if ((uint8_t) *i < (uint8_t) ' ' || *i == ':') {
+                        *i = ' ';
+                        continue;
+                }
+
+                len = utf8_encoded_valid_unichar(i, SIZE_MAX);
+                if (len < 0) {
+                        *i = ' ';
+                        continue;
+                }
+
+                i += len - 1;
+        }
+
+        return mangled;
+}
+
+bool valid_home(const char *p) {
+        /* Note that this function is also called by valid_shell(), any
+         * changes must account for that. */
+
+        if (isempty(p))
+                return false;
+
+        if (!utf8_is_valid(p))
+                return false;
+
+        if (string_has_cc(p, NULL))
+                return false;
+
+        if (!path_is_absolute(p))
+                return false;
+
+        if (!path_is_normalized(p))
+                return false;
+
+        /* Colons are used as field separators, and hence not OK */
+        if (strchr(p, ':'))
+                return false;
+
+        return true;
+}
+
+int maybe_setgroups(size_t size, const gid_t *list) {
+        int r;
+
+        /* Check if setgroups is allowed before we try to drop all the auxiliary groups */
+        if (size == 0) { /* Dropping all aux groups? */
+                _cleanup_free_ char *setgroups_content = NULL;
+                bool can_setgroups;
+
+                r = read_one_line_file("/proc/self/setgroups", &setgroups_content);
+                if (r == -ENOENT)
+                        /* Old kernels don't have /proc/self/setgroups, so assume we can use setgroups */
+                        can_setgroups = true;
+                else if (r < 0)
+                        return r;
+                else
+                        can_setgroups = streq(setgroups_content, "allow");
+
+                if (!can_setgroups) {
+                        log_debug("Skipping setgroups(), /proc/self/setgroups is set to 'deny'");
+                        return 0;
+                }
+        }
+
+        return RET_NERRNO(setgroups(size, list));
+}
+
+bool synthesize_nobody(void) {
+        /* Returns true when we shall synthesize the "nobody" user (which we do by default). This can be turned off by
+         * touching /etc/systemd/dont-synthesize-nobody in order to provide upgrade compatibility with legacy systems
+         * that used the "nobody" user name and group name for other UIDs/GIDs than 65534.
+         *
+         * Note that we do not employ any kind of synchronization on the following caching variable. If the variable is
+         * accessed in multi-threaded programs in the worst case it might happen that we initialize twice, but that
+         * shouldn't matter as each initialization should come to the same result. */
+        static int cache = -1;
+
+        if (cache < 0)
+                cache = access("/etc/systemd/dont-synthesize-nobody", F_OK) < 0;
+
+        return cache;
+}
+
+int putpwent_sane(const struct passwd *pw, FILE *stream) {
+        assert(pw);
+        assert(stream);
+
+        errno = 0;
+        if (putpwent(pw, stream) != 0)
+                return errno_or_else(EIO);
+
+        return 0;
+}
+
+int putspent_sane(const struct spwd *sp, FILE *stream) {
+        assert(sp);
+        assert(stream);
+
+        errno = 0;
+        if (putspent(sp, stream) != 0)
+                return errno_or_else(EIO);
+
+        return 0;
+}
+
+int putgrent_sane(const struct group *gr, FILE *stream) {
+        assert(gr);
+        assert(stream);
+
+        errno = 0;
+        if (putgrent(gr, stream) != 0)
+                return errno_or_else(EIO);
+
+        return 0;
+}
+
+#if ENABLE_GSHADOW
+int putsgent_sane(const struct sgrp *sg, FILE *stream) {
+        assert(sg);
+        assert(stream);
+
+        errno = 0;
+        if (putsgent(sg, stream) != 0)
+                return errno_or_else(EIO);
+
+        return 0;
+}
+#endif
+
+int fgetpwent_sane(FILE *stream, struct passwd **pw) {
+        assert(stream);
+        assert(pw);
+
+        errno = 0;
+        struct passwd *p = fgetpwent(stream);
+        if (!p && errno != ENOENT)
+                return errno_or_else(EIO);
+
+        *pw = p;
+        return !!p;
+}
+
+int fgetspent_sane(FILE *stream, struct spwd **sp) {
+        assert(stream);
+        assert(sp);
+
+        errno = 0;
+        struct spwd *s = fgetspent(stream);
+        if (!s && errno != ENOENT)
+                return errno_or_else(EIO);
+
+        *sp = s;
+        return !!s;
+}
+
+int fgetgrent_sane(FILE *stream, struct group **gr) {
+        assert(stream);
+        assert(gr);
+
+        errno = 0;
+        struct group *g = fgetgrent(stream);
+        if (!g && errno != ENOENT)
+                return errno_or_else(EIO);
+
+        *gr = g;
+        return !!g;
+}
+
+#if ENABLE_GSHADOW
+int fgetsgent_sane(FILE *stream, struct sgrp **sg) {
+        assert(stream);
+        assert(sg);
+
+        errno = 0;
+        struct sgrp *s = fgetsgent(stream);
+        if (!s && errno != ENOENT)
+                return errno_or_else(EIO);
+
+        *sg = s;
+        return !!s;
+}
+#endif
+
+int is_this_me(const char *username) {
+        uid_t uid;
+        int r;
+
+        /* Checks if the specified username is our current one. Passed string might be a UID or a user name. */
+
+        r = get_user_creds(&username, &uid, NULL, NULL, NULL, USER_CREDS_ALLOW_MISSING);
+        if (r < 0)
+                return r;
+
+        return uid == getuid();
+}
+
+const char* get_home_root(void) {
+        const char *e;
+
+        /* For debug purposes allow overriding where we look for home dirs */
+        e = secure_getenv("SYSTEMD_HOME_ROOT");
+        if (e && path_is_absolute(e) && path_is_normalized(e))
+                return e;
+
+        return "/home";
+}