mergerfs/libfuse/lib/mount_util.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 "mount_util.h"
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <paths.h>
#ifndef __NetBSD__
#include <mntent.h>
#endif
#include <sys/stat.h>
#include <sys/wait.h>
#include <sys/mount.h>
#include <sys/param.h>

#ifdef __NetBSD__
#define umount2(mnt, flags) unmount(mnt, (flags == 2) ? MNT_FORCE : 0)
#define mtab_needs_update(mnt) 0
#else
static int mtab_needs_update(const char *mnt)
{
  int res;
  struct stat stbuf;

  /* If mtab is within new mount, don't touch it */
  if (strncmp(mnt, _PATH_MOUNTED, strlen(mnt)) == 0 &&
      _PATH_MOUNTED[strlen(mnt)] == '/')
    return 0;

  /*
   * Skip mtab update if /etc/mtab:
   *
   *  - doesn't exist,
   *  - is a symlink,
   *  - is on a read-only filesystem.
   */
  res = lstat(_PATH_MOUNTED, &stbuf);
  if (res == -1) {
    if (errno == ENOENT)
      return 0;
  } else {
    uid_t ruid;
    int err;

    if (S_ISLNK(stbuf.st_mode))
      return 0;

    ruid = getuid();
    if (ruid != 0)
      setreuid(0, -1);

    res = access(_PATH_MOUNTED, W_OK);
    err = (res == -1) ? errno : 0;
    if (ruid != 0)
      setreuid(ruid, -1);

    if (err == EROFS)
      return 0;
  }

  return 1;
}
#endif /* __NetBSD__ */

static int add_mount(const char *progname, const char *fsname,
                     const char *mnt, const char *type, const char *opts)
{
  int res;
  int status;
  sigset_t blockmask;
  sigset_t oldmask;

  sigemptyset(&blockmask);
  sigaddset(&blockmask, SIGCHLD);
  res = sigprocmask(SIG_BLOCK, &blockmask, &oldmask);
  if (res == -1) {
    fprintf(stderr, "%s: sigprocmask: %s\n", progname, strerror(errno));
    return -1;
  }

  res = fork();
  if (res == -1) {
    fprintf(stderr, "%s: fork: %s\n", progname, strerror(errno));
    goto out_restore;
  }
  if (res == 0) {
    char *env = NULL;

    sigprocmask(SIG_SETMASK, &oldmask, NULL);
    setuid(geteuid());
    execle("/bin/mount", "/bin/mount", "--no-canonicalize", "-i",
           "-f", "-t", type, "-o", opts, fsname, mnt, NULL, &env);
    fprintf(stderr, "%s: failed to execute /bin/mount: %s\n",
            progname, strerror(errno));
    exit(1);
  }
  res = waitpid(res, &status, 0);
  if (res == -1)
    fprintf(stderr, "%s: waitpid: %s\n", progname, strerror(errno));

  if (status != 0)
    res = -1;

 out_restore:
  sigprocmask(SIG_SETMASK, &oldmask, NULL);

  return res;
}

int fuse_mnt_add_mount(const char *progname, const char *fsname,
		       const char *mnt, const char *type, const char *opts)
{
  if (!mtab_needs_update(mnt))
    return 0;

  return add_mount(progname, fsname, mnt, type, opts);
}

static int exec_umount(const char *progname, const char *rel_mnt, int lazy)
{
  int res;
  int status;
  sigset_t blockmask;
  sigset_t oldmask;

  sigemptyset(&blockmask);
  sigaddset(&blockmask, SIGCHLD);
  res = sigprocmask(SIG_BLOCK, &blockmask, &oldmask);
  if (res == -1) {
    fprintf(stderr, "%s: sigprocmask: %s\n", progname, strerror(errno));
    return -1;
  }

  res = fork();
  if (res == -1) {
    fprintf(stderr, "%s: fork: %s\n", progname, strerror(errno));
    goto out_restore;
  }
  if (res == 0) {
    char *env = NULL;

    sigprocmask(SIG_SETMASK, &oldmask, NULL);
    setuid(geteuid());
    if (lazy) {
      execle("/bin/umount", "/bin/umount", "-i", rel_mnt,
             "-l", NULL, &env);
    } else {
      execle("/bin/umount", "/bin/umount", "-i", rel_mnt,
             NULL, &env);
    }
    fprintf(stderr, "%s: failed to execute /bin/umount: %s\n",
            progname, strerror(errno));
    exit(1);
  }
  res = waitpid(res, &status, 0);
  if (res == -1)
    fprintf(stderr, "%s: waitpid: %s\n", progname, strerror(errno));

  if (status != 0) {
    res = -1;
  }

 out_restore:
  sigprocmask(SIG_SETMASK, &oldmask, NULL);
  return res;

