bugfix: miner: fix addPackageTxs unsigned integer overflow

[ismaelsadeeq]

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 c9530cf.

This fix can be tested by cherry-picking the commits from #33421 without the static cast fix and running:

echo "AQAAAAAAA
AAnJycnAAAAAAAAAAAAAAAAAA" | base64 --decode > miner.crash

FUZZ=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.

[DrahtBot]

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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33475.

Reviews

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Type	Reviewers
ACK	glozow, furszy
Concept ACK	luke-jr

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Conflicts

Reviewers, this pull request conflicts with the following ones:

• #33421 (node: add BlockTemplateCache by ismaelsadeeq)
• #28676 (Cluster mempool implementation by sdaftuar)

If you consider this pull request important, please also help to review the conflicting pull requests. Ideally, start with the one that should be merged first.

[glozow]

nice, utACK b807dfc

[furszy]

Code ACK b807dfc

[luke-jr]

utACK

[fanquake]

Backported to 30.x in #33473.