fusermount.c

/*
  FUSE: Filesystem in Userspace
  Copyright (C) 2001-2007  Miklos Szeredi <miklos@szeredi.hu>

  This program can be distributed under the terms of the GNU GPL.
  See the file COPYING.
*/
/* This program does the mounting and unmounting of FUSE filesystems */

#define _GNU_SOURCE /* for clone */
#include "config.h"
#include "mount_util.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <unistd.h>
#include <getopt.h>
#include <errno.h>
#include <fcntl.h>
#include <pwd.h>
#include <paths.h>
#include <mntent.h>
#include <sys/wait.h>
#include <sys/stat.h>
#include <sys/mount.h>
#include <sys/fsuid.h>
#include <sys/socket.h>
#include <sys/utsname.h>
#include <sched.h>
#include <stdbool.h>
#include <sys/vfs.h>

#define FUSE_COMMFD_ENV         "_FUSE_COMMFD"

#define FUSE_DEV "/dev/fuse"

#ifndef MS_DIRSYNC
#define MS_DIRSYNC 128
#endif
#ifndef MS_REC
#define MS_REC 16384
#endif
#ifndef MS_PRIVATE
#define MS_PRIVATE (1<<18)
#endif

#ifndef UMOUNT_DETACH
#define UMOUNT_DETACH   0x00000002      /* Just detach from the tree */
#endif
#ifndef UMOUNT_NOFOLLOW
#define UMOUNT_NOFOLLOW 0x00000008      /* Don't follow symlink on umount */
#endif
#ifndef UMOUNT_UNUSED
#define UMOUNT_UNUSED   0x80000000      /* Flag guaranteed to be unused */
#endif

static const char *progname;

static int user_allow_other = 0;
static int mount_max = 1000;

static int auto_unmount = 0;

static const char *get_user_name(void)
{
        struct passwd *pw = getpwuid(getuid());
        if (pw != NULL && pw->pw_name != NULL)
                return pw->pw_name;
        else {
                fprintf(stderr, "%s: could not determine username\n", progname);
                return NULL;
        }
}

static uid_t oldfsuid;
static gid_t oldfsgid;

static void drop_privs(void)
{
        if (getuid() != 0) {
                oldfsuid = setfsuid(getuid());
                oldfsgid = setfsgid(getgid());
        }
}

static void restore_privs(void)
{
        if (getuid() != 0) {
                setfsuid(oldfsuid);
                setfsgid(oldfsgid);
        }
}

#ifndef IGNORE_MTAB
/*
 * Make sure that /etc/mtab is checked and updated atomically
 */
static int lock_umount(void)
{
        const char *mtab_lock = _PATH_MOUNTED ".fuselock";
        int mtablock;
        int res;
        struct stat mtab_stat;

        /* /etc/mtab could be a symlink to /proc/mounts */
        if (lstat(_PATH_MOUNTED, &mtab_stat) == 0 && S_ISLNK(mtab_stat.st_mode))
                return -1;

        mtablock = open(mtab_lock, O_RDWR | O_CREAT, 0600);
        if (mtablock == -1) {
                fprintf(stderr, "%s: unable to open fuse lock file: %s\n",
                        progname, strerror(errno));
                return -1;
        }
        res = lockf(mtablock, F_LOCK, 0);
        if (res < 0) {
                fprintf(stderr, "%s: error getting lock: %s\n", progname,
                        strerror(errno));
                close(mtablock);
                return -1;
        }

        return mtablock;
}

static void unlock_umount(int mtablock)
{
        if (mtablock >= 0) {
                int res;

                res = lockf(mtablock, F_ULOCK, 0);
                if (res < 0) {
                        fprintf(stderr, "%s: error releasing lock: %s\n",
                                progname, strerror(errno));
                }
                close(mtablock);
        }
}

static int add_mount(const char *source, const char *mnt, const char *type,
                     const char *opts)
{
        return fuse_mnt_add_mount(progname, source, mnt, type, opts);
}

static int may_unmount(const char *mnt, int quiet)
{
        struct mntent *entp;
        FILE *fp;
        const char *user = NULL;
        char uidstr[32];
        unsigned uidlen = 0;
        int found;
        const char *mtab = _PATH_MOUNTED;

        user = get_user_name();
        if (user == NULL)
                return -1;

        fp = setmntent(mtab, "r");
        if (fp == NULL) {
                fprintf(stderr, "%s: failed to open %s: %s\n", progname, mtab,
                        strerror(errno));
                return -1;
        }

        uidlen = sprintf(uidstr, "%u", getuid());

        found = 0;
        while ((entp = getmntent(fp)) != NULL) {
                if (!found && strcmp(entp->mnt_dir, mnt) == 0 &&
                    (strcmp(entp->mnt_type, "fuse") == 0 ||
                     strcmp(entp->mnt_type, "fuseblk") == 0 ||
                     strncmp(entp->mnt_type, "fuse.", 5) == 0 ||
                     strncmp(entp->mnt_type, "fuseblk.", 8) == 0)) {
                        char *p = strstr(entp->mnt_opts, "user=");
                        if (p &&
                            (p == entp->mnt_opts || *(p-1) == ',') &&
                            strcmp(p + 5, user) == 0) {
                                found = 1;
                                break;
                        }
                        /* /etc/mtab is a link pointing to
                           /proc/mounts: */
                        else if ((p =
                                  strstr(entp->mnt_opts, "user_id=")) &&
                                 (p == entp->mnt_opts ||
                                  *(p-1) == ',') &&
                                 strncmp(p + 8, uidstr, uidlen) == 0 &&
                                 (*(p+8+uidlen) == ',' ||
                                  *(p+8+uidlen) == '\0')) {
                                found = 1;
                                break;
                        }
                }
        }
        endmntent(fp);

