Inherit parent in clone(CLONE_THREAD) under TaskSet.mu.

PiperOrigin-RevId: 203849534
Change-Id: I4d81513bfd32e0b7fc40c8a4c194eba7abc35a83

pkg/sentry/kernel/task_clone.go

@@ -220,18 +220,15 @@ func (t *Task) Clone(opts *CloneOptions) (ThreadID, *SyscallControl, error) {
 		pidns = pidns.NewChild(userns)
 	}
 	tg := t.tg
-	parent := t.parent
 	if opts.NewThreadGroup {
 		sh := t.tg.signalHandlers
 		if opts.NewSignalHandlers {
 			sh = sh.Fork()
 		}
 		tg = NewThreadGroup(pidns, sh, opts.TerminationSignal, tg.limits.GetCopy(), t.k.monotonicClock)
-		parent = t
 	}
 	cfg := &TaskConfig{
 		Kernel:            t.k,
-		Parent:            parent,
 		ThreadGroup:       tg,
 		TaskContext:       tc,
 		TaskResources:     t.tr.Fork(!opts.NewFiles, !opts.NewFSContext),
@@ -242,6 +239,11 @@ func (t *Task) Clone(opts *CloneOptions) (ThreadID, *SyscallControl, error) {
 		UTSNamespace:      utsns,
 		IPCNamespace:      ipcns,
 	}
+	if opts.NewThreadGroup {
+		cfg.Parent = t
+	} else {
+		cfg.InheritParent = t
+	}
 	if opts.NewNetworkNamespace {
 		cfg.NetworkNamespaced = true
 	}

pkg/sentry/kernel/task_start.go

@@ -31,6 +31,10 @@ type TaskConfig struct {
 	// Parent is the new task's parent. Parent may be nil.
 	Parent *Task
 
+	// If InheritParent is not nil, use InheritParent's parent as the new
+	// task's parent.
+	InheritParent *Task
+
 	// ThreadGroup is the ThreadGroup the new task belongs to.
 	*ThreadGroup
 
@@ -133,6 +137,9 @@ func (ts *TaskSet) newTask(cfg *TaskConfig) (*Task, error) {
 	// IDs).
 	t.updateLogPrefixLocked()
 
+	if cfg.InheritParent != nil {
+		t.parent = cfg.InheritParent.parent
+	}
 	if t.parent != nil {
 		t.parent.children[t] = struct{}{}
 	}