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crypto: avoid reusing randomInt() cache bytes - #66597
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Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #66597 +/- ##
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+ Coverage 90.45% 90.48% +0.02%
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Files 791 791
Lines 276562 277097 +535
Branches 53111 53278 +167
==========================================
+ Hits 250154 250718 +564
+ Misses 16801 16799 -2
+ Partials 9607 9580 -27
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panva
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Oct 13, 2026
When an asynchronous randomInt() call finds the cache empty, it queues itself and starts randomFill() on the shared cache buffer. A synchronous call made before that job completes refills the same buffer with randomFillSync() and returns values from offset 0. The completion callback then reset the offset to 0, so the queued call and later calls returned the bytes that synchronous calls had already used. The threadpool job and randomFillSync() could also write the buffer at the same time. Fill a separate buffer asynchronously and copy it into the cache once the job is done. Fixes: nodejs#66595 Refs: nodejs#35110 Signed-off-by: Jiawen Geng <technicalcute@gmail.com> Assisted-by: claude:opus-5.5
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When an asynchronous
crypto.randomInt()call finds the cache empty, it queues itself and refills the shared cache withrandomFill(). A synchronous call made before the refill callback runs refills the same buffer withrandomFillSync()and takes values from offset 0. The callback then reset the offset to 0, so the queued call and later calls got the bytes that synchronous calls had already returned. The threadpool job andrandomFillSync()could also write the buffer at the same time.The asynchronous refill now fills a separate buffer, allocated on first use and reused after that. The callback copies it into the cache before resetting the offset. Synchronous calls and the threadpool never touch the same memory, and resetting the offset only hands out bytes nobody has used. The synchronous path is unchanged. The asynchronous path does one extra 6 KiB copy per refill (every 1024 values).
The new test makes the first
randomInt()call in a process asynchronous. It wrapsondoneof the refill job, which runs only after the threadpool has written the buffer, and makes synchronous calls there before the refill callback runs. It then checks that the async value and the values after the callback differ from the synchronous ones. Without the fix it fails every time, also when the threadpool is busy.Fixes: #66595
Refs: #35110
AI disclosure: written with the help of Claude (claude:opus-5.5). I checked the bug against the source and the latest nightly, and reviewed the fix and the test.