Fix validateConsensus (#15548)

* Fix validateConsensus

Reported by NuConstruct

The stater package looks for a stateroot using the head state from the
blockchain package. However, this state is very unlikely to have the
poststateroot since that's only added after slot processing. I assume
that essentially any REST endpoint that uses this mechanism to get head
is broken if it needs to gather a state by stateroot.

This PR is a placeholder to verify this is the issue, here I just check
if the NSC already has the post-state since that will have already the
processing state cached.

* Add changelog

* add fallback

* Fix tests

beacon-chain/rpc/eth/beacon/handlers.go

@@ -1008,9 +1008,29 @@ func (s *Server) validateConsensus(ctx context.Context, b *eth.GenericSignedBeac
 	}
 
 	parentStateRoot := parentBlock.Block().StateRoot()
-	parentState, err := s.Stater.State(ctx, parentStateRoot[:])
-	if err != nil {
-		return errors.Wrap(err, "could not get parent state")
+	// Check if the state is already cached
+	parentState := transition.NextSlotState(parentBlockRoot[:], blk.Block().Slot())
+	if parentState == nil {
+		// The state is not advanced in the NSC, check first if the parent post-state is head
+		headRoot, err := s.HeadFetcher.HeadRoot(ctx)
+		if err != nil {
+			return errors.Wrap(err, "could not get head root")
+		}
+		if bytes.Equal(headRoot, parentBlockRoot[:]) {
+			parentState, err = s.HeadFetcher.HeadState(ctx)
+			if err != nil {
+				return errors.Wrap(err, "could not get head state")
+			}
+			parentState, err = transition.ProcessSlots(ctx, parentState, blk.Block().Slot())
+			if err != nil {
+				return errors.Wrap(err, "could not process slots to get parent state")
+			}
+		} else {
+			parentState, err = s.Stater.State(ctx, parentStateRoot[:])
+			if err != nil {
+				return errors.Wrap(err, "could not get parent state")
+			}
+		}
 	}
 	_, err = transition.ExecuteStateTransition(ctx, parentState, blk)
 	if err != nil {

beacon-chain/rpc/eth/beacon/handlers_test.go

@@ -3504,9 +3504,14 @@ func TestValidateConsensus(t *testing.T) {
 	require.NoError(t, err)
 	parentRoot, err := parentSbb.Block().HashTreeRoot()
 	require.NoError(t, err)
+	mockChainService := &chainMock.ChainService{
+		State: parentState,
+		Root:  parentRoot[:],
+	}
 	server := &Server{
-		Blocker: &testutil.MockBlocker{RootBlockMap: map[[32]byte]interfaces.ReadOnlySignedBeaconBlock{parentRoot: parentSbb}},
-		Stater:  &testutil.MockStater{StatesByRoot: map[[32]byte]state.BeaconState{bytesutil.ToBytes32(parentBlock.Block.StateRoot): parentState}},
+		Blocker:     &testutil.MockBlocker{RootBlockMap: map[[32]byte]interfaces.ReadOnlySignedBeaconBlock{parentRoot: parentSbb}},
+		Stater:      &testutil.MockStater{StatesByRoot: map[[32]byte]state.BeaconState{bytesutil.ToBytes32(parentBlock.Block.StateRoot): parentState}},
+		HeadFetcher: mockChainService,
 	}
 
 	require.NoError(t, server.validateConsensus(ctx, &eth.GenericSignedBeaconBlock{

changelog/potuz_fix_stater.md

@@ -0,0 +1,2 @@
+### Fixed
+- Fix the validateConsensus endpoint handler.