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buffer: add bounds validation to SlowCopy and FastCopy #60264

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buffer: add bounds validation to SlowCopy and FastCopy #60264

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buffer: add bounds validation to SlowCopy and FastCopy
Rabie45 Oct 15, 2025
75cfdfb
Use IsArrayBufferView() and ByteLength() instead of Buffer::HasInstan…
Rabie45 Oct 15, 2025
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33 changes: 33 additions & 0 deletions src/node_buffer.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -578,9 +578,28 @@ void CopyImpl(Local<Value> source_obj,
void SlowCopy(const FunctionCallbackInfo<Value>& args) {
Local<Value> source_obj = args[0];
Local<Value> target_obj = args[1];
Environment* env = Environment::GetCurrent(args);
Isolate* isolate = env->isolate();

// Add validation before call CopyImpl blindly
if (!Buffer::HasInstance(source_obj) || !Buffer::HasInstance(target_obj)) {
isolate->ThrowException(v8::Exception::TypeError(String::NewFromUtf8Literal(
isolate, "Arguments must be Buffer instances")));
return;
}
const uint32_t target_start = args[2].As<Uint32>()->Value();
const uint32_t source_start = args[3].As<Uint32>()->Value();
const uint32_t to_copy = args[4].As<Uint32>()->Value();
size_t source_len = Buffer::Length(source_obj.As<Object>());
size_t target_len = Buffer::Length(target_obj.As<Object>());

if (source_start > source_len || target_start > target_len ||
to_copy > source_len - source_start ||
to_copy > target_len - target_start) {
isolate->ThrowException(v8::Exception::RangeError(
String::NewFromUtf8Literal(isolate, "Buffer copy out of range")));
return;
}

CopyImpl(source_obj, target_obj, target_start, source_start, to_copy);

Expand All @@ -597,7 +616,21 @@ uint32_t FastCopy(Local<Value> receiver,
// NOLINTNEXTLINE(runtime/references)
FastApiCallbackOptions& options) {
HandleScope scope(options.isolate);
Isolate* isolate = options.isolate;

if (!node::Buffer::HasInstance(source_obj) ||
!node::Buffer::HasInstance(target_obj)) {
return 0;
}
// Validate First before call CopyImpl blindly
size_t src_len = Buffer::Length(source_obj.As<v8::Object>());
size_t dst_len = Buffer::Length(target_obj.As<v8::Object>());
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Just fyi, Buffer::HasInstance(obj) is an alias for obj->IsArrayBufferView() and Buffer::Length(obj) is an alias for obj.As<ArrayBufferView>()->ByteLength(). I'd suggest just using those here directly

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Thanks for the note you’re absolutely right. I’ve updated the code to use IsArrayBufferView() and ByteLength() directly instead of Buffer::HasInstance() and Buffer::Length() for consistency with the V8 API.


if (source_start > src_len || target_start > dst_len ||
to_copy > src_len - source_start || to_copy > dst_len - target_start) {
// options.fallback = true; // Let JS slow path handle it (safe fallback)
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This seems to be an unresolved comment here? We don't do fallbacks anymore, but we still need to handle the situation in this case.

Maybe we could return -1 and check for that on the JS side?

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You’re right, returning a sentinel like -1 would be clearer to signal an invalid range. However, since the function currently returns a uint32_t, using -1 would actually wrap around to 4294967295, which could cause unexpected behavior.

If we want to use -1 safely, we should change the return type to int32_t so the error code is properly represented.

return 0;
}
CopyImpl(source_obj, target_obj, target_start, source_start, to_copy);

return to_copy;
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