state_processing: remove spurious withdrawal credentials check

eth2/state_processing/src/per_block_processing.rs

@@ -386,8 +386,6 @@ pub fn process_deposits<T: EthSpec>(
 
         // Get an `Option<u64>` where `u64` is the validator index if this deposit public key
         // already exists in the beacon_state.
-        //
-        // This function also verifies the withdrawal credentials.
         let validator_index =
             get_existing_validator_index(state, deposit).map_err(|e| e.into_with_index(i))?;
 

eth2/state_processing/src/per_block_processing/errors.rs

@@ -323,9 +323,6 @@ pub enum DepositInvalid {
     BadIndex { state: u64, deposit: u64 },
     /// The signature (proof-of-possession) does not match the given pubkey.
     BadSignature,
-    /// The withdrawal credentials for the depositing validator did not match the withdrawal
-    /// credentials of an existing validator with the same public key.
-    BadWithdrawalCredentials,
     /// The specified `branch` and `index` did not form a valid proof that the deposit is included
     /// in the eth1 deposit root.
     BadMerkleProof,

eth2/state_processing/src/per_block_processing/verify_deposit.rs

@@ -52,19 +52,7 @@ pub fn get_existing_validator_index<T: EthSpec>(
     deposit: &Deposit,
 ) -> Result<Option<u64>, Error> {
     let validator_index = state.get_validator_index(&deposit.data.pubkey)?;
-
+    Ok(validator_index.map(|idx| idx as u64))
-    // NOTE: it seems that v0.6.1 doesn't require the withdrawal credentials to be checked
-    match validator_index {
-        None => Ok(None),
-        Some(index) => {
-            verify!(
-                deposit.data.withdrawal_credentials
-                    == state.validator_registry[index].withdrawal_credentials,
-                Invalid::BadWithdrawalCredentials
-            );
-            Ok(Some(index as u64))
-        }
-    }
 }
 
 /// Verify that a deposit is included in the state's eth1 deposit root.