proxycommand.go

package ssh

import (
	"io"
	"net"
	"os"
	"strings"
	"sync"

	"github.com/pkg/errors"
	"github.com/urfave/cli"

	"github.com/smallstep/certificates/api"
	"github.com/smallstep/cli-utils/command"
	"github.com/smallstep/cli-utils/errs"

	"github.com/smallstep/cli/exec"
	"github.com/smallstep/cli/flags"
	"github.com/smallstep/cli/internal/sshutil"
	"github.com/smallstep/cli/utils/cautils"
)

const sshDefaultPath = "/usr/bin/ssh"

func proxycommandCommand() cli.Command {
	return cli.Command{
		Name:   "proxycommand",
		Action: command.ActionFunc(proxycommandAction),
		Usage:  "proxy ssh connections according to the host registry",
		UsageText: `**step ssh proxycommand** <user> <host> <port>
[**--provisioner**=<name>] [**--set**=<key=value>] [**--set-file**=<file>]
[**--console**] [**--offline**] [**--ca-config**=<file>]
[**--ca-url**=<uri>] [**--root**=<file>]
[**--context**=<name>] [**--fallback-context**=<name>]`,
		Description: `**step ssh proxycommand** looks into the host registry
and proxies the ssh connection according to its configuration. This command
is used in the ssh client config with <ProxyCommand> keyword.

This command will add the user to the ssh-agent if necessary.

## POSITIONAL ARGUMENTS

<user>
:  The remote username, and the subject used to login.

<host>
:  The host to connect to.

<port>
:  The port to connect to.`,
		Flags: []cli.Flag{
			flags.Provisioner,
			flags.ProvisionerPasswordFileWithAlias,
			flags.TemplateSet,
			flags.TemplateSetFile,
			flags.Console,
			flags.Offline,
			flags.CaConfig,
			flags.CaURL,
			flags.Root,
			flags.Context,
			flags.FallbackContext,
		},
	}
}

func proxycommandAction(ctx *cli.Context) error {
	if err := errs.NumberOfArguments(ctx, 3); err != nil {
		return err
	}

	args := ctx.Args()
	user, host, port := args[0], args[1], args[2]

	// Check if user is logged in
	if err := doLoginIfNeeded(ctx, user); err != nil {
		return err
	}

	// Get the configured bastion if any
	r, err := getBastion(ctx, user, host)
	if err != nil {
		return err
	}

	// Connect through bastion
	if r.Bastion != nil && r.Bastion.Hostname != "" {
		return proxyBastion(r, user, host, port)
	}

	// Connect directly
	return proxyDirect(host, port)
}

// doLoginIfNeeded check if the user is logged in looking at the ssh agent, if
// it's not it will do the login flow.
func doLoginIfNeeded(ctx *cli.Context, subject string) error {
	return loginIfNeeded(ctx, subject, withRetryFunc(runOnFallbackContext))
}

func getBastion(ctx *cli.Context, user, host string) (*api.SSHBastionResponse, error) {
	client, err := cautils.NewClient(ctx)
	if err != nil {
		return nil, err
	}
	return client.SSHBastion(&api.SSHBastionRequest{
		User:     user,
		Hostname: host,
	})
}

func proxyDirect(host, port string) error {
	address := net.JoinHostPort(host, port)
	addr, err := net.ResolveTCPAddr("tcp", address)
	if err != nil {
		return errors.Wrap(err, "error resolving address")
	}

	conn, err := net.DialTCP("tcp", nil, addr)
	if err != nil {
		return errors.Wrapf(err, "error connecting to %s", address)
	}

	var wg sync.WaitGroup
	wg.Add(1)
	go func() {
		io.Copy(conn, os.Stdin)
		conn.CloseWrite()
		wg.Done()
	}()
	wg.Add(1)
	go func() {
		io.Copy(os.Stdout, conn)
		conn.CloseRead()
		wg.Done()
	}()

	wg.Wait()
	return nil
}

func proxyBastion(r *api.SSHBastionResponse, user, host, port string) error {
	sshPath, err := exec.LookPath("ssh")
	if err != nil {
		sshPath = sshDefaultPath
	}

	args := []string{}
	if r.Bastion.User != "" {
		args = append(args, "-l", r.Bastion.User)
	}
	if r.Bastion.Port != "" {
		args = append(args, "-p", r.Bastion.Port)
	}
	if r.Bastion.Flags != "" {
		// BUG(mariano): This is a naive way of doing it as it doesn't
		// support strings, but it should work for most of the cases in ssh.
		// For more advance cases the package
		// github.com/kballard/go-shellquote can be used.
		fields := strings.Fields(r.Bastion.Flags)
		args = append(args, fields...)
	}
	args = append(args, r.Bastion.Hostname)
	if r.Bastion.Command != "" {
		args = append(args, sshutil.ProxyCommand(r.Bastion.Command, user, host, port))
	} else {
		args = append(args, "nc", host, port)
	}
	exec.Exec(sshPath, args...)
	return nil
}