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fix: Guard against conn leak after server close #1

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fix: Guard against conn leak after server close #1

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22 changes: 22 additions & 0 deletions server.go
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Original file line number Diff line number Diff line change
Expand Up @@ -73,6 +73,7 @@ type Server struct {
conns map[*gossh.ServerConn]struct{}
connWg sync.WaitGroup
doneChan chan struct{}
closedAt time.Time
}

func (srv *Server) ensureHostSigner() error {
Expand Down Expand Up @@ -180,6 +181,8 @@ func (srv *Server) Close() error {
srv.mu.Lock()
defer srv.mu.Unlock()

srv.closedAt = time.Now()

srv.closeDoneChanLocked()
err := srv.closeListenersLocked()
for c := range srv.conns {
Expand Down Expand Up @@ -260,6 +263,17 @@ func (srv *Server) Serve(l net.Listener) error {
}

func (srv *Server) HandleConn(newConn net.Conn) {
// Best effort, track start time in case the server is closed
// between here and trackConn. If trackConn is called after the
// server is closed, this connection would leak.
//
// A better approach would be to have a clearer signal between the
// server being "started" and "closed", but that would require a
// larger refactor or change in logic.
srv.mu.RLock()
start := time.Now()
srv.mu.RUnlock()

ctx, cancel := newContext(srv)
if srv.ConnCallback != nil {
cbConn := srv.ConnCallback(ctx, newConn)
Expand Down Expand Up @@ -289,6 +303,14 @@ func (srv *Server) HandleConn(newConn net.Conn) {
srv.trackConn(sshConn, true)
defer srv.trackConn(sshConn, false)

srv.mu.RLock()
if srv.closedAt.After(start) {
srv.mu.RUnlock()
sshConn.Close()
return
}
srv.mu.RUnlock()

ctx.SetValue(ContextKeyConn, sshConn)
applyConnMetadata(ctx, sshConn)
//go gossh.DiscardRequests(reqs)
Expand Down
103 changes: 103 additions & 0 deletions server_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,8 @@ import (
"io"
"testing"
"time"

gossh "golang.org/x/crypto/ssh"
)

func TestAddHostKey(t *testing.T) {
Expand Down Expand Up @@ -124,3 +126,104 @@ func TestServerClose(t *testing.T) {
return
}
}

func TestServerClose_ConnectionLeak(t *testing.T) {
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Member Author

@mafredri mafredri Apr 4, 2023 •
edited
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This test is a bit finicky, but without the fix it will usually time out (as a proof of the issue being fixed).

l := newLocalListener()
s := &Server{
Handler: func(s Session) {
time.Sleep(5 * time.Second)
},
}
go func() {
err := s.Serve(l)
if err != nil && err != ErrServerClosed {
t.Error(err)
}
}()

clientDoneChan := make(chan struct{})
closeDoneChan := make(chan struct{})

num := 3
ch := make(chan struct{}, num)
go func() {
for i := 0; i < num; i++ {
<-ch
}
close(clientDoneChan)
}()
prepare := make(chan struct{}, num)
go func() {
for i := 0; i < num; i++ {
go func() {
defer func() {
ch <- struct{}{}
}()
sess, _, cleanup, err := newClientSession2(t, l.Addr().String(), nil)
prepare <- struct{}{}
if err != nil {
t.Log(err)
return
}
defer cleanup()
if err := sess.Run(""); err != nil && err != io.EOF {
t.Log(err)
}
}()
}
}()

go func() {
for i := 0; i < num-1; i++ {
<-prepare
}
err := s.Close()
if err != nil {
t.Error(err)
}
close(closeDoneChan)
}()

timeout := time.After(1000 * time.Millisecond)
select {
case <-timeout:
t.Error("timeout")
return
case <-closeDoneChan:
}
select {
case <-timeout:
t.Error("timeout")
return
case <-clientDoneChan:
}
}

func newClientSession2(t *testing.T, addr string, config *gossh.ClientConfig) (*gossh.Session, *gossh.Client, func(), error) {
t.Helper()

if config == nil {
config = &gossh.ClientConfig{
User: "testuser",
Auth: []gossh.AuthMethod{
gossh.Password("testpass"),
},
}
}
if config.HostKeyCallback == nil {
config.HostKeyCallback = gossh.InsecureIgnoreHostKey()
}
client, err := gossh.Dial("tcp", addr, config)
if err != nil {
return nil, nil, nil, err
}
session, err := client.NewSession()
if err != nil {
client.Close()
return nil, nil, nil, err
}
return session, client, func() {
session.Close()
client.Close()
}, nil
}
6 changes: 3 additions & 3 deletions session_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -230,9 +230,9 @@ func TestPty(t *testing.T) {

func TestPtyResize(t *testing.T) {
t.Parallel()
winch0 := Window{40, 80}
winch1 := Window{80, 160}
winch2 := Window{20, 40}
winch0 := Window{Width: 40, Height: 80}
winch1 := Window{Width: 80, Height: 160}
winch2 := Window{Width: 20, Height: 40}
winches := make(chan Window)
done := make(chan bool)
session, _, cleanup := newTestSession(t, &Server{
Expand Down