        if (!found) {
                if (!quiet)
                        fprintf(stderr,
                                "%s: entry for %s not found in %s\n",
                                progname, mnt, mtab);
                return -1;
        }

        return 0;
}

/*
 * Check whether the file specified in "fusermount3 -u" is really a
 * mountpoint and not a symlink.  This is necessary otherwise the user
 * could move the mountpoint away and replace it with a symlink
 * pointing to an arbitrary mount, thereby tricking fusermount3 into
 * unmounting that (umount(2) will follow symlinks).
 *
 * This is the child process running in a separate mount namespace, so
 * we don't mess with the global namespace and if the process is
 * killed for any reason, mounts are automatically cleaned up.
 *
 * First make sure nothing is propagated back into the parent
 * namespace by marking all mounts "private".
 *
 * Then bind mount parent onto a stable base where the user can't move
 * it around.
 *
 * Finally check /proc/mounts for an entry matching the requested
 * mountpoint.  If it's found then we are OK, and the user can't move
 * it around within the parent directory as rename() will return
 * EBUSY.  Be careful to ignore any mounts that existed before the
 * bind.
 */
static int check_is_mount_child(void *p)
{
        const char **a = p;
        const char *last = a[0];
        const char *mnt = a[1];
        const char *type = a[2];
        int res;
        const char *procmounts = "/proc/mounts";
        int found;
        FILE *fp;
        struct mntent *entp;
        int count;

        res = mount("", "/", "", MS_PRIVATE | MS_REC, NULL);
        if (res == -1) {
                fprintf(stderr, "%s: failed to mark mounts private: %s\n",
                        progname, strerror(errno));
                return 1;
        }

        fp = setmntent(procmounts, "r");
        if (fp == NULL) {
                fprintf(stderr, "%s: failed to open %s: %s\n", progname,
                        procmounts, strerror(errno));
                return 1;
        }

        count = 0;
        while (getmntent(fp) != NULL)
                count++;
        endmntent(fp);

        fp = setmntent(procmounts, "r");
        if (fp == NULL) {
                fprintf(stderr, "%s: failed to open %s: %s\n", progname,
                        procmounts, strerror(errno));
                return 1;
        }

        res = mount(".", "/", "", MS_BIND | MS_REC, NULL);
        if (res == -1) {
                fprintf(stderr, "%s: failed to bind parent to /: %s\n",
                        progname, strerror(errno));
                return 1;
        }

        found = 0;
        while ((entp = getmntent(fp)) != NULL) {
                if (count > 0) {
                        count--;
                        continue;
                }
                if (entp->mnt_dir[0] == '/' &&
                    strcmp(entp->mnt_dir + 1, last) == 0 &&
                    (!type || strcmp(entp->mnt_type, type) == 0)) {
                        found = 1;
                        break;
                }
        }
        endmntent(fp);

        if (!found) {
                fprintf(stderr, "%s: %s not mounted\n", progname, mnt);
                return 1;
        }

        return 0;
}

static pid_t clone_newns(void *a)
{
        char buf[131072];
        char *stack = buf + (sizeof(buf) / 2 - ((size_t) buf & 15));

#ifdef __ia64__
        extern int __clone2(int (*fn)(void *),
                            void *child_stack_base, size_t stack_size,
                            int flags, void *arg, pid_t *ptid,
                            void *tls, pid_t *ctid);

        return __clone2(check_is_mount_child, stack, sizeof(buf) / 2,
                        CLONE_NEWNS, a, NULL, NULL, NULL);
#else
        return clone(check_is_mount_child, stack, CLONE_NEWNS, a);
#endif
}

static int check_is_mount(const char *last, const char *mnt, const char *type)
{
        pid_t pid, p;
        int status;
        const char *a[3] = { last, mnt, type };

        pid = clone_newns((void *) a);
        if (pid == (pid_t) -1) {
                fprintf(stderr, "%s: failed to clone namespace: %s\n",
                        progname, strerror(errno));
                return -1;
        }
        p = waitpid(pid, &status, __WCLONE);
        if (p == (pid_t) -1) {
                fprintf(stderr, "%s: waitpid failed: %s\n",
                        progname, strerror(errno));
                return -1;
        }
        if (!WIFEXITED(status)) {
                fprintf(stderr, "%s: child terminated abnormally (status %i)\n",
                        progname, status);
                return -1;
        }
        if (WEXITSTATUS(status) != 0)
                return -1;

        return 0;
}

static int chdir_to_parent(char *copy, const char **lastp)
{
        char *tmp;
        const char *parent;
        char buf[65536];
        int res;

        tmp = strrchr(copy, '/');
        if (tmp == NULL || tmp[1] == '\0') {
                fprintf(stderr, "%s: internal error: invalid abs path: <%s>\n",
                        progname, copy);
                return -1;
        }
        if (tmp != copy) {
                *tmp = '\0';
                parent = copy;
                *lastp = tmp + 1;
        } else if (tmp[1] != '\0') {
                *lastp = tmp + 1;
                parent = "/";
        } else {
                *lastp = ".";
                parent = "/";
        }

        res = chdir(parent);
        if (res == -1) {
                fprintf(stderr, "%s: failed to chdir to %s: %s\n",
                        progname, parent, strerror(errno));
                return -1;
        }

        if (getcwd(buf, sizeof(buf)) == NULL) {
                fprintf(stderr, "%s: failed to obtain current directory: %s\n",
                        progname, strerror(errno));
                return -1;
        }
        if (strcmp(buf, parent) != 0) {
                fprintf(stderr, "%s: mountpoint moved (%s -> %s)\n", progname,
                        parent, buf);
                return -1;

