Merge branch 'lslocks' of https://github.com/jwilk-forks/util-linux

[thirdparty/util-linux.git] / sys-utils / unshare.c

/*
 * unshare(1) - command-line interface for unshare(2)
 *
 * Copyright (C) 2009 Mikhail Gusarov <dottedmag@dottedmag.net>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2, or (at your option) any
 * later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include <errno.h>
#include <getopt.h>
#include <poll.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/eventfd.h>
#include <sys/wait.h>
#include <sys/mount.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/prctl.h>
#include <grp.h>

/* we only need some defines missing in sys/mount.h, no libmount linkage */
#include <libmount.h>

#include "nls.h"
#include "c.h"
#include "caputils.h"
#include "closestream.h"
#include "namespace.h"
#include "pidfd-utils.h"
#include "exec_shell.h"
#include "xalloc.h"
#include "pathnames.h"
#include "all-io.h"
#include "signames.h"
#include "strutils.h"
#include "pwdutils.h"

/* synchronize parent and child by pipe */
#define PIPE_SYNC_BYTE  0x06

/* 'private' is kernel default */
#define UNSHARE_PROPAGATION_DEFAULT     (MS_REC | MS_PRIVATE)

/* /proc namespace files and mountpoints for binds */
static struct namespace_file {
        int             type;           /* CLONE_NEW* */
        const char      *name;          /* ns/<type> */
        const char      *target;        /* user specified target for bind mount */
} namespace_files[] = {
        { .type = CLONE_NEWUSER,  .name = "ns/user" },
        { .type = CLONE_NEWCGROUP,.name = "ns/cgroup" },
        { .type = CLONE_NEWIPC,   .name = "ns/ipc"  },
        { .type = CLONE_NEWUTS,   .name = "ns/uts"  },
        { .type = CLONE_NEWNET,   .name = "ns/net"  },
        { .type = CLONE_NEWPID,   .name = "ns/pid_for_children" },
        { .type = CLONE_NEWNS,    .name = "ns/mnt"  },
        { .type = CLONE_NEWTIME,  .name = "ns/time_for_children" },
        { .name = NULL }
};

static int npersists;   /* number of persistent namespaces */

enum {
        SETGROUPS_NONE = -1,
        SETGROUPS_DENY = 0,
        SETGROUPS_ALLOW = 1,
};

static const char *setgroups_strings[] =
{
        [SETGROUPS_DENY] = "deny",
        [SETGROUPS_ALLOW] = "allow"
};

static int setgroups_str2id(const char *str)
{
        size_t i;

        for (i = 0; i < ARRAY_SIZE(setgroups_strings); i++)
                if (strcmp(str, setgroups_strings[i]) == 0)
                        return i;

        errx(EXIT_FAILURE, _("unsupported --setgroups argument '%s'"), str);
}

static void setgroups_control(int action)
{
        const char *file = _PATH_PROC_SETGROUPS;
        const char *cmd;
        int fd;

        if (action < 0 || (size_t) action >= ARRAY_SIZE(setgroups_strings))
                return;
        cmd = setgroups_strings[action];

        fd = open(file, O_WRONLY);
        if (fd < 0) {
                if (errno == ENOENT)
                        return;
                err(EXIT_FAILURE, _("cannot open %s"), file);
        }

        if (write_all(fd, cmd, strlen(cmd)))
                err(EXIT_FAILURE, _("write failed %s"), file);
        close(fd);
}

static void map_id(const char *file, uint32_t from, uint32_t to)
{
        char *buf;
        int fd;

        fd = open(file, O_WRONLY);
        if (fd < 0)
                 err(EXIT_FAILURE, _("cannot open %s"), file);

        xasprintf(&buf, "%u %u 1", from, to);
        if (write_all(fd, buf, strlen(buf)))
                err(EXIT_FAILURE, _("write failed %s"), file);
        free(buf);
        close(fd);
}

static unsigned long parse_propagation(const char *str)
{
        size_t i;
        static const struct prop_opts {
                const char *name;
                unsigned long flag;
        } opts[] = {
                { "slave",      MS_REC | MS_SLAVE },
                { "private",    MS_REC | MS_PRIVATE },
                { "shared",     MS_REC | MS_SHARED },
                { "unchanged",        0 }
        };

        for (i = 0; i < ARRAY_SIZE(opts); i++) {
                if (strcmp(opts[i].name, str) == 0)
                        return opts[i].flag;
        }

        errx(EXIT_FAILURE, _("unsupported propagation mode: %s"), str);
}

static void set_propagation(unsigned long flags)
{
        if (flags == 0)
                return;

        if (mount("none", "/", NULL, flags, NULL) != 0)
                err(EXIT_FAILURE, _("cannot change root filesystem propagation"));
}


static int set_ns_target(int type, const char *path)
{
        struct namespace_file *ns;

