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fix: reject proposer preferences with dependent root at/after lookahead epoch #9630

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fix: reject proposer preferences with dependent root at/after lookahead epoch #9630

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2499e3a
fix: reject proposer preferences with dependent root at/after lookahe…
lodekeeper Jul 9, 2026
7996f4d
fix: clamp dependent-root decision slot and reject before proposer lo…
lodekeeper Jul 9, 2026
f1137d0
fix: keep dependent-root REJECT after the state-availability IGNORE
lodekeeper Jul 9, 2026
bd6b61a
docs(beacon-node): trim verbose dependent-root REJECT comment
lodekeeper Jul 10, 2026
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6 changes: 6 additions & 0 deletions packages/beacon-node/src/chain/errors/proposerPreferences.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ export enum ProposerPreferencesErrorCode {
INVALID_EPOCH = "PROPOSER_PREFERENCES_ERROR_INVALID_EPOCH",
PROPOSAL_SLOT_PASSED = "PROPOSER_PREFERENCES_ERROR_PROPOSAL_SLOT_PASSED",
UNKNOWN_DEPENDENT_ROOT = "PROPOSER_PREFERENCES_ERROR_UNKNOWN_DEPENDENT_ROOT",
INVALID_DEPENDENT_ROOT = "PROPOSER_PREFERENCES_ERROR_INVALID_DEPENDENT_ROOT",
INVALID_PROPOSER = "PROPOSER_PREFERENCES_ERROR_INVALID_PROPOSER",
ALREADY_KNOWN = "PROPOSER_PREFERENCES_ERROR_ALREADY_KNOWN",
INVALID_SIGNATURE = "PROPOSER_PREFERENCES_ERROR_INVALID_SIGNATURE",
Expand All @@ -26,6 +27,11 @@ export type ProposerPreferencesErrorType =
proposalSlot: Slot;
dependentRoot: RootHex;
}
| {
code: ProposerPreferencesErrorCode.INVALID_DEPENDENT_ROOT;
proposalSlot: Slot;
dependentRoot: RootHex;
}
| {
code: ProposerPreferencesErrorCode.INVALID_PROPOSER;
proposalSlot: Slot;
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21 changes: 20 additions & 1 deletion packages/beacon-node/src/chain/validation/proposerPreferences.ts
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
import {SLOTS_PER_EPOCH} from "@lodestar/params";
import {GENESIS_SLOT, MIN_SEED_LOOKAHEAD, SLOTS_PER_EPOCH} from "@lodestar/params";
import {
computeEpochAtSlot,
computeStartSlotAtEpoch,
createSingleSignatureSetFromComponents,
getProposerPreferencesSigningRoot,
} from "@lodestar/state-transition";
Expand Down Expand Up @@ -70,6 +71,24 @@ export async function validateGossipProposerPreferences(
});
}

// [REJECT] A dependent block after the lookahead decision slot cannot be the block the proposer
// lookahead was derived from. `get_proposer_dependent_root` is `block_root_at_slot(
// start_slot(proposal_epoch - MIN_SEED_LOOKAHEAD) - 1)` clamped to `GENESIS_SLOT`, so a valid
// dependent block is at or before that (clamped) decision slot. Clamping keeps genesis-epoch
// dependents (`proposalEpoch <= MIN_SEED_LOOKAHEAD` → the genesis block) valid instead of
// underflowing to a negative slot and rejecting every early-epoch preference. Kept after the
// proposer-resolution IGNORE so a dependent root whose state is unavailable stays IGNORE (per the
// `ignore_dependent_root_state_unavailable` spec fixture), not REJECT.
const decisionSlot = Math.max(GENESIS_SLOT, computeStartSlotAtEpoch(proposalEpoch - MIN_SEED_LOOKAHEAD) - 1);

@nflaig nflaig Jul 10, 2026

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can we make the comment less verbose please

@lodekeeper lodekeeper Jul 10, 2026

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Trimmed to 2 lines in bd6b61ac72 (kept the GENESIS_SLOT clamp + the after-IGNORE ordering note).

const dependentBlock = chain.forkChoice.getBlockHexDefaultStatus(dependentRootHex);
if (dependentBlock !== null && dependentBlock.slot > decisionSlot) {
throw new ProposerPreferencesError(GossipAction.REJECT, {
code: ProposerPreferencesErrorCode.INVALID_DEPENDENT_ROOT,
proposalSlot,
dependentRoot: dependentRootHex,
});
}

// [REJECT] `is_valid_proposal_slot(state, preferences)` returns True.
if (proposers[proposalSlot % SLOTS_PER_EPOCH] !== validatorIndex) {
throw new ProposerPreferencesError(GossipAction.REJECT, {
Expand Down
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