        }

        return 0;
}

/* Check whether the kernel supports UMOUNT_NOFOLLOW flag */
static int umount_nofollow_support(void)
{
        int res = umount2("", UMOUNT_UNUSED);
        if (res != -1 || errno != EINVAL)
                return 0;

        res = umount2("", UMOUNT_NOFOLLOW);
        if (res != -1 || errno != ENOENT)
                return 0;

        return 1;
}

static int unmount_fuse_locked(const char *mnt, int quiet, int lazy)
{
        int res;
        char *copy;
        const char *last;
        int umount_flags = lazy ? UMOUNT_DETACH : 0;

        if (getuid() != 0) {
                res = may_unmount(mnt, quiet);
                if (res == -1)
                        return -1;
        }

        copy = strdup(mnt);
        if (copy == NULL) {
                fprintf(stderr, "%s: failed to allocate memory\n", progname);
                return -1;
        }

        drop_privs();
        res = chdir_to_parent(copy, &last);
        restore_privs();
        if (res == -1)
                goto out;

        if (umount_nofollow_support()) {
                umount_flags |= UMOUNT_NOFOLLOW;
        } else {
                res = check_is_mount(last, mnt, NULL);
                if (res == -1)
                        goto out;
        }

        res = umount2(last, umount_flags);
        if (res == -1 && !quiet) {
                fprintf(stderr, "%s: failed to unmount %s: %s\n",
                        progname, mnt, strerror(errno));
        }

out:
        free(copy);
        if (res == -1)
                return -1;

        res = chdir("/");
        if (res == -1) {
                fprintf(stderr, "%s: failed to chdir to '/'\n", progname);
                return -1;
        }

        return fuse_mnt_remove_mount(progname, mnt);
}

static int unmount_fuse(const char *mnt, int quiet, int lazy)
{
        int res;
        int mtablock = lock_umount();

        res = unmount_fuse_locked(mnt, quiet, lazy);
        unlock_umount(mtablock);

        return res;
}

static int count_fuse_fs(void)
{
        struct mntent *entp;
        int count = 0;
        const char *mtab = _PATH_MOUNTED;
        FILE *fp = setmntent(mtab, "r");
        if (fp == NULL) {
                fprintf(stderr, "%s: failed to open %s: %s\n", progname, mtab,
                        strerror(errno));
                return -1;
        }
        while ((entp = getmntent(fp)) != NULL) {
                if (strcmp(entp->mnt_type, "fuse") == 0 ||
                    strncmp(entp->mnt_type, "fuse.", 5) == 0)
                        count ++;
        }
        endmntent(fp);
        return count;
}


#else /* IGNORE_MTAB */
static int count_fuse_fs(void)
{
        return 0;
}

static int add_mount(const char *source, const char *mnt, const char *type,
                     const char *opts)
{
        (void) source;
        (void) mnt;
        (void) type;
        (void) opts;
        return 0;
}

static int unmount_fuse(const char *mnt, int quiet, int lazy)
{
        (void) quiet;
        return fuse_mnt_umount(progname, mnt, mnt, lazy);
}
#endif /* IGNORE_MTAB */

static void strip_line(char *line)
{
        char *s = strchr(line, '#');
        if (s != NULL)
                s[0] = '\0';
        for (s = line + strlen(line) - 1;
             s >= line && isspace((unsigned char) *s); s--);
        s[1] = '\0';
        for (s = line; isspace((unsigned char) *s); s++);
        if (s != line)
                memmove(line, s, strlen(s)+1);
}

static void parse_line(char *line, int linenum)
{
        int tmp;
        if (strcmp(line, "user_allow_other") == 0)
                user_allow_other = 1;
        else if (sscanf(line, "mount_max = %i", &tmp) == 1)
                mount_max = tmp;
        else if(line[0])
                fprintf(stderr,
                        "%s: unknown parameter in %s at line %i: '%s'\n",
                        progname, FUSE_CONF, linenum, line);
}

static void read_conf(void)
{
        FILE *fp = fopen(FUSE_CONF, "r");
        if (fp != NULL) {
                int linenum = 1;
                char line[256];
                int isnewline = 1;
                while (fgets(line, sizeof(line), fp) != NULL) {
                        if (isnewline) {
                                if (line[strlen(line)-1] == '\n') {
                                        strip_line(line);
                                        parse_line(line, linenum);
                                } else {
                                        isnewline = 0;
                                }
                        } else if(line[strlen(line)-1] == '\n') {
                                fprintf(stderr, "%s: reading %s: line %i too long\n", progname, FUSE_CONF, linenum);

                                isnewline = 1;
                        }
                        if (isnewline)
                                linenum ++;
                }
                if (!isnewline) {
                        fprintf(stderr, "%s: reading %s: missing newline at end of file\n", progname, FUSE_CONF);

