mergerfs/libfuse/lib/mount_generic.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 LGPLv2.
  See the file COPYING.LIB.
*/

#include "config.h"
#include "fuse_i.h"
#include "fuse_misc.h"
#include "fuse_opt.h"
#include "mount_util.h"

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <stddef.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/poll.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/wait.h>
#include <sys/mount.h>

#ifdef __NetBSD__
#include <perfuse.h>

#define MS_RDONLY 	MNT_RDONLY
#define MS_NOSUID 	MNT_NOSUID
#define MS_NODEV 	MNT_NODEV
#define MS_NOEXEC 	MNT_NOEXEC
#define MS_SYNCHRONOUS 	MNT_SYNCHRONOUS
#define MS_NOATIME 	MNT_NOATIME

#define umount2(mnt, flags) unmount(mnt, (flags == 2) ? MNT_FORCE : 0)
#endif

#define FUSERMOUNT_PROG		"fusermount"
#define FUSE_COMMFD_ENV		"_FUSE_COMMFD"

#ifndef HAVE_FORK
#define fork() vfork()
#endif

#ifndef MS_DIRSYNC
#define MS_DIRSYNC 128
#endif

enum {
  KEY_KERN_FLAG,
  KEY_KERN_OPT,
  KEY_FUSERMOUNT_OPT,
  KEY_SUBTYPE_OPT,
  KEY_MTAB_OPT,
  KEY_ALLOW_ROOT,
  KEY_RO,
  KEY_HELP,
  KEY_VERSION,
};

struct mount_opts {
  int allow_other;
  int allow_root;
  int ishelp;
  int flags;
  int nonempty;
  int auto_unmount;
  int blkdev;
  char *fsname;
  char *subtype;
  char *subtype_opt;
  char *mtab_opts;
  char *fusermount_opts;
  char *kernel_opts;
};

#define FUSE_MOUNT_OPT(t, p) { t, offsetof(struct mount_opts, p), 1 }

static const struct fuse_opt fuse_mount_opts[] = {
  FUSE_MOUNT_OPT("allow_other",		allow_other),
  FUSE_MOUNT_OPT("allow_root",		allow_root),
  FUSE_MOUNT_OPT("nonempty",		nonempty),
  FUSE_MOUNT_OPT("blkdev",		blkdev),
  FUSE_MOUNT_OPT("auto_unmount",		auto_unmount),
  FUSE_MOUNT_OPT("fsname=%s",		fsname),
  FUSE_MOUNT_OPT("subtype=%s",		subtype),
  FUSE_OPT_KEY("allow_other",		KEY_KERN_OPT),
  FUSE_OPT_KEY("allow_root",		KEY_ALLOW_ROOT),
  FUSE_OPT_KEY("nonempty",		KEY_FUSERMOUNT_OPT),
  FUSE_OPT_KEY("auto_unmount",		KEY_FUSERMOUNT_OPT),
  FUSE_OPT_KEY("blkdev",			KEY_FUSERMOUNT_OPT),
  FUSE_OPT_KEY("fsname=",			KEY_FUSERMOUNT_OPT),
  FUSE_OPT_KEY("subtype=",		KEY_SUBTYPE_OPT),
  FUSE_OPT_KEY("large_read",		KEY_KERN_OPT),
  FUSE_OPT_KEY("blksize=",		KEY_KERN_OPT),
  FUSE_OPT_KEY("default_permissions",	KEY_KERN_OPT),
  FUSE_OPT_KEY("context=",		KEY_KERN_OPT),
  FUSE_OPT_KEY("fscontext=",		KEY_KERN_OPT),
  FUSE_OPT_KEY("defcontext=",		KEY_KERN_OPT),
  FUSE_OPT_KEY("rootcontext=",		KEY_KERN_OPT),
  FUSE_OPT_KEY("max_read=",		KEY_KERN_OPT),
  FUSE_OPT_KEY("max_read=",		FUSE_OPT_KEY_KEEP),
  FUSE_OPT_KEY("user=",			KEY_MTAB_OPT),
  FUSE_OPT_KEY("-r",			KEY_RO),
  FUSE_OPT_KEY("ro",			KEY_KERN_FLAG),
  FUSE_OPT_KEY("rw",			KEY_KERN_FLAG),
  FUSE_OPT_KEY("suid",			KEY_KERN_FLAG),
  FUSE_OPT_KEY("nosuid",			KEY_KERN_FLAG),
  FUSE_OPT_KEY("dev",			KEY_KERN_FLAG),
  FUSE_OPT_KEY("nodev",			KEY_KERN_FLAG),
  FUSE_OPT_KEY("exec",			KEY_KERN_FLAG),
  FUSE_OPT_KEY("noexec",			KEY_KERN_FLAG),
  FUSE_OPT_KEY("async",			KEY_KERN_FLAG),
  FUSE_OPT_KEY("sync",			KEY_KERN_FLAG),
  FUSE_OPT_KEY("dirsync",			KEY_KERN_FLAG),
  FUSE_OPT_KEY("atime",			KEY_KERN_FLAG),
  FUSE_OPT_KEY("noatime",			KEY_KERN_FLAG),
  FUSE_OPT_KEY("-h",			KEY_HELP),
  FUSE_OPT_KEY("--help",			KEY_HELP),
  FUSE_OPT_KEY("-V",			KEY_VERSION),
  FUSE_OPT_KEY("--version",		KEY_VERSION),
  FUSE_OPT_END
};

