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srv.go
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/*
Copyright 2015 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 reversetunnel
import (
"fmt"
"net"
"net/http"
"strings"
"sync"
"sync/atomic"
"github.com/gravitational/teleport"
"github.com/gravitational/teleport/lib/auth"
"github.com/gravitational/teleport/lib/defaults"
"github.com/gravitational/teleport/lib/limiter"
"github.com/gravitational/teleport/lib/services"
"github.com/gravitational/teleport/lib/sshutils"
"github.com/gravitational/teleport/lib/state"
"github.com/gravitational/teleport/lib/utils"
log "github.com/Sirupsen/logrus"
"github.com/gravitational/trace"
"golang.org/x/crypto/ssh"
)
// server is a "reverse tunnel server". it exposes the cluster capabilities
// (like access to a cluster's auth) to remote trusted clients
// (also known as 'reverse tunnel agents'.
type server struct {
sync.RWMutex
// localAuth points to the cluster's auth server API
localAuth auth.AccessPoint
hostCertChecker ssh.CertChecker
userCertChecker ssh.CertChecker
// srv is the "base class" i.e. the underlying SSH server
srv *sshutils.Server
limiter *limiter.Limiter
// remoteSites is the list of conencted remote clusters
remoteSites []*remoteSite
// localSites is the list of local (our own cluster) tunnel clients,
// usually each of them is a local proxy.
localSites []*localSite
// newAccessPoint returns new caching access point
newAccessPoint state.NewCachingAccessPoint
}
// ServerOption sets reverse tunnel server options
type ServerOption func(s *server) error
// DirectSite instructs server to proxy access to this site not using
// reverse tunnel
func DirectSite(domainName string, clt auth.ClientI) ServerOption {
return func(s *server) error {
site, err := newlocalSite(s, domainName, clt)
if err != nil {
return trace.Wrap(err)
}
s.localSites = append(s.localSites, site)
return nil
}
}
// SetLimiter sets rate limiter for reverse tunnel
func SetLimiter(limiter *limiter.Limiter) ServerOption {
return func(s *server) error {
s.limiter = limiter
return nil
}
}
// NewServer creates and returns a reverse tunnel server which is fully
// initialized but hasn't been started yet
func NewServer(addr utils.NetAddr, hostSigners []ssh.Signer,
authAPI auth.AccessPoint, fn state.NewCachingAccessPoint, opts ...ServerOption) (Server, error) {
srv := &server{
localSites: []*localSite{},
remoteSites: []*remoteSite{},
localAuth: authAPI,
newAccessPoint: fn,
}
var err error
srv.limiter, err = limiter.NewLimiter(limiter.LimiterConfig{})
if err != nil {
return nil, trace.Wrap(err)
}
for _, o := range opts {
if err := o(srv); err != nil {
return nil, trace.Wrap(err)
}
}
s, err := sshutils.NewServer(
teleport.ComponentReverseTunnel,
addr,
srv,
hostSigners,
sshutils.AuthMethods{
PublicKey: srv.keyAuth,
},
sshutils.SetLimiter(srv.limiter),
)
if err != nil {
return nil, err
}
srv.hostCertChecker = ssh.CertChecker{IsAuthority: srv.isHostAuthority}
srv.userCertChecker = ssh.CertChecker{IsAuthority: srv.isUserAuthority}
srv.srv = s
return srv, nil
}
func (s *server) Wait() {
s.srv.Wait()
}
func (s *server) Start() error {
return s.srv.Start()
}
func (s *server) Close() error {
return s.srv.Close()
}
func (s *server) HandleNewChan(conn net.Conn, sconn *ssh.ServerConn, nch ssh.NewChannel) {
// apply read/write timeouts to the server connection
conn = utils.ObeyIdleTimeout(conn,
defaults.ReverseTunnelAgentHeartbeatPeriod*10,
"reverse tunnel server")
ct := nch.ChannelType()
if ct != chanHeartbeat {
msg := fmt.Sprintf("reversetunnel received unknown channel request %v from %v",
nch.ChannelType(), sconn)
// if someone is trying to open a new SSH session by talking to a reverse tunnel,
// they're most likely using the wrong port number. Lets give them the explicit hint:
if ct == "session" {
msg = "Cannot open new SSH session on reverse tunnel. Are you connecting to the right port?"