                }
                if (ferror(fp)) {
                        fprintf(stderr, "%s: reading %s: read failed\n", progname, FUSE_CONF);
                        exit(1);
                }
                fclose(fp);
        } else if (errno != ENOENT) {
                bool fatal = (errno != EACCES && errno != ELOOP &&
                              errno != ENAMETOOLONG && errno != ENOTDIR &&
                              errno != EOVERFLOW);
                fprintf(stderr, "%s: failed to open %s: %s\n",
                        progname, FUSE_CONF, strerror(errno));
                if (fatal)
                        exit(1);
        }
}

static int begins_with(const char *s, const char *beg)
{
        if (strncmp(s, beg, strlen(beg)) == 0)
                return 1;
        else
                return 0;
}

struct mount_flags {
        const char *opt;
        unsigned long flag;
        int on;
        int safe;
};

static struct mount_flags mount_flags[] = {
        {"rw",      MS_RDONLY,      0, 1},
        {"ro",      MS_RDONLY,      1, 1},
        {"suid",    MS_NOSUID,      0, 0},
        {"nosuid",  MS_NOSUID,      1, 1},
        {"dev",     MS_NODEV,       0, 0},
        {"nodev",   MS_NODEV,       1, 1},
        {"exec",    MS_NOEXEC,      0, 1},
        {"noexec",  MS_NOEXEC,      1, 1},
        {"async",   MS_SYNCHRONOUS, 0, 1},
        {"sync",    MS_SYNCHRONOUS, 1, 1},
        {"atime",   MS_NOATIME,     0, 1},
        {"noatime", MS_NOATIME,     1, 1},
        {"dirsync", MS_DIRSYNC,     1, 1},
        {NULL,      0,              0, 0}
};

static int find_mount_flag(const char *s, unsigned len, int *on, int *flag)
{
        int i;

        for (i = 0; mount_flags[i].opt != NULL; i++) {
                const char *opt = mount_flags[i].opt;
                if (strlen(opt) == len && strncmp(opt, s, len) == 0) {
                        *on = mount_flags[i].on;
                        *flag = mount_flags[i].flag;
                        if (!mount_flags[i].safe && getuid() != 0) {
                                *flag = 0;
                                fprintf(stderr,
                                        "%s: unsafe option %s ignored\n",
                                        progname, opt);
                        }
                        return 1;
                }
        }
        return 0;
}

static int add_option(char **optsp, const char *opt, unsigned expand)
{
        char *newopts;
        if (*optsp == NULL)
                newopts = strdup(opt);
        else {
                unsigned oldsize = strlen(*optsp);
                unsigned newsize = oldsize + 1 + strlen(opt) + expand + 1;
                newopts = (char *) realloc(*optsp, newsize);
                if (newopts)
                        sprintf(newopts + oldsize, ",%s", opt);
        }
        if (newopts == NULL) {
                fprintf(stderr, "%s: failed to allocate memory\n", progname);
                return -1;
        }
        *optsp = newopts;
        return 0;
}

static int get_mnt_opts(int flags, char *opts, char **mnt_optsp)
{
        int i;
        int l;

        if (!(flags & MS_RDONLY) && add_option(mnt_optsp, "rw", 0) == -1)
                return -1;

        for (i = 0; mount_flags[i].opt != NULL; i++) {
                if (mount_flags[i].on && (flags & mount_flags[i].flag) &&
                    add_option(mnt_optsp, mount_flags[i].opt, 0) == -1)
                        return -1;
        }

        if (add_option(mnt_optsp, opts, 0) == -1)
                return -1;
        /* remove comma from end of opts*/
        l = strlen(*mnt_optsp);
        if ((*mnt_optsp)[l-1] == ',')
                (*mnt_optsp)[l-1] = '\0';
        if (getuid() != 0) {
                const char *user = get_user_name();
                if (user == NULL)
                        return -1;

                if (add_option(mnt_optsp, "user=", strlen(user)) == -1)
                        return -1;
                strcat(*mnt_optsp, user);
        }
        return 0;
}

static int opt_eq(const char *s, unsigned len, const char *opt)
{
        if(strlen(opt) == len && strncmp(s, opt, len) == 0)
                return 1;
        else
                return 0;
}

static int get_string_opt(const char *s, unsigned len, const char *opt,
                          char **val)
{
        int i;
        unsigned opt_len = strlen(opt);
        char *d;

        if (*val)
                free(*val);
        *val = (char *) malloc(len - opt_len + 1);
        if (!*val) {
                fprintf(stderr, "%s: failed to allocate memory\n", progname);
                return 0;
        }

        d = *val;
        s += opt_len;
        len -= opt_len;
        for (i = 0; i < len; i++) {
                if (s[i] == '\\' && i + 1 < len)
                        i++;
                *d++ = s[i];
        }
        *d = '\0';
        return 1;
}