static void mount_help(void)
{
  fprintf(stderr,
          "    -o allow_other         allow access to other users\n"
          "    -o allow_root          allow access to root\n"
          "    -o auto_unmount        auto unmount on process termination\n"
          "    -o nonempty            allow mounts over non-empty file/dir\n"
          "    -o default_permissions enable permission checking by kernel\n"
          "    -o fsname=NAME         set filesystem name\n"
          "    -o subtype=NAME        set filesystem type\n"
          "    -o large_read          issue large read requests (2.4 only)\n"
          "    -o max_read=N          set maximum size of read requests\n"
          "\n");
}

static void exec_fusermount(const char *argv[])
{
  execv(FUSERMOUNT_DIR "/mergerfs-" FUSERMOUNT_PROG, (char **) argv);
  execvp("mergerfs-" FUSERMOUNT_PROG, (char **) argv);
  execv(FUSERMOUNT_DIR "/" FUSERMOUNT_PROG, (char **) argv);
  execvp(FUSERMOUNT_PROG, (char **) argv);
}

static void mount_version(void)
{
  int pid = fork();
  if (!pid) {
    const char *argv[] = { FUSERMOUNT_PROG, "--version", NULL };
    exec_fusermount(argv);
    _exit(1);
  } else if (pid != -1)
    waitpid(pid, NULL, 0);
}

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

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

static void set_mount_flag(const char *s, int *flags)
{
  int i;

  for (i = 0; mount_flags[i].opt != NULL; i++) {
    const char *opt = mount_flags[i].opt;
    if (strcmp(opt, s) == 0) {
      if (mount_flags[i].on)
        *flags |= mount_flags[i].flag;
      else
        *flags &= ~mount_flags[i].flag;
      return;
    }
  }
  fprintf(stderr, "fuse: internal error, can't find mount flag\n");
  abort();
}

static int fuse_mount_opt_proc(void *data, const char *arg, int key,
			       struct fuse_args *outargs)
{
  struct mount_opts *mo = data;

  switch (key) {
  case KEY_ALLOW_ROOT:
    if (fuse_opt_add_opt(&mo->kernel_opts, "allow_other") == -1 ||
        fuse_opt_add_arg(outargs, "-oallow_root") == -1)
      return -1;
    return 0;

  case KEY_RO:
    arg = "ro";
    /* fall through */
  case KEY_KERN_FLAG:
    set_mount_flag(arg, &mo->flags);
    return 0;

  case KEY_KERN_OPT:
    return fuse_opt_add_opt(&mo->kernel_opts, arg);

  case KEY_FUSERMOUNT_OPT:
    return fuse_opt_add_opt_escaped(&mo->fusermount_opts, arg);

  case KEY_SUBTYPE_OPT:
    return fuse_opt_add_opt(&mo->subtype_opt, arg);

  case KEY_MTAB_OPT:
    return fuse_opt_add_opt(&mo->mtab_opts, arg);

  case KEY_HELP:
    mount_help();
    mo->ishelp = 1;
    break;

  case KEY_VERSION:
    mount_version();
    mo->ishelp = 1;
    break;
  }
  return 1;
}

/* return value:
 * >= 0	 => fd
 * -1	 => error
 */
static int receive_fd(int fd)
{
  struct msghdr msg;
  struct iovec iov;
  char buf[1];
  int rv;
  size_t ccmsg[CMSG_SPACE(sizeof(int)) / sizeof(size_t)];
  struct cmsghdr *cmsg;

  iov.iov_base = buf;
  iov.iov_len = 1;

  memset(&msg, 0, sizeof(msg));
  msg.msg_name = 0;
  msg.msg_namelen = 0;
  msg.msg_iov = &iov;
  msg.msg_iovlen = 1;
  /* old BSD implementations should use msg_accrights instead of
   * msg_control; the interface is different. */
  msg.msg_control = ccmsg;
  msg.msg_controllen = sizeof(ccmsg);

  while(((rv = recvmsg(fd, &msg, 0)) == -1) && errno == EINTR);
  if (rv == -1) {
    perror("recvmsg");
    return -1;
  }
  if(!rv) {
    /* EOF */
    return -1;
  }

  cmsg = CMSG_FIRSTHDR(&msg);
  if (cmsg->cmsg_type != SCM_RIGHTS) {
    fprintf(stderr, "got control message of unknown type %d\n",
            cmsg->cmsg_type);
    return -1;
  }
  return *(int*)CMSG_DATA(cmsg);
}

void fuse_kern_unmount(const char *mountpoint, int fd)
{
  int res;
  int pid;

  if (!mountpoint)
    return;

  if (fd != -1) {
    struct pollfd pfd;

    pfd.fd = fd;
    pfd.events = 0;
    res = poll(&pfd, 1, 0);

