ffi: throw on allocation failure in toArrayBuffer()

The copy path of toArrayBuffer() allocated its backing store with
V8's default failure mode, so a large length aborted the process
with a fatal out-of-memory error. toBuffer() throws a catchable
ERR_MEMORY_ALLOCATION_FAILED for the same input.

Allocate with kReturnNull and throw ERR_MEMORY_ALLOCATION_FAILED
when the allocation fails. The memory is left uninitialized because
memcpy() fills it right after.

Signed-off-by: Trivikram Kamat <16024985+trivikr@users.noreply.github.com>
Assisted-by: claude:opus-5.5

Author: trivikr

src/ffi/data.cc

@@ -15,6 +15,8 @@
 using v8::ArrayBuffer;
 using v8::ArrayBufferView;
 using v8::BackingStore;
+using v8::BackingStoreInitializationMode;
+using v8::BackingStoreOnFailureMode;
 using v8::BigInt;
 using v8::FunctionCallbackInfo;
 using v8::Integer;
@@ -670,8 +672,15 @@ void ToArrayBuffer(const FunctionCallbackInfo<Value>& args) {
 
   Local<ArrayBuffer> ab;
   if (copy) {
-    std::unique_ptr<BackingStore> store =
-        ArrayBuffer::NewBackingStore(isolate, len);
+    std::unique_ptr<BackingStore> store = ArrayBuffer::NewBackingStore(
+        isolate,
+        len,
+        BackingStoreInitializationMode::kUninitialized,
+        BackingStoreOnFailureMode::kReturnNull);
+    if (!store) [[unlikely]] {
+      THROW_ERR_MEMORY_ALLOCATION_FAILED(env);
+      return;
+    }
     if (len > 0) memcpy(store->Data(), reinterpret_cast<void*>(ptr), len);
     ab = ArrayBuffer::New(isolate, std::move(store));
   } else {

test/ffi/test-ffi-memory.js

@@ -371,6 +371,16 @@ test('ffi rejects unsafe integers as an offset or length', () => {
   }));
 });
 
+test('ffi toBuffer and toArrayBuffer throw when the copy cannot be allocated', {
+  skip: (bufferConstants.MAX_LENGTH < 2 ** 50 && 'requires a 64-bit buffer length limit') ||
+        (common.isASan && 'ASan aborts on huge allocations'),
+}, () => {
+  // The allocation fails before the source pointer is read.
+  const error = { code: 'ERR_MEMORY_ALLOCATION_FAILED' };
+  assert.throws(() => ffi.toBuffer(1n, 2 ** 50), error);
+  assert.throws(() => ffi.toArrayBuffer(1n, 2 ** 50), error);
+});
+
 test('ffi memory helpers reject missing required arguments', () => {
   const widths = ['Int8', 'Uint8', 'Int16', 'Uint16', 'Int32', 'Uint32',
                   'Int64', 'Uint64', 'Float32', 'Float64'];