# beacon_chain # Copyright (c) 2018-2020 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: [Defect].} import chronicles, sequtils, tables, metrics, stew/results, ../ssz/merkleization, ../state_transition, ../extras, ../spec/[crypto, datatypes, digest, helpers, signatures], block_pools_types, candidate_chains export results # Clearance # --------------------------------------------- # # This module is in charge of making the # "quarantined" network blocks # pass the firewall and be stored in the blockpool logScope: topics = "clearance" func getOrResolve*(dag: CandidateChains, quarantine: var Quarantine, root: Eth2Digest): BlockRef = ## Fetch a block ref, or nil if not found (will be added to list of ## blocks-to-resolve) result = dag.getRef(root) if result.isNil: quarantine.missing[root] = MissingBlock(slots: 1) proc add*( dag: var CandidateChains, quarantine: var Quarantine, blockRoot: Eth2Digest, signedBlock: SignedBeaconBlock): Result[BlockRef, BlockError] {.gcsafe.} proc addResolvedBlock( dag: var CandidateChains, quarantine: var Quarantine, state: BeaconState, blockRoot: Eth2Digest, signedBlock: SignedBeaconBlock, parent: BlockRef): BlockRef = logScope: pcs = "block_resolution" doAssert state.slot == signedBlock.message.slot, "state must match block" let blockRef = BlockRef.init(blockRoot, signedBlock.message) blockRef.epochsInfo = filterIt(parent.epochsInfo, it.epoch + 1 >= state.slot.compute_epoch_at_slot) link(parent, blockRef) dag.blocks[blockRoot] = blockRef trace "Populating block dag", key = blockRoot, val = blockRef # Resolved blocks should be stored in database dag.putBlock(blockRoot, signedBlock) # This block *might* have caused a justification - make sure we stow away # that information: let justifiedSlot = state.current_justified_checkpoint.epoch.compute_start_slot_at_epoch() var foundHead: Option[Head] for head in dag.heads.mitems(): if head.blck.isAncestorOf(blockRef): if head.justified.slot != justifiedSlot: head.justified = blockRef.atSlot(justifiedSlot) head.blck = blockRef foundHead = some(head) break if foundHead.isNone(): foundHead = some(Head( blck: blockRef, justified: blockRef.atSlot(justifiedSlot))) dag.heads.add(foundHead.get()) info "Block resolved", blck = shortLog(signedBlock.message), blockRoot = shortLog(blockRoot), justifiedHead = foundHead.get().justified, heads = dag.heads.len(), cat = "filtering" # Now that we have the new block, we should see if any of the previously # unresolved blocks magically become resolved # TODO there are more efficient ways of doing this that don't risk # running out of stack etc # TODO This code is convoluted because when there are more than ~1.5k # blocks being synced, there's a stack overflow as `add` gets called # for the whole chain of blocks. Instead we use this ugly field in `dag` # which could be avoided by refactoring the code if not quarantine.inAdd: quarantine.inAdd = true defer: quarantine.inAdd = false var keepGoing = true while keepGoing: let retries = quarantine.pending for k, v in retries: discard add(dag, quarantine, k, v) # Keep going for as long as the pending dag is shrinking # TODO inefficient! so what? keepGoing = quarantine.pending.len < retries.len blockRef proc add*( dag: var CandidateChains, quarantine: var Quarantine, blockRoot: Eth2Digest, signedBlock: SignedBeaconBlock): Result[BlockRef, BlockError] {.gcsafe.} = ## return the block, if resolved... ## the state parameter may be updated to include the given block, if ## everything checks out # TODO reevaluate passing the state in like this # TODO: to facilitate adding the block to the attestation pool # this should also return justified and finalized epoch corresponding # to each block. # This would be easy apart from the "Block already exists" # early return. let blck = signedBlock.message doAssert blockRoot == hash_tree_root(blck) logScope: pcs = "block_addition" # Already seen this block?? dag.blocks.withValue(blockRoot, blockRef): debug "Block already exists", blck = shortLog(blck), blockRoot = shortLog(blockRoot), cat = "filtering" return ok blockRef[] quarantine.missing.del(blockRoot) # If the block we get is older than what we finalized already, we drop it. # One way this can happen is that we start resolving a block and finalization # happens in the meantime - the block we requested will then be stale # by the time it gets here. if blck.slot <= dag.finalizedHead.slot: debug "Old block, dropping", blck = shortLog(blck), finalizedHead = shortLog(dag.finalizedHead), tail = shortLog(dag.tail), blockRoot = shortLog(blockRoot), cat = "filtering" return err Old let parent = dag.blocks.getOrDefault(blck.parent_root) if parent != nil: if parent.slot >= blck.slot: # TODO Malicious block? inform peer dag? notice "Invalid block slot", blck = shortLog(blck), blockRoot = shortLog(blockRoot), parentBlock = shortLog(parent) return err Invalid # The block might have been in either of pending or missing - we don't want # any more work done on its behalf quarantine.pending.del(blockRoot) # The block is resolved, now it's time to validate it to ensure that the # blocks we add to the database are clean for the given state # TODO if the block is from the future, we should not be resolving it (yet), # but maybe we should use it as a hint that our clock is wrong? updateStateData( dag, dag.tmpState, BlockSlot(blck: parent, slot: blck.slot - 1)) let poolPtr = unsafeAddr dag # safe because restore is short-lived func restore(v: var HashedBeaconState) = # TODO address this ugly workaround - there should probably be a # `state_transition` that takes a `StateData` instead and updates # the block as well doAssert v.addr == addr poolPtr.tmpState.data assign(poolPtr.tmpState, poolPtr.headState) var stateCache = getEpochCache(parent, dag.tmpState.data.data) if not state_transition( dag.tmpState.data, signedBlock, stateCache, dag.updateFlags, restore): # TODO find a better way to log all this block data notice "Invalid block", blck = shortLog(blck), blockRoot = shortLog(blockRoot), cat = "filtering" return err Invalid # Careful, tmpState.data has been updated but not blck - we need to create # the BlockRef first! dag.tmpState.blck = addResolvedBlock( dag, quarantine, dag.tmpState.data.data, blockRoot, signedBlock, parent) dag.putState(dag.tmpState.data, dag.tmpState.blck) return ok dag.tmpState.blck # TODO already checked hash though? main reason to keep this is because # the pending dag calls this function back later in a loop, so as long # as dag.add(...) requires a SignedBeaconBlock, easier to keep them in # pending too. quarantine.pending[blockRoot] = signedBlock # TODO possibly, it makes sense to check the database - that would allow sync # to simply fill up the database with random blocks the other clients # think are useful - but, it would also risk filling the database with # junk that's not part of the block graph if blck.parent_root in quarantine.missing or blck.parent_root in quarantine.pending: return err MissingParent # This is an unresolved block - put its parent on the missing list for now... # TODO if we receive spam blocks, one heurestic to implement might be to wait # for a couple of attestations to appear before fetching parents - this # would help prevent using up network resources for spam - this serves # two purposes: one is that attestations are likely to appear for the # block only if it's valid / not spam - the other is that malicious # validators that are not proposers can sign invalid blocks and send # them out without penalty - but signing invalid attestations carries # a risk of being slashed, making attestations a more valuable spam # filter. # TODO when we receive the block, we don't know how many others we're missing # from that branch, so right now, we'll just do a blind guess let parentSlot = blck.slot - 1 quarantine.missing[blck.parent_root] = MissingBlock( slots: # The block is at least two slots ahead - try to grab whole history if parentSlot > dag.head.blck.slot: parentSlot - dag.head.blck.slot else: # It's a sibling block from a branch that we're missing - fetch one # epoch at a time max(1.uint64, SLOTS_PER_EPOCH.uint64 - (parentSlot.uint64 mod SLOTS_PER_EPOCH.uint64)) ) debug "Unresolved block (parent missing)", blck = shortLog(blck), blockRoot = shortLog(blockRoot), pending = quarantine.pending.len, missing = quarantine.missing.len, cat = "filtering" return err MissingParent # https://github.com/ethereum/eth2.0-specs/blob/v0.11.1/specs/phase0/p2p-interface.md#global-topics proc isValidBeaconBlock*( dag: CandidateChains, quarantine: var Quarantine, signed_beacon_block: SignedBeaconBlock, current_slot: Slot, flags: UpdateFlags): Result[void, BlockError] = logScope: topics = "clearance valid_blck" received_block = shortLog(signed_beacon_block.message) # In general, checks are ordered from cheap to expensive. Especially, crypto # verification could be quite a bit more expensive than the rest. This is an # externally easy-to-invoke function by tossing network packets at the node. # The block is not from a future slot # TODO allow `MAXIMUM_GOSSIP_CLOCK_DISPARITY` leniency, especially towards # seemingly future slots. # TODO using +1 here while this is being sorted - should queue these until # they're within the DISPARITY limit if not (signed_beacon_block.message.slot <= current_slot + 1): debug "block is from a future slot", current_slot return err(Invalid) # The block is from a slot greater than the latest finalized slot (with a # MAXIMUM_GOSSIP_CLOCK_DISPARITY allowance) -- i.e. validate that # signed_beacon_block.message.slot > # compute_start_slot_at_epoch(state.finalized_checkpoint.epoch) if not (signed_beacon_block.message.slot > dag.finalizedHead.slot): debug "block is not from a slot greater than the latest finalized slot" return err(Invalid) # The block is the first block with valid signature received for the proposer # for the slot, signed_beacon_block.message.slot. # # While this condition is similar to the proposer slashing condition at # https://github.com/ethereum/eth2.0-specs/blob/v0.12.1/specs/phase0/validator.md#proposer-slashing # it's not identical, and this check does not address slashing: # # (1) The beacon blocks must be conflicting, i.e. different, for the same # slot and proposer. This check also catches identical blocks. # # (2) By this point in the function, it's not been checked whether they're # signed yet. As in general, expensive checks should be deferred, this # would add complexity not directly relevant this function. # # (3) As evidenced by point (1), the similarity in the validation condition # and slashing condition, while not coincidental, aren't similar enough # to combine, as one or the other might drift. # # (4) Furthermore, this function, as much as possible, simply returns a yes # or no answer, without modifying other state for p2p network interface # validation. Complicating this interface, for the sake of sharing only # couple lines of code, wouldn't be worthwhile. # # TODO might check unresolved/orphaned blocks too, and this might not see all # blocks at a given slot (though, in theory, those get checked elsewhere), or # adding metrics that count how often these conditions occur. let slotBlockRef = getBlockBySlot(dag, signed_beacon_block.message.slot) if not slotBlockRef.isNil: let blck = dag.get(slotBlockRef).data if blck.message.proposer_index == signed_beacon_block.message.proposer_index and blck.message.slot == signed_beacon_block.message.slot and blck.signature.toRaw() != signed_beacon_block.signature.toRaw(): debug "block isn't first block with valid signature received for the proposer", blckRef = slotBlockRef, existing_block = shortLog(blck.message) return err(Invalid) # If this block doesn't have a parent we know about, we can't/don't really # trace it back to a known-good state/checkpoint to verify its prevenance; # while one could getOrResolve to queue up searching for missing parent it # might not be the best place. As much as feasible, this function aims for # answering yes/no, not queuing other action or otherwise altering state. let parent_ref = dag.getRef(signed_beacon_block.message.parent_root) if parent_ref.isNil: # This doesn't mean a block is forever invalid, only that we haven't seen # its ancestor blocks yet. While that means for now it should be blocked, # at least, from libp2p propagation, it shouldn't be ignored. TODO, if in # the future this block moves from pending to being resolved, consider if # it's worth broadcasting it then. # Pending dag gets checked via `CandidateChains.add(...)` later, and relevant # checks are performed there. In usual paths beacon_node adds blocks via # CandidateChains.add(...) directly, with no additional validity checks. TODO, # not specific to this, but by the pending dag keying on the htr of the # BeaconBlock, not SignedBeaconBlock, opens up certain spoofing attacks. debug "parent unknown, putting block in quarantine" quarantine.pending[hash_tree_root(signed_beacon_block.message)] = signed_beacon_block return err(MissingParent) # The proposer signature, signed_beacon_block.signature, is valid with # respect to the proposer_index pubkey. let proposer = getProposer(dag, parent_ref, signed_beacon_block.message.slot) if proposer.isNone: notice "cannot compute proposer for message" return err(Invalid) if proposer.get()[0] != ValidatorIndex(signed_beacon_block.message.proposer_index): debug "block had unexpected proposer", expected_proposer = proposer.get()[0] return err(Invalid) if not verify_block_signature( dag.headState.data.data.fork, dag.headState.data.data.genesis_validators_root, signed_beacon_block.message.slot, signed_beacon_block.message, proposer.get()[1], signed_beacon_block.signature): debug "block failed signature verification", signature = shortLog(signed_beacon_block.signature) return err(Invalid) ok()