Fix use-after-free in Atomics operations with resizable ArrayBuffers #480
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The Atomics operations (add, sub, and, or, xor, exchange, compareExchange,
store) capture a pointer to the buffer element before calling JS_ToUint32()
or JS_ToBigInt64() on the value arguments. These conversion functions can
execute arbitrary JavaScript via valueOf() callbacks, which may resize the
underlying ArrayBuffer.
After the value conversion, only a detached check was performed, but not a
bounds re-validation. If the buffer was resized (not detached), the stale
pointer would still be used, leading to a heap-use-after-free.
The fix re-validates the atomic access by calling js_atomics_get_ptr() again
after the value conversions. This follows the RevalidateAtomicAccess()
pattern already present in js_atomics_get_ptr() itself.
Proof of Concept:
let ab = new ArrayBuffer(1024, { maxByteLength: 2048 });
let int32Array = new Int32Array(ab);
let malicious = { valueOf: () => { ab.resize(8); return 1; } };
Atomics.add(int32Array, 200, malicious); // heap-use-after-free
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The Atomics operations (add, sub, and, or, xor, exchange, compareExchange, store) capture a pointer to the buffer element before calling JS_ToUint32() or JS_ToBigInt64() on the value arguments. These conversion functions can execute arbitrary JavaScript via valueOf() callbacks, which may resize the underlying ArrayBuffer.
After the value conversion, only a detached check was performed, but not a bounds re-validation. If the buffer was resized (not detached), the stale pointer would still be used, leading to a heap-use-after-free.
The fix re-validates the atomic access by calling js_atomics_get_ptr() again after the value conversions. This follows the RevalidateAtomicAccess() pattern already present in js_atomics_get_ptr() itself.
Proof of Concept: