test for eas going backward

This PR adds the dependent root of the latest finalized checkpoint to
forkchoice since this node will be typically pruned upon finalization.

beacon-chain/db/kv/custody.go

@@ -46,6 +46,14 @@ func (s *Store) UpdateCustodyInfo(ctx context.Context, earliestAvailableSlot pri
 			return nil
 		}
 
+		// When increasing custody group count, prevent earliestAvailableSlot from going backward.
+		if storedEarliestAvailableSlot != 0 && earliestAvailableSlot < storedEarliestAvailableSlot {
+			return errors.Errorf(
+				"cannot decrease earliest available slot from %d to %d when increasing custody group count from %d to %d",
+				storedEarliestAvailableSlot, earliestAvailableSlot, storedGroupCount, custodyGroupCount,
+			)
+		}
+
 		storedGroupCount, storedEarliestAvailableSlot = custodyGroupCount, earliestAvailableSlot
 
 		// Store the earliest available slot.

beacon-chain/db/kv/custody_test.go

@@ -134,6 +134,31 @@ func TestUpdateCustodyInfo(t *testing.T) {
 		require.Equal(t, initialSlot, storedSlot)
 		require.Equal(t, initialCount, storedCount)
 	})
+
+	t.Run("prevent earliest available slot from going backward when increasing group count", func(t *testing.T) {
+		const (
+			initialSlot  = primitives.Slot(200)
+			initialCount = uint64(5)
+			newSlot      = primitives.Slot(100) // Lower than initial - should be rejected
+			newCount     = uint64(10)           // Higher than initial - would trigger update
+		)
+
+		db := setupDB(t)
+
+		// Initialize custody info with slot 200 and group count 5
+		_, _, err := db.UpdateCustodyInfo(ctx, initialSlot, initialCount)
+		require.NoError(t, err)
+
+		// Try to increase group count (5 -> 10) but with a lower earliest slot (200 -> 100)
+		// This should fail because we can't move earliest available slot backward when increasing custody
+		_, _, err = db.UpdateCustodyInfo(ctx, newSlot, newCount)
+		require.ErrorContains(t, "cannot decrease earliest available slot", err)
+
+		// Verify the database wasn't updated
+		storedSlot, storedCount := getCustodyInfoFromDB(t, db)
+		require.Equal(t, initialSlot, storedSlot)
+		require.Equal(t, initialCount, storedCount)
+	})
 }
 
 func TestUpdateEarliestAvailableSlot(t *testing.T) {

beacon-chain/forkchoice/doubly-linked-tree/forkchoice.go

@@ -642,8 +642,12 @@ func (f *ForkChoice) DependentRootForEpoch(root [32]byte, epoch primitives.Epoch
 	if !ok || node == nil {
 		return [32]byte{}, ErrNilNode
 	}
-	if slots.ToEpoch(node.slot) >= epoch && node.parent != nil {
-		node = node.parent
+	if slots.ToEpoch(node.slot) >= epoch {
+		if node.parent != nil {
+			node = node.parent
+		} else {
+			return f.store.finalizedDependentRoot, nil
+		}
 	}
 	return node.root, nil
 }

beacon-chain/forkchoice/doubly-linked-tree/store.go

@@ -212,6 +212,9 @@ func (s *Store) prune(ctx context.Context) error {
 		return nil
 	}
 
+	// Save the new finalized dependent root because it will be pruned
+	s.finalizedDependentRoot = finalizedNode.parent.root
+
 	// Prune nodeByRoot starting from root
 	if err := s.pruneFinalizedNodeByRootMap(ctx, s.treeRootNode, finalizedNode); err != nil {
 		return err

beacon-chain/forkchoice/doubly-linked-tree/store_test.go

@@ -465,6 +465,7 @@ func TestStore_TargetRootForEpoch(t *testing.T) {
 	ctx := t.Context()
 	f := setup(1, 1)
 
+	// Insert a block in slot 32
 	state, blk, err := prepareForkchoiceState(ctx, params.BeaconConfig().SlotsPerEpoch, [32]byte{'a'}, params.BeaconConfig().ZeroHash, params.BeaconConfig().ZeroHash, 1, 1)
 	require.NoError(t, err)
 	require.NoError(t, f.InsertNode(ctx, state, blk))
@@ -475,6 +476,7 @@ func TestStore_TargetRootForEpoch(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, dependent, [32]byte{})
 
