Fuzz ProcessFinalUpdates (#4308)

beacon-chain/core/epoch/BUILD.bazel

@@ -24,6 +24,7 @@ go_test(
     name = "go_default_test",
     size = "small",
     srcs = [
+        "epoch_processing_fuzz_test.go",
         "epoch_processing_test.go",
         "participation_test.go",
     ],
@@ -34,6 +35,7 @@ go_test(
         "//shared/bytesutil:go_default_library",
         "//shared/params:go_default_library",
         "@com_github_gogo_protobuf//proto:go_default_library",
+        "@com_github_google_gofuzz//:go_default_library",
         "@com_github_prysmaticlabs_ethereumapis//eth/v1alpha1:go_default_library",
         "@com_github_prysmaticlabs_go_bitfield//:go_default_library",
     ],

beacon-chain/core/epoch/epoch_processing.go

@@ -286,6 +286,12 @@ func ProcessFinalUpdates(state *pb.BeaconState) (*pb.BeaconState, error) {
 
 	// Update effective balances with hysteresis.
 	for i, v := range state.Validators {
+		if v == nil {
+			return nil, fmt.Errorf("validator %d is nil in state", i)
+		}
+		if i >= len(state.Balances) {
+			return nil, fmt.Errorf("validator index exceeds validator length in state %d >= %d", i, len(state.Balances))
+		}
 		balance := state.Balances[i]
 		halfInc := params.BeaconConfig().EffectiveBalanceIncrement / 2
 		if balance < v.EffectiveBalance || v.EffectiveBalance+3*halfInc < balance {
@@ -298,10 +304,17 @@ func ProcessFinalUpdates(state *pb.BeaconState) (*pb.BeaconState, error) {
 
 	// Set total slashed balances.
 	slashedExitLength := params.BeaconConfig().EpochsPerSlashingsVector
-	state.Slashings[nextEpoch%slashedExitLength] = 0
+	slashedEpoch := int(nextEpoch % slashedExitLength)
+	if len(state.Slashings) != int(slashedExitLength) {
+		return nil, fmt.Errorf("state slashing length %d different than EpochsPerHistoricalVector %d", len(state.Slashings), slashedExitLength)
+	}
+	state.Slashings[slashedEpoch] = 0
 
 	// Set RANDAO mix.
 	randaoMixLength := params.BeaconConfig().EpochsPerHistoricalVector
+	if len(state.RandaoMixes) != int(randaoMixLength) {
+		return nil, fmt.Errorf("state randao length %d different than EpochsPerHistoricalVector %d", len(state.RandaoMixes), randaoMixLength)
+	}
 	mix := helpers.RandaoMix(state, currentEpoch)
 	state.RandaoMixes[nextEpoch%randaoMixLength] = mix
 

beacon-chain/core/epoch/epoch_processing_fuzz_test.go

@@ -0,0 +1,18 @@
+package epoch
+
+import (
+	"testing"
+
+	fuzz "github.com/google/gofuzz"
+	ethereum_beacon_p2p_v1 "github.com/prysmaticlabs/prysm/proto/beacon/p2p/v1"
+)
+
+func TestFuzzFinalUpdates_10000(t *testing.T) {
+	fuzzer := fuzz.NewWithSeed(0)
+	state := &ethereum_beacon_p2p_v1.BeaconState{}
+
+	for i := 0; i < 10000; i++ {
+		fuzzer.Fuzz(state)
+		_, _ = ProcessFinalUpdates(state)
+	}
+}

beacon-chain/core/state/transition_test.go

@@ -477,11 +477,11 @@ func TestProcessEpochPrecompute_CanProcess(t *testing.T) {
 	epoch := uint64(1)
 
 	atts := []*pb.PendingAttestation{{Data: &ethpb.AttestationData{Target: &ethpb.Checkpoint{}}}}
-
+	slashing := make([]uint64, params.BeaconConfig().EpochsPerSlashingsVector)
 	newState, err := state.ProcessEpochPrecompute(context.Background(), &pb.BeaconState{
 		Slot:                       epoch*params.BeaconConfig().SlotsPerEpoch + 1,
 		BlockRoots:                 make([][]byte, 128),
-		Slashings:                  []uint64{0, 1e9, 1e9},
+		Slashings:                  slashing,
 		RandaoMixes:                make([][]byte, params.BeaconConfig().EpochsPerHistoricalVector),
 		CurrentEpochAttestations:   atts,
 		FinalizedCheckpoint:        &ethpb.Checkpoint{},