Gloas PayloadAttestation gossip verification (#9145)

Co-Authored-By: hopinheimer <knmanas6@gmail.com>

Co-Authored-By: hopinheimer <48147533+hopinheimer@users.noreply.github.com>

Co-Authored-By: Eitan Seri-Levi <eserilev@ucsc.edu>

Co-Authored-By: Jimmy Chen <jchen.tc@gmail.com>

beacon_node/beacon_chain/src/payload_attestation_verification/gossip_verified_payload_attestation.rs

@@ -0,0 +1,255 @@
+use super::Error;
+use crate::beacon_chain::BeaconStore;
+use crate::canonical_head::CanonicalHead;
+use crate::observed_attesters::ObservedPayloadAttesters;
+use crate::validator_pubkey_cache::ValidatorPubkeyCache;
+use crate::{BeaconChain, BeaconChainError, BeaconChainTypes, metrics};
+use bls::AggregateSignature;
+use educe::Educe;
+use parking_lot::RwLock;
+use safe_arith::SafeArith;
+use slot_clock::SlotClock;
+use state_processing::per_block_processing::signature_sets::indexed_payload_attestation_signature_set;
+use state_processing::state_advance::partial_state_advance;
+use std::borrow::Cow;
+use types::{ChainSpec, EthSpec, IndexedPayloadAttestation, PTC, PayloadAttestationMessage, Slot};
+
+pub struct GossipVerificationContext<'a, T: BeaconChainTypes> {
+    pub slot_clock: &'a T::SlotClock,
+    pub spec: &'a ChainSpec,
+    pub observed_payload_attesters: &'a RwLock<ObservedPayloadAttesters<T::EthSpec>>,
+    pub canonical_head: &'a CanonicalHead<T>,
+    pub validator_pubkey_cache: &'a RwLock<ValidatorPubkeyCache<T>>,
+    pub store: &'a BeaconStore<T>,
+}
+
+/// A `PayloadAttestationMessage` that has been verified for propagation on the gossip network.
+#[derive(Educe)]
+#[educe(Clone, Debug)]
+pub struct VerifiedPayloadAttestationMessage<T: BeaconChainTypes> {
+    payload_attestation_message: PayloadAttestationMessage,
+    indexed_payload_attestation: IndexedPayloadAttestation<T::EthSpec>,
+    ptc: PTC<T::EthSpec>,
+}
+
+impl<T: BeaconChainTypes> VerifiedPayloadAttestationMessage<T> {
+    pub fn new(
+        payload_attestation_message: PayloadAttestationMessage,
+        ctx: &GossipVerificationContext<'_, T>,
+    ) -> Result<Self, Error> {
+        let slot = payload_attestation_message.data.slot;
+        let validator_index = payload_attestation_message.validator_index;
+
+        // [IGNORE] `data.slot` is within the `MAXIMUM_GOSSIP_CLOCK_DISPARITY` allowance.
+        verify_propagation_slot_range(ctx.slot_clock, slot, ctx.spec)?;
+
+        // [IGNORE] There has been no other valid payload attestation message for this
+        // validator index.
+        if ctx
+            .observed_payload_attesters
+            .read()
+            .validator_has_been_observed(slot, validator_index as usize)
+            .map_err(BeaconChainError::from)?
+        {
+            return Err(Error::PriorPayloadAttestationMessageKnown {
+                validator_index,
+                slot,
+            });
+        }
+
+        // [IGNORE] `data.beacon_block_root` has been seen
+        // [REJECT] `data.beacon_block_root` passes validation.
+        //
+        // TODO(gloas): These two conditions are conflated. We need a status table to
+        // differentiate between:
+        // 1. Blocks we haven't seen (IGNORE), and
+        // 2. Blocks we've seen that are invalid (REJECT).
+        // Presently both cases return IGNORE.
+        let beacon_block_root = payload_attestation_message.data.beacon_block_root;
+        if ctx
+            .canonical_head
+            .fork_choice_read_lock()
+            .get_block(&beacon_block_root)
+            .is_none()
+        {
+            return Err(Error::UnknownHeadBlock { beacon_block_root });
+        }
+
+        // Get head state for PTC computation. If the cached head state is too stale
+        // (e.g. during liveness failures with many skipped slots), fall back to loading
+        // a more recent state from the store and advancing it if necessary.
+        let head = ctx.canonical_head.cached_head();
+        let head_state = &head.snapshot.beacon_state;
+
+        let message_epoch = slot.epoch(T::EthSpec::slots_per_epoch());
+        let state_epoch = head_state.current_epoch();
+
+        // get_ptc can serve epochs in [state_epoch - 1, state_epoch + min_seed_lookahead].
+        // If the message epoch is beyond that range, the head state is stale.
+        let advanced_state = if message_epoch
+            > state_epoch
+                .safe_add(ctx.spec.min_seed_lookahead)
+                .map_err(BeaconChainError::from)?
+        {
+            let head_block_root = head.head_block_root();
+            let target_slot = message_epoch.start_slot(T::EthSpec::slots_per_epoch());
+
+            let (state_root, mut state) = ctx
+                .store
+                .get_advanced_hot_state(
+                    head_block_root,
+                    target_slot,
+                    head.snapshot.beacon_state_root(),
+                )
+                .map_err(BeaconChainError::from)?
+                .ok_or(BeaconChainError::MissingBeaconState(
+                    head.snapshot.beacon_state_root(),
+                ))?;
+
+            if state
+                .current_epoch()
+                .safe_add(ctx.spec.min_seed_lookahead)
+                .map_err(BeaconChainError::from)?
+                < message_epoch
+            {
+                partial_state_advance(&mut state, Some(state_root), target_slot, ctx.spec)
+                    .map_err(BeaconChainError::from)?;
+            }
+
+            Some(state)
+        } else {
+            None
+        };
+
+        let state = advanced_state.as_ref().unwrap_or(head_state);
+
+        // [REJECT] `validator_index` is within `get_ptc(state, data.slot)`.
+        let ptc = state.get_ptc(slot, ctx.spec)?;
+        if !ptc.0.contains(&(validator_index as usize)) {
+            return Err(Error::NotInPTC {
+                validator_index,
+                slot,
+            });
+        }
+
+        // Build the indexed form for signature verification and downstream fork choice.
+        let indexed_payload_attestation = IndexedPayloadAttestation {
+            attesting_indices: vec![validator_index]
+                .try_into()
+                .map_err(|_| Error::UnknownValidatorIndex(validator_index))?,
+            data: payload_attestation_message.data.clone(),
+            signature: AggregateSignature::from(&payload_attestation_message.signature),
+        };
+
+        {
+            // [REJECT] The signature is valid with respect to the `validator_index`.
+            let pubkey_cache = ctx.validator_pubkey_cache.read();
+            let signature_set = indexed_payload_attestation_signature_set(
+                state,
+                |validator_index| pubkey_cache.get(validator_index).map(Cow::Borrowed),
+                &indexed_payload_attestation.signature,
+                &indexed_payload_attestation,
+                ctx.spec,
+            )
+            .map_err(|_| Error::UnknownValidatorIndex(validator_index))?;
+
+            if !signature_set.verify() {
+                return Err(Error::InvalidSignature);
+            }
+        }
+
+        // Record that we have received a valid payload attestation message from this
+        // validator. Double check with the write lock to handle race conditions.
+        if ctx
+            .observed_payload_attesters
+            .write()
+            .observe_validator(slot, validator_index as usize, ())
+            .map_err(BeaconChainError::from)?
+        {
+            return Err(Error::PriorPayloadAttestationMessageKnown {
+                validator_index,
+                slot,
+            });
+        }
+
+        Ok(Self {
+            payload_attestation_message,
+            indexed_payload_attestation,
+            ptc,
+        })
+    }
+
+    pub fn payload_attestation_message(&self) -> &PayloadAttestationMessage {
+        &self.payload_attestation_message
+    }
+
+    pub fn indexed_payload_attestation(&self) -> &IndexedPayloadAttestation<T::EthSpec> {
+        &self.indexed_payload_attestation
+    }
+
+    pub fn ptc(&self) -> &PTC<T::EthSpec> {
+        &self.ptc
+    }
+
+    pub fn into_payload_attestation_message(self) -> PayloadAttestationMessage {
+        self.payload_attestation_message
+    }
+}
+
+impl<T: BeaconChainTypes> BeaconChain<T> {
+    pub fn payload_attestation_gossip_context(&self) -> GossipVerificationContext<'_, T> {
+        GossipVerificationContext {
+            slot_clock: &self.slot_clock,
+            spec: &self.spec,
+            observed_payload_attesters: &self.observed_payload_attesters,
+            canonical_head: &self.canonical_head,
+            validator_pubkey_cache: &self.validator_pubkey_cache,
+            store: &self.store,
+        }
+    }
+
+    pub fn verify_payload_attestation_message_for_gossip(
+        &self,
+        payload_attestation_message: PayloadAttestationMessage,
+    ) -> Result<VerifiedPayloadAttestationMessage<T>, Error> {
+        metrics::inc_counter(&metrics::PAYLOAD_ATTESTATION_PROCESSING_REQUESTS);
+        let _timer = metrics::start_timer(&metrics::PAYLOAD_ATTESTATION_GOSSIP_VERIFICATION_TIMES);
+
+        let ctx = self.payload_attestation_gossip_context();
+        VerifiedPayloadAttestationMessage::new(payload_attestation_message, &ctx).inspect(|_| {
+            metrics::inc_counter(&metrics::PAYLOAD_ATTESTATION_PROCESSING_SUCCESSES);
+        })
+    }
+}
+
+/// Verify that the `slot` is within the acceptable gossip propagation range, with reference
+/// to the current slot of the clock.
