private_hidden_loop_devices.c

#ifndef _GNU_SOURCE
#define _GNU_SOURCE 1
#endif
#include <linux/loop.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <limits.h>
#include <linux/bpf.h>
#include <linux/magic.h>
#include <linux/sched.h>
#include <malloc.h>
#include <poll.h>
#include <pthread.h>
#include <sched.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/fsuid.h>
#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/param.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <linux/types.h>
#include <sys/un.h>
#include <sys/wait.h>
#include <unistd.h>

int attach_image_to_loop(const char *source, int loop_fd)
{
	int ret, fret = -1;
	struct loop_info64 lo64;
	int fd_img = -1;

	fd_img = open(source, O_RDWR | O_CLOEXEC);
	if (fd_img < 0) {
		fprintf(stderr, "Failed to open %s\n", source);
		goto on_error;
	}

	ret = ioctl(loop_fd, LOOP_SET_FD, fd_img);
	if (ret < 0) {
		fprintf(stderr, "%m - Failed to set loop device to %s\n", source);
		goto on_error;
	}

	memset(&lo64, 0, sizeof(lo64));

	snprintf((char *)lo64.lo_file_name, LO_NAME_SIZE, "%s", source);

	ret = ioctl(loop_fd, LOOP_SET_STATUS64, &lo64);
	if (ret < 0) {
		fprintf(stderr, "%m - Failed to set loop device status for %s\n", source);
		goto on_error;
	}

	fret = 0;

on_error:
	if (fd_img >= 0)
		close(fd_img);

	return fret;
}

int main(int argc, char *argv[])
{
	int ret, mntfd, loop_ctl_fd, loopidx, loop_fd;
	char *image, *mntpt, *target, *fstype;
	char path[4096];
	int n = 1;

	if (argc < 5)
		exit(EXIT_FAILURE);

	mntpt = argv[1];
	image = argv[2];
	target = argv[3];
	fstype = argv[4];

	ret = mount("none", mntpt, "loop", 0, 0);
	if (ret) {
		fprintf(stderr, "%m - Failed to mount loopfs at %s\n", mntpt);
		exit(EXIT_FAILURE);
	}

	mntfd = open(mntpt, O_DIRECTORY | O_CLOEXEC);
	if (mntfd < 0) {
		fprintf(stderr, "%m - Failed to open loopfs mount %s\n", mntpt);
		exit(EXIT_FAILURE);
	}

	(void)snprintf(path, sizeof(path), "%s/loop-control", mntpt);
	loop_ctl_fd = open(path, O_RDWR | O_CLOEXEC);
	if (loop_ctl_fd < 0) {
		fprintf(stderr,
			"%m - Failed to open loopfs loop-control device %s\n",
			path);
		exit(EXIT_FAILURE);
	}

	ret = umount2(mntpt, MNT_DETACH);
	if (ret) {
		fprintf(stderr, "%m - Failed to unmount loopfs at %s\n", mntpt);
		exit(EXIT_FAILURE);
	}

	loopidx = ioctl(loop_ctl_fd, LOOP_CTL_GET_FREE);
	if (loopidx < 0) {
		fprintf(stderr, "%m - Failed to get new loopfs loop device\n");
		exit(EXIT_FAILURE);
	}

	(void)snprintf(path, sizeof(path), "loop%d", loopidx);
	loop_fd = openat(mntfd, path, O_RDWR | O_CLOEXEC);
	if (loop_fd < 0) {
		fprintf(stderr, "%m - Failed to open loop device %s\n", path);
		exit(EXIT_FAILURE);
	}
	printf("Opened loop device %s\n", path);

	ret = attach_image_to_loop(image, loop_fd);
	if (ret) {
		fprintf(stderr,
			"%m - Failed to attach image %s to loop device %s\n",
			image, path);
		exit(EXIT_FAILURE);
	}
	printf("Attached image %s to loop device %s\n", image, path);

	snprintf(path, sizeof(path), "/proc/self/fd/%d", loop_fd);
	ret = mount(path, tardetachedget, fstype, 0, 0);
	if (ret) {
		fprintf(stderr, "%m - Failed to mount %s to %s\n", path, target);
		exit(EXIT_FAILURE);
	}
	printf("Mounted %s to %s\n", path, target);

	exit(EXIT_SUCCESS);
}