cmd/run: Ensure underlying container is stopped when toolbox is killed

Right now "toolbox enter" creates a container on the fly, but
then lets it linger after the foreground toolbox process is
killed (for instance, from a terminal hangup).

Not killing the underlying container has the negative side effect of
stalling shutdown if a toolbox shell is running.

This commit addresses that problem by detecting when the toolbox process
is signaled, and then in response, kills off the entire cgroup associated
with the underlying container.

Closes #1157

src/cmd/run.go

@@ -21,7 +21,9 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"os/signal"
 	"strings"
+	"syscall"
 	"time"
 
 	"github.com/containers/toolbox/pkg/podman"
@@ -263,6 +265,30 @@ func runCommand(container string,
 		return fmt.Errorf("invalid entry point PID of container %s", container)
 	}
 
+	logrus.Debugf("Setting up monitor to stop container %s on termination", container)
+	signalChannel := make(chan os.Signal, 1)
+	signal.Notify(signalChannel, os.Interrupt, syscall.SIGTERM, syscall.SIGHUP)
+
+	go func() {
+		signal := <-signalChannel
+
+		logrus.Debugf("Got signal %d, killing cgroup", signal)
+		cgroupFilePath := fmt.Sprintf("/proc/%d/cgroup", entryPointPID);
+		cgroupId, err := os.ReadFile(cgroupFilePath);
+		if err != nil {
+			logrus.Debugf("Could not look up cgroup of container %s: %s", container, err)
+			return
+		}
+
+		cgroup := strings.Trim(string(cgroupId), "0:/\n")
+		killPath := fmt.Sprintf("/sys/fs/cgroup/%s/cgroup.kill", cgroup)
+
+		if err := os.WriteFile(killPath, []byte("1"), 0644); err != nil {
+			logrus.Debugf("Could not write 1 to %s: %s", killPath, err)
+			return
+		}
+	}()
+
 	logrus.Debugf("Waiting for container %s to finish initializing", container)
 
 	toolboxRuntimeDirectory, err := utils.GetRuntimeDirectory(currentUser)