+	// Insert a block in slot 33
 	state, blk1, err := prepareForkchoiceState(ctx, params.BeaconConfig().SlotsPerEpoch+1, [32]byte{'b'}, blk.Root(), params.BeaconConfig().ZeroHash, 1, 1)
 	require.NoError(t, err)
 	require.NoError(t, f.InsertNode(ctx, state, blk1))
@@ -488,7 +490,7 @@ func TestStore_TargetRootForEpoch(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, dependent, [32]byte{})
 
-	// Insert a block for the next epoch (missed slot 0)
+	// Insert a block for the next epoch (missed slot 0), slot 65
 
 	state, blk2, err := prepareForkchoiceState(ctx, 2*params.BeaconConfig().SlotsPerEpoch+1, [32]byte{'c'}, blk1.Root(), params.BeaconConfig().ZeroHash, 1, 1)
 	require.NoError(t, err)
@@ -509,6 +511,7 @@ func TestStore_TargetRootForEpoch(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, dependent, blk1.Root())
 
+	// Insert a block at slot 66
 	state, blk3, err := prepareForkchoiceState(ctx, 2*params.BeaconConfig().SlotsPerEpoch+2, [32]byte{'d'}, blk2.Root(), params.BeaconConfig().ZeroHash, 1, 1)
 	require.NoError(t, err)
 	require.NoError(t, f.InsertNode(ctx, state, blk3))
@@ -533,8 +536,11 @@ func TestStore_TargetRootForEpoch(t *testing.T) {
 	dependent, err = f.DependentRoot(1)
 	require.NoError(t, err)
 	require.Equal(t, [32]byte{}, dependent)
+	dependent, err = f.DependentRoot(2)
+	require.NoError(t, err)
+	require.Equal(t, blk1.Root(), dependent)
 
-	// Insert a block for next epoch (slot 0 present)
+	// Insert a block for the next epoch, slot 96 (descends from finalized at slot 33)
 	state, blk4, err := prepareForkchoiceState(ctx, 3*params.BeaconConfig().SlotsPerEpoch, [32]byte{'e'}, blk1.Root(), params.BeaconConfig().ZeroHash, 1, 1)
 	require.NoError(t, err)
 	require.NoError(t, f.InsertNode(ctx, state, blk4))
@@ -551,6 +557,7 @@ func TestStore_TargetRootForEpoch(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, dependent, blk1.Root())
 
+	// Insert a block at slot 97
 	state, blk5, err := prepareForkchoiceState(ctx, 3*params.BeaconConfig().SlotsPerEpoch+1, [32]byte{'f'}, blk4.Root(), params.BeaconConfig().ZeroHash, 1, 1)
 	require.NoError(t, err)
 	require.NoError(t, f.InsertNode(ctx, state, blk5))
@@ -600,12 +607,16 @@ func TestStore_TargetRootForEpoch(t *testing.T) {
 	require.NoError(t, err)
 	require.Equal(t, target, blk1.Root())
 
-	// Prune finalization
+	// Prune finalization, finalize the block at slot 96
 	s.finalizedCheckpoint.Root = blk4.Root()
 	require.NoError(t, s.prune(ctx))
 	target, err = f.TargetRootForEpoch(blk4.Root(), 3)
 	require.NoError(t, err)
 	require.Equal(t, blk4.Root(), target)
+	// Dependent root for the finalized block should be the root of the pruned block at slot 33
+	dependent, err = f.DependentRootForEpoch(blk4.Root(), 3)
+	require.NoError(t, err)
+	require.Equal(t, blk1.Root(), dependent)
 }
 
 func TestStore_DependentRootForEpoch(t *testing.T) {

beacon-chain/forkchoice/doubly-linked-tree/types.go

@@ -31,6 +31,7 @@ type Store struct {
 	proposerBoostRoot             [fieldparams.RootLength]byte           // latest block root that was boosted after being received in a timely manner.
 	previousProposerBoostRoot     [fieldparams.RootLength]byte           // previous block root that was boosted after being received in a timely manner.
 	previousProposerBoostScore    uint64                                 // previous proposer boosted root score.
+	finalizedDependentRoot        [fieldparams.RootLength]byte           // dependent root at finalized checkpoint.
 	committeeWeight               uint64                                 // tracks the total active validator balance divided by the number of slots per Epoch.
 	treeRootNode                  *Node                                  // the root node of the store tree.
 	headNode                      *Node                                  // last head Node

changelog/potuz_finalized_deproot.md

@@ -0,0 +1,3 @@
+### Added
+
+- Track the dependent root of the latest finalized checkpoint in forkchoice.

changelog/satushh-eas-bug.md

@@ -0,0 +1,2 @@
+### Fixed
+- prevent eas from going backward when increasing cgc