Fix sshd goroutine leak and other cleanup

sshd/server.go

@@ -16,16 +16,13 @@ type SSHServer struct {
 	config *ssh.ServerConfig
 	l      *logrus.Entry
 
-	certChecker *ssh.CertChecker
-
 	// Map of user -> authorized keys
 	trustedKeys map[string]map[string]bool
 	trustedCAs  []ssh.PublicKey
 
 	// List of available commands
-	helpCommand *Command
-	commands    *radix.Tree
-	listener    net.Listener
+	commands *radix.Tree
+	listener net.Listener
 
 	// Locks the conns/counter to avoid concurrent map access
 	connsLock sync.Mutex
@@ -184,7 +181,11 @@ func (s *SSHServer) run() {
 
 		if err != nil {
 			l := s.l.WithError(err).WithField("remoteAddress", c.RemoteAddr())
-			if conn != nil {
+			if conn == nil {
+				// conn is nil when the handshake failed before authentication
+				// close the raw TCP connection to avoid leaking the file descriptor.
+				c.Close()
+			} else {
 				l = l.WithField("sshUser", conn.User())
 				conn.Close()
 			}

sshd/session.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"sort"
 	"strings"
+	"sync"
 
 	"github.com/anmitsu/go-shlex"
 	"github.com/armon/go-radix"
@@ -13,11 +14,12 @@ import (
 )
 
 type session struct {
-	l        *logrus.Entry
-	c        *ssh.ServerConn
-	term     *term.Terminal
-	commands *radix.Tree
-	exitChan chan bool
+	l         *logrus.Entry
+	c         *ssh.ServerConn
+	term      *term.Terminal
+	commands  *radix.Tree
+	exitChan  chan struct{}
+	closeOnce sync.Once
 }
 
 func NewSession(commands *radix.Tree, conn *ssh.ServerConn, chans <-chan ssh.NewChannel, l *logrus.Entry) *session {
@@ -25,7 +27,7 @@ func NewSession(commands *radix.Tree, conn *ssh.ServerConn, chans <-chan ssh.New
 		commands: radix.NewFromMap(commands.ToMap()),
 		l:        l,
 		c:        conn,
-		exitChan: make(chan bool),
+		exitChan: make(chan struct{}),
 	}
 
 	s.commands.Insert("logout", &Command{
@@ -37,7 +39,10 @@ func NewSession(commands *radix.Tree, conn *ssh.ServerConn, chans <-chan ssh.New
 		},
 	})
 
-	go s.handleChannels(chans)
+	go func() {
+		s.handleChannels(chans)
+		s.Close()
+	}()
 	return s
 }
 
@@ -82,6 +87,7 @@ func (s *session) handleRequests(in <-chan *ssh.Request, channel ssh.Channel) {
 			cErr := ssh.Unmarshal(req.Payload, &payload)
 			if cErr != nil {
 				req.Reply(false, nil)
+				channel.Close()
 				return
 			}
 
@@ -123,11 +129,11 @@ func (s *session) createTerm(channel ssh.Channel) *term.Terminal {
 		return "", 0, false
 	}
 
-	go s.handleInput(channel)
+	go s.handleInput()
 	return term
 }
 
-func (s *session) handleInput(channel ssh.Channel) {
+func (s *session) handleInput() {
 	defer s.Close()
 	w := &stringWriter{w: s.term}
 	for {
@@ -174,6 +180,8 @@ func (s *session) dispatchCommand(line string, w StringWriter) {
 }
 
 func (s *session) Close() {
-	s.c.Close()
-	s.exitChan <- true
+	s.closeOnce.Do(func() {
+		s.c.Close()
+		close(s.exitChan)
+	})
 }