    /* Need to close file descriptor, otherwise synchronous umount
       would recurse into filesystem, and deadlock.

       Caller expects fuse_kern_unmount to close the fd, so close it
       anyway. */
    close(fd);

    /* If file poll returns POLLERR on the device file descriptor,
       then the filesystem is already unmounted */
    if (res == 1 && (pfd.revents & POLLERR))
      return;
  }

  if (geteuid() == 0) {
    fuse_mnt_umount("fuse", mountpoint, mountpoint,  1);
    return;
  }

  res = umount2(mountpoint, 2);
  if (res == 0)
    return;

  pid = fork();
  if(pid == -1)
    return;

  if(pid == 0) {
    const char *argv[] = { FUSERMOUNT_PROG, "-u", "-q", "-z",
                           "--", mountpoint, NULL };

    exec_fusermount(argv);
    _exit(1);
  }
  waitpid(pid, NULL, 0);
}

static int fuse_mount_fusermount(const char *mountpoint, struct mount_opts *mo,
                                 const char *opts, int quiet)
{
  int fds[2], pid;
  int res;
  int rv;

  if (!mountpoint) {
    fprintf(stderr, "fuse: missing mountpoint parameter\n");
    return -1;
  }

  res = socketpair(PF_UNIX, SOCK_STREAM, 0, fds);
  if(res == -1) {
    perror("fuse: socketpair() failed");
    return -1;
  }

  pid = fork();
  if(pid == -1) {
    perror("fuse: fork() failed");
    close(fds[0]);
    close(fds[1]);
    return -1;
  }

  if(pid == 0) {
    char env[10];
    const char *argv[32];
    int a = 0;

    if (quiet) {
      int fd = open("/dev/null", O_RDONLY);
      if (fd != -1) {
        dup2(fd, 1);
        dup2(fd, 2);
      }
    }

    argv[a++] = FUSERMOUNT_PROG;
    if (opts) {
      argv[a++] = "-o";
      argv[a++] = opts;
    }
    argv[a++] = "--";
    argv[a++] = mountpoint;
    argv[a++] = NULL;

    close(fds[1]);
    fcntl(fds[0], F_SETFD, 0);
    snprintf(env, sizeof(env), "%i", fds[0]);
    setenv(FUSE_COMMFD_ENV, env, 1);
    exec_fusermount(argv);
    perror("fuse: failed to exec fusermount");
    _exit(1);
  }

  close(fds[0]);
  rv = receive_fd(fds[1]);

  if (!mo->auto_unmount) {
    /* with auto_unmount option fusermount will not exit until
       this socket is closed */
    close(fds[1]);
    waitpid(pid, NULL, 0); /* bury zombie */
  }

  return rv;
}

static int fuse_mount_sys(const char *mnt, struct mount_opts *mo,
			  const char *mnt_opts)
{
  char tmp[128];
  const char *devname = "/dev/fuse";
  char *source = NULL;
  char *type = NULL;
  struct stat stbuf;
  int fd;
  int res;

  if (!mnt) {
    fprintf(stderr, "fuse: missing mountpoint parameter\n");
    return -1;
  }

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

  if (!mo->nonempty) {
    res = fuse_mnt_check_empty("fuse", mnt, stbuf.st_mode,
                               stbuf.st_size);
    if (res == -1)
      return -1;
  }

  if (mo->auto_unmount) {
    /* Tell the caller to fallback to fusermount because
       auto-unmount does not work otherwise. */
    return -2;
  }

  fd = open(devname, O_RDWR);
  if (fd == -1) {
    if (errno == ENODEV || errno == ENOENT)
      fprintf(stderr, "fuse: device not found, try 'modprobe fuse' first\n");
    else
      fprintf(stderr, "fuse: failed to open %s: %s\n",
              devname, strerror(errno));
    return -1;
  }

  snprintf(tmp, sizeof(tmp),  "fd=%i,rootmode=%o,user_id=%u,group_id=%u",
           fd, stbuf.st_mode & S_IFMT, getuid(), getgid());

  res = fuse_opt_add_opt(&mo->kernel_opts, tmp);
  if (res == -1)
    goto out_close;