/* The kernel silently truncates the "data" argument to PAGE_SIZE-1 characters.
 * This can be dangerous if it e.g. truncates the option "group_id=1000" to
 * "group_id=1".
 * This wrapper detects this case and bails out with an error.
 */
static int mount_notrunc(const char *source, const char *target,
                         const char *filesystemtype, unsigned long mountflags,
                         const char *data) {
        if (strlen(data) > sysconf(_SC_PAGESIZE) - 1) {
                fprintf(stderr, "%s: mount options too long\n", progname);
                errno = EINVAL;
                return -1;
        }
        return mount(source, target, filesystemtype, mountflags, data);
}


static int do_mount(const char *mnt, const char **typep, mode_t rootmode,
                    int fd, const char *opts, const char *dev, char **sourcep,
                    char **mnt_optsp)
{
        int res;
        int flags = MS_NOSUID | MS_NODEV;
        char *optbuf;
        char *mnt_opts = NULL;
        const char *s;
        char *d;
        char *fsname = NULL;
        char *subtype = NULL;
        char *source = NULL;
        char *type = NULL;
        int blkdev = 0;

        optbuf = (char *) malloc(strlen(opts) + 128);
        if (!optbuf) {
                fprintf(stderr, "%s: failed to allocate memory\n", progname);
                return -1;
        }

        for (s = opts, d = optbuf; *s;) {
                unsigned len;
                const char *fsname_str = "fsname=";
                const char *subtype_str = "subtype=";
                bool escape_ok = begins_with(s, fsname_str) ||
                                 begins_with(s, subtype_str);
                for (len = 0; s[len]; len++) {
                        if (escape_ok && s[len] == '\\' && s[len + 1])
                                len++;
                        else if (s[len] == ',')
                                break;
                }
                if (begins_with(s, fsname_str)) {
                        if (!get_string_opt(s, len, fsname_str, &fsname))
                                goto err;
                } else if (begins_with(s, subtype_str)) {
                        if (!get_string_opt(s, len, subtype_str, &subtype))
                                goto err;
                } else if (opt_eq(s, len, "blkdev")) {
                        if (getuid() != 0) {
                                fprintf(stderr,
                                        "%s: option blkdev is privileged\n",
                                        progname);
                                goto err;
                        }
                        blkdev = 1;
                } else if (opt_eq(s, len, "auto_unmount")) {
                        auto_unmount = 1;
                } else if (!begins_with(s, "fd=") &&
                           !begins_with(s, "rootmode=") &&
                           !begins_with(s, "user_id=") &&
                           !begins_with(s, "group_id=")) {
                        int on;
                        int flag;
                        int skip_option = 0;
                        if (opt_eq(s, len, "large_read")) {
                                struct utsname utsname;
                                unsigned kmaj, kmin;
                                res = uname(&utsname);
                                if (res == 0 &&
                                    sscanf(utsname.release, "%u.%u",
                                           &kmaj, &kmin) == 2 &&
                                    (kmaj > 2 || (kmaj == 2 && kmin > 4))) {
                                        fprintf(stderr, "%s: note: 'large_read' mount option is deprecated for %i.%i kernels\n", progname, kmaj, kmin);
                                        skip_option = 1;
                                }
                        }
                        if (getuid() != 0 && !user_allow_other &&
                            (opt_eq(s, len, "allow_other") ||
                             opt_eq(s, len, "allow_root"))) {
                                fprintf(stderr, "%s: option %.*s only allowed if 'user_allow_other' is set in %s\n", progname, len, s, FUSE_CONF);
                                goto err;
                        }
                        if (!skip_option) {
                                if (find_mount_flag(s, len, &on, &flag)) {
                                        if (on)
                                                flags |= flag;
                                        else
                                                flags  &= ~flag;
                                } else if (opt_eq(s, len, "default_permissions") ||
                                           opt_eq(s, len, "allow_other") ||
                                           begins_with(s, "max_read=") ||
                                           begins_with(s, "blksize=")) {
                                        memcpy(d, s, len);
                                        d += len;
                                        *d++ = ',';
                                } else {
                                        fprintf(stderr, "%s: unknown option '%.*s'\n", progname, len, s);
                                        exit(1);
                                }
                        }
                }
                s += len;
                if (*s)
                        s++;
        }
        *d = '\0';
        res = get_mnt_opts(flags, optbuf, &mnt_opts);
        if (res == -1)
                goto err;

        sprintf(d, "fd=%i,rootmode=%o,user_id=%u,group_id=%u",
                fd, rootmode, getuid(), getgid());

        source = malloc((fsname ? strlen(fsname) : 0) +
                        (subtype ? strlen(subtype) : 0) + strlen(dev) + 32);

        type = malloc((subtype ? strlen(subtype) : 0) + 32);
        if (!type || !source) {
                fprintf(stderr, "%s: failed to allocate memory\n", progname);
                goto err;
        }

        if (subtype)
                sprintf(type, "%s.%s", blkdev ? "fuseblk" : "fuse", subtype);
        else
                strcpy(type, blkdev ? "fuseblk" : "fuse");

        if (fsname)
                strcpy(source, fsname);
        else
                strcpy(source, subtype ? subtype : dev);

        res = mount_notrunc(source, mnt, type, flags, optbuf);
        if (res == -1 && errno == ENODEV && subtype) {
                /* Probably missing subtype support */
                strcpy(type, blkdev ? "fuseblk" : "fuse");
                if (fsname) {
                        if (!blkdev)
                                sprintf(source, "%s#%s", subtype, fsname);
                } else {
                        strcpy(source, type);
                }

                res = mount_notrunc(source, mnt, type, flags, optbuf);
        }
        if (res == -1 && errno == EINVAL) {
                /* It could be an old version not supporting group_id */
                sprintf(d, "fd=%i,rootmode=%o,user_id=%u",
                        fd, rootmode, getuid());
                res = mount_notrunc(source, mnt, type, flags, optbuf);
        }
        if (res == -1) {
                int errno_save = errno;
                if (blkdev && errno == ENODEV && !fuse_mnt_check_fuseblk())
                        fprintf(stderr, "%s: 'fuseblk' support missing\n",
                                progname);
                else
                        fprintf(stderr, "%s: mount failed: %s\n", progname,
                                strerror(errno_save));
                goto err;
        }
        *sourcep = source;
        *typep = type;
        *mnt_optsp = mnt_opts;
        free(fsname);
        free(optbuf);