+///
+/// Accounts for `MAXIMUM_GOSSIP_CLOCK_DISPARITY`.
+fn verify_propagation_slot_range<S: SlotClock>(
+    slot_clock: &S,
+    message_slot: Slot,
+    spec: &ChainSpec,
+) -> Result<(), Error> {
+    let latest_permissible_slot = slot_clock
+        .now_with_future_tolerance(spec.maximum_gossip_clock_disparity())
+        .ok_or(BeaconChainError::UnableToReadSlot)?;
+    if message_slot > latest_permissible_slot {
+        return Err(Error::FutureSlot {
+            message_slot,
+            latest_permissible_slot,
+        });
+    }
+
+    let earliest_permissible_slot = slot_clock
+        .now_with_past_tolerance(spec.maximum_gossip_clock_disparity())
+        .ok_or(BeaconChainError::UnableToReadSlot)?;
+    if message_slot < earliest_permissible_slot {
+        return Err(Error::PastSlot {
+            message_slot,
+            earliest_permissible_slot,
+        });
+    }
+
+    Ok(())
+}

beacon_node/beacon_chain/src/payload_attestation_verification/mod.rs

@@ -0,0 +1,110 @@
+//! Provides verification for `PayloadAttestationMessage` received from the gossip network.
+//!
+//! ```ignore
+//!      types::PayloadAttestationMessage
+//!              |
+//!              ▼
+//!      VerifiedPayloadAttestationMessage
+//! ```
+
+use crate::BeaconChainError;
+use strum::AsRefStr;
+use types::{BeaconStateError, Hash256, Slot};
+
+pub mod gossip_verified_payload_attestation;
+
+pub use gossip_verified_payload_attestation::{
+    GossipVerificationContext, VerifiedPayloadAttestationMessage,
+};
+
+/// Returned when a payload attestation message was not successfully verified. It might not have
+/// been verified for two reasons:
+///
+/// - The message is malformed or inappropriate for the context (indicated by all variants
+///   other than `BeaconChainError`).
+/// - The application encountered an internal error whilst attempting to determine validity
+///   (the `BeaconChainError` variant)
+#[derive(Debug, AsRefStr)]
+pub enum Error {
+    /// The payload attestation message is from a slot that is later than the current slot
+    /// (with respect to the gossip clock disparity).
+    ///
+    /// ## Peer scoring
+    ///
+    /// Assuming the local clock is correct, the peer has sent an invalid message.
+    FutureSlot {
+        message_slot: Slot,
+        latest_permissible_slot: Slot,
+    },
+    /// The payload attestation message is from a slot that is prior to the earliest
+    /// permissible slot (with respect to the gossip clock disparity).
+    ///
+    /// ## Peer scoring
+    ///
+    /// Assuming the local clock is correct, the peer has sent an invalid message.
+    PastSlot {
+        message_slot: Slot,
+        earliest_permissible_slot: Slot,
+    },
+    /// We have already observed a valid payload attestation message from this validator
+    /// for this slot.
+    ///
+    /// ## Peer scoring
+    ///
+    /// The peer is not necessarily faulty.
+    PriorPayloadAttestationMessageKnown { validator_index: u64, slot: Slot },
+    /// The beacon block referenced by the payload attestation message is not known.