        for (ns = namespace_files; ns->name; ns++) {
                if (ns->type != type)
                        continue;
                ns->target = path;
                npersists++;
                return 0;
        }

        return -EINVAL;
}

static int bind_ns_files(pid_t pid)
{
        struct namespace_file *ns;
        char src[PATH_MAX];

        for (ns = namespace_files; ns->name; ns++) {
                if (!ns->target)
                        continue;

                snprintf(src, sizeof(src), "/proc/%u/%s", (unsigned) pid, ns->name);

                if (mount(src, ns->target, NULL, MS_BIND, NULL) != 0)
                        err(EXIT_FAILURE, _("mount %s on %s failed"), src, ns->target);
        }

        return 0;
}

static ino_t get_mnt_ino(pid_t pid)
{
        struct stat st;
        char path[PATH_MAX];

        snprintf(path, sizeof(path), "/proc/%u/ns/mnt", (unsigned) pid);

        if (stat(path, &st) != 0)
                err(EXIT_FAILURE, _("stat of %s failed"), path);
        return st.st_ino;
}

static void settime(int64_t offset, clockid_t clk_id)
{
        char buf[sizeof(stringify_value(ULONG_MAX)) * 3];
        int fd, len;

        len = snprintf(buf, sizeof(buf), "%d %" PRId64 " 0", clk_id, offset);

        fd = open("/proc/self/timens_offsets", O_WRONLY);
        if (fd < 0)
                err(EXIT_FAILURE, _("failed to open /proc/self/timens_offsets"));

        if (write(fd, buf, len) != len)
                err(EXIT_FAILURE, _("failed to write to /proc/self/timens_offsets"));

        close(fd);
}

/**
 * waitchild() - Wait for a process to exit successfully
 * @pid: PID of the process to wait for
 *
 * Wait for a process to exit successfully. If it exits with a non-zero return
 * code, then exit() with the same status.
 */
static void waitchild(int pid)
{
        int rc, status;

        do {
                rc = waitpid(pid, &status, 0);
                if (rc < 0) {
                        if (errno == EINTR)
                                continue;
                        err(EXIT_FAILURE, _("waitpid failed"));
                }
                if (WIFEXITED(status) &&
                    WEXITSTATUS(status) != EXIT_SUCCESS)
                        exit(WEXITSTATUS(status));
        } while (rc < 0);
}

/**
 * sync_with_child() - Tell our child we're ready and wait for it to exit
 * @pid: The pid of our child
 * @fd: A file descriptor created with eventfd()
 *
 * This tells a child created with fork_and_wait() that we are ready for it to
 * continue. Once we have done that, wait for our child to exit.
 */
static void sync_with_child(pid_t pid, int fd)
{
        uint64_t ch = PIPE_SYNC_BYTE;

        write_all(fd, &ch, sizeof(ch));
        close(fd);

        waitchild(pid);
}

/**
 * fork_and_wait() - Fork and wait to be sync'd with
 * @fd - A file descriptor created with eventfd() which should be passed to
 *       sync_with_child()
 *
 * This creates an eventfd and forks. The parent process returns immediately,
 * but the child waits for a %PIPE_SYNC_BYTE on the eventfd before returning.
 * This allows the parent to perform some tasks before the child starts its
 * work. The parent should call sync_with_child() once it is ready for the
 * child to continue.
 *
 * Return: The pid from fork()
 */
static pid_t fork_and_wait(int *fd)
{
        pid_t pid;
        uint64_t ch;

        *fd = eventfd(0, 0);
        if (*fd < 0)
                err(EXIT_FAILURE, _("eventfd failed"));

        pid = fork();
        if (pid < 0)
                err(EXIT_FAILURE, _("fork failed"));

        if (!pid) {
                /* wait for the our parent to tell us to continue */
                if (read_all(*fd, (char *)&ch, sizeof(ch)) != sizeof(ch) ||
                    ch != PIPE_SYNC_BYTE)
                        err(EXIT_FAILURE, _("failed to read eventfd"));
                close(*fd);
        }

        return pid;
}

static pid_t bind_ns_files_from_child(int *fd)
{
        pid_t child, ppid = getpid();
        ino_t ino = get_mnt_ino(ppid);

        child = fork_and_wait(fd);
        if (child)
                return child;

        if (get_mnt_ino(ppid) == ino)
                exit(EXIT_FAILURE);
        bind_ns_files(ppid);
        exit(EXIT_SUCCESS);
}

static uid_t get_user(const char *s, const char *err)
{
        struct passwd *pw;
        char *buf = NULL;
        uid_t ret;

        pw = xgetpwnam(s, &buf);
        if (pw) {
                ret = pw->pw_uid;
                free(pw);
                free(buf);
        } else {
                ret = strtoul_or_err(s, err);
        }

        return ret;
}

static gid_t get_group(const char *s, const char *err)
{
        struct group *gr;
        char *buf = NULL;
        gid_t ret;

        gr = xgetgrnam(s, &buf);
        if (gr) {
                ret = gr->gr_gid;
                free(gr);
                free(buf);
        } else {
                ret = strtoul_or_err(s, err);
        }

        return ret;
}

/**
 * struct map_range - A range of IDs to map
 * @outer: First ID mapped on the outside of the namespace
 * @inner: First ID mapped on the inside of the namespace
 * @count: Length of the inside and outside ranges
 *
 * A range of uids/gids to map using new[gu]idmap.
 */
struct map_range {
        unsigned int outer;
        unsigned int inner;
        unsigned int count;
};

