feat(GODT-1891): kick client that send too many invalid IMAP command

internal/session/errors.go

@@ -11,5 +11,7 @@ var (
 	ErrNotAuthenticated     = errors.New("session is not authenticated")
 	ErrAlreadyAuthenticated = errors.New("session is already authenticated")
 
+	ErrTooManyInvalid = errors.New("too many invalid IMAP commands")
+
 	ErrNotImplemented = errors.New("not implemented")
 )

internal/session/session.go

@@ -21,12 +21,15 @@ import (
 	"github.com/ProtonMail/gluon/internal/response"
 	"github.com/ProtonMail/gluon/internal/state"
 	"github.com/ProtonMail/gluon/profiling"
+	"github.com/ProtonMail/gluon/reporter"
 	"github.com/ProtonMail/gluon/version"
 	"github.com/ProtonMail/gluon/wait"
 	"github.com/sirupsen/logrus"
 	"golang.org/x/exp/slices"
 )
 
+const maxSessionError = 20
+
 type Session struct {
 	// conn is the underlying TCP connection to the client. It is wrapped by a buffered liner.
 	conn net.Conn
@@ -73,6 +76,9 @@ type Session struct {
 
 	// handleWG is used to wait for all commands to finish before closing the session.
 	handleWG wait.Group
+
+	/// errorCount error counter
+	errorCount int
 }
 
 func New(
@@ -165,17 +171,27 @@ func (s *Session) serve(ctx context.Context) error {
 
 			if res.err != nil {
 				logrus.WithError(res.err).Debugf("Error during command parsing")
+				s.errorCount++
 
 				if errors.Is(res.err, io.EOF) {
 					logrus.Debugf("Connection to client lost")
 					return nil
+				} else if s.errorCount >= maxSessionError {
+					_ = response.Bad(tag).WithError(ErrTooManyInvalid).Send(s)
+					reporter.MessageWithContext(ctx,
+						ErrTooManyInvalid.Error(),
+						reporter.Context{"error": ErrTooManyInvalid, "ID": s.imapID.String()},
+					)
+					return ErrTooManyInvalid
 				} else if err := response.Bad(tag).WithError(res.err).Send(s); err != nil {
 					return err
 				}
 
 				continue
 			}
 
+			s.errorCount = 0
+
 		case <-s.state.Done():
 			return nil
 

tests/session_test.go

@@ -324,3 +324,29 @@ func parseDateFromDelimiter(messageDelimiter string) (t time.Time, err error) {
 
 	return time.Parse("Mon Jan _2 15:04:05 2006", strings.TrimSpace(strings.Join(split[2:], " ")))
 }
+
+func TestTooManyInvalidCommand(t *testing.T) {
+	runOneToOneTestWithAuth(t, defaultServerOptions(t), func(c *testConnection, s *testSession) {
+		for i := 1; i <= 19; i++ {
+			c.Cf("%d FOO", i).BAD(fmt.Sprintf("%d", i))
+		}
+		c.Cf("100 FOO").BAD("100")
+		// expect server to trigger the error as well
+		require.Errorf(t, <-s.server.GetErrorCh(), "100 BAD too many invalid IMAP commands")
+	})
+}
+
+func TestResetTooManyInvalidCommand(t *testing.T) {
+	runOneToOneTestWithAuth(t, defaultServerOptions(t), func(c *testConnection, s *testSession) {
+		for i := 1; i <= 19; i++ {
+			c.Cf("%d FOO", i).BAD(fmt.Sprintf("%d", i))
+		}
+		c.C("100 NOOP").OK("100")
+		for i := 1; i <= 19; i++ {
+			c.Cf("%d FOO", i).BAD(fmt.Sprintf("%d", i))
+		}
+		c.Cf("100 FOO").BAD("100")
+		// expect server to trigger the error as well
+		require.Errorf(t, <-s.server.GetErrorCh(), "100 BAD too many invalid IMAP commands")
+	})
+}