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Fix edge-case when finding the finalized descendant (#3924)

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## Issue Addressed

NA

## Description

We were missing an edge case when checking to see if a block is a descendant of the finalized checkpoint. This edge case is described for one of the tests in this PR:

a119edc739/consensus/proto_array/src/proto_array_fork_choice.rs (L1018-L1047)

This bug presented itself in the following mainnet log:

```
Jan 26 15:12:42.841 ERRO Unable to validate attestation error: MissingBeaconState(0x7c30cb80ec3d4ec624133abfa70e4c6cfecfca456bfbbbff3393e14e5b20bf25), peer_id: 16Uiu2HAm8RPRciXJYtYc5c3qtCRdrZwkHn2BXN3XP1nSi1gxHYit, type: "unaggregated", slot: Slot(5660161), beacon_block_root: 0x4a45e59da7cb9487f4836c83bdd1b741b4f31c67010c7ae343fa6771b3330489
```

Here the BN is rejecting an attestation because of a "missing beacon state". Whilst it was correct to reject the attestation, it should have rejected it because it attests to a block that conflicts with finality rather than claiming that the database is inconsistent.

The block that this attestation points to (`0x4a45`) is block `C` in the above diagram. It is a non-canonical block in the first slot of an epoch that conflicts with the finalized checkpoint. Due to our lazy pruning of proto array, `0x4a45` was still present in proto-array. Our missed edge-case in [`ForkChoice::is_descendant_of_finalized`](38514c07f2/consensus/fork_choice/src/fork_choice.rs (L1375-L1379)) would have indicated to us that the block is a descendant of the finalized block. Therefore, we would have accepted the attestation thinking that it attests to a descendant of the finalized *checkpoint*.

Since we didn't have the shuffling for this erroneously processed block, we attempted to read its state from the database. This failed because we prune states from the database by keeping track of the tips of the chain and iterating back until we find a finalized block. This would have deleted `C` from the database, hence the `MissingBeaconState` error.
This commit is contained in:
Paul Hauner
2023-02-09 23:51:18 +00:00
parent 2b735a9e8b
commit 5276dd0cb0
6 changed files with 276 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
beacon_node/beacon_chain/src/beacon_chain.rs
View File

@@ -8,7 +8,7 @@ use crate::beacon_proposer_cache::compute_proposer_duties_from_head;
use crate::beacon_proposer_cache::BeaconProposerCache;
use crate::block_times_cache::BlockTimesCache;
use crate::block_verification::{
check_block_is_finalized_descendant, check_block_relevancy, get_block_root,
check_block_is_finalized_checkpoint_or_descendant, check_block_relevancy, get_block_root,
signature_verify_chain_segment, BlockError, ExecutionPendingBlock, GossipVerifiedBlock,
IntoExecutionPendingBlock, PayloadVerificationOutcome, POS_PANDA_BANNER,
};
@@ -2736,7 +2736,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
let mut fork_choice = self.canonical_head.fork_choice_write_lock();
// Do not import a block that doesn't descend from the finalized root.
check_block_is_finalized_descendant(self, &fork_choice, &signed_block)?;
check_block_is_finalized_checkpoint_or_descendant(self, &fork_choice, &signed_block)?;
// Register the new block with the fork choice service.
{

6
beacon_node/beacon_chain/src/block_verification.rs
View File

@@ -744,7 +744,7 @@ impl<T: BeaconChainTypes> GossipVerifiedBlock<T> {
// Do not process a block that doesn't descend from the finalized root.
//
// We check this *before* we load the parent so that we can return a more detailed error.
check_block_is_finalized_descendant(
check_block_is_finalized_checkpoint_or_descendant(
chain,
&chain.canonical_head.fork_choice_write_lock(),
&block,
@@ -1564,12 +1564,12 @@ fn check_block_against_finalized_slot<T: BeaconChainTypes>(
/// ## Warning
///
/// Taking a lock on the `chain.canonical_head.fork_choice` might cause a deadlock here.
pub fn check_block_is_finalized_descendant<T: BeaconChainTypes>(
pub fn check_block_is_finalized_checkpoint_or_descendant<T: BeaconChainTypes>(
chain: &BeaconChain<T>,
fork_choice: &BeaconForkChoice<T>,
block: &Arc<SignedBeaconBlock<T::EthSpec>>,
) -> Result<(), BlockError<T::EthSpec>> {
if fork_choice.is_descendant_of_finalized(block.parent_root()) {
if fork_choice.is_finalized_checkpoint_or_descendant(block.parent_root()) {
Ok(())
} else {
// If fork choice does *not* consider the parent to be a descendant of the finalized block,