[gh-6980] Client: clean up old allocs before running new ones using t…

…he `exec` task driver. (#20500) (#20584)

Whenever the "exec" task driver is being used, nomad runs a plug in that in time runs the task on a container under the hood. If by any circumstance the executor is killed, the task is reparented to the init service and wont be stopped by Nomad in case of a job updated or stop.

This commit introduces two mechanisms to avoid this behaviour:

* Adds signal catching and handling to the executor, so in case of a SIGTERM, the signal will also be passed on to the task.
* Adds a pre start clean up of the processes in the container, ensuring only the ones the executor runs are present at any given time.

Co-authored-by: Juana De La Cuesta <juanita.delacuestamorales@hashicorp.com>

.changelog/20500.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+client: terminate old exec task processes before starting new ones, to avoid accidentally leaving running processes in case of an error
+```

client/lib/cgroupslib/editor.go

@@ -21,6 +21,10 @@ const (
 	root = "/sys/fs/cgroup"
 )
 
+func GetDefaultRoot() string {
+	return root
+}
+
 // OpenPath creates a handle for modifying cgroup interface files under
 // the given directory.
 //

drivers/shared/executor/executor_linux.go

@@ -12,6 +12,7 @@ import (
 	"io"
 	"os"
 	"os/exec"
+	"os/signal"
 	"path"
 	"path/filepath"
 	"strings"
@@ -78,17 +79,43 @@ type LibcontainerExecutor struct {
 	userProc       *libcontainer.Process
 	userProcExited chan interface{}
 	exitState      *ProcessState
+	sigChan        chan os.Signal
+}
+
+func (l *LibcontainerExecutor) catchSignals() {
+	l.logger.Trace("waiting for signals")
+	defer signal.Stop(l.sigChan)
+	defer close(l.sigChan)
+
+	signal.Notify(l.sigChan, syscall.SIGHUP, syscall.SIGQUIT, syscall.SIGTERM, syscall.SIGINT, syscall.SIGSEGV)
+	for {
+		signal := <-l.sigChan
+		if signal == syscall.SIGTERM || signal == syscall.SIGINT {
+			l.Shutdown("SIGINT", 0)
+			break
+		}
+
+		if l.container != nil {
+			l.container.Signal(signal, false)
+		}
+	}
 }
 
 func NewExecutorWithIsolation(logger hclog.Logger, compute cpustats.Compute) Executor {
+	sigch := make(chan os.Signal, 4)
+
 	le := &LibcontainerExecutor{
 		id:             strings.ReplaceAll(uuid.Generate(), "-", "_"),
 		logger:         logger.Named("isolated_executor"),
 		compute:        compute,
 		totalCpuStats:  cpustats.New(compute),
 		userCpuStats:   cpustats.New(compute),
 		systemCpuStats: cpustats.New(compute),
+		sigChan:        sigch,
 	}
+
+	go le.catchSignals()
+
 	le.processStats = procstats.New(compute, le)
 	return le
 }
@@ -97,6 +124,34 @@ func (l *LibcontainerExecutor) ListProcesses() *set.Set[int] {
 	return procstats.List(l.command)
 }
 
+// cleanOldProcessesInCGroup kills processes that might ended up orphans when the
+// executor was unexpectedly killed and nomad can't reconnect to them.
+func (l *LibcontainerExecutor) cleanOldProcessesInCGroup(nomadRelativePath string) {
+	l.logger.Debug("looking for old processes", "path", nomadRelativePath)
+
+	root := cgroupslib.GetDefaultRoot()
+	orphansPIDs, err := cgroups.GetAllPids(filepath.Join(root, nomadRelativePath))
+	if err != nil {
+		l.logger.Error("unable to get orphaned task PIDs", "error", err)
+		return
+	}
+
+	for _, pid := range orphansPIDs {
+		l.logger.Info("killing orphaned process", "pid", pid)
+
+		// Avoid bringing down the whole node by mistake, very unlikely case,
+		// but it's better to be sure.
+		if pid == 1 {
+			continue
+		}
+
+		err := syscall.Kill(pid, syscall.SIGKILL)
+		if err != nil {
+			l.logger.Error("unable to send signal to process", "pid", pid, "error", err)
+		}
+	}
+}
+
 // Launch creates a new container in libcontainer and starts a new process with it
 func (l *LibcontainerExecutor) Launch(command *ExecCommand) (*ProcessState, error) {
 	l.logger.Trace("preparing to launch command", "command", command.Cmd, "args", strings.Join(command.Args, " "))
@@ -127,6 +182,7 @@ func (l *LibcontainerExecutor) Launch(command *ExecCommand) (*ProcessState, erro
 		return nil, fmt.Errorf("failed to configure container(%s): %v", l.id, err)
 	}
 