+    ///
+    /// ## Peer scoring
+    ///
+    /// The attestation points to a block we have not yet imported. It's unclear if the
+    /// attestation is valid or not.
+    UnknownHeadBlock { beacon_block_root: Hash256 },
+    /// The validator index is not a member of the PTC for this slot.
+    ///
+    /// ## Peer scoring
+    ///
+    /// The peer has sent an invalid message.
+    NotInPTC { validator_index: u64, slot: Slot },
+    /// The validator index is unknown.
+    ///
+    /// ## Peer scoring
+    ///
+    /// The peer has sent an invalid message.
+    UnknownValidatorIndex(u64),
+    /// The signature on the payload attestation message is invalid.
+    ///
+    /// ## Peer scoring
+    ///
+    /// The peer has sent an invalid message.
+    InvalidSignature,
+    /// There was an error whilst processing the payload attestation message. It is not known
+    /// if it is valid or invalid.
+    ///
+    /// ## Peer scoring
+    ///
+    /// We were unable to process this message due to an internal error. It's unclear if the
+    /// message is valid.
+    BeaconChainError(Box<BeaconChainError>),
+    /// An error reading beacon state.
+    ///
+    /// ## Peer scoring
+    ///
+    /// We were unable to process this message due to an internal error.
+    BeaconStateError(BeaconStateError),
+}
+
+impl From<BeaconChainError> for Error {
+    fn from(e: BeaconChainError) -> Self {
+        Error::BeaconChainError(Box::new(e))
+    }
+}
+
+impl From<BeaconStateError> for Error {
+    fn from(e: BeaconStateError) -> Self {
+        Error::BeaconStateError(e)
+    }
+}
+
+#[cfg(test)]
+mod tests;

beacon_node/beacon_chain/src/payload_attestation_verification/tests.rs

@@ -0,0 +1,422 @@
+use std::sync::Arc;
+use std::time::Duration;
+
+use bls::{Keypair, Signature};
+use fork_choice::ForkChoice;
+use genesis::{generate_deterministic_keypairs, interop_genesis_state};
+use parking_lot::RwLock;
+use proto_array::PayloadStatus;
+use slot_clock::{SlotClock, TestingSlotClock};
+use state_processing::AllCaches;
+use state_processing::genesis::genesis_block;
+use store::{HotColdDB, StoreConfig};
+use types::{
+    ChainSpec, Checkpoint, Domain, Epoch, EthSpec, Hash256, MinimalEthSpec, PayloadAttestationData,
+    PayloadAttestationMessage, SignedBeaconBlock, SignedRoot, Slot,
+};
+
+use crate::{
+    beacon_fork_choice_store::BeaconForkChoiceStore,
+    beacon_snapshot::BeaconSnapshot,
+    canonical_head::CanonicalHead,
+    observed_attesters::ObservedPayloadAttesters,
+    payload_attestation_verification::{
+        Error as PayloadAttestationError,
+        gossip_verified_payload_attestation::{
+            GossipVerificationContext, VerifiedPayloadAttestationMessage,
+        },
+    },
+    test_utils::{BeaconChainHarness, EphemeralHarnessType, fork_name_from_env, test_spec},
+    validator_pubkey_cache::ValidatorPubkeyCache,
+};
+
+type E = MinimalEthSpec;
+type T = EphemeralHarnessType<E>;
+
+const NUM_VALIDATORS: usize = 64;
+
+struct TestContext {
+    canonical_head: CanonicalHead<T>,
+    observed_payload_attesters: RwLock<ObservedPayloadAttesters<E>>,
+    validator_pubkey_cache: RwLock<ValidatorPubkeyCache<T>>,
+    slot_clock: TestingSlotClock,
+    keypairs: Vec<Keypair>,
+    spec: ChainSpec,
+    genesis_block_root: Hash256,
+    store: Arc<store::HotColdDB<E, store::MemoryStore<E>, store::MemoryStore<E>>>,
+}
+
+impl TestContext {
+    fn new() -> Self {
+        let spec = test_spec::<E>();
+        let store = Arc::new(
+            HotColdDB::open_ephemeral(StoreConfig::default(), Arc::new(spec.clone()))
+                .expect("should open ephemeral store"),
+        );
+
+        let keypairs = generate_deterministic_keypairs(NUM_VALIDATORS);
+
+        let mut state =
+            interop_genesis_state::<E>(&keypairs, 0, Hash256::repeat_byte(0x42), None, &spec)
+                .expect("should build genesis state");
+
+        *state.finalized_checkpoint_mut() = Checkpoint {
+            epoch: Epoch::new(1),
+            root: Hash256::ZERO,
+        };
+
+        let mut block = genesis_block(&state, &spec).expect("should build genesis block");
+        *block.state_root_mut() = state
+            .update_tree_hash_cache()
