fuse/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 <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <mntent.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <sys/mount.h>
#include <sys/param.h>

#include <paths.h>

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

		res = access(_PATH_MOUNTED, W_OK);
		if (res == -1 && errno == EROFS)
			return 0;
	}

	return 1;
}

static int add_mount_legacy(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 templ[] = "/tmp/fusermountXXXXXX";
		char *tmp;

		sigprocmask(SIG_SETMASK, &oldmask, NULL);
		setuid(geteuid());

		/*
		 * hide in a directory, where mount isn't able to resolve
		 * fsname as a valid path
		 */
		tmp = mkdtemp(templ);
		if (!tmp) {
			fprintf(stderr,
				"%s: failed to create temporary directory\n",
				progname);
			exit(1);
		}
		if (chdir(tmp)) {
			fprintf(stderr, "%s: failed to chdir to %s: %s\n",
				progname, tmp, strerror(errno));
			exit(1);
		}
		rmdir(tmp);
		execl("/bin/mount", "/bin/mount", "-i", "-f", "-t", type,
		      "-o", opts, fsname, mnt, NULL);
		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;
}

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) {
		/*
		 * Hide output, because old versions don't support
		 * --no-canonicalize
		 */
		int fd = open("/dev/null", O_RDONLY);
		dup2(fd, 1);
		dup2(fd, 2);

		sigprocmask(SIG_SETMASK, &oldmask, NULL);
		setuid(geteuid());
		execl("/bin/mount", "/bin/mount", "--no-canonicalize", "-i",
		      "-f", "-t", type, "-o", opts, fsname, mnt, NULL);
		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)
{
	int res;

	if (!mtab_needs_update(mnt))
		return 0;

	res = add_mount(progname, fsname, mnt, type, opts);
	if (res == -1)
		res = add_mount_legacy(progname, fsname, mnt, type, opts);

	return res;
}

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) {
		sigprocmask(SIG_SETMASK, &oldmask, NULL);
		setuid(geteuid());
		execl("/bin/umount", "/bin/umount", "-i", rel_mnt,
		      lazy ? "-l" : NULL, NULL);
		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);
}

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, off64_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;
}