+	l.cleanOldProcessesInCGroup(containerCfg.Cgroups.Path)
 	container, err := factory.Create(l.id, containerCfg)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create container(%s): %v", l.id, err)
@@ -166,6 +222,7 @@ func (l *LibcontainerExecutor) Launch(command *ExecCommand) (*ProcessState, erro
 	if command.User != "" {
 		process.User = command.User
 	}
+
 	l.userProc = process
 
 	l.totalCpuStats = cpustats.New(l.compute)
@@ -187,7 +244,6 @@ func (l *LibcontainerExecutor) Launch(command *ExecCommand) (*ProcessState, erro
 	// start a goroutine to wait on the process to complete, so Wait calls can
 	// be multiplexed
 	l.userProcExited = make(chan interface{})
-
 	go l.wait()
 
 	return &ProcessState{
@@ -779,6 +835,7 @@ func (l *LibcontainerExecutor) configureCG2(cfg *runc.Config, command *ExecComma
 
 func (l *LibcontainerExecutor) newLibcontainerConfig(command *ExecCommand) (*runc.Config, error) {
 	cfg := &runc.Config{
+		ParentDeathSignal: 9,
 		Cgroups: &runc.Cgroup{
 			Resources: &runc.Resources{
 				MemorySwappiness: nil,

drivers/shared/executor/executor_linux_test.go

@@ -7,10 +7,12 @@ import (
 	"context"
 	"fmt"
 	"os"
+	"os/exec"
 	"path/filepath"
 	"regexp"
 	"strconv"
 	"strings"
+	"syscall"
 	"testing"
 	"time"
 
@@ -26,6 +28,7 @@ import (
 	tu "github.com/hashicorp/nomad/testutil"
 	lconfigs "github.com/opencontainers/runc/libcontainer/configs"
 	"github.com/opencontainers/runc/libcontainer/devices"
+	"github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/shoenig/test"
 	"github.com/shoenig/test/must"
 	"github.com/stretchr/testify/require"
@@ -792,3 +795,117 @@ func TestExecutor_cmdMounts(t *testing.T) {
 
 	require.EqualValues(t, expected, cmdMounts(input))
 }
+
+func createCGroup(fullpath string) (cgroupslib.Interface, error) {
+	if err := os.MkdirAll(fullpath, 0755); err != nil {
+		return nil, err
+	}
+
+	return cgroupslib.OpenPath(fullpath), nil
+}
+
+func TestExecutor_CleanOldProcessesInCGroup(t *testing.T) {
+	ci.Parallel(t)
+
+	testutil.ExecCompatible(t)
+	testutil.CgroupsCompatible(t)
+
+	testExecCmd := testExecutorCommandWithChroot(t)
+
+	allocDir := testExecCmd.allocDir
+	defer allocDir.Destroy()
+
+	fullCGroupPath := testExecCmd.command.Resources.LinuxResources.CpusetCgroupPath
+
+	execCmd := testExecCmd.command
+	execCmd.Cmd = "/bin/sleep"
+	execCmd.Args = []string{"1"}
+	execCmd.ResourceLimits = true
+	execCmd.ModePID = "private"
+	execCmd.ModeIPC = "private"
+
+	// Create the CGroup the executor's command will run in and populate it with one process
+	cgInterface, err := createCGroup(fullCGroupPath)
+	must.NoError(t, err)
+
+	cmd := exec.Command("/bin/sleep", "3000")
+	err = cmd.Start()
+	must.NoError(t, err)
+
+	go func() {
+		err := cmd.Wait()
+		//This process will be killed by the executor as a prerequisite to run
+		// the executors command.
+		must.Error(t, err)
+	}()
+
+	pid := cmd.Process.Pid
+	must.Positive(t, pid)
+
+	err = cgInterface.Write("cgroup.procs", strconv.Itoa(pid))
+	must.NoError(t, err)
+
+	pids, err := cgInterface.PIDs()
+	must.NoError(t, err)
+	must.One(t, pids.Size())
+
+	// Run the executor normally and make sure the process that was originally running
+	// as part of the CGroup was killed, and only the executor's process is running.
+	execInterface := NewExecutorWithIsolation(testlog.HCLogger(t), compute)
+	executor := execInterface.(*LibcontainerExecutor)
+	defer executor.Shutdown("SIGKILL", 0)
+
+	ps, err := executor.Launch(execCmd)
+	must.NoError(t, err)
+	must.Positive(t, ps.Pid)
+
+	pids, err = cgInterface.PIDs()
+	must.NoError(t, err)
+	must.One(t, pids.Size())
+	must.True(t, pids.Contains(ps.Pid))
+	must.False(t, pids.Contains(pid))
+
+	estate, err := executor.Wait(context.Background())
+	must.NoError(t, err)
+	must.Zero(t, estate.ExitCode)
+
+	must.NoError(t, executor.Shutdown("", 0))
+	executor.Wait(context.Background())
+}
+
+func TestExecutor_SignalCatching(t *testing.T) {
+	ci.Parallel(t)
+
+	testutil.ExecCompatible(t)
+	testutil.CgroupsCompatible(t)
+
+	testExecCmd := testExecutorCommandWithChroot(t)
+
+	allocDir := testExecCmd.allocDir
+	defer allocDir.Destroy()
+
+	execCmd := testExecCmd.command
+	execCmd.Cmd = "/bin/sleep"
+	execCmd.Args = []string{"100"}
+	execCmd.ResourceLimits = true
+	execCmd.ModePID = "private"
+	execCmd.ModeIPC = "private"
+
+	execInterface := NewExecutorWithIsolation(testlog.HCLogger(t), compute)
+
+	ps, err := execInterface.Launch(execCmd)
+	must.NoError(t, err)
+	must.Positive(t, ps.Pid)
+
+	executor := execInterface.(*LibcontainerExecutor)
+	status, err := executor.container.OCIState()
+	must.NoError(t, err)
+	must.Eq(t, specs.StateRunning, status.Status)
+
+	executor.sigChan <- syscall.SIGTERM
+	time.Sleep(1 * time.Second)
+
+	status, err = executor.container.OCIState()
+	must.NoError(t, err)
+	must.Eq(t, specs.StateStopped, status.Status)
+}