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When cache memory usage is over the configured cache size (overmem) and we are cleaning unused entries, it might not be enough to clean just two entries if the entries to be expired are smaller than the newly added rdata. This could be abused by an attacker to cause a remote Denial of Service by possibly running out of the operating system memory. Currently, the addrdataset() tries to do a single TTL-based cleaning considering the serve-stale TTL and then optionally moves to overmem cleaning if we are in that condition. Then the overmem_purge() tries to do another single TTL based cleaning from the TTL heap and then continue with LRU-based cleaning up to 2 entries cleaned. Squash the TTL-cleaning mechanism into single call from addrdataset(), but ignore the serve-stale TTL if we are currently overmem. Then instead of having a fixed number of entries to clean, pass the size of newly added rdatasetheader to the overmem_purge() function and cleanup at least the size of the newly added data. This prevents the cache going over the configured memory limit (`max-cache-size`). Additionally, refactor the overmem_purge() function to reduce for-loop nesting for readability. |
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