Check signal is unset before using user stopsignal

This fixes an issue where if a stop signal is set, and a user sends
SIGKILL, `container.ExitOnNext()` is not set, thus causing the container
to restart.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

daemon/kill.go

@@ -68,7 +68,7 @@ func (daemon *Daemon) killWithSignal(container *container.Container, sig int) er
 		return errNotRunning{container.ID}
 	}
 
-	if container.Config.StopSignal != "" {
+	if container.Config.StopSignal != "" && syscall.Signal(sig) != syscall.SIGKILL {
 		containerStopSignal, err := signal.ParseSignal(container.Config.StopSignal)
 		if err != nil {
 			return err

integration-cli/docker_api_containers_test.go

@@ -1933,3 +1933,18 @@ func (s *DockerSuite) TestContainersAPICreateMountsTmpfs(c *check.C) {
 		}
 	}
 }
+
+// Regression test for #33334
+// Makes sure that when a container which has a custom stop signal + restart=always
+// gets killed (with SIGKILL) by the kill API, that the restart policy is cancelled.
+func (s *DockerSuite) TestContainerKillCustomStopSignal(c *check.C) {
+	id := strings.TrimSpace(runSleepingContainer(c, "--stop-signal=SIGTERM", "--restart=always"))
+	res, _, err := request.Post("/containers/" + id + "/kill")
+	c.Assert(err, checker.IsNil)
+	defer res.Body.Close()
+
+	b, err := ioutil.ReadAll(res.Body)
+	c.Assert(res.StatusCode, checker.Equals, http.StatusNoContent, check.Commentf(string(b)))
+	err = waitInspect(id, "{{.State.Running}} {{.State.Restarting}}", "false false", 30*time.Second)
+	c.Assert(err, checker.IsNil)
+}