drivers/exec+java: Add configuration to restore previous PID/IPC namespace behavior.

This PR adds default_pid_mode and default_ipc_mode options to the exec and java
task drivers. By default these will default to "private" mode, enabling PID and
IPC isolation for tasks. Setting them to "host" mode disables isolation. Doing
so is not recommended, but may be necessary to support legacy job configurations.

Closes #9969

drivers/java/driver.go

@@ -63,7 +63,16 @@ var (
 	}
 
 	// configSpec is the hcl specification returned by the ConfigSchema RPC
-	configSpec = hclspec.NewObject(map[string]*hclspec.Spec{})
+	configSpec = hclspec.NewObject(map[string]*hclspec.Spec{
+		"default_pid_mode": hclspec.NewDefault(
+			hclspec.NewAttr("default_pid_mode", "string", false),
+			hclspec.NewLiteral(`"private"`),
+		),
+		"default_ipc_mode": hclspec.NewDefault(
+			hclspec.NewAttr("default_ipc_mode", "string", false),
+			hclspec.NewLiteral(`"private"`),
+		),
+	})
 
 	// taskConfigSpec is the hcl specification for the driver config section of
 	// a taskConfig within a job. It is returned in the TaskConfigSchema RPC
@@ -101,6 +110,33 @@ func init() {
 	}
 }
 
+// Config is the driver configuration set by the SetConfig RPC call
+type Config struct {
+	// DefaultModePID is the default PID isolation set for all tasks using
+	// exec-based task drivers.
+	DefaultModePID string `codec:"default_pid_mode"`
+
+	// DefaultModeIPC is the default IPC isolation set for all tasks using
+	// exec-based task drivers.
+	DefaultModeIPC string `codec:"default_ipc_mode"`
+}
+
+func (c *Config) validate() error {
+	switch c.DefaultModePID {
+	case executor.IsoModePrivate, executor.IsoModeHost:
+	default:
+		return fmt.Errorf("default_pid_mode must be %q or %q, got %q", executor.IsoModePrivate, executor.IsoModeHost, c.DefaultModePID)
+	}
+
+	switch c.DefaultModeIPC {
+	case executor.IsoModePrivate, executor.IsoModeHost:
+	default:
+		return fmt.Errorf("default_ipc_mode must be %q or %q, got %q", executor.IsoModePrivate, executor.IsoModeHost, c.DefaultModeIPC)
+	}
+
+	return nil
+}
+
 // TaskConfig is the driver configuration of a taskConfig within a job
 type TaskConfig struct {
 	Class     string   `codec:"class"`
@@ -126,6 +162,9 @@ type Driver struct {
 	// event can be broadcast to all callers
 	eventer *eventer.Eventer
 
+	// config is the driver configuration set by the SetConfig RPC
+	config Config
+
 	// tasks is the in memory datastore mapping taskIDs to taskHandle
 	tasks *taskStore
 
@@ -159,6 +198,18 @@ func (d *Driver) ConfigSchema() (*hclspec.Spec, error) {
 }
 
 func (d *Driver) SetConfig(cfg *base.Config) error {
+	// unpack, validate, and set agent plugin config
+	var config Config
+	if len(cfg.PluginConfig) != 0 {
+		if err := base.MsgPackDecode(cfg.PluginConfig, &config); err != nil {
+			return err
+		}
+	}
+	if err := config.validate(); err != nil {
+		return err
+	}
+	d.config = config
+
 	if cfg != nil && cfg.AgentConfig != nil {
 		d.nomadConfig = cfg.AgentConfig.Driver
 	}
@@ -374,6 +425,8 @@ func (d *Driver) StartTask(cfg *drivers.TaskConfig) (*drivers.TaskHandle, *drive
 		Mounts:           cfg.Mounts,
 		Devices:          cfg.Devices,
 		NetworkIsolation: cfg.NetworkIsolation,
+		DefaultModePID:   d.config.DefaultModePID,
+		DefaultModeIPC:   d.config.DefaultModeIPC,
 	}
 
 	ps, err := exec.Launch(execCmd)