[v10] Fix nil pointer exception when joining non-existent session

api/client/client.go

@@ -2687,7 +2687,10 @@ func (c *Client) CreateSessionTracker(ctx context.Context, st types.SessionTrack
 func (c *Client) GetSessionTracker(ctx context.Context, sessionID string) (types.SessionTracker, error) {
 	req := &proto.GetSessionTrackerRequest{SessionID: sessionID}
 	resp, err := c.grpc.GetSessionTracker(ctx, req, c.callOpts...)
-	return resp, trail.FromGRPC(err)
+	if err != nil {
+		return nil, trail.FromGRPC(err)
+	}
+	return resp, nil
 }
 
 // GetActiveSessionTrackers returns a list of active session trackers.

lib/client/api.go

@@ -1950,7 +1950,6 @@ func (tc *TeleportClient) Join(ctx context.Context, mode types.SessionParticipan
 	if sessionID.Check() != nil {
 		return trace.Errorf("Invalid session ID format: %s", string(sessionID))
 	}
-	notFoundErrorMessage := fmt.Sprintf("session '%s' not found or it has ended", sessionID)
 
 	// connect to proxy:
 	if !tc.Config.ProxySpecified() {
@@ -1974,14 +1973,13 @@ func (tc *TeleportClient) Join(ctx context.Context, mode types.SessionParticipan
 	}
 
 	session, err := site.GetSessionTracker(ctx, string(sessionID))
-	if err != nil && !trace.IsNotFound(err) {
+	if err != nil {
+		if trace.IsNotFound(err) {
+			return trace.NotFound("session %q not found or it has ended", sessionID)
+		}
 		return trace.Wrap(err)
 	}
 
-	if session == nil {
-		return trace.NotFound(notFoundErrorMessage)
-	}
-
 	if session.GetSessionKind() != types.SSHSessionKind {
 		return trace.BadParameter("session joining is only supported for ssh sessions, not %q sessions", session.GetSessionKind())
 	}