Chrome: Use-after-free in WasmMemoryObject::Grow VULNERABILITY DETAILS https://cs.chromium.org/chromium/src/v8/src/wasm/wasm-objects.cc?rcl=783343158eb1b147df7e6669f1d03c690c878e21&l=1253 ``` int32_t WasmMemoryObject::Grow(Isolate* isolate, Handle memory_object, uint32_t pages) { [...] Handle new_buffer; if (old_buffer->is_shared()) { // Adjust protections for the buffer. if (!AdjustBufferPermissions(isolate, old_buffer, new_size)) { return -1; } void* backing_store = old_buffer->backing_store(); if (memory_tracker->IsWasmSharedMemory(backing_store)) { // This memory is shared between different isolates. DCHECK(old_buffer->is_shared()); // Update pending grow state, and trigger a grow interrupt on all the // isolates that share this buffer. memory_tracker->SetPendingUpdateOnGrow(old_buffer, new_size); // Handle interrupts for this isolate so that the instances with this // isolate are updated. isolate->stack_guard()->HandleInterrupts(); // Failure to allocate, or adjust pemissions already handled here, and // updates to instances handled in the interrupt handler safe to return. return static_cast(old_size / wasm::kWasmPageSize); } // SharedArrayBuffer, but not shared across isolates. Setup a new buffer // with updated permissions and update the instances. new_buffer = wasm::SetupArrayBuffer(isolate, backing_store, new_size, // ***1*** old_buffer->is_external(), SharedFlag::kShared); memory_object->update_instances(isolate, new_buffer); [...] ``` When `Grow` is called on a `WebAssembly.Memory` object that's backed by a `SharedArrayBuffer`, it uses the buffer's backing store pointer to construct a new array buffer[1]. Calling `Detach` on shared buffers is prohibited by the spec, so the the method just leaves the old one as it is. Thus two array buffers might end up owning the same backing store, and if one of the them got garbage collected, the other one would point to a freed memory region. Blink's SharedArrayBuffer implementation uses reference-counted backing stores, so v8 should probably implement something similar. VERSION Google Chrome 73.0.3683.103 (Official Build) (64-bit) (cohort: Stable) Chromium 75.0.3758.0 (Developer Build) (64-bit) This bug affects the stable branch due to the currently active \"WebAssembly Threads\" Origin Trial. https://developers.chrome.com/origintrials/#/view_trial/-5026017184145473535 REPRODUCTION CASE CREDIT INFORMATION Sergei Glazunov of Google Project Zero This bug is subject to a 90 day disclosure deadline. After 90 days elapse or a patch has been made broadly available (whichever is earlier), the bug report will become visible to the public. Found by: glazunov@google.com