        return 0;

err:
        free(fsname);
        free(subtype);
        free(source);
        free(type);
        free(mnt_opts);
        free(optbuf);
        return -1;
}

static int check_perm(const char **mntp, struct stat *stbuf, int *mountpoint_fd)
{
        int res;
        const char *mnt = *mntp;
        const char *origmnt = mnt;
        struct statfs fs_buf;
        size_t i;

        res = lstat(mnt, stbuf);
        if (res == -1) {
                fprintf(stderr, "%s: failed to access mountpoint %s: %s\n",
                        progname, mnt, strerror(errno));
                return -1;
        }

        /* No permission checking is done for root */
        if (getuid() == 0)
                return 0;

        if (S_ISDIR(stbuf->st_mode)) {
                res = chdir(mnt);
                if (res == -1) {
                        fprintf(stderr,
                                "%s: failed to chdir to mountpoint: %s\n",
                                progname, strerror(errno));
                        return -1;
                }
                mnt = *mntp = ".";
                res = lstat(mnt, stbuf);
                if (res == -1) {
                        fprintf(stderr,
                                "%s: failed to access mountpoint %s: %s\n",
                                progname, origmnt, strerror(errno));
                        return -1;
                }

                if ((stbuf->st_mode & S_ISVTX) && stbuf->st_uid != getuid()) {
                        fprintf(stderr, "%s: mountpoint %s not owned by user\n",
                                progname, origmnt);
                        return -1;
                }

                res = access(mnt, W_OK);
                if (res == -1) {
                        fprintf(stderr, "%s: user has no write access to mountpoint %s\n",
                                progname, origmnt);
                        return -1;
                }
        } else if (S_ISREG(stbuf->st_mode)) {
                static char procfile[256];
                *mountpoint_fd = open(mnt, O_WRONLY);
                if (*mountpoint_fd == -1) {
                        fprintf(stderr, "%s: failed to open %s: %s\n",
                                progname, mnt, strerror(errno));
                        return -1;
                }
                res = fstat(*mountpoint_fd, stbuf);
                if (res == -1) {
                        fprintf(stderr,
                                "%s: failed to access mountpoint %s: %s\n",
                                progname, mnt, strerror(errno));
                        return -1;
                }
                if (!S_ISREG(stbuf->st_mode)) {
                        fprintf(stderr,
                                "%s: mountpoint %s is no longer a regular file\n",
                                progname, mnt);
                        return -1;
                }

                sprintf(procfile, "/proc/self/fd/%i", *mountpoint_fd);
                *mntp = procfile;
        } else {
                fprintf(stderr,
                        "%s: mountpoint %s is not a directory or a regular file\n",
                        progname, mnt);
                return -1;
        }

        /* Do not permit mounting over anything in procfs - it has a couple
         * places to which we have "write access" without being supposed to be
         * able to just put anything we want there.
         * Luckily, without allow_other, we can't get other users to actually
         * use any fake information we try to put there anyway.
         * Use a whitelist to be safe. */
        if (statfs(*mntp, &fs_buf)) {
                fprintf(stderr, "%s: failed to access mountpoint %s: %s\n",
                        progname, mnt, strerror(errno));
                return -1;
        }

        /* Define permitted filesystems for the mount target. This was
         * originally the same list as used by the ecryptfs mount helper
         * (https://bazaar.launchpad.net/~ecryptfs/ecryptfs/trunk/view/head:/src/utils/mount.ecryptfs_private.c#L225)
         * but got expanded as we found more filesystems that needed to be
         * overlayed. */
        typeof(fs_buf.f_type) f_type_whitelist[] = {
                0x61756673 /* AUFS_SUPER_MAGIC */,
                0x00000187 /* AUTOFS_SUPER_MAGIC */,
                0xCA451A4E /* BCACHEFS_STATFS_MAGIC */,
                0x9123683E /* BTRFS_SUPER_MAGIC */,
                0x00C36400 /* CEPH_SUPER_MAGIC */,
                0xFF534D42 /* CIFS_MAGIC_NUMBER */,
                0x0000F15F /* ECRYPTFS_SUPER_MAGIC */,
                0x0000EF53 /* EXT[234]_SUPER_MAGIC */,
                0xF2F52010 /* F2FS_SUPER_MAGIC */,
                0x65735546 /* FUSE_SUPER_MAGIC */,
                0x01161970 /* GFS2_MAGIC */,
                0x47504653 /* GPFS_SUPER_MAGIC */,
                0x0000482b /* HFSPLUS_SUPER_MAGIC */,
                0x000072B6 /* JFFS2_SUPER_MAGIC */,
                0x3153464A /* JFS_SUPER_MAGIC */,
                0x0BD00BD0 /* LL_SUPER_MAGIC */,
                0X00004D44 /* MSDOS_SUPER_MAGIC */,
                0x0000564C /* NCP_SUPER_MAGIC */,
                0x00006969 /* NFS_SUPER_MAGIC */,
                0x00003434 /* NILFS_SUPER_MAGIC */,
                0x5346544E /* NTFS_SB_MAGIC */,
                0x5346414f /* OPENAFS_SUPER_MAGIC */,
                0x794C7630 /* OVERLAYFS_SUPER_MAGIC */,
                0x52654973 /* REISERFS_SUPER_MAGIC */,
                0xFE534D42 /* SMB2_SUPER_MAGIC */,
                0x73717368 /* SQUASHFS_MAGIC */,
                0x01021994 /* TMPFS_MAGIC */,
                0x24051905 /* UBIFS_SUPER_MAGIC */,
                0x58465342 /* XFS_SB_MAGIC */,
                0x2FC12FC1 /* ZFS_SUPER_MAGIC */,
        };
        for (i = 0; i < sizeof(f_type_whitelist)/sizeof(f_type_whitelist[0]); i++) {
                if (f_type_whitelist[i] == fs_buf.f_type)
                        return 0;
        }

