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n-api: unlink reference during its destructor #35933

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dd7d042
n-api: unlink reference during its destructor
Nov 2, 2020
b2cf693
fixup! make the destructor virtual
Nov 3, 2020
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n-api: unlink reference during its destructor 
Currently, a reference is being unlinked from the list of references
tracked by the environment when `v8impl::Reference::Delete` is called.
This causes a leak when deletion must be deferred because the finalizer
hasn't yet run, but the finalizer does not run because environment
teardown is in progress, and so no more gc runs will happen, and the
`FinalizeAll` run that happens during environment teardown does not
catch the reference because it's no longer in the list. The test below
will fail when running with ASAN:
```
./node ./test/node-api/test_worker_terminate_finalization/test.js
```

OTOH if, to address the above leak, we make a special case to not
unlink a reference during environment teardown, we run into a
situation where the reference gets deleted by
`v8impl::Reference::Delete` but does not get unlinked because it's
environment teardown time. This leaves a stale pointer in the linked
list which will result in a use-after-free in `FinalizeAll` during
environment teardown. The test below will fail if we make the above
change:
```
./node -e "require('./test/node-api/test_instance_data/build/Release/test_ref_then_set.node');"
```

Thus, we unlink a reference precisely when we destroy it – in its
destructor.

Refs: #34731
Refs: #34839
Refs: #35620
Refs: #35777
Fixes: #35778
Signed-off-by: Gabriel Schulhof <gabriel.schulhof@intel.com>
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Gabriel Schulhof committed Nov 2, 2020
commit dd7d042c51f8ee363bc81f40446ea790e992a721
3 changes: 2 additions & 1 deletion src/js_native_api_v8.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -220,6 +220,8 @@ class RefBase : protected Finalizer, RefTracker {
finalize_hint);
}

~RefBase() { Unlink(); }

inline void* Data() {
return _finalize_data;
}
Expand All @@ -240,7 +242,6 @@ class RefBase : protected Finalizer, RefTracker {
// the finalizer and _delete_self is set. In this case we
// know we need to do the deletion so just do it.
static inline void Delete(RefBase* reference) {
reference->Unlink();
if ((reference->RefCount() != 0) ||
(reference->_delete_self) ||
(reference->_finalize_ran)) {
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2 changes: 0 additions & 2 deletions test/node-api/test_worker_terminate_finalization/test.js
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@@ -1,11 +1,9 @@
'use strict';
const common = require('../../common');

// TODO(addaleax): Run this test once it stops failing under ASAN/valgrind.
// Refs: https://github.com/nodejs/node/issues/34731
// Refs: https://github.com/nodejs/node/pull/35777
// Refs: https://github.com/nodejs/node/issues/35778
common.skip('Reference management in N-API leaks memory');

const { Worker, isMainThread } = require('worker_threads');

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