core, rpcdaemon: add check on NoPreMergeConfig and terminal total difficulty

[lupin012]

No description provided.

[canepat]

Let's try to avoid this kind of defensive programming and see if we can instead identify where and why pre-merge rule set can be null in the first place

[canepat]

Let's try to avoid this kind of defensive programming and see if we can instead identify where and why pre-merge rule set can be null in the first place

In order to trigger a nullptr dereference in MergeRuleSet the following conditions must be true:

1. ChainConfig instance has NoPreMergeConfig rule set config as a result of parsing any JSON chain config containing an unknown rule set
2. the same ChainConfig instance has non-null terminal_total_difficulty as a result of parsing the same JSON

As a consequence of both 1. and 2. being met, pre_merge_rule_set function returns a nullptr, which is then received at construction time by the MergeRuleSet instance created in rule_set_factory.

However, here the point is that an implicit invariant of ChainConfig is violated. Theoretically, the conditions 1. and 2. cannot be true at the same time because the first one means the chain has no pre-merge rule set because the merge happens at genesis and the second one means the chain has non-zero terminal total difficulty identifying where the merge point is (clearly not at genesis).

Hence, a proper solution here implies making the ChainConfig invariant explicit by:

• enforcing the invariant when building a new ChainConfig instance in ChainConfig::from_json by returning std::nullopt (i.e. invalid configuration) if this is not the case
• put an assertion in rule_set_factory to check the invariant immediately after the pre-merge rule set creation

[canepat]

@yperbasis this PR looks good to me at least for preventing null pointer dereference when pre_merge_rule_set_ is nullptr in MergeRuleSet (e.g. for Holesky config when checked against empty block), so I'm going to merge it right now. Please review it sooner or later and suggest any improvement.