+            .expect("should hash genesis state");
+        let signed_block = SignedBeaconBlock::from_block(block, Signature::empty());
+        let block_root = signed_block.canonical_root();
+
+        let snapshot = BeaconSnapshot::new(
+            Arc::new(signed_block.clone()),
+            None,
+            block_root,
+            state.clone(),
+        );
+
+        let fc_store = BeaconForkChoiceStore::get_forkchoice_store(store.clone(), snapshot.clone())
+            .expect("should create fork choice store");
+        let fork_choice =
+            ForkChoice::from_anchor(fc_store, block_root, &signed_block, &state, None, &spec)
+                .expect("should create fork choice");
+
+        let canonical_head =
+            CanonicalHead::new(fork_choice, Arc::new(snapshot), PayloadStatus::Pending);
+
+        let slot_clock = TestingSlotClock::new(
+            Slot::new(0),
+            Duration::from_secs(0),
+            spec.get_slot_duration(),
+        );
+        // Advance past genesis so `now_with_past_tolerance` doesn't underflow.
+        slot_clock.set_current_time(spec.get_slot_duration());
+
+        let validator_pubkey_cache =
+            ValidatorPubkeyCache::new(&state, store.clone()).expect("should create pubkey cache");
+
+        Self {
+            canonical_head,
+            observed_payload_attesters: RwLock::new(ObservedPayloadAttesters::default()),
+            validator_pubkey_cache: RwLock::new(validator_pubkey_cache),
+            slot_clock,
+            keypairs,
+            spec,
+            genesis_block_root: block_root,
+            store,
+        }
+    }
+
+    fn gossip_ctx(&self) -> GossipVerificationContext<'_, T> {
+        GossipVerificationContext {
+            slot_clock: &self.slot_clock,
+            spec: &self.spec,
+            observed_payload_attesters: &self.observed_payload_attesters,
+            canonical_head: &self.canonical_head,
+            validator_pubkey_cache: &self.validator_pubkey_cache,
+            store: &self.store,
+        }
+    }
+
+    fn ptc_members(&self, slot: Slot) -> Vec<usize> {
+        let head = self.canonical_head.cached_head();
+        let state = &head.snapshot.beacon_state;
+        let ptc = state.get_ptc(slot, &self.spec).expect("should get PTC");
+        ptc.0.to_vec()
+    }
+
+    fn sign_payload_attestation(
+        &self,
+        data: PayloadAttestationData,
+        validator_index: u64,
+    ) -> PayloadAttestationMessage {
+        let head = self.canonical_head.cached_head();
+        let state = &head.snapshot.beacon_state;
+        let domain = self.spec.get_domain(
+            data.slot.epoch(E::slots_per_epoch()),
+            Domain::PTCAttester,
+            &state.fork(),
+            state.genesis_validators_root(),
+        );
+        let message = data.signing_root(domain);
+        let signature = self.keypairs[validator_index as usize].sk.sign(message);
+        PayloadAttestationMessage {
+            validator_index,
+            data,
+            signature,
+        }
+    }
+}
+
+fn make_payload_attestation(
+    slot: Slot,
+    validator_index: u64,
+    beacon_block_root: Hash256,
+) -> PayloadAttestationMessage {
+    PayloadAttestationMessage {
+        validator_index,
+        data: PayloadAttestationData {
+            beacon_block_root,
+            slot,
+            payload_present: true,
+            blob_data_available: true,
+        },
+        signature: Signature::empty(),
+    }
+}
+
+#[test]
+fn future_slot() {
+    if !fork_name_from_env().is_some_and(|f| f.gloas_enabled()) {
+        return;
+    }
+    let ctx = TestContext::new();
+    let gossip = ctx.gossip_ctx();
+
+    let future_slot = Slot::new(5);
+    let msg = make_payload_attestation(future_slot, 0, ctx.genesis_block_root);
+    let result = VerifiedPayloadAttestationMessage::new(msg, &gossip);
+    assert!(matches!(
+        result,
+        Err(PayloadAttestationError::FutureSlot { .. })
+    ));
+}
+
+#[test]
+fn past_slot() {
+    if !fork_name_from_env().is_some_and(|f| f.gloas_enabled()) {
+        return;
+    }
+    let ctx = TestContext::new();
+    ctx.slot_clock.set_slot(5);
+    let gossip = ctx.gossip_ctx();
+