}
log.Warningf(msg)
nch.Reject(ssh.ConnectionFailed, msg)
return
}
log.Debugf("[TUNNEL] new tunnel from %s", sconn.RemoteAddr())
if sconn.Permissions.Extensions[extCertType] != extCertTypeHost {
log.Error(trace.BadParameter("can't retrieve certificate type in certType"))
return
}
// add the incoming site (cluster) to the list of active connections:
site, remoteConn, err := s.upsertSite(conn, sconn)
if err != nil {
log.Error(trace.Wrap(err))
nch.Reject(ssh.ConnectionFailed, "failed to accept incoming cluster connection")
return
}
// accept the request and start the heartbeat on it:
ch, req, err := nch.Accept()
if err != nil {
log.Error(trace.Wrap(err))
sconn.Close()
return
}
go site.handleHeartbeat(remoteConn, ch, req)
}
// isHostAuthority is called during checking the client key, to see if the signing
// key is the real host CA authority key.
func (s *server) isHostAuthority(auth ssh.PublicKey) bool {
keys, err := s.getTrustedCAKeys(services.HostCA)
if err != nil {
log.Errorf("failed to retrieve trusted keys, err: %v", err)
return false
}
for _, k := range keys {
if sshutils.KeysEqual(k, auth) {
return true
}
}
return false
}
// isUserAuthority is called during checking the client key, to see if the signing
// key is the real user CA authority key.
func (s *server) isUserAuthority(auth ssh.PublicKey) bool {
keys, err := s.getTrustedCAKeys(services.UserCA)
if err != nil {
log.Errorf("failed to retrieve trusted keys, err: %v", err)
return false
}
for _, k := range keys {
if sshutils.KeysEqual(k, auth) {
return true
}
}
return false
}
func (s *server) getTrustedCAKeys(CertType services.CertAuthType) ([]ssh.PublicKey, error) {
cas, err := s.localAuth.GetCertAuthorities(CertType, false)
if err != nil {
return nil, err
}
out := []ssh.PublicKey{}
for _, ca := range cas {
checkers, err := ca.Checkers()
if err != nil {
return nil, trace.Wrap(err)
}
out = append(out, checkers...)
}
return out, nil
}
func (s *server) checkTrustedKey(CertType services.CertAuthType, domainName string, key ssh.PublicKey) error {
cas, err := s.localAuth.GetCertAuthorities(CertType, false)
if err != nil {
return trace.Wrap(err)
}
for _, ca := range cas {
if ca.GetClusterName() != domainName {
continue
}
checkers, err := ca.Checkers()
if err != nil {
return trace.Wrap(err)
}
for _, checker := range checkers {
if sshutils.KeysEqual(key, checker) {
return nil
}
}
}
return trace.NotFound("authority domain %v not found or has no mathching keys", domainName)
}
func (s *server) keyAuth(conn ssh.ConnMetadata, key ssh.PublicKey) (*ssh.Permissions, error) {
logger := log.WithFields(log.Fields{
"remote": conn.RemoteAddr(),
"user": conn.User(),
})
cert, ok := key.(*ssh.Certificate)
if !ok {
logger.Warningf("server doesn't support provided key type")
return nil, trace.BadParameter("server doesn't support provided key type")
}
switch cert.CertType {
case ssh.HostCert:
authDomain, ok := cert.Extensions[utils.CertExtensionAuthority]
if !ok || authDomain == "" {
err := trace.BadParameter("missing authority domainName parameter")
logger.Warningf("failed authenticate host, err: %v", err)
return nil, err
}
err := s.hostCertChecker.CheckHostKey(conn.User(), conn.RemoteAddr(), key)
if err != nil {
logger.Warningf("failed authenticate host, err: %v", err)
return nil, trace.Wrap(err)
}
if err := s.hostCertChecker.CheckCert(conn.User(), cert); err != nil {
logger.Warningf("failed to authenticate host err: %v", err)
return nil, trace.Wrap(err)
}
// this fixes possible injection attack
// when we have 2 trusted remote sites, and one can simply
// pose as another. so we have to check that authority
// matches by some other way (in absence of x509 chains)
if err := s.checkTrustedKey(services.HostCA, authDomain, cert.SignatureKey); err != nil {
logger.Warningf("this claims to be signed as authDomain %v, but no matching signing keys found")
return nil, trace.Wrap(err)
}
return &ssh.Permissions{
Extensions: map[string]string{
extHost: conn.User(),
extCertType: extCertTypeHost,
extAuthority: authDomain,
},
}, nil
case ssh.UserCert:
