Fix electra balance update (#14410)

CHANGELOG.md

@@ -38,6 +38,7 @@ The format is based on Keep a Changelog, and this project adheres to Semantic Ve
 - Electra: build blocks with blobs.
 - E2E: fixed gas limit at genesis
 - Light client support: use LightClientHeader instead of BeaconBlockHeader.
+- Core: Fix process effective balance update to safe copy validator for Electra.
 
 ### Security
 

beacon-chain/core/electra/effective_balance_updates.go

@@ -55,8 +55,9 @@ func ProcessEffectiveBalanceUpdates(state state.BeaconState) error {
 
 		if balance+downwardThreshold < val.EffectiveBalance || val.EffectiveBalance+upwardThreshold < balance {
 			effectiveBal := min(balance-balance%effBalanceInc, effectiveBalanceLimit)
-			val.EffectiveBalance = effectiveBal
-			return true, val, nil
+			newVal := ethpb.CopyValidator(val)
+			newVal.EffectiveBalance = effectiveBal
+			return true, newVal, nil
 		}
 		return false, val, nil
 	}

beacon-chain/core/electra/effective_balance_updates_test.go

@@ -11,6 +11,29 @@ import (
 	"github.com/prysmaticlabs/prysm/v5/testing/require"
 )
 
+func TestProcessEffectiveBalanceUpdates_SafeCopy(t *testing.T) {
+	pb := &eth.BeaconStateElectra{
+		Validators: []*eth.Validator{
+			{
+				EffectiveBalance:      params.BeaconConfig().MinActivationBalance,
+				WithdrawalCredentials: []byte{params.BeaconConfig().CompoundingWithdrawalPrefixByte, 0x11},
+			},
+		},
+		Balances: []uint64{
+			params.BeaconConfig().MaxEffectiveBalanceElectra * 2,
+		},
+	}
+	st, err := state_native.InitializeFromProtoElectra(pb)
+	require.NoError(t, err)
+	copiedState := st.Copy()
+
+	err = electra.ProcessEffectiveBalanceUpdates(copiedState)
+	require.NoError(t, err)
+
+	require.Equal(t, st.Validators()[0].EffectiveBalance, params.BeaconConfig().MinActivationBalance)
+	require.Equal(t, copiedState.Validators()[0].EffectiveBalance, params.BeaconConfig().MaxEffectiveBalanceElectra)
+}
+
 func TestProcessEffectiveBalnceUpdates(t *testing.T) {
 	effBalanceInc := params.BeaconConfig().EffectiveBalanceIncrement
 	hysteresisInc := effBalanceInc / params.BeaconConfig().HysteresisQuotient