teleport/lib/sshutils/marshal.go

/*
Copyright 2018 Gravitational, Inc.

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 sshutils

import (
	"errors"
	"fmt"
	"io"
	"net/url"
	"strings"

	"github.com/gravitational/trace"
	"golang.org/x/crypto/ssh"
)

// MarshalAuthorizedKeysFormat returns the certificate authority public key exported as a single
// line that can be placed in ~/.ssh/authorized_keys file. The format adheres to the
// man sshd (8) authorized_keys format, a space-separated list of: options, keytype,
// base64-encoded key, comment.
// For example:
//
//	cert-authority AAA... type=user&clustername=cluster-a
//
// URL encoding is used to pass the CA type and cluster name into the comment field.
func MarshalAuthorizedKeysFormat(clusterName string, keyBytes []byte) (string, error) {
	comment := url.Values{
		"type":        []string{"user"},
		"clustername": []string{clusterName},
	}

	return fmt.Sprintf("cert-authority %s %s\n", strings.TrimSpace(string(keyBytes)), comment.Encode()), nil
}

// KnownHost is a structural representation of a known hosts entry for a Teleport host.
type KnownHost struct {
	AuthorizedKey []byte
	ProxyHost     string
	Hostname      string
	Comment       map[string][]string
}

// MarshalKnownHost returns the certificate authority public key exported as a single line
// that can be placed in ~/.ssh/known_hosts. The format adheres to the man sshd (8)
// known_hosts format, a space-separated list of: marker, hosts, key, and comment.
// For example:
//
//	@cert-authority proxy.example.com,cluster-a,*.cluster-a ssh-rsa AAA... type=host
//
// URL encoding is used to pass the CA type and allowed logins into the comment field.
func MarshalKnownHost(kh KnownHost) (string, error) {
	if kh.Hostname == "" {
		return "", trace.BadParameter("missing required argument clusterName")
	}

	if len(kh.AuthorizedKey) == 0 {
		return "", trace.BadParameter("missing required argument keyBytes")
	}

	comment := url.Values(kh.Comment)
	if comment == nil {
		comment = url.Values{}
	}

	if _, ok := comment["type"]; !ok {
		comment["type"] = []string{"host"}
	}

	hosts := []string{kh.Hostname, "*." + kh.Hostname}
	if kh.ProxyHost != "" {
		hosts = append([]string{kh.ProxyHost}, hosts...)
	}

	return fmt.Sprintf("@cert-authority %s %s %s\n", strings.Join(hosts, ","), strings.TrimSpace(string(kh.AuthorizedKey)), comment.Encode()), nil
}

// UnmarshalKnownHosts returns a list of authorized hosts from the given known_hosts
// file. Entries in the given file should adhere to the man sshd (8) known_hosts format,
// a space-separated list of: marker, hosts, key, and comment.
// For example:
//
//	@cert-authority proxy.example.com,cluster-a,*.cluster-a ssh-rsa AAA... type=host
//
// UnmarshalKnownHosts will try to guess the proxy host and cluster name for entries that
// look like Teleport authorized host entries, generated with MarshalKnownHost.
func UnmarshalKnownHosts(knownHostsFile [][]byte) ([]KnownHost, error) {
	var knownHosts []KnownHost
	for _, line := range knownHostsFile {
		for {
			_, hosts, publicKey, commentString, rest, err := ssh.ParseKnownHosts(line)
			if errors.Is(err, io.EOF) {
				break
			} else if err != nil {
				return nil, trace.Wrap(err, "failed parsing known hosts: %v; raw line: %q", err, line)
			}

			ah := KnownHost{
				AuthorizedKey: ssh.MarshalAuthorizedKey(publicKey),
			}

			comment, err := url.ParseQuery(commentString)
			if err != nil {
				return nil, trace.Wrap(err)
			}
			ah.Comment = map[string][]string(comment)

			// Assuming the known host was generated from MarshalKnownHost,
			// we can get the proxyHost and clusterName for the host.
			switch len(hosts) {
			case 1, 2:
				ah.Hostname = hosts[0]
			case 3:
				ah.ProxyHost = hosts[0]
				ah.Hostname = hosts[1]
			}

			knownHosts = append(knownHosts, ah)

			line = rest
		}
	}

	return knownHosts, nil
}