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Fix a heap-use-after-free in a dropdown lambda function #3601

merged 1 commit into from Dec 5, 2019
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Just for now

@@ -45,6 +45,17 @@ namespace UI {

int BaseDropdown::next_id_ = 0;

// Dropdowns hook into parent elements to be notified of layouting changes. We need to keep track of
// whether a dropdown actually still exists when notified to avoid heap-use-after-free's.
static std::map<int, BaseDropdown*> living_dropdowns_;
// static
void BaseDropdown::layout_if_alive(int id) {
auto it = living_dropdowns_.find(id);
if (it != living_dropdowns_.end()) {

BaseDropdown::BaseDropdown(UI::Panel* parent,
const std::string& name,
int32_t x,
@@ -137,10 +148,13 @@ BaseDropdown::BaseDropdown(UI::Panel* parent,

const int serial = id_; // Not a member variable, because when the lambda below is triggered we
// might no longer exist
living_dropdowns_.insert(std::make_pair(serial, this));
// Find parent windows, boxes etc. so that we can move the list along with them
UI::Panel* ancestor = this;
while ((ancestor = ancestor->get_parent()) != nullptr) {
ancestor->position_changed.connect([this] { layout(); });
ancestor->position_changed.connect([serial] { layout_if_alive(serial); });
@@ -149,6 +163,10 @@ BaseDropdown::~BaseDropdown() {
// The list needs to be able to drop outside of windows, so it won't close with the window.
// So, we tell it to die.

// Unsubscribe from layouting hooks
assert(living_dropdowns_.find(id_) != living_dropdowns_.end());

void BaseDropdown::set_height(int height) {
@@ -213,6 +213,8 @@ class BaseDropdown : public NamedPanel {
uint32_t current_selection_;
DropdownType type_;
bool is_enabled_;

static void layout_if_alive(int);

/// A dropdown menu that lets the user select a value of the datatype 'Entry'.
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