Restrict Proposer Lookup to the Current Epoch (#7542)

* checkpoint

* add test

* Update beacon-chain/core/helpers/committee_test.go

* preston's review

Co-authored-by: Victor Farazdagi <simple.square@gmail.com>
Co-authored-by: Raul Jordan <raul@prysmaticlabs.com>

beacon-chain/core/helpers/committee.go

@@ -186,7 +186,9 @@ func CommitteeAssignments(
 		return nil, nil, err
 	}
 	proposerIndexToSlots := make(map[uint64][]uint64, params.BeaconConfig().SlotsPerEpoch)
-	for slot := startSlot; slot < startSlot+params.BeaconConfig().SlotsPerEpoch; slot++ {
+	// Proposal epochs do not have a look ahead, so we skip them over here.
+	validProposalEpoch := epoch < nextEpoch
+	for slot := startSlot; slot < startSlot+params.BeaconConfig().SlotsPerEpoch && validProposalEpoch; slot++ {
 		// Skip proposer assignment for genesis slot.
 		if slot == 0 {
 			continue

beacon-chain/core/helpers/committee_test.go

@@ -203,6 +203,36 @@ func TestCommitteeAssignments_CanRetrieve(t *testing.T) {
 	}
 }
 
+func TestCommitteeAssignments_CannotRetrieveFuture(t *testing.T) {
+	// Initialize test with 256 validators, each slot and each index gets 4 validators.
+	validators := make([]*ethpb.Validator, 4*params.BeaconConfig().SlotsPerEpoch)
+	for i := 0; i < len(validators); i++ {
+		// First 2 epochs only half validators are activated.
+		var activationEpoch uint64
+		if i >= len(validators)/2 {
+			activationEpoch = 3
+		}
+		validators[i] = &ethpb.Validator{
+			ActivationEpoch: activationEpoch,
+			ExitEpoch:       params.BeaconConfig().FarFutureEpoch,
+		}
+	}
+
+	state, err := beaconstate.InitializeFromProto(&pb.BeaconState{
+		Validators:  validators,
+		Slot:        2 * params.BeaconConfig().SlotsPerEpoch, // epoch 2
+		RandaoMixes: make([][]byte, params.BeaconConfig().EpochsPerHistoricalVector),
+	})
+	require.NoError(t, err)
+	_, proposerIndxs, err := CommitteeAssignments(state, CurrentEpoch(state))
+	require.NoError(t, err)
+	require.NotEqual(t, 0, len(proposerIndxs), "wanted non-zero proposer index set")
+
+	_, proposerIndxs, err = CommitteeAssignments(state, CurrentEpoch(state)+1)
+	require.NoError(t, err)
+	require.Equal(t, 0, len(proposerIndxs), "wanted empty proposer index set")
+}
+
 func TestCommitteeAssignments_EverySlotHasMin1Proposer(t *testing.T) {
 	// Initialize test with 256 validators, each slot and each index gets 4 validators.
 	validators := make([]*ethpb.Validator, 4*params.BeaconConfig().SlotsPerEpoch)

beacon-chain/core/helpers/validators_test.go

@@ -275,6 +275,39 @@ func TestBeaconProposerIndex_OK(t *testing.T) {
 	}
 }
 
+func TestBeaconProposerIndex_BadState(t *testing.T) {
+	params.SetupTestConfigCleanup(t)
+	ClearCache()
+	c := params.BeaconConfig()
+	c.MinGenesisActiveValidatorCount = 16384
+	params.OverrideBeaconConfig(c)
+	validators := make([]*ethpb.Validator, params.BeaconConfig().MinGenesisActiveValidatorCount/8)
+	for i := 0; i < len(validators); i++ {
+		validators[i] = &ethpb.Validator{
+			ExitEpoch: params.BeaconConfig().FarFutureEpoch,
+		}
+	}
+	roots := make([][]byte, params.BeaconConfig().SlotsPerHistoricalRoot)
+	for i := uint64(0); i < params.BeaconConfig().SlotsPerHistoricalRoot; i++ {
+		roots[i] = make([]byte, 32)
+	}
+
+	state, err := beaconstate.InitializeFromProto(&pb.BeaconState{
+		Validators:  validators,
+		Slot:        0,
+		RandaoMixes: make([][]byte, params.BeaconConfig().EpochsPerHistoricalVector),
+		BlockRoots:  roots,
+		StateRoots:  roots,
+	})
+	require.NoError(t, err)
+	// Set a very high slot, so that retrieved block root will be
+	// non existent for the proposer cache.
+	require.NoError(t, state.SetSlot(100))
+	_, err = BeaconProposerIndex(state)
+	require.NoError(t, err)
+	assert.Equal(t, 0, len(proposerIndicesCache.ProposerIndicesCache.ListKeys()))
+}
+
 func TestComputeProposerIndex_Compatibility(t *testing.T) {
 	validators := make([]*ethpb.Validator, params.BeaconConfig().MinGenesisActiveValidatorCount)
 	for i := 0; i < len(validators); i++ {

beacon-chain/rpc/validator/assignments.go

@@ -128,7 +128,7 @@ func (vs *Server) duties(ctx context.Context, req *ethpb.DutiesRequest) (*ethpb.
 		return nil, status.Errorf(codes.Internal, "Could not compute committee assignments: %v", err)
 	}
 	// Query the next epoch assignments for committee subnet subscriptions.
-	nextCommitteeAssignments, nextProposerIndexToSlots, err := helpers.CommitteeAssignments(s, req.Epoch+1)
+	nextCommitteeAssignments, _, err := helpers.CommitteeAssignments(s, req.Epoch+1)
 	if err != nil {
 		return nil, status.Errorf(codes.Internal, "Could not compute next committee assignments: %v", err)
 	}
@@ -153,9 +153,9 @@ func (vs *Server) duties(ctx context.Context, req *ethpb.DutiesRequest) (*ethpb.
 			assignment.Status = assignmentStatus(s, idx)
 			assignment.ProposerSlots = proposerIndexToSlots[idx]
 
+			// The next epoch has no lookup for proposer indexes.
 			nextAssignment.ValidatorIndex = idx
 			nextAssignment.Status = assignmentStatus(s, idx)
-			nextAssignment.ProposerSlots = nextProposerIndexToSlots[idx]
 
 			ca, ok := committeeAssignments[idx]
 			if ok {