#define UID_BUFSIZ  sizeof(stringify_value(ULONG_MAX))

/**
 * get_map_range() - Parse a mapping range from a string
 * @s: A string of the format inner:outer:count or outer,inner,count
 *
 * Parse a string of the form inner:outer:count or outer,inner,count into
 * a new mapping range.
 *
 * Return: A new &struct map_range
 */
static struct map_range *get_map_range(const char *s)
{
        int end;
        struct map_range *ret;

        ret = xmalloc(sizeof(*ret));

        if (sscanf(s, "%u:%u:%u%n", &ret->inner, &ret->outer, &ret->count,
                   &end) >= 3 && !s[end])
                return ret; /* inner:outer:count */

        if (sscanf(s, "%u,%u,%u%n", &ret->outer, &ret->inner, &ret->count,
                   &end) >= 3 && !s[end])
                return ret; /* outer,inner,count */

        errx(EXIT_FAILURE, _("invalid mapping '%s'"), s);
}

/**
 * read_subid_range() - Look up a user's sub[gu]id range
 * @filename: The file to look up the range from. This should be either
 *            ``/etc/subuid`` or ``/etc/subgid``.
 * @uid: The uid of the user whose range we should look up.
 *
 * This finds the first subid range matching @uid in @filename.
 */
static struct map_range *read_subid_range(char *filename, uid_t uid)
{
        char *line = NULL, *pwbuf;
        FILE *idmap;
        size_t n = 0;
        struct passwd *pw;
        struct map_range *map;

        map = xmalloc(sizeof(*map));
        map->inner = -1;

        pw = xgetpwuid(uid, &pwbuf);
        if (!pw)
                errx(EXIT_FAILURE, _("you (user %d) don't exist."), uid);

        idmap = fopen(filename, "r");
        if (!idmap)
                err(EXIT_FAILURE, _("could not open '%s'"), filename);

        /*
        * Each line in sub[ug]idmap looks like
        * username:subuid:count
        * OR
        * uid:subuid:count
        */
        while (getline(&line, &n, idmap) != -1) {
                char *rest, *s;

                rest = strchr(line, ':');
                if (!rest)
                        continue;
                *rest = '\0';

                if (strcmp(line, pw->pw_name) &&
                    strtoul(line, NULL, 10) != pw->pw_uid)
                        continue;

                s = rest + 1;
                rest = strchr(s, ':');
                if (!rest)
                        continue;
                *rest = '\0';
                map->outer = strtoul_or_err(s, _("failed to parse subid map"));

                s = rest + 1;
                rest = strchr(s, '\n');
                if (rest)
                        *rest = '\0';
                map->count = strtoul_or_err(s, _("failed to parse subid map"));

                fclose(idmap);
                free(pw);
                free(pwbuf);

                return map;
        }

        errx(EXIT_FAILURE, _("no line matching user \"%s\" in %s"),
        pw->pw_name, filename);
}

/**
 * map_ids() - Create a new uid/gid map
 * @idmapper: Either newuidmap or newgidmap
 * @ppid: Pid to set the map for
 * @outer: ID outside the namespace for a single map.
 * @inner: ID inside the namespace for a single map. May be -1 to only use @map.
 * @map: A range of IDs to map
 *
 * This creates a new uid/gid map for @ppid using @idmapper. The ID @outer in
 * the parent (our) namespace is mapped to the ID @inner in the child (@ppid's)
 * namespace. In addition, the range of IDs beginning at @map->outer is mapped
 * to the range of IDs beginning at @map->inner. The tricky bit is that we
 * cannot let these mappings overlap. We accomplish this by removing a "hole"
 * from @map, if @outer or @inner overlap it. This may result in one less than
 * @map->count IDs being mapped from @map. The unmapped IDs are always the
 * topmost IDs of the mapping (either in the parent or the child namespace).
 *
 * Most of the time, this function will be called with @map->outer as some
 * large ID, @map->inner as 0, and @map->count as a large number (at least
 * 1000, but less than @map->outer). Typically, there will be no conflict with
 * @outer. However, @inner may split the mapping for e.g. --map-current-user.
 *
 * This function always exec()s or errors out and does not return.
 */
static void __attribute__((__noreturn__))
map_ids(const char *idmapper, int ppid, unsigned int outer, unsigned int inner,
        struct map_range *map)
{
        /* idmapper + pid + 4 * map + NULL */
        char *argv[15];
        /* argv - idmapper - "1" - NULL */
        char args[12][UID_BUFSIZ];
        int i = 0, j = 0;
        struct map_range lo, mid, hi;
        unsigned int inner_offset, outer_offset;

