check blob versioned hashes when no EL is connected (#6501)

* check blob versioned hashes when no EL is connected

When no EL is conencted, we have to at the very least ensure that the
data in the beacon block is consistent with the execution payload.
We already do this for the block hash, but also have to do it for the
`blob_kzg_commitments`. To validate that they are linked with the
execution payload, we have to RLP decode all EIP-4844 blob transactions
and compare their blob versioned hashes with the hashed commitments.

* simplify loop in case where `blob_versioned_hashes` doesn't exist

* skip blob transaction parsing pre Deneb

beacon_chain/gossip_processing/block_processor.nim

@@ -9,7 +9,7 @@
 
 import
   chronicles, chronos, metrics,
-  ../spec/[forks, signatures, signatures_batch],
+  ../spec/[forks, helpers_el, signatures, signatures_batch],
   ../sszdump
 
 from std/deques import Deque, addLast, contains, initDeque, items, len, shrink
@@ -548,8 +548,11 @@ proc storeBlock(
       if signedBlock.message.is_execution_block:
         template payload(): auto = signedBlock.message.body.execution_payload
 
-        template returnWithError(msg: string): untyped =
-          debug msg, executionPayload = shortLog(payload)
+        template returnWithError(msg: string, extraMsg = ""): untyped =
+          if extraMsg != "":
+            debug msg, reason = extraMsg, executionPayload = shortLog(payload)
+          else:
+            debug msg, executionPayload = shortLog(payload)
           self[].dumpInvalidBlock(signedBlock)
           doAssert strictVerification notin dag.updateFlags
           self.consensusManager.quarantine[].addUnviable(signedBlock.root)
@@ -563,10 +566,16 @@ proc storeBlock(
           returnWithError "Execution block hash validation failed"
 
         # [New in Deneb:EIP4844]
-        # TODO run https://github.com/ethereum/consensus-specs/blob/v1.3.0/specs/deneb/beacon-chain.md#blob-kzg-commitments
-        # https://github.com/ethereum/execution-apis/blob/main/src/engine/experimental/blob-extension.md#specification
-        # "This validation MUST be instantly run in all cases even during active
-        # sync process."
+        when typeof(signedBlock).kind >= ConsensusFork.Deneb:
+          let blobsRes = signedBlock.message.is_valid_versioned_hashes
+          if blobsRes.isErr:
+            returnWithError "Blob versioned hashes invalid", blobsRes.error
+        else:
+          # If there are EIP-4844 (type 3) transactions in the payload with
+          # versioned hashes, the transactions would be rejected by the EL
+          # based on payload timestamp (only allowed post Deneb);
+          # There are no `blob_kzg_commitments` before Deneb to compare against
+          discard
 
   let newPayloadTick = Moment.now()
 

beacon_chain/spec/helpers_el.nim

@@ -0,0 +1,46 @@
+# beacon_chain
+# Copyright (c) 2024 Status Research & Development GmbH
+# Licensed and distributed under either of
+#   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
+#   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
+# at your option. This file may not be copied, modified, or distributed except according to those terms.
+
+{.push raises: [].}
+
+import
+  std/typetraits,
+  eth/common/eth_types_rlp,
+  "."/[helpers, state_transition_block]
+
+func readExecutionTransaction(
+    txBytes: bellatrix.Transaction): Result[ExecutionTransaction, string] =
+  # Nim 2.0.8: `rlp.decode(distinctBase(txBytes), ExecutionTransaction)`
+  # uses the generic `read` from `rlp.nim` instead of the specific `read`
+  # from `eth_types_rlp.nim`, leading to compilation error.
+  # Doing this in two steps works around this resolution order issue.
+  var rlp = rlpFromBytes(distinctBase(txBytes))
+  try:
+    ok rlp.read(ExecutionTransaction)
+  except RlpError as exc:
+    err("Invalid transaction: " & exc.msg)
+
+# https://github.com/ethereum/consensus-specs/blob/v1.5.0-alpha.4/specs/deneb/beacon-chain.md#is_valid_versioned_hashes
+func is_valid_versioned_hashes*(blck: ForkyBeaconBlock): Result[void, string] =
+  static: doAssert typeof(blck).kind >= ConsensusFork.Deneb
+  template transactions: untyped = blck.body.execution_payload.transactions
+  template commitments: untyped = blck.body.blob_kzg_commitments
+
+  var i = 0
+  for txBytes in transactions:
+    if txBytes.len == 0 or txBytes[0] != TxEip4844.byte:
+      continue  # Only blob transactions may have blobs
+    let tx = ? txBytes.readExecutionTransaction()
+    for vHash in tx.versionedHashes:
+      if commitments.len <= i:
+        return err("Extra blobs without matching `blob_kzg_commitments`")
+      if vHash.data != kzg_commitment_to_versioned_hash(commitments[i]):
+        return err("Invalid `blob_versioned_hash` at index " & $i)
+      inc i
+  if i != commitments.len:
+    return err("Extra `blob_kzg_commitments` without matching blobs")
+  ok()