2 files changed, 42 insertions, 5 deletions
diff --git a/internal/sshd/sshd.go b/internal/sshd/sshd.go
index 19fa661..d765faf 100644
--- a/internal/sshd/sshd.go
+++ b/internal/sshd/sshd.go
@@ -94,6 +94,7 @@ func (s *Server) listen(ctx context.Context) error {
 	if s.Config.Server.ProxyProtocol {
 		sshListener = &proxyproto.Listener{
 			Listener:          sshListener,
+			Policy:            unconditionalRequirePolicy,
 			ReadHeaderTimeout: ProxyHeaderTimeout,
 		}
 
@@ -185,3 +186,7 @@ func (s *Server) handleConn(ctx context.Context, nconn net.Conn) {
 
 	ctxlog.Info("server: handleConn: done")
 }
+
+func unconditionalRequirePolicy(_ net.Addr) (proxyproto.Policy, error) {
+	return proxyproto.REQUIRE, nil
+}
diff --git a/internal/sshd/sshd_test.go b/internal/sshd/sshd_test.go
index 71f7733..455a830 100644
--- a/internal/sshd/sshd_test.go
+++ b/internal/sshd/sshd_test.go
@@ -47,6 +47,19 @@ func TestListenAndServe(t *testing.T) {
 	verifyStatus(t, s, StatusClosed)
 }
 
+func TestListenAndServeRejectsPlainConnectionsWhenProxyProtocolEnabled(t *testing.T) {
+	s := setupServerWithProxyProtocolEnabled(t)
+	defer s.Shutdown()
+
+	client, err := ssh.Dial("tcp", serverUrl, clientConfig(t))
+	if client != nil {
+		client.Close()
+	}
+
+	require.Error(t, err, "Expected plain SSH request to be failed")
+	require.Equal(t, err.Error(), "ssh: handshake failed: EOF")
+}
+
 func TestCorrelationId(t *testing.T) {
 	setupServer(t)
 
@@ -125,6 +138,18 @@ func TestInvalidServerConfig(t *testing.T) {
 func setupServer(t *testing.T) *Server {
 	t.Helper()
 
+	return setupServerWithConfig(t, nil)
+}
+
+func setupServerWithProxyProtocolEnabled(t *testing.T) *Server {
+	t.Helper()
+
+	return setupServerWithConfig(t, &config.Config{Server: config.ServerConfig{ProxyProtocol: true}})
+}
+
+func setupServerWithConfig(t *testing.T, cfg *config.Config) *Server {
+	t.Helper()
+
 	requests := []testserver.TestRequestHandler{
 		{
 			Path: "/api/v4/internal/authorized_keys",
@@ -148,13 +173,20 @@ func setupServer(t *testing.T) *Server {
 	testhelper.PrepareTestRootDir(t)
 
 	url := testserver.StartSocketHttpServer(t, requests)
-	srvCfg := config.ServerConfig{
-		Listen:                  serverUrl,
-		ConcurrentSessionsLimit: 1,
-		HostKeyFiles:            []string{path.Join(testhelper.TestRoot, "certs/valid/server.key")},
+
+	if cfg == nil {
+		cfg = &config.Config{}
 	}
 
-	s, err := NewServer(&config.Config{User: user, RootDir: "/tmp", GitlabUrl: url, Server: srvCfg})
+	// All things that don't need to be configurable in tests yet
+	cfg.GitlabUrl = url
+	cfg.RootDir = "/tmp"
+	cfg.User = user
+	cfg.Server.Listen = serverUrl
+	cfg.Server.ConcurrentSessionsLimit = 1
+	cfg.Server.HostKeyFiles = []string{path.Join(testhelper.TestRoot, "certs/valid/server.key")}
+
+	s, err := NewServer(cfg)
 	require.NoError(t, err)
 
 	go func() { require.NoError(t, s.ListenAndServe(context.Background())) }()