+    let msg = make_payload_attestation(Slot::new(0), 0, ctx.genesis_block_root);
+    let result = VerifiedPayloadAttestationMessage::new(msg, &gossip);
+    assert!(matches!(
+        result,
+        Err(PayloadAttestationError::PastSlot { .. })
+    ));
+}
+
+#[test]
+fn unknown_head_block() {
+    if !fork_name_from_env().is_some_and(|f| f.gloas_enabled()) {
+        return;
+    }
+    let ctx = TestContext::new();
+    let gossip = ctx.gossip_ctx();
+
+    let unknown_root = Hash256::repeat_byte(0xff);
+    let msg = make_payload_attestation(Slot::new(1), 0, unknown_root);
+    let result = VerifiedPayloadAttestationMessage::new(msg, &gossip);
+    assert!(
+        matches!(
+            result,
+            Err(PayloadAttestationError::UnknownHeadBlock { .. })
+        ),
+        "expected UnknownHeadBlock, got: {:?}",
+        result
+    );
+}
+
+#[test]
+fn not_in_ptc() {
+    if !fork_name_from_env().is_some_and(|f| f.gloas_enabled()) {
+        return;
+    }
+    let ctx = TestContext::new();
+    let gossip = ctx.gossip_ctx();
+    let slot = Slot::new(1);
+
+    let ptc_members = ctx.ptc_members(slot);
+    let non_ptc_validator = (0..NUM_VALIDATORS as u64)
+        .find(|&i| !ptc_members.contains(&(i as usize)))
+        .expect("should find non-PTC validator");
+
+    let msg = make_payload_attestation(slot, non_ptc_validator, ctx.genesis_block_root);
+    let result = VerifiedPayloadAttestationMessage::new(msg, &gossip);
+    assert!(matches!(
+        result,
+        Err(PayloadAttestationError::NotInPTC { .. })
+    ));
+}
+
+#[test]
+fn invalid_signature() {
+    if !fork_name_from_env().is_some_and(|f| f.gloas_enabled()) {
+        return;
+    }
+    let ctx = TestContext::new();
+    let gossip = ctx.gossip_ctx();
+    let slot = Slot::new(1);
+
+    let ptc_members = ctx.ptc_members(slot);
+    let validator_index = ptc_members[0] as u64;
+
+    let msg = make_payload_attestation(slot, validator_index, ctx.genesis_block_root);
+    let result = VerifiedPayloadAttestationMessage::new(msg, &gossip);
+    assert!(matches!(
+        result,
+        Err(PayloadAttestationError::InvalidSignature)
+    ));
+}
+
+#[test]
+fn valid_payload_attestation() {
+    if !fork_name_from_env().is_some_and(|f| f.gloas_enabled()) {
+        return;
+    }
+    let ctx = TestContext::new();
+    let gossip = ctx.gossip_ctx();
+    let slot = Slot::new(1);
+
+    let ptc_members = ctx.ptc_members(slot);
+    let validator_index = ptc_members[0] as u64;
+
+    let data = PayloadAttestationData {
+        beacon_block_root: ctx.genesis_block_root,
+        slot,
+        payload_present: true,
+        blob_data_available: true,
+    };
+    let msg = ctx.sign_payload_attestation(data, validator_index);
+    let result = VerifiedPayloadAttestationMessage::new(msg, &gossip);
+    assert!(
+        result.is_ok(),
+        "expected Ok, got: {:?}",
+        result.unwrap_err()
+    );
+}
+
+#[test]
+fn duplicate_after_valid() {
+    if !fork_name_from_env().is_some_and(|f| f.gloas_enabled()) {
+        return;
+    }
+    let ctx = TestContext::new();
+    let gossip = ctx.gossip_ctx();
+    let slot = Slot::new(1);
+
+    let ptc_members = ctx.ptc_members(slot);
+    let validator_index = ptc_members[0] as u64;
+
+    let data = PayloadAttestationData {
+        beacon_block_root: ctx.genesis_block_root,
+        slot,
+        payload_present: true,
+        blob_data_available: true,
+    };
+
+    let msg1 = ctx.sign_payload_attestation(data.clone(), validator_index);
+    let result1 = VerifiedPayloadAttestationMessage::new(msg1, &gossip);
+    assert!(
+        result1.is_ok(),
+        "first message should pass: {:?}",
+        result1.unwrap_err()
+    );
+
+    let msg2 = ctx.sign_payload_attestation(data, validator_index);
+    let result2 = VerifiedPayloadAttestationMessage::new(msg2, &gossip);
+    assert!(matches!(
+        result2,
+        Err(PayloadAttestationError::PriorPayloadAttestationMessageKnown { .. })
+    ));
+}
+
+/// Exercises the `partial_state_advance` fallback in gossip verification when
+/// the head state is too stale to compute PTC membership (e.g., during a
+/// network liveness failure with many missed slots).