        /* Some helper macros to reduce bookkeeping */
#define push_str(s) do { \
        argv[i++] = s; \
} while (0)
#define push_ul(x) do { \
        snprintf(args[j], sizeof(args[j]), "%u", x); \
        push_str(args[j++]); \
} while (0)

        push_str(xstrdup(idmapper));
        push_ul(ppid);
        if ((int)inner == -1) {
                /*
                 * If we don't have a "single" mapping, then we can just use map
                 * directly, starting inner IDs from zero for an auto mapping
                 */
                push_ul(map->inner + 1 ? map->inner : 0);
                push_ul(map->outer);
                push_ul(map->count);
                push_str(NULL);

                execvp(idmapper, argv);
                errexec(idmapper);
        }

        /*
         * Start inner IDs from zero for an auto mapping; otherwise, if the two
         * fixed mappings overlap, remove an ID from map
         */
        if (map->inner + 1 == 0)
                map->inner = 0;
        else if ((outer >= map->outer && outer <= map->outer + map->count) ||
                 (inner >= map->inner && inner <= map->inner + map->count))
                map->count--;

        /* Determine where the splits between lo, mid, and hi will be */
        outer_offset = min(outer > map->outer ? outer - map->outer : 0,
                           map->count);
        inner_offset = min(inner > map->inner ? inner - map->inner : 0,
                           map->count);

        /*
         * In the worst case, we need three mappings:
         * From the bottom of map to either inner or outer
         */
        lo.outer = map->outer;
        lo.inner = map->inner;
        lo.count = min(inner_offset, outer_offset);

        /* From the lower of inner or outer to the higher */
        mid.outer = lo.outer + lo.count;
        mid.outer += mid.outer == outer;
        mid.inner = lo.inner + lo.count;
        mid.inner += mid.inner == inner;
        mid.count = abs_diff(outer_offset, inner_offset);

        /* And from the higher of inner or outer to the end of the map */
        hi.outer = mid.outer + mid.count;
        hi.outer += hi.outer == outer;
        hi.inner = mid.inner + mid.count;
        hi.inner += hi.inner == inner;
        hi.count = map->count - lo.count - mid.count;

        push_ul(inner);
        push_ul(outer);
        push_str("1");
        /* new[gu]idmap doesn't like zero-length mappings, so skip them */
        if (lo.count) {
                push_ul(lo.inner);
                push_ul(lo.outer);
                push_ul(lo.count);
        }
        if (mid.count) {
                push_ul(mid.inner);
                push_ul(mid.outer);
                push_ul(mid.count);
        }
        if (hi.count) {
                push_ul(hi.inner);
                push_ul(hi.outer);
                push_ul(hi.count);
        }
        push_str(NULL);
        execvp(idmapper, argv);
        errexec(idmapper);
}

/**
 * map_ids_from_child() - Set up a new uid/gid map
 * @fd: The eventfd to wait on
 * @mapuser: The user to map the current user to (or -1)
 * @usermap: The range of UIDs to map (or %NULL)
 * @mapgroup: The group to map the current group to (or -1)
 * @groupmap: The range of GIDs to map (or %NULL)
 *
 * fork_and_wait() for our parent to call sync_with_child() on @fd. Upon
 * recieving the go-ahead, use newuidmap and newgidmap to set the uid/gid map
 * for our parent's PID.
 *
 * Return: The pid of the child.
 */
static pid_t map_ids_from_child(int *fd, uid_t mapuser,
                                struct map_range *usermap, gid_t mapgroup,
                                struct map_range *groupmap)
{
        pid_t child, pid = 0;
        pid_t ppid = getpid();

        child = fork_and_wait(fd);
        if (child)
                return child;

