runc/namespaces/execin.go

// +build linux

package namespaces

import (
	"encoding/json"
	"fmt"
	"io"
	"os"
	"os/exec"
	"path/filepath"
	"strconv"
	"syscall"

	"github.com/docker/libcontainer"
	"github.com/docker/libcontainer/apparmor"
	"github.com/docker/libcontainer/cgroups"
	"github.com/docker/libcontainer/label"
	"github.com/docker/libcontainer/system"
)

// ExecIn reexec's the initPath with the argv 0 rewrite to "nsenter" so that it is able to run the
// setns code in a single threaded environment joining the existing containers' namespaces.
func ExecIn(container *libcontainer.Config, state *libcontainer.State, userArgs []string, initPath, action string,
	stdin io.Reader, stdout, stderr io.Writer, console string, startCallback func(*exec.Cmd)) (int, error) {

	args := []string{fmt.Sprintf("nsenter-%s", action), "--nspid", strconv.Itoa(state.InitPid)}

	if console != "" {
		args = append(args, "--console", console)
	}

	cmd := &exec.Cmd{
		Path: initPath,
		Args: append(args, append([]string{"--"}, userArgs...)...),
	}

	if filepath.Base(initPath) == initPath {
		if lp, err := exec.LookPath(initPath); err == nil {
			cmd.Path = lp
		}
	}

	parent, child, err := newInitPipe()
	if err != nil {
		return -1, err
	}
	defer parent.Close()

	// Note: these are only used in non-tty mode
	// if there is a tty for the container it will be opened within the namespace and the
	// fds will be duped to stdin, stdiout, and stderr
	cmd.Stdin = stdin
	cmd.Stdout = stdout
	cmd.Stderr = stderr
	cmd.ExtraFiles = []*os.File{child}

	if err := cmd.Start(); err != nil {
		child.Close()
		return -1, err
	}
	child.Close()

	terminate := func(terr error) (int, error) {
		// TODO: log the errors for kill and wait
		cmd.Process.Kill()
		cmd.Wait()
		return -1, terr
	}

	// Enter cgroups.
	if err := EnterCgroups(state, cmd.Process.Pid); err != nil {
		return terminate(err)
	}

	if err := json.NewEncoder(parent).Encode(container); err != nil {
		return terminate(err)
	}

	if startCallback != nil {
		startCallback(cmd)
	}

	if err := cmd.Wait(); err != nil {
		if _, ok := err.(*exec.ExitError); !ok {
			return -1, err
		}
	}
	return cmd.ProcessState.Sys().(syscall.WaitStatus).ExitStatus(), nil
}

// Finalize expects that the setns calls have been setup and that is has joined an
// existing namespace
func FinalizeSetns(container *libcontainer.Config, args []string) error {
	// clear the current processes env and replace it with the environment defined on the container
	if err := LoadContainerEnvironment(container); err != nil {
		return err
	}

	if err := FinalizeNamespace(container); err != nil {
		return err
	}

	if err := apparmor.ApplyProfile(container.AppArmorProfile); err != nil {
		return fmt.Errorf("set apparmor profile %s: %s", container.AppArmorProfile, err)
	}

	if container.ProcessLabel != "" {
		if err := label.SetProcessLabel(container.ProcessLabel); err != nil {
			return err
		}
	}

	if err := system.Execv(args[0], args[0:], os.Environ()); err != nil {
		return err
	}

	panic("unreachable")
}

func EnterCgroups(state *libcontainer.State, pid int) error {
	return cgroups.EnterPid(state.CgroupPaths, pid)
}