may kill other process when container has been stopped

Signed-off-by: Lifubang <lifubang@acmcoder.com>

libcontainer/container_linux.go

@@ -370,7 +370,18 @@ func (c *linuxContainer) start(process *Process) error {
 	return nil
 }
 
+func (c *linuxContainer) Kill(s os.Signal, all bool) error {
+}
+
 func (c *linuxContainer) Signal(s os.Signal, all bool) error {
+	status, err := c.currentStatus()
+	if err != nil {
+		return err
+	}
+	// to avoid a PID reuse attack
+	if status == Stopped {
+		return newGenericError(fmt.Errorf("container not running"), ContainerNotRunning)
+	}
 	if all {
 		return signalAllProcesses(c.cgroupManager, s)
 	}