258 lines
7.6 KiB
Go
258 lines
7.6 KiB
Go
package main
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import (
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"fmt"
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"os"
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"os/exec"
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"path/filepath"
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"strconv"
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"syscall"
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)
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// 这个 demo 没有加 CLONE_NEWUSER(user namespace)。
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// 加了之后容器里的"root"会映射成宿主机上一个无权限的普通用户,
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// mount/mknod 这类系统调用会被内核直接拒绝——从根上堵死设备逃逸这条路。
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// 现在故意不加,是因为这个工具还在用来练习/演示逃逸技术;
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// 如果以后想让它变成一个"正经"的隔离环境,这是必须补的一项。
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func main() {
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if len(os.Args) < 2 {
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fmt.Fprintf(os.Stderr, "Usage: %s run [cmd] [args...]\n", os.Args[0])
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os.Exit(1)
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}
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switch os.Args[1] {
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case "run":
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run()
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case "child":
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child()
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default:
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panic("Unknown command")
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}
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}
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func run() {
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args := os.Args[2:]
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if len(args) == 0 {
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args = []string{"/bin/sh"}
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}
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hostPID := os.Getpid()
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fmt.Printf("[run] Running %v as PID %d\n", args, hostPID)
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overlayBase := fmt.Sprintf("/tmp/maingo-%d", hostPID)
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upperDir := overlayBase + "/upper"
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workDir := overlayBase + "/work"
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mergedDir := overlayBase + "/merged"
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vethHost := fmt.Sprintf("veth0-%d", hostPID)
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vethCtr := fmt.Sprintf("veth1-%d", hostPID)
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cgroupName := fmt.Sprintf("maingo-%d", hostPID)
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ipSuffix := hostPID % 253
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hostIP := fmt.Sprintf("10.0.%d.1", ipSuffix)
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ctrIP := fmt.Sprintf("10.0.%d.2", ipSuffix)
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subnet := fmt.Sprintf("10.0.%d.0/24", ipSuffix)
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must(os.MkdirAll(upperDir, 0755))
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must(os.MkdirAll(workDir, 0755))
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must(os.MkdirAll(mergedDir, 0755))
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// 用 defer 而不是"cmd.Wait() 之后顺序执行"：
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// must(cmd.Wait()) 在子进程非 0 退出时会 panic,
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// 之前的写法一旦这里 panic，后面的清理代码一行都不会跑，
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// 会在宿主机上留下孤儿 veth / iptables 规则 / cgroup / 临时目录。
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// defer 保证不管中间从哪里 panic，清理都会按 LIFO 顺序跑完。
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defer safeRemoveAll(overlayBase)
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defer cleanupCgroup(cgroupName)
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defer cleanupVeth(vethHost)
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defer cleanupNAT(subnet)
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r, w, err := os.Pipe()
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must(err)
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cmd := exec.Command("/proc/self/exe", append([]string{"child"}, args...)...)
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cmd.Stdin = os.Stdin
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cmd.Stdout = os.Stdout
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cmd.Stderr = os.Stderr
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cmd.ExtraFiles = []*os.File{r}
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cmd.SysProcAttr = &syscall.SysProcAttr{
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Cloneflags: syscall.CLONE_NEWUTS |
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syscall.CLONE_NEWPID |
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syscall.CLONE_NEWNS |
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syscall.CLONE_NEWNET,
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}
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cmd.Env = append(os.Environ(),
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"MAINGO_MERGED="+mergedDir,
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"MAINGO_UPPER="+upperDir,
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"MAINGO_WORK="+workDir,
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"MAINGO_CGROUP="+cgroupName)
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must(cmd.Start())
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r.Close()
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setupVeth(cmd.Process.Pid, vethHost, vethCtr, hostIP, ctrIP, subnet)
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setupNAT(cmd.Process.Pid, ctrIP, subnet)
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w.Write([]byte{1})
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w.Close()
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must(cmd.Wait())
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}
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func child() {
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fmt.Printf("[child] Running %v as PID %d\n", os.Args[2:], os.Getpid())
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must(syscall.Sethostname([]byte("container")))
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// 必须在任何 mount 操作之前执行。
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// CLONE_NEWNS 只是给了子进程一份 mount 表的独立拷贝，
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// 但拷贝出来的挂载点默认继承宿主机的 propagation 类型（多数发行版根挂载点是 shared）。
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// shared 状态下，容器里新增的任何挂载（包括后面的 overlay、以及测试用的宿主机磁盘挂载）
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// 都会自动同步回宿主机自己的 mount namespace。
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// 把根挂载点递归改成 MS_PRIVATE，彻底切断这个双向同步，
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// 容器里再怎么 mount，宿主机那边都看不见、也不会被波及。
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must(syscall.Mount("", "/", "", syscall.MS_PRIVATE|syscall.MS_REC, ""))
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setupCgroup(os.Getenv("MAINGO_CGROUP"))
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waitForNetwork()
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mergedDir := os.Getenv("MAINGO_MERGED")
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upperDir := os.Getenv("MAINGO_UPPER")
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workDir := os.Getenv("MAINGO_WORK")
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lowerDir := "/home/mingdax/alpine-rootfs"
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opts := fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", lowerDir, upperDir, workDir)
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must(syscall.Mount("overlay", mergedDir, "overlay", 0, opts))
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fmt.Printf("[overlay] mounted\n")
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must(syscall.Chroot(mergedDir))
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must(syscall.Chdir("/"))
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must(os.MkdirAll("/proc", 0555))
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must(syscall.Mount("proc", "proc", "proc", 0, ""))
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cmd := exec.Command(os.Args[2], os.Args[3:]...)
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cmd.Stdin = os.Stdin
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cmd.Stdout = os.Stdout
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cmd.Stderr = os.Stderr
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must(cmd.Run())
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must(syscall.Unmount("proc", 0))
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}
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func setupVeth(childPID int, vethHost, vethCtr, hostIP, ctrIP, subnet string) {
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pid := strconv.Itoa(childPID)
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runCmdSilent("ip", "link", "del", vethHost)
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runCmd("ip", "link", "add", vethHost, "type", "veth", "peer", "name", vethCtr)
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runCmd("ip", "link", "set", vethCtr, "netns", pid)
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runCmd("ip", "addr", "add", hostIP+"/24", "dev", vethHost)
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runCmd("ip", "link", "set", vethHost, "up")
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runCmd("nsenter", "-t", pid, "-n", "ip", "addr", "add", ctrIP+"/24", "dev", vethCtr)
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runCmd("nsenter", "-t", pid, "-n", "ip", "link", "set", vethCtr, "up")
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runCmd("nsenter", "-t", pid, "-n", "ip", "link", "set", "lo", "up")
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fmt.Printf("[veth] pair ready: host=%s, container=%s\n", hostIP, ctrIP)
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}
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func setupNAT(childPID int, ctrIP, subnet string) {
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pid := strconv.Itoa(childPID)
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must(os.WriteFile("/proc/sys/net/ipv4/ip_forward", []byte("1"), 0644))
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runCmd("iptables", "-t", "nat", "-A", "POSTROUTING", "-s", subnet, "-j", "MASQUERADE")
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runCmd("nsenter", "-t", pid, "-n", "ip", "route", "add", "default", "via",
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ctrIP[:len(ctrIP)-1]+"1")
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fmt.Printf("[nat] NAT enabled: %s → internet\n", subnet)
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}
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func cleanupVeth(vethHost string) {
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runCmdSilent("ip", "link", "del", vethHost)
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}
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func cleanupNAT(subnet string) {
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runCmdSilent("iptables", "-t", "nat", "-D", "POSTROUTING", "-s", subnet, "-j",
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"MASQUERADE")
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fmt.Printf("[nat] cleaned up\n")
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}
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func waitForNetwork() {
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f := os.NewFile(3, "syncpipe")
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buf := make([]byte, 1)
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_, err := f.Read(buf)
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must(err)
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f.Close()
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fmt.Printf("[net] network ready\n")
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}
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func setupCgroup(name string) {
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cg := "/sys/fs/cgroup/" + name
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must(os.MkdirAll(cg, 0755))
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must(os.WriteFile(cg+"/cpu.max", []byte("100000 100000"), 0644))
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must(os.WriteFile(cg+"/memory.max", []byte("134217728"), 0644))
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must(os.WriteFile(cg+"/cgroup.procs", []byte(strconv.Itoa(os.Getpid())), 0644))
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fmt.Printf("[cgroup] limits set: 1 CPU, 128MB memory\n")
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}
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func cleanupCgroup(name string) {
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cg := "/sys/fs/cgroup/" + name
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os.WriteFile(cg+"/cgroup.kill", []byte("1"), 0644)
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os.Remove(cg)
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fmt.Printf("[cgroup] cleaned up\n")
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}
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// safeRemoveAll 是 os.RemoveAll 的一层保险。
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// 就算上面的 MS_PRIVATE 隔离出于某种原因失效（比如以后改了挂载逻辑忘记加），
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// 这里也会在真正删除前检查每个子路径的设备号（st_dev），
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// 一旦发现和 overlayBase 本身不是同一个设备，直接拒绝删除，
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// 而不是像 os.RemoveAll 那样无视挂载边界、一路删穿到别的文件系统上。
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func safeRemoveAll(path string) {
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rootFi, err := os.Lstat(path)
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if err != nil {
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return // 目录已经不在了，没什么好删的
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}
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rootDev := rootFi.Sys().(*syscall.Stat_t).Dev
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err = filepath.Walk(path, func(p string, info os.FileInfo, err error) error {
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if err != nil {
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return err
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}
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if st, ok := info.Sys().(*syscall.Stat_t); ok && st.Dev != rootDev {
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return fmt.Errorf("safeRemoveAll: %s 跨越了挂载边界（dev %d != %d），拒绝删除", p, st.Dev, rootDev)
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}
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return nil
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})
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if err != nil {
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fmt.Fprintf(os.Stderr, "[overlay] 清理中止，未删除任何内容: %v\n", err)
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return
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}
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if err := os.RemoveAll(path); err != nil {
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fmt.Fprintf(os.Stderr, "[overlay] 清理 %s 失败: %v\n", path, err)
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return
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}
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fmt.Printf("[overlay] cleaned up %s\n", path)
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}
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func runCmd(args ...string) {
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cmd := exec.Command(args[0], args[1:]...)
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cmd.Stderr = os.Stderr
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must(cmd.Run())
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}
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func runCmdSilent(args ...string) {
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cmd := exec.Command(args[0], args[1:]...)
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cmd.Run()
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}
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func must(err error) {
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if err != nil {
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panic(err)
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}
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}
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