ssh/tailssh,tailcfg: add connID to ssheventnotifyrequest and castheader

This change adds a ConnectionID field to both SSHEventNotifyRequest and
CastHeader that identifies the ID of a connection to the SSH server.

Updates tailscale/corp#9967

Signed-off-by: Charlotte Brandhorst-Satzkorn <charlotte@tailscale.com>

ssh/tailssh/tailssh.go

@@ -1410,6 +1410,11 @@ type CastHeader struct {
 
 	// LocalUser is the effective username on the server.
 	LocalUser string `json:"localUser"`
+
+	// ConnectionID uniquely identifies a connection made to the SSH server.
+	// It may be shared across multiple sessions over the same connection in
+	// case of SSH multiplexing.
+	ConnectionID string `json:"connectionID"`
 }
 
 // sessionRecordingClient returns an http.Client that uses srv.lb.Dialer() to
@@ -1458,7 +1463,6 @@ func (ss *sshSession) connectToRecorder(ctx context.Context, recs []netip.AddrPo
 	if len(recs) == 0 {
 		return nil, nil, nil, errors.New("no recorders configured")
 	}
-	var attempts []*tailcfg.SSHRecordingAttempt
 	// We use a special context for dialing the recorder, so that we can
 	// limit the time we spend dialing to 30 seconds and still have an
 	// unbounded context for the upload.
@@ -1466,12 +1470,11 @@ func (ss *sshSession) connectToRecorder(ctx context.Context, recs []netip.AddrPo
 	defer dialCancel()
 	hc, err := ss.sessionRecordingClient(dialCtx)
 	if err != nil {
-		attempts = append(attempts, &tailcfg.SSHRecordingAttempt{
+		return nil, nil, nil, err
-			FailureMessage: err.Error(),
-		})
-		return nil, attempts, nil, err
 	}
+
 	var errs []error
+	var attempts []*tailcfg.SSHRecordingAttempt
 	for _, ap := range recs {
 		attempt := &tailcfg.SSHRecordingAttempt{
 			Recorder: ap,
@@ -1557,11 +1560,9 @@ func (ss *sshSession) openFileForRecording(now time.Time) (_ io.WriteCloser, err
 func (ss *sshSession) startNewRecording() (_ *recording, err error) {
 	// We store the node key as soon as possible when creating
 	// a new recording incase of FUS.
-	var nodeKey key.NodePublic
+	nodeKey := ss.conn.srv.lb.NodeKey()
-	if nk := ss.conn.srv.lb.NodeKey(); nk.IsZero() {
+	if nodeKey.IsZero() {
 		return nil, errors.New("ssh server is unavailable: no node key")
-	} else {
-		nodeKey = nk
 	}
 
 	recorders, onFailure := ss.recorders()
@@ -1664,6 +1665,7 @@ func (ss *sshSession) startNewRecording() (_ *recording, err error) {
 		LocalUser:    ss.conn.localUser.Username,
 		SrcNode:      strings.TrimSuffix(ss.conn.info.node.Name, "."),
 		SrcNodeID:    ss.conn.info.node.StableID,
+		ConnectionID: ss.conn.connID,
 	}
 	if !ss.conn.info.node.IsTagged() {
 		ch.SrcNodeUser = ss.conn.info.uprof.LoginName
@@ -1694,6 +1696,7 @@ func (ss *sshSession) startNewRecording() (_ *recording, err error) {
 func (ss *sshSession) notifyControl(ctx context.Context, nodeKey key.NodePublic, notifyType tailcfg.SSHEventType, attempts []*tailcfg.SSHRecordingAttempt, url string) {
 	re := tailcfg.SSHEventNotifyRequest{
 		EventType:         notifyType,
+		ConnectionID:      ss.conn.connID,
 		CapVersion:        tailcfg.CurrentCapabilityVersion,
 		NodeKey:           nodeKey,
 		SrcNode:           ss.conn.info.node.ID,

tailcfg/tailcfg.go

@@ -2080,6 +2080,12 @@ type SSHRecorderFailureAction struct {
 type SSHEventNotifyRequest struct {
 	// EventType is the type of notify request being sent.
 	EventType SSHEventType
+
+	// ConnectionID uniquely identifies a connection made to the SSH server.
+	// It may be shared across multiple sessions over the same connection in
+	// case a single connection creates multiple sessions.
+	ConnectionID string
+
 	// CapVersion is the client's current CapabilityVersion.
 	CapVersion CapabilityVersion