ensure only forward progress with eth1data voting

setup.py

@@ -150,7 +150,10 @@ def get_eth1_data(block: Eth1Block) -> Eth1Data:
     """
     A stub function return mocking Eth1Data.
     """
-    return Eth1Data(block_hash=hash_tree_root(block))
+    return Eth1Data(
+        deposit_root=block.deposit_root,
+        deposit_count=block.deposit_count,
+        block_hash=hash_tree_root(block))
 
 
 def hash(x: bytes) -> Bytes32:  # type: ignore

specs/phase0/validator.md

@@ -252,11 +252,13 @@ The `block.body.eth1_data` field is for block proposers to vote on recent Eth1 d
 
 ###### `Eth1Block`
 
-Let `Eth1Block` be an abstract object representing Eth1 blocks with the `timestamp` field available.
+Let `Eth1Block` be an abstract object representing Eth1 blocks with the `timestamp` and depost contract data available.
 
 ```python
 class Eth1Block(Container):
     timestamp: uint64
+    deposit_root: Root
+    deposit_count: uint64
     # All other eth1 block fields
 ```
 
@@ -289,8 +291,14 @@ def is_candidate_block(block: Eth1Block, period_start: uint64) -> bool:
 def get_eth1_vote(state: BeaconState, eth1_chain: Sequence[Eth1Block]) -> Eth1Data:
     period_start = voting_period_start_time(state)
     # `eth1_chain` abstractly represents all blocks in the eth1 chain sorted by ascending block height
-    votes_to_consider = [get_eth1_data(block) for block in eth1_chain if
-                         is_candidate_block(block, period_start)]
+    votes_to_consider = [
+        get_eth1_data(block) for block in eth1_chain
+        if (
+            is_candidate_block(block, period_start)
+            # Ensure cannot move back to earlier deposit contract states
+            and get_eth1_data(block).deposit_count >= state.eth1_data.deposit_count
+        )
+    ]
 
     # Valid votes already cast during this period
     valid_votes = [vote for vote in state.eth1_data_votes if vote in votes_to_consider]

tests/core/pyspec/eth2spec/test/validator/test_validator_unittest.py

@@ -190,8 +190,14 @@ def test_get_eth1_vote_consensus_vote(spec, state):
     assert votes_length >= 3  # We need to have the majority vote
     state.eth1_data_votes = ()
 
-    block_1 = spec.Eth1Block(timestamp=period_start - spec.SECONDS_PER_ETH1_BLOCK * spec.ETH1_FOLLOW_DISTANCE - 1)
-    block_2 = spec.Eth1Block(timestamp=period_start - spec.SECONDS_PER_ETH1_BLOCK * spec.ETH1_FOLLOW_DISTANCE)
+    block_1 = spec.Eth1Block(
+        timestamp=period_start - spec.SECONDS_PER_ETH1_BLOCK * spec.ETH1_FOLLOW_DISTANCE - 1,
+        deposit_count=state.eth1_data.deposit_count,
+    )
+    block_2 = spec.Eth1Block(
+        timestamp=period_start - spec.SECONDS_PER_ETH1_BLOCK * spec.ETH1_FOLLOW_DISTANCE,
+        deposit_count=state.eth1_data.deposit_count,
+    )
     eth1_chain = [block_1, block_2]
     eth1_data_votes = []
 
@@ -218,8 +224,14 @@ def test_get_eth1_vote_tie(spec, state):
     assert votes_length > 0 and votes_length % 2 == 0
 
     state.eth1_data_votes = ()
-    block_1 = spec.Eth1Block(timestamp=period_start - spec.SECONDS_PER_ETH1_BLOCK * spec.ETH1_FOLLOW_DISTANCE - 1)
-    block_2 = spec.Eth1Block(timestamp=period_start - spec.SECONDS_PER_ETH1_BLOCK * spec.ETH1_FOLLOW_DISTANCE)
+    block_1 = spec.Eth1Block(
+        timestamp=period_start - spec.SECONDS_PER_ETH1_BLOCK * spec.ETH1_FOLLOW_DISTANCE - 1,
+        deposit_count=state.eth1_data.deposit_count,
+    )
+    block_2 = spec.Eth1Block(
+        timestamp=period_start - spec.SECONDS_PER_ETH1_BLOCK * spec.ETH1_FOLLOW_DISTANCE,
+        deposit_count=state.eth1_data.deposit_count,
+    )
     eth1_chain = [block_1, block_2]
     eth1_data_votes = []
     # Half votes are for block_1, another half votes are for block_2
@@ -237,6 +249,32 @@ def test_get_eth1_vote_tie(spec, state):
     assert eth1_data.block_hash == eth1_chain[0].hash_tree_root()
 
 
+@with_all_phases
+@spec_state_test
+def test_get_eth1_vote_chain_in_past(spec, state):
+    min_new_period_epochs = get_min_new_period_epochs(spec)
+    for _ in range(min_new_period_epochs + 1):
+        next_epoch(spec, state)
+
+    period_start = spec.voting_period_start_time(state)
+    votes_length = spec.get_current_epoch(state) % spec.EPOCHS_PER_ETH1_VOTING_PERIOD
+    assert votes_length > 0 and votes_length % 2 == 0
+
+    state.eth1_data_votes = ()
+    block_1 = spec.Eth1Block(
+        timestamp=period_start - spec.SECONDS_PER_ETH1_BLOCK * spec.ETH1_FOLLOW_DISTANCE,
+        deposit_count=state.eth1_data.deposit_count - 1,  # Chain prior to current eth1data
+    )
+    eth1_chain = [block_1]
+    eth1_data_votes = []
+
+    state.eth1_data_votes = eth1_data_votes
+    eth1_data = spec.get_eth1_vote(state, eth1_chain)
+
+    # Should be default vote
+    assert eth1_data == state.eth1_data
+
+
 @with_all_phases
 @spec_state_test
 def test_compute_new_state_root(spec, state):