  source = malloc((mo->fsname ? strlen(mo->fsname) : 0) +
                  (mo->subtype ? strlen(mo->subtype) : 0) +
                  strlen(devname) + 32);

  type = malloc((mo->subtype ? strlen(mo->subtype) : 0) + 32);
  if (!type || !source) {
    fprintf(stderr, "fuse: failed to allocate memory\n");
    goto out_close;
  }

  strcpy(type, mo->blkdev ? "fuseblk" : "fuse");
  if (mo->subtype) {
    strcat(type, ".");
    strcat(type, mo->subtype);
  }
  strcpy(source,
         mo->fsname ? mo->fsname : (mo->subtype ? mo->subtype : devname));

  res = mount(source, mnt, type, mo->flags, mo->kernel_opts);
  if (res == -1 && errno == ENODEV && mo->subtype) {
    /* Probably missing subtype support */
    strcpy(type, mo->blkdev ? "fuseblk" : "fuse");
    if (mo->fsname) {
      if (!mo->blkdev)
        sprintf(source, "%s#%s", mo->subtype,
                mo->fsname);
    } else {
      strcpy(source, type);
    }
    res = mount(source, mnt, type, mo->flags, mo->kernel_opts);
  }
  if (res == -1) {
    /*
     * Maybe kernel doesn't support unprivileged mounts, in this
     * case try falling back to fusermount
     */
    if (errno == EPERM) {
      res = -2;
    } else {
      int errno_save = errno;
      if (mo->blkdev && errno == ENODEV &&
          !fuse_mnt_check_fuseblk())
        fprintf(stderr,
                "fuse: 'fuseblk' support missing\n");
      else
        fprintf(stderr, "fuse: mount failed: %s\n",
                strerror(errno_save));
    }

    goto out_close;
  }

#ifndef __NetBSD__
#ifndef IGNORE_MTAB
  if (geteuid() == 0) {
    char *newmnt = fuse_mnt_resolve_path("fuse", mnt);
    res = -1;
    if (!newmnt)
      goto out_umount;

    res = fuse_mnt_add_mount("fuse", source, newmnt, type,
                             mnt_opts);
    free(newmnt);
    if (res == -1)
      goto out_umount;
  }
#endif /* IGNORE_MTAB */
#endif /* __NetBSD__ */
  free(type);
  free(source);

  return fd;

 out_umount:
  umount2(mnt, 2); /* lazy umount */
 out_close:
  free(type);
  free(source);
  close(fd);
  return res;
}

static int get_mnt_flag_opts(char **mnt_optsp, int flags)
{
  int i;

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

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

int fuse_kern_mount(const char *mountpoint, struct fuse_args *args)
{
  struct mount_opts mo;
  int res = -1;
  char *mnt_opts = NULL;

  memset(&mo, 0, sizeof(mo));
  mo.flags = MS_NOSUID | MS_NODEV;

  if (args &&
      fuse_opt_parse(args, &mo, fuse_mount_opts, fuse_mount_opt_proc) == -1)
    return -1;

  if (mo.allow_other && mo.allow_root) {
    fprintf(stderr, "fuse: 'allow_other' and 'allow_root' options are mutually exclusive\n");
    goto out;
  }
  res = 0;
  if (mo.ishelp)
    goto out;

  res = -1;
  if (get_mnt_flag_opts(&mnt_opts, mo.flags) == -1)
    goto out;
  if (mo.kernel_opts && fuse_opt_add_opt(&mnt_opts, mo.kernel_opts) == -1)
    goto out;
  if (mo.mtab_opts &&  fuse_opt_add_opt(&mnt_opts, mo.mtab_opts) == -1)
    goto out;

  res = fuse_mount_sys(mountpoint, &mo, mnt_opts);
  if (res == -2) {
    if (mo.fusermount_opts &&
        fuse_opt_add_opt(&mnt_opts, mo.fusermount_opts) == -1)
      goto out;

    if (mo.subtype) {
      char *tmp_opts = NULL;

      res = -1;
      if (fuse_opt_add_opt(&tmp_opts, mnt_opts) == -1 ||
          fuse_opt_add_opt(&tmp_opts, mo.subtype_opt) == -1) {
        free(tmp_opts);
        goto out;
      }

      res = fuse_mount_fusermount(mountpoint, &mo, tmp_opts, 1);
      free(tmp_opts);
      if (res == -1)
        res = fuse_mount_fusermount(mountpoint, &mo,
                                    mnt_opts, 0);
    } else {
      res = fuse_mount_fusermount(mountpoint, &mo, mnt_opts, 0);
    }
  }
 out:
  free(mnt_opts);
  free(mo.fsname);
  free(mo.subtype);
  free(mo.fusermount_opts);
  free(mo.subtype_opt);
  free(mo.kernel_opts);
  free(mo.mtab_opts);
  return res;
}