gnosis/lighthouse
1
0
Fork 0
mirror of https://github.com/sigp/lighthouse.git synced 2026-03-14 10:22:38 +00:00
Code Issues Packages Projects Releases Wiki Activity

Fix bad assumption when checking finalized descendant (#1629)

Browse Source 
## Issue Addressed

- Resolves #1616

## Proposed Changes

Fixes a bug where we are unable to read the finalized block from fork choice.

## Detail

I had made an assumption that the finalized block always has a parent root of `None`:

e5fc6bab48/consensus/fork_choice/src/fork_choice.rs (L749-L752)

This was a faulty assumption, we don't set parent *roots* to `None`. Instead we *sometimes* set parent *indices* to `None`, depending if this pruning condition is satisfied: 

e5fc6bab48/consensus/proto_array/src/proto_array.rs (L229-L232) 

The bug manifested itself like this:

1. We attempt to get the finalized block from fork choice
1. We try to check that the block is descendant of the finalized block (note: they're the same block).
1. We expect the parent root to be `None`, but it's actually the parent root of the finalized root.
1. We therefore end up checking if the parent of the finalized root is a descendant of itself. (note: it's an *ancestor* not a *descendant*).
1. We therefore declare that the finalized block is not a descendant of (or eq to) the finalized block. Bad.

## Additional Info

In reflection, I made a poor assumption in the quest to obtain a probably negligible performance gain. The performance gain wasn't worth the risk and we got burnt.
This commit is contained in:
Paul Hauner
2020-09-18 05:14:31 +00:00
parent 49ab414594
commit a17f74896a
3 changed files with 42 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
beacon_node/beacon_chain/src/block_verification.rs
View File

@@ -980,14 +980,17 @@ fn load_parent<T: BeaconChainTypes>(
// exist in fork choice but not in the database yet. In such a case we simply
// indicate that we don't yet know the parent.
let root = block.parent_root();
let parent_block = if let Some(block) = chain
let parent_block = chain
.get_block(&block.parent_root())
.map_err(BlockError::BeaconChainError)?
{
block
} else {
return Err(BlockError::ParentUnknown(Box::new(block)));
};
.ok_or_else(|| {
// Return a `MissingBeaconBlock` error instead of a `ParentUnknown` error since
// we've already checked fork choice for this block.
//
// It's an internal error if the block exists in fork choice but not in the
// database.
BlockError::from(BeaconChainError::MissingBeaconBlock(block.parent_root()))
})?;
// Load the parent blocks state from the database, returning an error if it is not found.
// It is an error because if we know the parent block we should also know the parent state.