fusermount.c

UNIX/LINUX下面的用户文件系统

/*
    FUSE: Filesystem in Userspace
    Copyright (C) 2001-2007  Miklos Szeredi <[e-mail]>

    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 */

#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 <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>

#define FUSE_COMMFD_ENV         "_FUSE_COMMFD"

#define FUSE_DEV_OLD "/proc/fs/fuse/dev"
#define FUSE_DEV_NEW "/dev/fuse"
#define FUSE_VERSION_FILE_OLD "/proc/fs/fuse/version"
#define FUSE_CONF "/etc/fuse.conf"

#ifndef MS_DIRSYNC
#define MS_DIRSYNC 128
#endif

static const char *progname;

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

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
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 unmount_fuse(const char *mnt, int quiet, int lazy)
{
    if (getuid() != 0) {
        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 fuse_mnt_umount(progname, mnt, lazy);
}

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()
{
    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)
{
    return fuse_mnt_umount(progname, 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 {
                    fprintf(stderr, "%s: reading %s: line %i too long\n",
                            progname, FUSE_CONF, linenum);
                    isnewline = 0;
                }
            } else if(line[strlen(line)-1] == '\n')
                isnewline = 1;
            if (isnewline)
                linenum ++;
        }
        fclose(fp);
    } else if (errno != ENOENT) {
        fprintf(stderr, "%s: failed to open %s: %s\n", progname, FUSE_CONF,
                strerror(errno));
    }
}

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)
{
    unsigned opt_len = strlen(opt);

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

    memcpy(*val, s + opt_len, len - opt_len);
    (*val)[len - opt_len] = '\0';
    return 1;
}

static int do_mount(const char *mnt, char **typep, mode_t rootmode,
                    int fd, const char *opts, const char *dev, char **sourcep,
                    char **mnt_optsp, off_t rootsize)
{
    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 check_empty = 1;
    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=";
        for (len = 0; s[len] && s[len] != ','; len++);
        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, "nonempty")) {
            check_empty = 0;
        } 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 /etc/fuse.conf\n", progname, len, s);
                goto err;
            }
            if (!skip_option) {
                if (find_mount_flag(s, len, &on, &flag)) {
                    if (on)
                        flags |= flag;
                    else
                        flags  &= ~flag;
                } else {
                    memcpy(d, s, len);
                    d += len;
                    *d++ = ',';
                }
            }
        }
        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=%i,group_id=%i",
            fd, rootmode, getuid(), getgid());

    if (check_empty &&
        fuse_mnt_check_empty(progname, mnt, rootmode, rootsize) == -1)
        goto err;

    source = malloc((fsname ? strlen(fsname) : 0) +