        /* Avoid forking more than we need to */
        if (usermap && groupmap) {
                pid = fork();
                if (pid < 0)
                        err(EXIT_FAILURE, _("fork failed"));
                if (pid)
                        waitchild(pid);
        }

        if (!pid && usermap)
                map_ids("newuidmap", ppid, geteuid(), mapuser, usermap);
        if (groupmap)
                map_ids("newgidmap", ppid, getegid(), mapgroup, groupmap);
        exit(EXIT_SUCCESS);
}

static void __attribute__((__noreturn__)) usage(void)
{
        FILE *out = stdout;

        fputs(USAGE_HEADER, out);
        fprintf(out, _(" %s [options] [<program> [<argument>...]]\n"),
                program_invocation_short_name);

        fputs(USAGE_SEPARATOR, out);
        fputs(_("Run a program with some namespaces unshared from the parent.\n"), out);

        fputs(USAGE_OPTIONS, out);
        fputs(_(" -m, --mount[=<file>]      unshare mounts namespace\n"), out);
        fputs(_(" -u, --uts[=<file>]        unshare UTS namespace (hostname etc)\n"), out);
        fputs(_(" -i, --ipc[=<file>]        unshare System V IPC namespace\n"), out);
        fputs(_(" -n, --net[=<file>]        unshare network namespace\n"), out);
        fputs(_(" -p, --pid[=<file>]        unshare pid namespace\n"), out);
        fputs(_(" -U, --user[=<file>]       unshare user namespace\n"), out);
        fputs(_(" -C, --cgroup[=<file>]     unshare cgroup namespace\n"), out);
        fputs(_(" -T, --time[=<file>]       unshare time namespace\n"), out);
        fputs(USAGE_SEPARATOR, out);
        fputs(_(" -f, --fork                fork before launching <program>\n"), out);
        fputs(_(" --map-user=<uid>|<name>   map current user to uid (implies --user)\n"), out);
        fputs(_(" --map-group=<gid>|<name>  map current group to gid (implies --user)\n"), out);
        fputs(_(" -r, --map-root-user       map current user to root (implies --user)\n"), out);
        fputs(_(" -c, --map-current-user    map current user to itself (implies --user)\n"), out);
        fputs(_(" --map-auto                map users and groups automatically (implies --user)\n"), out);
        fputs(_(" --map-users=<inneruid>:<outeruid>:<count>\n"
                "                           map count users from outeruid to inneruid (implies --user)\n"), out);
        fputs(_(" --map-groups=<innergid>:<outergid>:<count>\n"
                "                           map count groups from outergid to innergid (implies --user)\n"), out);
        fputs(USAGE_SEPARATOR, out);
        fputs(_(" --kill-child[=<signame>]  when dying, kill the forked child (implies --fork)\n"
                "                             defaults to SIGKILL\n"), out);
        fputs(_(" --mount-proc[=<dir>]      mount proc filesystem first (implies --mount)\n"), out);
        fputs(_(" --propagation slave|shared|private|unchanged\n"
                "                           modify mount propagation in mount namespace\n"), out);
        fputs(_(" --setgroups allow|deny    control the setgroups syscall in user namespaces\n"), out);
        fputs(_(" --keep-caps               retain capabilities granted in user namespaces\n"), out);
        fputs(USAGE_SEPARATOR, out);
        fputs(_(" -R, --root=<dir>          run the command with root directory set to <dir>\n"), out);
        fputs(_(" -w, --wd=<dir>            change working directory to <dir>\n"), out);
        fputs(_(" -S, --setuid <uid>        set uid in entered namespace\n"), out);
        fputs(_(" -G, --setgid <gid>        set gid in entered namespace\n"), out);
        fputs(_(" --monotonic <offset>      set clock monotonic offset (seconds) in time namespaces\n"), out);
        fputs(_(" --boottime <offset>       set clock boottime offset (seconds) in time namespaces\n"), out);

        fputs(USAGE_SEPARATOR, out);
        printf(USAGE_HELP_OPTIONS(27));
        printf(USAGE_MAN_TAIL("unshare(1)"));

        exit(EXIT_SUCCESS);
}

int main(int argc, char *argv[])
{
        enum {
                OPT_MOUNTPROC = CHAR_MAX + 1,
                OPT_PROPAGATION,
                OPT_SETGROUPS,
                OPT_KILLCHILD,
                OPT_KEEPCAPS,
                OPT_MONOTONIC,
                OPT_BOOTTIME,
                OPT_MAPUSER,
                OPT_MAPUSERS,
                OPT_MAPGROUP,
                OPT_MAPGROUPS,
                OPT_MAPAUTO,
        };
        static const struct option longopts[] = {
                { "help",          no_argument,       NULL, 'h'             },
                { "version",       no_argument,       NULL, 'V'             },

                { "mount",         optional_argument, NULL, 'm'             },
                { "uts",           optional_argument, NULL, 'u'             },
                { "ipc",           optional_argument, NULL, 'i'             },
                { "net",           optional_argument, NULL, 'n'             },
                { "pid",           optional_argument, NULL, 'p'             },
                { "user",          optional_argument, NULL, 'U'             },
                { "cgroup",        optional_argument, NULL, 'C'             },
                { "time",          optional_argument, NULL, 'T'             },