        fprintf(stderr, "%s: mounting over filesystem type %#010lx is forbidden\n",
                progname, (unsigned long)fs_buf.f_type);
        return -1;
}

static int try_open(const char *dev, char **devp, int silent)
{
        int fd = open(dev, O_RDWR);
        if (fd != -1) {
                *devp = strdup(dev);
                if (*devp == NULL) {
                        fprintf(stderr, "%s: failed to allocate memory\n",
                                progname);
                        close(fd);
                        fd = -1;
                }
        } else if (errno == ENODEV ||
                   errno == ENOENT)/* check for ENOENT too, for the udev case */
                return -2;
        else if (!silent) {
                fprintf(stderr, "%s: failed to open %s: %s\n", progname, dev,
                        strerror(errno));
        }
        return fd;
}

static int try_open_fuse_device(char **devp)
{
        int fd;

        drop_privs();
        fd = try_open(FUSE_DEV, devp, 0);
        restore_privs();
        return fd;
}

static int open_fuse_device(char **devp)
{
        int fd = try_open_fuse_device(devp);
        if (fd >= -1)
                return fd;

        fprintf(stderr,
                "%s: fuse device not found, try 'modprobe fuse' first\n",
                progname);

        return -1;
}


static int mount_fuse(const char *mnt, const char *opts, const char **type)
{
        int res;
        int fd;
        char *dev;
        struct stat stbuf;
        char *source = NULL;
        char *mnt_opts = NULL;
        const char *real_mnt = mnt;
        int mountpoint_fd = -1;

        fd = open_fuse_device(&dev);
        if (fd == -1)
                return -1;

        drop_privs();
        read_conf();

        if (getuid() != 0 && mount_max != -1) {
                int mount_count = count_fuse_fs();
                if (mount_count >= mount_max) {
                        fprintf(stderr, "%s: too many FUSE filesystems mounted; mount_max=N can be set in %s\n", progname, FUSE_CONF);
                        goto fail_close_fd;
                }
        }

        res = check_perm(&real_mnt, &stbuf, &mountpoint_fd);
        restore_privs();
        if (res != -1)
                res = do_mount(real_mnt, type, stbuf.st_mode & S_IFMT,
                               fd, opts, dev, &source, &mnt_opts);

        if (mountpoint_fd != -1)
                close(mountpoint_fd);

        if (res == -1)
                goto fail_close_fd;

        res = chdir("/");
        if (res == -1) {
                fprintf(stderr, "%s: failed to chdir to '/'\n", progname);
                goto fail_close_fd;
        }

        if (geteuid() == 0) {
                res = add_mount(source, mnt, *type, mnt_opts);
                if (res == -1) {
                        /* Can't clean up mount in a non-racy way */
                        goto fail_close_fd;
                }
        }

out_free:
        free(source);
        free(mnt_opts);
        free(dev);

        return fd;

fail_close_fd:
        close(fd);
        fd = -1;
        goto out_free;
}

static int send_fd(int sock_fd, int fd)
{
        int retval;
        struct msghdr msg;
        struct cmsghdr *p_cmsg;
        struct iovec vec;
        size_t cmsgbuf[CMSG_SPACE(sizeof(fd)) / sizeof(size_t)];
        int *p_fds;
        char sendchar = 0;

        msg.msg_control = cmsgbuf;
        msg.msg_controllen = sizeof(cmsgbuf);
        p_cmsg = CMSG_FIRSTHDR(&msg);
        p_cmsg->cmsg_level = SOL_SOCKET;
        p_cmsg->cmsg_type = SCM_RIGHTS;
        p_cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
        p_fds = (int *) CMSG_DATA(p_cmsg);
        *p_fds = fd;
        msg.msg_controllen = p_cmsg->cmsg_len;
        msg.msg_name = NULL;
        msg.msg_namelen = 0;
        msg.msg_iov = &vec;
        msg.msg_iovlen = 1;
        msg.msg_flags = 0;
        /* "To pass file descriptors or credentials you need to send/read at
         * least one byte" (man 7 unix) */
        vec.iov_base = &sendchar;
        vec.iov_len = sizeof(sendchar);
        while ((retval = sendmsg(sock_fd, &msg, 0)) == -1 && errno == EINTR);
        if (retval != 1) {
                perror("sending file descriptor");
                return -1;
        }
        return 0;
}