}

int fuse_mnt_umount(const char *progname, const char *abs_mnt,
		    const char *rel_mnt, int lazy)
{
  int res;

  if (!mtab_needs_update(abs_mnt)) {
    res = umount2(rel_mnt, lazy ? 2 : 0);
    if (res == -1)
      fprintf(stderr, "%s: failed to unmount %s: %s\n",
              progname, abs_mnt, strerror(errno));
    return res;
  }

  return exec_umount(progname, rel_mnt, lazy);
}

static int remove_mount(const char *progname, const char *mnt)
{
  int res;
  int status;
  sigset_t blockmask;
  sigset_t oldmask;

  sigemptyset(&blockmask);
  sigaddset(&blockmask, SIGCHLD);
  res = sigprocmask(SIG_BLOCK, &blockmask, &oldmask);
  if (res == -1) {
    fprintf(stderr, "%s: sigprocmask: %s\n", progname, strerror(errno));
    return -1;
  }

  res = fork();
  if (res == -1) {
    fprintf(stderr, "%s: fork: %s\n", progname, strerror(errno));
    goto out_restore;
  }
  if (res == 0) {
    char *env = NULL;

    sigprocmask(SIG_SETMASK, &oldmask, NULL);
    setuid(geteuid());
    execle("/bin/umount", "/bin/umount", "--no-canonicalize", "-i",
           "--fake", mnt, NULL, &env);
    fprintf(stderr, "%s: failed to execute /bin/umount: %s\n",
            progname, strerror(errno));
    exit(1);
  }
  res = waitpid(res, &status, 0);
  if (res == -1)
    fprintf(stderr, "%s: waitpid: %s\n", progname, strerror(errno));

  if (status != 0)
    res = -1;

 out_restore:
  sigprocmask(SIG_SETMASK, &oldmask, NULL);
  return res;
}

int fuse_mnt_remove_mount(const char *progname, const char *mnt)
{
  if (!mtab_needs_update(mnt))
    return 0;

  return remove_mount(progname, mnt);
}

char *fuse_mnt_resolve_path(const char *progname, const char *orig)
{
  char buf[PATH_MAX];
  char *copy;
  char *dst;
  char *end;
  char *lastcomp;
  const char *toresolv;

  if (!orig[0]) {
    fprintf(stderr, "%s: invalid mountpoint '%s'\n", progname,
            orig);
    return NULL;
  }

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

  toresolv = copy;
  lastcomp = NULL;
  for (end = copy + strlen(copy) - 1; end > copy && *end == '/'; end --);
  if (end[0] != '/') {
    char *tmp;
    end[1] = '\0';
    tmp = strrchr(copy, '/');
    if (tmp == NULL) {
      lastcomp = copy;
      toresolv = ".";
    } else {
      lastcomp = tmp + 1;
      if (tmp == copy)
        toresolv = "/";
    }
    if (strcmp(lastcomp, ".") == 0 || strcmp(lastcomp, "..") == 0) {
      lastcomp = NULL;
      toresolv = copy;
    }
    else if (tmp)
      tmp[0] = '\0';
  }
  if (realpath(toresolv, buf) == NULL) {
    fprintf(stderr, "%s: bad mount point %s: %s\n", progname, orig,
            strerror(errno));
    free(copy);
    return NULL;
  }
  if (lastcomp == NULL)
    dst = strdup(buf);
  else {
    dst = (char *) malloc(strlen(buf) + 1 + strlen(lastcomp) + 1);
    if (dst) {
      unsigned buflen = strlen(buf);
      if (buflen && buf[buflen-1] == '/')
        sprintf(dst, "%s%s", buf, lastcomp);
      else
        sprintf(dst, "%s/%s", buf, lastcomp);
    }
  }
  free(copy);
  if (dst == NULL)
    fprintf(stderr, "%s: failed to allocate memory\n", progname);
  return dst;
}

int fuse_mnt_check_empty(const char *progname, const char *mnt,
			 mode_t rootmode, off_t rootsize)
{
  int isempty = 1;

  if (S_ISDIR(rootmode)) {
    struct dirent *ent;
    DIR *dp = opendir(mnt);
    if (dp == NULL) {
      fprintf(stderr,
              "%s: failed to open mountpoint for reading: %s\n",
              progname, strerror(errno));
      return -1;
    }
    while ((ent = readdir(dp)) != NULL) {
      if (strcmp(ent->d_name, ".") != 0 &&
          strcmp(ent->d_name, "..") != 0) {
        isempty = 0;
        break;
      }
    }
    closedir(dp);
  } else if (rootsize)
    isempty = 0;

  if (!isempty) {
    fprintf(stderr, "%s: mountpoint is not empty\n", progname);
    fprintf(stderr, "%s: if you are sure this is safe, use the 'nonempty' mount option\n", progname);
    return -1;
  }
  return 0;
}

int fuse_mnt_check_fuseblk(void)
{
  char buf[256];
  FILE *f = fopen("/proc/filesystems", "r");
  if (!f)
    return 1;

  while (fgets(buf, sizeof(buf), f))
    if (strstr(buf, "fuseblk\n")) {
      fclose(f);
      return 1;
    }

  fclose(f);
  return 0;
}