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package sshd
import (
"context"
"encoding/base64"
"errors"
"fmt"
"io/ioutil"
"net"
"net/http"
"strconv"
"sync"
"time"
"github.com/pires/go-proxyproto"
"golang.org/x/crypto/ssh"
"gitlab.com/gitlab-org/gitlab-shell/internal/config"
"gitlab.com/gitlab-org/gitlab-shell/internal/gitlabnet/authorizedkeys"
"gitlab.com/gitlab-org/labkit/correlation"
"gitlab.com/gitlab-org/labkit/log"
)
type status int
const (
StatusStarting status = iota
StatusReady
StatusOnShutdown
StatusClosed
ProxyHeaderTimeout = 90 * time.Second
)
type Server struct {
Config *config.Config
status status
statusMu sync.Mutex
wg sync.WaitGroup
listener net.Listener
}
func (s *Server) ListenAndServe(ctx context.Context) error {
if err := s.listen(); err != nil {
return err
}
defer s.listener.Close()
return s.serve(ctx)
}
func (s *Server) Shutdown() error {
if s.listener == nil {
return nil
}
s.changeStatus(StatusOnShutdown)
return s.listener.Close()
}
func (s *Server) MonitoringServeMux() *http.ServeMux {
mux := http.NewServeMux()
mux.HandleFunc(s.Config.Server.ReadinessProbe, func(w http.ResponseWriter, r *http.Request) {
if s.getStatus() == StatusReady {
w.WriteHeader(http.StatusOK)
} else {
w.WriteHeader(http.StatusServiceUnavailable)
}
})
mux.HandleFunc(s.Config.Server.LivenessProbe, func(w http.ResponseWriter, r *http.Request) {
w.WriteHeader(http.StatusOK)
})
return mux
}
func (s *Server) listen() error {
sshListener, err := net.Listen("tcp", s.Config.Server.Listen)
if err != nil {
return fmt.Errorf("failed to listen for connection: %w", err)
}
if s.Config.Server.ProxyProtocol {
sshListener = &proxyproto.Listener{
Listener: sshListener,
ReadHeaderTimeout: ProxyHeaderTimeout,
}
log.Info("Proxy protocol is enabled")
}
log.WithFields(log.Fields{"tcp_address": sshListener.Addr().String()}).Info("Listening for SSH connections")
s.listener = sshListener
return nil
}
func (s *Server) serve(ctx context.Context) error {
sshCfg, err := s.initConfig(ctx)
if err != nil {
return err
}
s.changeStatus(StatusReady)
for {
nconn, err := s.listener.Accept()
if err != nil {
if s.getStatus() == StatusOnShutdown {
break
}
log.WithError(err).Warn("Failed to accept connection")
continue
}
s.wg.Add(1)
go s.handleConn(ctx, sshCfg, nconn)
}
s.wg.Wait()
s.changeStatus(StatusClosed)
return nil
}
func (s *Server) changeStatus(st status) {
s.statusMu.Lock()
s.status = st
s.statusMu.Unlock()
}
func (s *Server) getStatus() status {
s.statusMu.Lock()
defer s.statusMu.Unlock()
return s.status
}
func (s *Server) initConfig(ctx context.Context) (*ssh.ServerConfig, error) {
authorizedKeysClient, err := authorizedkeys.NewClient(s.Config)
if err != nil {
return nil, fmt.Errorf("failed to initialize GitLab client: %w", err)
}
sshCfg := &ssh.ServerConfig{
PublicKeyCallback: func(conn ssh.ConnMetadata, key ssh.PublicKey) (*ssh.Permissions, error) {
if conn.User() != s.Config.User {
return nil, errors.New("unknown user")
}
if key.Type() == ssh.KeyAlgoDSA {
return nil, errors.New("DSA is prohibited")
}
ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
defer cancel()
res, err := authorizedKeysClient.GetByKey(ctx, base64.RawStdEncoding.EncodeToString(key.Marshal()))
if err != nil {
return nil, err
}
return &ssh.Permissions{
// Record the public key used for authentication.
Extensions: map[string]string{
"key-id": strconv.FormatInt(res.Id, 10),
},
}, nil
},
}
var loadedHostKeys uint
for _, filename := range s.Config.Server.HostKeyFiles {
keyRaw, err := ioutil.ReadFile(filename)
if err != nil {
log.WithError(err).Warnf("Failed to read host key %v", filename)
continue
}
key, err := ssh.ParsePrivateKey(keyRaw)
if err != nil {
log.WithError(err).Warnf("Failed to parse host key %v", filename)
continue
}
loadedHostKeys++
sshCfg.AddHostKey(key)
}
if loadedHostKeys == 0 {
return nil, fmt.Errorf("No host keys could be loaded, aborting")
}
return sshCfg, nil
}
func (s *Server) handleConn(ctx context.Context, sshCfg *ssh.ServerConfig, nconn net.Conn) {
remoteAddr := nconn.RemoteAddr().String()
defer s.wg.Done()
defer nconn.Close()
// Prevent a panic in a single connection from taking out the whole server
defer func() {
if err := recover(); err != nil {
log.WithFields(log.Fields{"recovered_error": err}).Warnf("panic handling session from %s", remoteAddr)
}
}()
ctx, cancel := context.WithCancel(correlation.ContextWithCorrelation(ctx, correlation.SafeRandomID()))
defer cancel()
sconn, chans, reqs, err := ssh.NewServerConn(nconn, sshCfg)
if err != nil {
log.WithError(err).Info("Failed to initialize SSH connection")
return
}
go ssh.DiscardRequests(reqs)
conn := newConnection(s.Config.Server.ConcurrentSessionsLimit, remoteAddr)
conn.handle(ctx, chans, func(ctx context.Context, channel ssh.Channel, requests <-chan *ssh.Request) {
session := &session{
cfg: s.Config,
channel: channel,
gitlabKeyId: sconn.Permissions.Extensions["key-id"],
remoteAddr: remoteAddr,
}
session.handle(ctx, requests)
})
}
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