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getLastEntry in EntryMemTable could return incorrect results if metadata (entries with negative entry IDs) is in use for the ledger. The KeyComparator used within EntryMemTable uses a simple subtraction for comparison, and when Long.MAX_VALUE was compared against a negative value (e.g. an explicit LAC entry), this would result in a long overflow, and incorrect comparison results. The proposed fix here is to ensure that the comparison within getLastEntry does not ever hit an integer overflow condition, by having the floorKey comparison occur against a long value that can accommodate subtracting the lowest possible metadata ID (a subtraction of a negative value, ultimately becoming an addition) so that a long overflow does not occur. This does reduce the highest possible entry ID within EntryMemTable by 32,768 as of this commit, but it seems incredibly unlikely that real world BookKeeper clusters will see entry IDs close to 2^64.
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Descriptions of the changes in this PR:
Fixes #4895.
Motivation
getLastEntryinEntryMemTablecould return incorrect results if metadata (entries with negative entry IDs) is in use for the ledger. TheKeyComparatorused withinEntryMemTableuses a simple subtraction for comparison, and whenLong.MAX_VALUEwas compared against a negative value (e.g. an explicit LAC entry), this would result in a long overflow, and incorrect comparison results.Changes
The proposed fix here is to ensure that the comparison within
getLastEntrydoes not ever hit an integer overflow condition, by having thefloorKeycomparison occur against a long value that can accommodate subtracting the lowest possible metadata ID (a subtraction of a negative value, ultimately becoming an addition) so that a long overflow does not occur.This does reduce the highest possible entry ID within
EntryMemTableby 32,768 as of this commit, but it seems incredibly unlikely that real world BookKeeper clusters will see entry IDs close to 2^64.