_, err := s.userCertChecker.Authenticate(conn, key)
if err != nil {
logger.Warningf("failed to authenticate user, err: %v", err)
return nil, err
}
if err := s.userCertChecker.CheckCert(conn.User(), cert); err != nil {
logger.Warningf("failed to authenticate user err: %v", err)
return nil, trace.Wrap(err)
}
return &ssh.Permissions{
Extensions: map[string]string{
extHost: conn.User(),
extCertType: extCertTypeUser,
},
}, nil
default:
return nil, trace.BadParameter("unsupported cert type: %v", cert.CertType)
}
}
func (s *server) upsertSite(conn net.Conn, sshConn *ssh.ServerConn) (*remoteSite, *remoteConn, error) {
domainName := sshConn.Permissions.Extensions[extAuthority]
if strings.TrimSpace(domainName) == "" {
return nil, nil, trace.BadParameter("Cannot create reverse tunnel: empty domain name")
}
s.Lock()
defer s.Unlock()
var site *remoteSite
for _, st := range s.remoteSites {
if st.domainName == domainName {
site = st
break
}
}
var err error
var remoteConn *remoteConn
if site != nil {
if remoteConn, err = site.addConn(conn, sshConn); err != nil {
return nil, nil, trace.Wrap(err)
}
} else {
site, err = newRemoteSite(s, domainName)
if err != nil {
return nil, nil, trace.Wrap(err)
}
if remoteConn, err = site.addConn(conn, sshConn); err != nil {
return nil, nil, trace.Wrap(err)
}
s.remoteSites = append(s.remoteSites, site)
}
log.Infof("[TUNNEL] site %v connected from %v. sites: %d",
domainName, conn.RemoteAddr(), len(s.remoteSites))
return site, remoteConn, nil
}
func (s *server) GetSites() []RemoteSite {
s.RLock()
defer s.RUnlock()
out := make([]RemoteSite, 0, len(s.remoteSites)+len(s.localSites))
for i := range s.localSites {
out = append(out, s.localSites[i])
}
for i := range s.remoteSites {
out = append(out, s.remoteSites[i])
}
return out
}
func (s *server) GetSite(domainName string) (RemoteSite, error) {
s.RLock()
defer s.RUnlock()
for i := range s.remoteSites {
if s.remoteSites[i].domainName == domainName {
return s.remoteSites[i], nil
}
}
for i := range s.localSites {
if s.localSites[i].domainName == domainName {
return s.localSites[i], nil
}
}
return nil, trace.NotFound("site '%v' not found", domainName)
}
func (s *server) RemoveSite(domainName string) error {
s.Lock()
defer s.Unlock()
for i := range s.remoteSites {
if s.remoteSites[i].domainName == domainName {
s.remoteSites = append(s.remoteSites[:i], s.remoteSites[i+1:]...)
return nil
}
}
for i := range s.localSites {
if s.localSites[i].domainName == domainName {
s.localSites = append(s.localSites[:i], s.localSites[i+1:]...)
return nil
}
}
return trace.NotFound("site '%v' not found", domainName)
}
type remoteConn struct {
sshConn ssh.Conn
conn net.Conn
invalid int32
log *log.Entry
counter int32
}
func (rc *remoteConn) String() string {
return fmt.Sprintf("remoteConn(remoteAddr=%v)", rc.conn.RemoteAddr())
}
func (rc *remoteConn) Close() error {
return rc.sshConn.Close()
}
func (rc *remoteConn) markInvalid(err error) {
atomic.StoreInt32(&rc.invalid, 1)
}
func (rc *remoteConn) isInvalid() bool {
return atomic.LoadInt32(&rc.invalid) == 1
}
// newRemoteSite helper creates and initializes 'remoteSite' instance
func newRemoteSite(srv *server, domainName string) (*remoteSite, error) {
remoteSite := &remoteSite{
srv: srv,
domainName: domainName,
log: log.WithFields(log.Fields{
teleport.Component: teleport.ComponentReverseTunnel,
teleport.ComponentFields: map[string]string{
"domainName": domainName,
"side": "server",
},
}),
}
// transport uses connection do dial out to the remote address
remoteSite.transport = &http.Transport{
Dial: remoteSite.dialAccessPoint,
}
clt, err := auth.NewClient("http://stub:0", remoteSite.dialAccessPoint)
if err != nil {
return nil, trace.Wrap(err)
}
remoteSite.clt = clt
accessPoint, err := srv.newAccessPoint(clt, []string{"reverse", domainName})
if err != nil {
return nil, trace.Wrap(err)
}
remoteSite.accessPoint = accessPoint
return remoteSite, nil
}
const (
extHost = "host@teleport"
extCertType = "certtype@teleport"
extAuthority = "auth@teleport"
extCertTypeHost = "host"
extCertTypeUser = "user"
)