fix(android): use-after-free in RAF choreographer frame callback#143
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AChoreographer_postFrameCallback cannot be cancelled, but clear_callback() freed the Box handed to the choreographer while a frame callback was still queued. The next vsync then fired with a dangling pointer, corrupting whatever had reused the allocation (often the V8 heap), crashing either inside libcanvasnative.so during dispatchVsync or later in unrelated V8 code (HandleScope::Extend, StubCache::Set). Every canvas teardown queued the UAF; framework HMR reboots made it reliably fatal. A stop()/start() restart could also spawn a duplicate callback chain whose stale sibling would free the new chain's allocation via lock.data.take(). Make each posted frame callback the sole owner of its allocation: on every fire it either re-posts the same FrameChain box or drops it, and no other code path frees it. A generation counter retires stale chains after a restart, and clear_callback() now only detaches the JS-side closure, which still guarantees the callback target is never invoked after release.
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AChoreographer_postFrameCallback cannot be cancelled, but clear_callback() freed the Box handed to the choreographer while a frame callback was still queued. The next vsync then fired with a dangling pointer, corrupting whatever had reused the allocation (often the V8 heap), crashing either inside libcanvasnative.so during dispatchVsync or later in unrelated V8 code (HandleScope::Extend, StubCache::Set). Every canvas teardown queued the UAF; framework HMR reboots made it reliably fatal.
A stop()/start() restart could also spawn a duplicate callback chain whose stale sibling would free the new chain's allocation via lock.data.take().
Make each posted frame callback the sole owner of its allocation: on every fire it either re-posts the same FrameChain box or drops it, and no other code path frees it. A generation counter retires stale chains after a restart, and clear_callback() now only detaches the JS-side closure, which still guarantees the callback target is never invoked after release.