Reply to invalid ACKs even when accept queue is full

Before checking if there is space in the accept queue, the listener
should verify that the cookie is valid. If it is not, instead of
silently dropping the packet, reply with an RST.

Fixes #6683

PiperOrigin-RevId: 400807346

1 files changed, 4 insertions, 11 deletions

diff --git a/test/packetimpact/tests/tcp_listen_backlog_test.go b/test/packetimpact/tests/tcp_listen_backlog_test.go
index 4b0f2e31f..e124002f6 100644
--- a/test/packetimpact/tests/tcp_listen_backlog_test.go
+++ b/test/packetimpact/tests/tcp_listen_backlog_test.go
@@ -150,17 +150,10 @@ func TestTCPListenBacklog(t *testing.T) {
 		conn := dut.Net.NewTCPIPv4(t, testbench.TCP{DstPort: &remotePort}, testbench.TCP{})
 		defer conn.Close(t)
 		conn.Send(t, testbench.TCP{Flags: testbench.TCPFlags(header.TCPFlagAck)})
-		if !dut.Uname.IsLinux() {
-			// TODO(https://gvisor.dev/issues/6683): Expect a RST.
-			if got, err := conn.Expect(t, testbench.TCP{}, time.Second); err == nil {
-				t.Errorf("expected no TCP frame, got %s", got)
-			}
-		} else {
-			if got, err := conn.Expect(t, testbench.TCP{}, time.Second); err != nil {
-				t.Errorf("expected TCP frame: %s", err)
-			} else if got, want := *got.Flags, header.TCPFlagRst; got != want {
-				t.Errorf("got %s, want %s", got, want)
-			}
+		if got, err := conn.Expect(t, testbench.TCP{}, time.Second); err != nil {
+			t.Errorf("expected TCP frame: %s", err)
+		} else if got, want := *got.Flags, header.TCPFlagRst; got != want {
+			t.Errorf("got %s, want %s", got, want)
 		}
 	}()