Potential memory leak in fs::WriteString

[joyeecheung]

• Version: master
• Subsystem: fs

I have not verified it yet, just discovered this when I went through the comments in node_file.cc to see if there is anything to update.

node/src/node_file.cc

Lines 1389 to 1391 in 040dd24

	buf = new char[len];
	// SYNC_CALL returns on error. Make sure to always free the memory.
	if (!is_async) delete_on_return.reset(buf);

Looks like in the async case, if the buffer was copied instead of being moved (in the external string cases up there), then the buf will not get deleted after the request is done. This seems to be introduced when the FSReqWrap:: Ownership was removed in 4b9ba9b
, and ReleaseEarly was no longer called upon destruction of FSReqWrap.

I am trying to come up with a fix, opening an issue in case this gets lost.

[joyeecheung]

cc @jasnell @addaleax

[joyeecheung]

==25808== 21 bytes in 3 blocks are definitely lost in loss record 7 of 51
==25808==    at 0x4C2E80F: operator new[](unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==25808==    by 0x8238CA: node::fs::WriteString(v8::FunctionCallbackInfo<v8::Value> const&) (in /home/ubuntu/projects/node/out/Release/node)
==25808==    by 0x97873B: v8::internal::FunctionCallbackArguments::Call(void (*)(v8::FunctionCallbackInfo<v8::Value> const&)) (in /home/ubuntu/projects/node/out/Release/node)
==25808==    by 0x9CFEA4: v8::internal::MaybeHandle<v8::internal::Object> v8::internal::(anonymous namespace)::HandleApiCallHelper<false>(v8::internal::Isolate*, v8::internal::Handle<v8::internal::HeapObject>, v8::internal::Handle<v8::internal::HeapObject>, v8::internal::Handle<v8::internal::FunctionTemplateInfo>, v8::internal::Handle<v8::internal::Object>, v8::internal::BuiltinArguments) (in /home/ubuntu/projects/node/out/Release/node)
==25808==    by 0x9CF5D5: v8::internal::Builtin_Impl_HandleApiCall(v8::internal::BuiltinArguments, v8::internal::Isolate*) (in /home/ubuntu/projects/node/out/Release/node)
==25808==    by 0x21191EE0427C: ???
==25808==    by 0x21191EE13616: ???
==25808==    by 0x21191EE0BF02: ???
==25808==    by 0x21191EE13616: ???
==25808==    by 0x21191EE13616: ???
==25808==    by 0x21191EE0BF02: ???
==25808==    by 0x21191EE13616: ???

Output from valgrind running test/parallel/test-fs-write.js