                { "fork",          no_argument,       NULL, 'f'             },
                { "kill-child",    optional_argument, NULL, OPT_KILLCHILD   },
                { "mount-proc",    optional_argument, NULL, OPT_MOUNTPROC   },
                { "map-user",      required_argument, NULL, OPT_MAPUSER     },
                { "map-users",     required_argument, NULL, OPT_MAPUSERS    },
                { "map-group",     required_argument, NULL, OPT_MAPGROUP    },
                { "map-groups",    required_argument, NULL, OPT_MAPGROUPS   },
                { "map-root-user", no_argument,       NULL, 'r'             },
                { "map-current-user", no_argument,    NULL, 'c'             },
                { "map-auto",      no_argument,       NULL, OPT_MAPAUTO     },
                { "propagation",   required_argument, NULL, OPT_PROPAGATION },
                { "setgroups",     required_argument, NULL, OPT_SETGROUPS   },
                { "keep-caps",     no_argument,       NULL, OPT_KEEPCAPS    },
                { "setuid",        required_argument, NULL, 'S'             },
                { "setgid",        required_argument, NULL, 'G'             },
                { "root",          required_argument, NULL, 'R'             },
                { "wd",            required_argument, NULL, 'w'             },
                { "monotonic",     required_argument, NULL, OPT_MONOTONIC   },
                { "boottime",      required_argument, NULL, OPT_BOOTTIME    },
                { NULL, 0, NULL, 0 }
        };

        int setgrpcmd = SETGROUPS_NONE;
        int unshare_flags = 0;
        int c, forkit = 0;
        uid_t mapuser = -1;
        gid_t mapgroup = -1;
        struct map_range *usermap = NULL;
        struct map_range *groupmap = NULL;
        int kill_child_signo = 0; /* 0 means --kill-child was not used */
        const char *procmnt = NULL;
        const char *newroot = NULL;
        const char *newdir = NULL;
        pid_t pid_bind = 0, pid_idmap = 0;
        pid_t pid = 0;
#ifdef UL_HAVE_PIDFD
        int fd_parent_pid = -1;
#endif
        int fd_idmap, fd_bind = -1;
        sigset_t sigset, oldsigset;
        int status;
        unsigned long propagation = UNSHARE_PROPAGATION_DEFAULT;
        int force_uid = 0, force_gid = 0;
        uid_t uid = 0, real_euid = geteuid();
        gid_t gid = 0, real_egid = getegid();
        int keepcaps = 0;
        int64_t monotonic = 0;
        int64_t boottime = 0;
        int force_monotonic = 0;
        int force_boottime = 0;

        setlocale(LC_ALL, "");
        bindtextdomain(PACKAGE, LOCALEDIR);
        textdomain(PACKAGE);
        close_stdout_atexit();

        while ((c = getopt_long(argc, argv, "+fhVmuinpCTUrR:w:S:G:c", longopts, NULL)) != -1) {
                switch (c) {
                case 'f':
                        forkit = 1;
                        break;
                case 'm':
                        unshare_flags |= CLONE_NEWNS;
                        if (optarg)
                                set_ns_target(CLONE_NEWNS, optarg);
                        break;
                case 'u':
                        unshare_flags |= CLONE_NEWUTS;
                        if (optarg)
                                set_ns_target(CLONE_NEWUTS, optarg);
                        break;
                case 'i':
                        unshare_flags |= CLONE_NEWIPC;
                        if (optarg)
                                set_ns_target(CLONE_NEWIPC, optarg);
                        break;
                case 'n':
                        unshare_flags |= CLONE_NEWNET;
                        if (optarg)
                                set_ns_target(CLONE_NEWNET, optarg);
                        break;
                case 'p':
                        unshare_flags |= CLONE_NEWPID;
                        if (optarg)
                                set_ns_target(CLONE_NEWPID, optarg);
                        break;
                case 'U':
                        unshare_flags |= CLONE_NEWUSER;
                        if (optarg)
                                set_ns_target(CLONE_NEWUSER, optarg);
                        break;
                case 'C':
                        unshare_flags |= CLONE_NEWCGROUP;
                        if (optarg)
                                set_ns_target(CLONE_NEWCGROUP, optarg);
                        break;
                case 'T':
                        unshare_flags |= CLONE_NEWTIME;
                        if (optarg)
                                set_ns_target(CLONE_NEWTIME, optarg);
                        break;
                case OPT_MOUNTPROC:
                        unshare_flags |= CLONE_NEWNS;
                        procmnt = optarg ? optarg : "/proc";
                        break;
                case OPT_MAPUSER:
                        unshare_flags |= CLONE_NEWUSER;
                        mapuser = get_user(optarg, _("failed to parse uid"));
                        break;
                case OPT_MAPGROUP:
                        unshare_flags |= CLONE_NEWUSER;
                        mapgroup = get_group(optarg, _("failed to parse gid"));
                        break;
                case 'r':
                        unshare_flags |= CLONE_NEWUSER;
                        mapuser = 0;
                        mapgroup = 0;
                        break;
                case 'c':
                        unshare_flags |= CLONE_NEWUSER;
                        mapuser = real_euid;
                        mapgroup = real_egid;
                        break;
                case OPT_MAPUSERS:
                        unshare_flags |= CLONE_NEWUSER;
                        if (!strcmp(optarg, "auto"))
                                usermap = read_subid_range(_PATH_SUBUID, real_euid);
                        else
                                usermap = get_map_range(optarg);
                        break;
                case OPT_MAPGROUPS:
                        unshare_flags |= CLONE_NEWUSER;
                        if (!strcmp(optarg, "auto"))
                                groupmap = read_subid_range(_PATH_SUBGID, real_euid);
                        else
                                groupmap = get_map_range(optarg);
                        break;
                case OPT_MAPAUTO:
                        unshare_flags |= CLONE_NEWUSER;
                        usermap = read_subid_range(_PATH_SUBUID, real_euid);
                        groupmap = read_subid_range(_PATH_SUBGID, real_euid);
                        break;
                case OPT_SETGROUPS:
                        setgrpcmd = setgroups_str2id(optarg);
                        break;
                case OPT_PROPAGATION:
                        propagation = parse_propagation(optarg);
                        break;
                case OPT_KILLCHILD:
                        forkit = 1;
                        if (optarg) {
                                if ((kill_child_signo = signame_to_signum(optarg)) < 0)
                                        errx(EXIT_FAILURE, _("unknown signal: %s"),
                                             optarg);
                        } else {
                                kill_child_signo = SIGKILL;
                        }
                        break;
                case OPT_KEEPCAPS:
                        keepcaps = 1;
                        cap_last_cap(); /* Force last cap to be cached before we fork. */
                        break;
                case 'S':
                        uid = strtoul_or_err(optarg, _("failed to parse uid"));
                        force_uid = 1;
                        break;
                case 'G':
                        gid = strtoul_or_err(optarg, _("failed to parse gid"));
                        force_gid = 1;
                        break;
                case 'R':
                        newroot = optarg;
                        break;
                case 'w':
                        newdir = optarg;
                        break;
                case OPT_MONOTONIC:
                        monotonic = strtos64_or_err(optarg, _("failed to parse monotonic offset"));
                        force_monotonic = 1;
                        break;
                case OPT_BOOTTIME:
                        boottime = strtos64_or_err(optarg, _("failed to parse boottime offset"));
                        force_boottime = 1;
                        break;