/* The parent fuse process has died: decide whether to auto_unmount.
 *
 * In the normal case (umount or fusermount -u), the filesystem
 * has already been unmounted. If we simply unmount again we can
 * cause problems with stacked mounts (e.g. autofs).
 *
 * So we unmount here only in abnormal case where fuse process has
 * died without unmount happening. To detect this, we first look in
 * the mount table to make sure the mountpoint is still mounted and
 * has proper type. If so, we then see if opening the mount dir is
 * returning 'Transport endpoint is not connected'.
 *
 * The order of these is important, because if autofs is in use,
 * opening the dir to check for ENOTCONN will cause a new mount
 * in the normal case where filesystem has been unmounted cleanly.
 */
static int should_auto_unmount(const char *mnt, const char *type)
{
        char *copy;
        const char *last;
        int result = 0;
        int fd;

        copy = strdup(mnt);
        if (copy == NULL) {
        fprintf(stderr, "%s: failed to allocate memory\n", progname);
                return 0;
        }

        if (chdir_to_parent(copy, &last) == -1)
                goto out;
        if (check_is_mount(last, mnt, type) == -1)
                goto out;

        fd = open(mnt, O_RDONLY);
        if (fd != -1) {
                close(fd);
        } else {
                result = errno == ENOTCONN;
        }
out:
        free(copy);
        return result;
}

static void usage(void)
{
        printf("%s: [options] mountpoint\n"
               "Options:\n"
               " -h                 print help\n"
               " -V                 print version\n"
               " -o opt[,opt...]   mount options\n"
               " -u                 unmount\n"
               " -q                 quiet\n"
               " -z                 lazy unmount\n",
               progname);
        exit(1);
}

static void show_version(void)
{
        printf("fusermount3 version: %s\n", PACKAGE_VERSION);
        exit(0);
}

int main(int argc, char *argv[])
{
        sigset_t sigset;
        int ch;
        int fd;
        int res;
        char *origmnt;
        char *mnt;
        static int unmount = 0;
        static int lazy = 0;
        static int quiet = 0;
        char *commfd;
        int cfd;
        const char *opts = "";
        const char *type = NULL;

        static const struct option long_opts[] = {
                {"unmount", no_argument, NULL, 'u'},
                {"lazy",    no_argument, NULL, 'z'},
                {"quiet",   no_argument, NULL, 'q'},
                {"help",    no_argument, NULL, 'h'},
                {"version", no_argument, NULL, 'V'},
                {0, 0, 0, 0}};

        progname = strdup(argv[0]);
        if (progname == NULL) {
                fprintf(stderr, "%s: failed to allocate memory\n", argv[0]);
                exit(1);
        }

        while ((ch = getopt_long(argc, argv, "hVo:uzq", long_opts,
                                 NULL)) != -1) {
                switch (ch) {
                case 'h':
                        usage();
                        break;

                case 'V':
                        show_version();
                        break;

                case 'o':
                        opts = optarg;
                        break;

                case 'u':
                        unmount = 1;
                        break;

                case 'z':
                        lazy = 1;
                        break;

                case 'q':
                        quiet = 1;
                        break;

                default:
                        exit(1);
                }
        }

        if (lazy && !unmount) {
                fprintf(stderr, "%s: -z can only be used with -u\n", progname);
                exit(1);
        }

        if (optind >= argc) {
                fprintf(stderr, "%s: missing mountpoint argument\n", progname);
                exit(1);
        } else if (argc > optind + 1) {
                fprintf(stderr, "%s: extra arguments after the mountpoint\n",
                        progname);
                exit(1);
        }

        origmnt = argv[optind];

        drop_privs();
        mnt = fuse_mnt_resolve_path(progname, origmnt);
        if (mnt != NULL) {
                res = chdir("/");
                if (res == -1) {
                        fprintf(stderr, "%s: failed to chdir to '/'\n", progname);
                        goto err_out;
                }
        }
        restore_privs();
        if (mnt == NULL)
                exit(1);

        umask(033);
        if (unmount)
                goto do_unmount;

        commfd = getenv(FUSE_COMMFD_ENV);
        if (commfd == NULL) {
                fprintf(stderr, "%s: old style mounting not supported\n",
                        progname);
                goto err_out;
        }

        fd = mount_fuse(mnt, opts, &type);
        if (fd == -1)
                goto err_out;

        cfd = atoi(commfd);
        res = send_fd(cfd, fd);
        if (res == -1)
                goto err_out;
        close(fd);

        if (!auto_unmount) {
                free(mnt);
                return 0;
        }

        /* Become a daemon and wait for the parent to exit or die.
           ie For the control socket to get closed.
           btw We don't want to use daemon() function here because
           it forks and messes with the file descriptors. */
        setsid();
        res = chdir("/");
        if (res == -1) {
                fprintf(stderr, "%s: failed to chdir to '/'\n", progname);
                goto err_out;
        }

        sigfillset(&sigset);
        sigprocmask(SIG_BLOCK, &sigset, NULL);

        lazy  = 1;
        quiet = 1;

        while (1) {
                unsigned char buf[16];
                int n = recv(cfd, buf, sizeof(buf), 0);
                if (!n)
                        break;

                if (n < 0) {
                        if (errno == EINTR)
                                continue;
                        break;
                }
        }

        if (!should_auto_unmount(mnt, type)) {
                goto success_out;
        }

do_unmount:
        if (geteuid() == 0)
                res = unmount_fuse(mnt, quiet, lazy);
        else {
                res = umount2(mnt, lazy ? UMOUNT_DETACH : 0);
                if (res == -1 && !quiet)
                        fprintf(stderr,
                                "%s: failed to unmount %s: %s\n",
                                progname, mnt, strerror(errno));
        }
        if (res == -1)
                goto err_out;

success_out:
        free(mnt);
        return 0;

err_out:
        free(mnt);
        exit(1);
}