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LibGC: Visit the edges of the cells that must survive garbage collection

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Previously, we would only keep the cell that must survive alive, but
none of it's edges.

This cropped up with a GC UAF in must_survive_garbage_collection of
WebSocket in .NET's SignalR frontend implementation, where an
out-of-scope WebSocket had it's underlying EventTarget properties
garbage collected, and must_survive_garbage_collection read from the
destroyed EventTarget properties.

See: https://github.com/dotnet/aspnetcore/blob/main/src/SignalR/clients/ts/signalr/src/WebSocketTransport.ts#L81
Found on https://www.formula1.com/ during a live session.

Co-Authored-By: Tim Flynn <trflynn89@pm.me>
This commit is contained in:
Luke Wilde 2025-02-27 14:50:22 +00:00 • committed by Tim Flynn
commit 5146bbe296
Notes: github-actions[bot] 2025-02-27 19:36:28 +00:00
3 changed files with 32 additions and 2 deletions
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12
Libraries/LibGC/Heap.cpp
View file

@ -430,6 +430,14 @@ void Heap::mark_live_cells(HashMap<Cell*, HeapRoot> const& roots)
for (auto& inverse_root : m_uprooted_cells)
inverse_root->set_marked(false);
for_each_block([&](auto& block) {
block.template for_each_cell_in_state<Cell::State::Live>([&](Cell* cell) {
if (!cell->is_marked() && cell_must_survive_garbage_collection(*cell))
cell->visit_edges(visitor);
});
return IterationDecision::Continue;
});
m_uprooted_cells.clear();
}
@ -444,7 +452,7 @@ void Heap::finalize_unmarked_cells()
{
for_each_block([&](auto& block) {
block.template for_each_cell_in_state<Cell::State::Live>([](Cell* cell) {
if (!cell->is_marked() && !cell_must_survive_garbage_collection(*cell))
if (!cell->is_marked())
cell->finalize();
});
return IterationDecision::Continue;
@ -466,7 +474,7 @@ void Heap::sweep_dead_cells(bool print_report, Core::ElapsedTimer const& measure
bool block_has_live_cells = false;
bool block_was_full = block.is_full();
block.template for_each_cell_in_state<Cell::State::Live>([&](Cell* cell) {
if (!cell->is_marked() && !cell_must_survive_garbage_collection(*cell)) {
if (!cell->is_marked()) {
dbgln_if(HEAP_DEBUG, " ~ {}", cell);
block.deallocate(cell);
++collected_cells;