                case 'h':
                        usage();
                case 'V':
                        print_version(EXIT_SUCCESS);
                default:
                        errtryhelp(EXIT_FAILURE);
                }
        }

        if ((force_monotonic || force_boottime) && !(unshare_flags & CLONE_NEWTIME))
                errx(EXIT_FAILURE, _("options --monotonic and --boottime require "
                        "unsharing of a time namespace (-T)"));

        /* clear any inherited settings */
        signal(SIGCHLD, SIG_DFL);

        if (npersists && (unshare_flags & CLONE_NEWNS))
                pid_bind = bind_ns_files_from_child(&fd_bind);

        if (usermap || groupmap)
                pid_idmap = map_ids_from_child(&fd_idmap, mapuser, usermap,
                                               mapgroup, groupmap);

        if (-1 == unshare(unshare_flags))
                err(EXIT_FAILURE, _("unshare failed"));

        /* Tell child we've called unshare() */
        if (usermap || groupmap)
                sync_with_child(pid_idmap, fd_idmap);

        if (force_boottime)
                settime(boottime, CLOCK_BOOTTIME);

        if (force_monotonic)
                settime(monotonic, CLOCK_MONOTONIC);

        if (forkit) {
                if (sigemptyset(&sigset) != 0 ||
                        sigaddset(&sigset, SIGINT) != 0 ||
                        sigaddset(&sigset, SIGTERM) != 0 ||
                        sigprocmask(SIG_BLOCK, &sigset, &oldsigset) != 0)
                        err(EXIT_FAILURE, _("sigprocmask block failed"));
#ifdef UL_HAVE_PIDFD
                if (kill_child_signo != 0) {
                        /* make a connection to the original process (parent) */
                        fd_parent_pid = pidfd_open(getpid(), 0);
                        if (0 > fd_parent_pid)
                                err(EXIT_FAILURE, _("pidfd_open failed"));
                }
#endif
                /* force child forking before mountspace binding so
                 * pid_for_children is populated */
                pid = fork();

                switch(pid) {
                case -1:
                        err(EXIT_FAILURE, _("fork failed"));
                case 0: /* child */
                        if (sigprocmask(SIG_SETMASK, &oldsigset, NULL))
                                err(EXIT_FAILURE,
                                        _("sigprocmask restore failed"));
                        if (npersists && (unshare_flags & CLONE_NEWNS))
                                close(fd_bind);
                        break;
                default: /* parent */
                        break;
                }
        }

        if (npersists && (pid || !forkit)) {
                /* run in parent */
                if (pid_bind && (unshare_flags & CLONE_NEWNS))
                        sync_with_child(pid_bind, fd_bind);
                else
                        /* simple way, just bind */
                        bind_ns_files(getpid());
        }

        if (pid) {
                if (waitpid(pid, &status, 0) == -1)
                        err(EXIT_FAILURE, _("waitpid failed"));

                if (WIFEXITED(status))
                        return WEXITSTATUS(status);
                if (WIFSIGNALED(status)) {

