further test bounce attack

configs/mainnet.yaml

@@ -23,6 +23,11 @@ MIN_GENESIS_ACTIVE_VALIDATOR_COUNT: 65536
 MIN_GENESIS_TIME: 1578009600
 
 
+# Fork Choice
+# ---------------------------------------------------------------
+# 2**3 (= 8)
+SAFE_SLOTS_TO_UPDATE_JUSTIFIED: 8
+
 
 # Deposit contract
 # ---------------------------------------------------------------

configs/minimal.yaml

@@ -21,6 +21,12 @@ MIN_GENESIS_ACTIVE_VALIDATOR_COUNT: 64
 # Jan 3, 2020
 MIN_GENESIS_TIME: 1578009600
 
+#
+#
+# Fork Choice
+# ---------------------------------------------------------------
+# 2**1 (= 1)
+SAFE_SLOTS_TO_UPDATE_JUSTIFIED: 2
 
 
 # Deposit contract

specs/core/0_fork-choice.md

@@ -150,7 +150,7 @@ def get_head(store: Store) -> Hash:
 def should_update_justified_checkpoint(store: Store, justified_checkpoint: Checkpoint) -> bool:
     current_epoch = compute_epoch_at_slot(get_current_slot(store))
 
-    if get_current_slot(store) - compute_start_slot_at_epoch(current_epoch) < SAFE_SLOTS_TO_UPDATE_JUSTIFIED:
+    if get_current_slot(store) % SLOTS_PER_EPOCH < SAFE_SLOTS_TO_UPDATE_JUSTIFIED:
         return True
 
     justified_block = store.blocks[justified_checkpoint.root]

test_libs/pyspec/eth2spec/test/fork_choice/test_on_block.py

@@ -132,3 +132,74 @@ def test_on_block_before_finalized(spec, state):
     block = build_empty_block_for_next_slot(spec, state)
     state_transition_and_sign_block(spec, state, block)
     run_on_block(spec, store, block, False)
+
+
+@with_all_phases
+@spec_state_test
+def test_on_block_update_justified_checkpoint_within_safe_slots(spec, state):
+    # Initialization
+    store = spec.get_genesis_store(state)
+    time = 100
+    spec.on_tick(store, time)
+
+    next_epoch(spec, state)
+    spec.on_tick(store, store.time + state.slot * spec.SECONDS_PER_SLOT)
+    state, store, last_block = apply_next_epoch_with_attestations(spec, state, store)
+    next_epoch(spec, state)
+    spec.on_tick(store, store.time + state.slot * spec.SECONDS_PER_SLOT)
+    last_block_root = signing_root(last_block)
+
+    # Mock the justified checkpoint
+    just_state = store.block_states[last_block_root]
+    new_justified = spec.Checkpoint(
+        epoch=just_state.current_justified_checkpoint.epoch + 1,
+        root=b'\x77' * 32,
+    )
+    just_state.current_justified_checkpoint = new_justified
+
+    block = build_empty_block_for_next_slot(spec, just_state)
+    state_transition_and_sign_block(spec, deepcopy(just_state), block)
+    assert spec.get_current_slot(store) % spec.SLOTS_PER_EPOCH < spec.SAFE_SLOTS_TO_UPDATE_JUSTIFIED
+    run_on_block(spec, store, block)
+
+    assert store.justified_checkpoint == new_justified
+
+
+@with_all_phases
+@spec_state_test
+def test_on_block_outside_safe_slots_and_old_block(spec, state):
+    # Initialization
+    store = spec.get_genesis_store(state)
+    time = 100
+    spec.on_tick(store, time)
+
+    next_epoch(spec, state)
+    spec.on_tick(store, store.time + state.slot * spec.SECONDS_PER_SLOT)
+    state, store, last_block = apply_next_epoch_with_attestations(spec, state, store)
+    next_epoch(spec, state)
+    spec.on_tick(store, store.time + state.slot * spec.SECONDS_PER_SLOT)
+    last_block_root = signing_root(last_block)
+
+    # Mock justified block in store
+    just_block = build_empty_block_for_next_slot(spec, state)
+    # Slot is same as justified checkpoint so does not trigger an override in the store
+    just_block.slot = spec.compute_start_slot_at_epoch(store.justified_checkpoint.epoch)
+    store.blocks[just_block.hash_tree_root()] = just_block
+
+    # Mock the justified checkpoint
+    just_state = store.block_states[last_block_root]
+    new_justified = spec.Checkpoint(
+        epoch=just_state.current_justified_checkpoint.epoch + 1,
+        root=just_block.hash_tree_root(),
+    )
+    just_state.current_justified_checkpoint = new_justified
+
+    block = build_empty_block_for_next_slot(spec, just_state)
+    state_transition_and_sign_block(spec, deepcopy(just_state), block)
+
+    spec.on_tick(store, store.time + spec.SAFE_SLOTS_TO_UPDATE_JUSTIFIED * spec.SECONDS_PER_SLOT)
+    assert spec.get_current_slot(store) % spec.SLOTS_PER_EPOCH >= spec.SAFE_SLOTS_TO_UPDATE_JUSTIFIED
+    run_on_block(spec, store, block)
+
+    assert store.justified_checkpoint != new_justified
+    assert store.queued_justified_checkpoints[0] == new_justified

