add conditoin that block must be later than latest_block_header

specs/phase0/beacon-chain.md

@@ -1494,6 +1494,8 @@ def process_block(state: BeaconState, block: BeaconBlock) -> None:
 def process_block_header(state: BeaconState, block: BeaconBlock) -> None:
     # Verify that the slots match
     assert block.slot == state.slot
+    # Verify that the block is newer than latest block header
+    assert block.slot > state.latest_block_header.slot
     # Verify that proposer index is the correct index
     assert block.proposer_index == get_beacon_proposer_index(state)
     # Verify that the parent matches

tests/core/pyspec/eth2spec/test/phase_0/block_processing/test_process_block_header.py

@@ -9,7 +9,7 @@ def prepare_state_for_header_processing(spec, state):
     spec.process_slots(state, state.slot + 1)
 
 
-def run_block_header_processing(spec, state, block, valid=True):
+def run_block_header_processing(spec, state, block, prepare_state=True, valid=True):
     """
     Run ``process_block_header``, yielding:
       - pre-state ('pre')
@@ -17,7 +17,8 @@ def run_block_header_processing(spec, state, block, valid=True):
       - post-state ('post').
     If ``valid == False``, run expecting ``AssertionError``
     """
-    prepare_state_for_header_processing(spec, state)
+    if prepare_state:
+        prepare_state_for_header_processing(spec, state)
 
     yield 'pre', state
     yield 'block', block
@@ -68,6 +69,22 @@ def test_invalid_parent_root(spec, state):
     yield from run_block_header_processing(spec, state, block, valid=False)
 
 
+@with_all_phases
+@spec_state_test
+def test_invalid_multiple_blocks_single_slot(spec, state):
+    block = build_empty_block_for_next_slot(spec, state)
+
+    prepare_state_for_header_processing(spec, state)
+    spec.process_block_header(state, block)
+
+    assert state.latest_block_header.slot == state.slot
+
+    child_block = block.copy()
+    child_block.parent_root = block.hash_tree_root()
+
+    yield from run_block_header_processing(spec, state, child_block, prepare_state=False, valid=False)
+
+
 @with_all_phases
 @spec_state_test
 def test_proposer_slashed(spec, state):

tests/core/pyspec/eth2spec/test/sanity/test_blocks.py

@@ -79,6 +79,34 @@ def test_empty_block_transition(spec, state):
     assert spec.get_randao_mix(state, spec.get_current_epoch(state)) != spec.Bytes32()
 
 
+def process_and_sign_block_without_header_validations(spec, state, block):
+    """
+    Artificially bypass the restrictions in the state transition to transition and sign block
+
+    WARNING UNSAFE: Only use when generating valid-looking invalid blocks for test vectors
+    """
+
+    # Perform single mutation in `process_block_header`
+    state.latest_block_header = spec.BeaconBlockHeader(
+        slot=block.slot,
+        proposer_index=block.proposer_index,
+        parent_root=block.parent_root,
+        state_root=spec.Bytes32(),
+        body_root=block.body.hash_tree_root(),
+    )
+
+    # Perform rest of process_block transitions
+    spec.process_randao(state, block.body)
+    spec.process_eth1_data(state, block.body)
+    spec.process_operations(state, block.body)
+
+    # Insert post-state rot
+    block.state_root = state.hash_tree_root()
+
+    # Sign block
+    return sign_block(spec, state, block)
+
+
 @with_phases(['phase0'])
 @spec_state_test
 def test_proposal_for_genesis_slot(spec, state):
@@ -95,10 +123,8 @@ def test_proposal_for_genesis_slot(spec, state):
         lambda: spec.state_transition(failed_state, spec.SignedBeaconBlock(message=block), validate_result=False)
     )
 
-    # Artifically bypass the restriction in the state transition to transition and sign block for test vectors
-    spec.process_block(state, block)
-    block.state_root = state.hash_tree_root()
-    signed_block = sign_block(spec, state, block)
+    # Artificially bypass the restriction in the state transition to transition and sign block for test vectors
+    signed_block = process_and_sign_block_without_header_validations(spec, state, block)
 
     yield 'blocks', [signed_block]
     yield 'post', None
@@ -121,10 +147,8 @@ def test_parent_from_same_slot(spec, state):
         lambda: spec.state_transition(failed_state, spec.SignedBeaconBlock(message=child_block), validate_result=False)
     )
 
-    # Artifically bypass the restriction in the state transition to transition and sign block for test vectors
-    spec.process_block(state, child_block)
-    child_block.state_root = state.hash_tree_root()
-    signed_child_block = sign_block(spec, state, child_block)
+    # Artificially bypass the restriction in the state transition to transition and sign block for test vectors
+    signed_child_block = process_and_sign_block_without_header_validations(spec, state, child_block)
 
     yield 'blocks', [signed_parent_block, signed_child_block]
     yield 'post', None