                        /* Ensure the signal that terminated the child will
                         * also terminate the parent. */

                        int termsig = WTERMSIG(status);

                        if (signal(termsig, SIG_DFL) == SIG_ERR ||
                                sigemptyset(&sigset) != 0 ||
                                sigaddset(&sigset, termsig) != 0 ||
                                sigprocmask(SIG_UNBLOCK, &sigset, NULL) != 0)
                                err(EXIT_FAILURE,
                                        _("sigprocmask unblock failed"));

                        kill(getpid(), termsig);
                }
                err(EXIT_FAILURE, _("child exit failed"));
        }

        if (kill_child_signo != 0) {
                if (prctl(PR_SET_PDEATHSIG, kill_child_signo) < 0)
                        err(EXIT_FAILURE, "prctl failed");
#ifdef UL_HAVE_PIDFD
                /* Use poll() to check that there is still the original parent. */
                if (fd_parent_pid != -1) {
                        struct pollfd pollfds[1] = {
                                { .fd = fd_parent_pid, .events = POLLIN }
                        };
                        int nfds = poll(pollfds, 1, 0);

                        if (0 > nfds)
                                err(EXIT_FAILURE, "poll parent pidfd failed");

                        /* If the child was re-parented before prctl(2) was called, the
                         * new parent will likely not be interested in the precise exit
                         * status of the orphan.
                         */
                        if (nfds)
                                exit(EXIT_FAILURE);

                        close(fd_parent_pid);
                        fd_parent_pid = -1;
                }
#endif
        }

        if (mapuser != (uid_t) -1 && !usermap)
                map_id(_PATH_PROC_UIDMAP, mapuser, real_euid);

        /* Since Linux 3.19 unprivileged writing of /proc/self/gid_map
         * has been disabled unless /proc/self/setgroups is written
         * first to permanently disable the ability to call setgroups
         * in that user namespace. */
        if (mapgroup != (gid_t) -1 && !groupmap) {
                if (setgrpcmd == SETGROUPS_ALLOW)
                        errx(EXIT_FAILURE, _("options --setgroups=allow and "
                                        "--map-group are mutually exclusive"));
                setgroups_control(SETGROUPS_DENY);
                map_id(_PATH_PROC_GIDMAP, mapgroup, real_egid);
        }

        if (setgrpcmd != SETGROUPS_NONE)
                setgroups_control(setgrpcmd);

        if ((unshare_flags & CLONE_NEWNS) && propagation)
                set_propagation(propagation);

        if (newroot) {
                if (chroot(newroot) != 0)
                        err(EXIT_FAILURE,
                            _("cannot change root directory to '%s'"), newroot);
                newdir = newdir ?: "/";
        }
        if (newdir && chdir(newdir))
                err(EXIT_FAILURE, _("cannot chdir to '%s'"), newdir);

        if (procmnt) {
                /* When not changing root and using the default propagation flags
                   then the recursive propagation change of root will
                   automatically change that of an existing proc mount. */
                if (!newroot && propagation != (MS_PRIVATE|MS_REC)) {
                        int rc = mount("none", procmnt, NULL, MS_PRIVATE|MS_REC, NULL);

                        /* Custom procmnt means that proc is very likely not mounted, causing EINVAL.
                           Ignoring the error in this specific instance is considered safe. */
                        if(rc != 0 && errno != EINVAL)
                                err(EXIT_FAILURE, _("cannot change %s filesystem propagation"), procmnt);
                }

                if (mount("proc", procmnt, "proc", MS_NOSUID|MS_NOEXEC|MS_NODEV, NULL) != 0)
                        err(EXIT_FAILURE, _("mount %s failed"), procmnt);
        }

        if (force_gid) {
                if (setgroups(0, NULL) != 0)    /* drop supplementary groups */
                        err(EXIT_FAILURE, _("setgroups failed"));
                if (setgid(gid) < 0)            /* change GID */
                        err(EXIT_FAILURE, _("setgid failed"));
        }
        if (force_uid && setuid(uid) < 0)       /* change UID */
                err(EXIT_FAILURE, _("setuid failed"));

        if (keepcaps && (unshare_flags & CLONE_NEWUSER))
                cap_permitted_to_ambient();

        if (optind < argc) {
                execvp(argv[optind], argv + optind);
                errexec(argv[optind]);
        }
        exec_shell();
}