test_libs/pyspec/eth2spec/test/fork_choice/test_on_tick.py

@@ -32,7 +32,6 @@ def test_update_justified_single(spec, state):
         epoch=store.justified_checkpoint.epoch + 1,
         root=b'\x55' * 32,
     )
-
     store.queued_justified_checkpoints.append(new_justified)
 
     run_on_tick(spec, store, store.time + seconds_per_epoch, new_justified)
@@ -57,16 +56,71 @@ def test_update_justified_multiple(spec, state):
 
 @with_all_phases
 @spec_state_test
-def test_no_update_(spec, state):
+def test_no_update_same_slot_at_epoch_boundary(spec, state):
     store = spec.get_genesis_store(state)
     seconds_per_epoch = spec.SECONDS_PER_SLOT * spec.SLOTS_PER_EPOCH
 
     new_justified = spec.Checkpoint(
         epoch=store.justified_checkpoint.epoch + 1,
         root=b'\x55' * 32,
     )
+    store.queued_justified_checkpoints.append(new_justified)
+
+    # set store time to already be at epoch boundary
+    store.time = seconds_per_epoch
+
+    run_on_tick(spec, store, store.time + 1)
+
 
+@with_all_phases
+@spec_state_test
+def test_no_update_not_epoch_boundary(spec, state):
+    store = spec.get_genesis_store(state)
+
+    new_justified = spec.Checkpoint(
+        epoch=store.justified_checkpoint.epoch + 1,
+        root=b'\x55' * 32,
+    )
     store.queued_justified_checkpoints.append(new_justified)
 
-    run_on_tick(spec, store, store.time + seconds_per_epoch, new_justified)
+    run_on_tick(spec, store, store.time + spec.SECONDS_PER_SLOT)
+
+
+@with_all_phases
+@spec_state_test
+def test_no_update_new_justified_equal_epoch(spec, state):
+    store = spec.get_genesis_store(state)
+    seconds_per_epoch = spec.SECONDS_PER_SLOT * spec.SLOTS_PER_EPOCH
+
+    new_justified = spec.Checkpoint(
+        epoch=store.justified_checkpoint.epoch + 1,
+        root=b'\x55' * 32,
+    )
+    store.queued_justified_checkpoints.append(new_justified)
+
+    store.justified_checkpoint = spec.Checkpoint(
+        epoch=new_justified.epoch,
+        root=b'\44' * 32,
+    )
+
+    run_on_tick(spec, store, store.time + seconds_per_epoch)
+
+
+@with_all_phases
+@spec_state_test
+def test_no_update_new_justified_later_epoch(spec, state):
+    store = spec.get_genesis_store(state)
+    seconds_per_epoch = spec.SECONDS_PER_SLOT * spec.SLOTS_PER_EPOCH
+
+    new_justified = spec.Checkpoint(
+        epoch=store.justified_checkpoint.epoch + 1,
+        root=b'\x55' * 32,
+    )
+    store.queued_justified_checkpoints.append(new_justified)
+
+    store.justified_checkpoint = spec.Checkpoint(
+        epoch=new_justified.epoch + 1,
+        root=b'\44' * 32,
+    )
 
+    run_on_tick(spec, store, store.time + seconds_per_epoch)