This PR fixes an unsigned integer overflow in the addPackageTxs method of the BlockAssembler.
The overflow is a rare edge case that might occur on master when a miner reserves 2000 WU and wants to create an block to be empty.
i.e, by starting with -blockmaxweight=2000, -blockreservedweight=2000, or just blockmaxweight=2000, and then calling the mining interface createNewBlock with blockReservedWeight set to 2000.
Instead of bailing out after going through transactions equivalent to MAX_CONSECUTIVE_FAILURES, the loop never breaks until all mempool transactions are visited.
See #33421 (comment)
The fix avoids the overflow by using addition instead adding BLOCK_FULL_ENOUGH_WEIGHT_DELTA to the block weight and comparing it with m_options.nBlockMaxWeight.
Another alternative that preserves the same structure is to use static_cast. See https://github.com/bitcoin/bitcoin/pull/33421/commits/c9530cf35d351628eea4992c66fc1df548d1b580.
This fix can be tested by cherry-picking the commits from #33421 without the static cast fix and running:
0echo "AQAAAAAAA
1AAnJycnAAAAAAAAAAAAAAAAAA" | base64 --decode > miner.crash
2
3FUZZ=block_template_cache ./build_fuzz/bin/fuzz miner.crash
This is part of a larger inconsistency in how size/weight is represented in the codebase. It may be worth defining a dedicated type for size/weight.