+#[tokio::test]
+async fn stale_head_with_partial_advance() {
+    if !fork_name_from_env().is_some_and(|f| f.gloas_enabled()) {
+        return;
+    }
+
+    let slots_per_epoch = E::slots_per_epoch();
+    // Head at epoch 1, message at epoch 5 — 4 epochs of missed slots.
+    // This exceeds min_seed_lookahead (1), triggering the fallback path:
+    // get_advanced_hot_state loads the stored state, then partial_state_advance
+    // advances it through epoch boundaries to populate ptc_window.
+    let head_slot = Slot::new(slots_per_epoch);
+    let missed_epochs = 4;
+    let target_slot = Slot::new(slots_per_epoch * (1 + missed_epochs));
+    let target_epoch = target_slot.epoch(slots_per_epoch);
+
+    // GIVEN a chain with blocks through epoch 1 (so the store has states).
+    let harness = BeaconChainHarness::builder(E::default())
+        .default_spec()
+        .deterministic_keypairs(64)
+        .fresh_ephemeral_store()
+        .mock_execution_layer()
+        .build();
+    harness.extend_to_slot(head_slot).await;
+
+    let head = harness.chain.canonical_head.cached_head();
+    let head_epoch = head.snapshot.beacon_state.current_epoch();
+    assert!(
+        target_epoch > head_epoch + harness.spec.min_seed_lookahead,
+        "precondition: message epoch must exceed head + min_seed_lookahead to trigger fallback"
+    );
+
+    // GIVEN a slot clock advanced to epoch 5 without producing blocks
+    // (simulating missed slots during a liveness failure).
+    harness.chain.slot_clock.set_slot(target_slot.as_u64());
+
+    // Advance a reference state to compute the PTC at the target slot.
+    let mut reference_state = head.snapshot.beacon_state.clone();
+    state_processing::state_advance::partial_state_advance(
+        &mut reference_state,
+        Some(head.snapshot.beacon_state_root()),
+        target_slot,
+        &harness.spec,
+    )
+    .expect("should advance reference state");
+    reference_state
+        .build_all_caches(&harness.spec)
+        .expect("should build caches");
+
+    let ptc = reference_state
+        .get_ptc(target_slot, &harness.spec)
+        .expect("should get PTC from reference state");
+    let validator_index = *ptc.0.first().expect("PTC should have at least one member") as u64;
+
+    // WHEN a properly-signed payload attestation from a PTC member is verified.
+    let domain = harness.spec.get_domain(
+        target_epoch,
+        Domain::PTCAttester,
+        &reference_state.fork(),
+        reference_state.genesis_validators_root(),
+    );
+    let data = PayloadAttestationData {
+        beacon_block_root: head.head_block_root(),
+        slot: target_slot,
+        payload_present: true,
+        blob_data_available: true,
+    };
+    let message = data.signing_root(domain);
+    let signature = harness.validator_keypairs[validator_index as usize]
+        .sk
+        .sign(message);
+    let msg = PayloadAttestationMessage {
+        validator_index,
+        data,
+        signature,
+    };
+
+    // THEN verification succeeds despite the head being 4 epochs stale.
+    let result = harness
+        .chain
+        .verify_payload_attestation_message_for_gossip(msg);
+    assert!(
+        result.is_ok(),
+        "expected Ok (head epoch {}, message epoch {}), got: {:?}",
+        head_epoch,
+        target_epoch,
+        result.unwrap_err()
+    );
+}