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Comment by duneroadrunner | Hacker News Reader

Ug. After closer inspection, it looks like those particular raw pointers seem to be managed by a garbage collector. (Specifically, the "Blink GC" [1].) As others have pointed out, this particular bug may not actually be a C++ issue. (Or at least not a typical one.)

[1] https://chromium.googlesource.com/chromium/src/+/master/thir...

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Not so sure. I haven't worked on this code for a while and have no non-public knowledge of the bug, but ArrayBufferBuilder does not inherit from any of the GCed base classes, and has the USING_FAST_MALLOC macro which is used for non-GC classes. https://chromium.googlesource.com/chromium/src/+/refs/heads/...

The ArrayBuffer itself also uses reference counters rather than the GC base classes from Oilpan. https://chromium.googlesource.com/chromium/src/+/refs/heads/...

ArrayBufferBuilder isn't, but DOMArrayBuffer seems to be a GC managed type [1], right? And, before the patch, the DOMArrayBuffer held a "refcounting pointer" potentially targeting raw_data_'s reference counted ArrayBuffer, right? I don't see any immediately apparent use-after-free with this, so I assume raw_data_'s ArrayBuffer is being messed with elsewhere? As someone who worked on the code, do you have an idea/hunch about where the invalid memory access actually occurs?

https://github.com/chromium/chromium/blob/ba9748e78ec7e9c0d5...

Yes, DOMArrayBuffer inherits via ScriptWrappable from GarbageCollectedFinalized<> so it's on the GCed heap. I don't understand the UAF yet, I'm hoping someone will write a blog post on it later :-).

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