ns_process.go

package main

import (
	"flag"
	"fmt"
	"os"
	"os/exec"
	"syscall"

	"github.com/docker/docker/pkg/reexec"
)

func init() {
	reexec.Register("nsInitialisation", nsInitialisation)
	if reexec.Init() {
		os.Exit(0)
	}
}

func nsInitialisation() {
	newrootPath := os.Args[1]

	if err := mountProc(newrootPath); err != nil {
		fmt.Printf("Error mounting /proc - %s\n", err)
		os.Exit(1)
	}

	if err := pivotRoot(newrootPath); err != nil {
		fmt.Printf("Error running pivot_root - %s\n", err)
		os.Exit(1)
	}

	if err := syscall.Sethostname([]byte("ns-process")); err != nil {
		fmt.Printf("Error setting hostname - %s\n", err)
		os.Exit(1)
	}

	if err := waitForNetwork(); err != nil {
		fmt.Printf("Error waiting for network - %s\n", err)
		os.Exit(1)
	}

	nsRun()
}

func nsRun() {
	cmd := exec.Command("/bin/sh")

	cmd.Stdin = os.Stdin
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr

	cmd.Env = []string{"PS1=-[ns-process]- # "}

	if err := cmd.Run(); err != nil {
		fmt.Printf("Error running the /bin/sh command - %s\n", err)
		os.Exit(1)
	}
}

func main() {
	var rootfsPath, netsetgoPath string
	flag.StringVar(&rootfsPath, "rootfs", "/tmp/ns-process/rootfs", "Path to the root filesystem to use")
	flag.StringVar(&netsetgoPath, "netsetgo", "/usr/local/bin/netsetgo", "Path to the netsetgo binary")
	flag.Parse()

	exitIfRootfsNotFound(rootfsPath)
	exitIfNetsetgoNotFound(netsetgoPath)

	cmd := reexec.Command("nsInitialisation", rootfsPath)

	cmd.Stdin = os.Stdin
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr

	cmd.SysProcAttr = &syscall.SysProcAttr{
		Cloneflags: syscall.CLONE_NEWNS |
			syscall.CLONE_NEWUTS |
			syscall.CLONE_NEWIPC |
			syscall.CLONE_NEWPID |
			syscall.CLONE_NEWNET |
			syscall.CLONE_NEWUSER,
		UidMappings: []syscall.SysProcIDMap{
			{
				ContainerID: 0,
				HostID:      os.Getuid(),
				Size:        1,
			},
		},
		GidMappings: []syscall.SysProcIDMap{
			{
				ContainerID: 0,
				HostID:      os.Getgid(),
				Size:        1,
			},
		},
	}

	if err := cmd.Start(); err != nil {
		fmt.Printf("Error starting the reexec.Command - %s\n", err)
		os.Exit(1)
	}

	// run netsetgo using default args
	// note that netsetgo must be owned by root with the setuid bit set
	pid := fmt.Sprintf("%d", cmd.Process.Pid)
	netsetgoCmd := exec.Command(netsetgoPath, "-pid", pid)
	if err := netsetgoCmd.Run(); err != nil {
		fmt.Printf("Error running netsetgo - %s\n", err)
		os.Exit(1)
	}

	if err := cmd.Wait(); err != nil {
		fmt.Printf("Error waiting for the reexec.Command - %s\n", err)
		os.Exit(1)
	}
}