Reject blocks with committed evidence (#37)

* evidence: NewEvidencePool takes evidenceDB

* evidence: failing TestStoreCommitDuplicate

tendermint/security#35

* GetEvidence -> GetEvidenceInfo

* fix TestStoreCommitDuplicate

* comment in VerifyEvidence

* add check if evidence was already seen
 - modify EventPool interface (EventStore is not known in ApplyBlock):
   - add IsCommitted method to iface
 - add test

* update changelog

* fix TestStoreMark:
 - priority in evidence info gets reset to zero after evidence gets committed

* review comments: simplify EvidencePool.IsCommitted
 - delete obsolete EvidenceStore.IsCommitted

* add simple test for IsCommitted

* update changelog: this is actually breaking (PR number still missing)

* fix TestStoreMark:
 - priority in evidence info gets reset to zero after evidence gets
 committed

* review suggestion: simplify return

state/execution.go

@@ -101,7 +101,7 @@ func (blockExec *BlockExecutor) CreateProposalBlock(
 // Validation does not mutate state, but does require historical information from the stateDB,
 // ie. to verify evidence from a validator at an old height.
 func (blockExec *BlockExecutor) ValidateBlock(state State, block *types.Block) error {
-	return validateBlock(blockExec.db, state, block)
+	return validateBlock(blockExec.evpool, blockExec.db, state, block)
 }
 
 // ApplyBlock validates the block against the state, executes it against the app,

state/services.go

@@ -85,6 +85,8 @@ type EvidencePool interface {
 	PendingEvidence(int64) []types.Evidence
 	AddEvidence(types.Evidence) error
 	Update(*types.Block, State)
+	// IsCommitted indicates if this evidence was already marked committed in another block.
+	IsCommitted(types.Evidence) bool
 }
 
 // MockMempool is an empty implementation of a Mempool, useful for testing.
@@ -93,3 +95,4 @@ type MockEvidencePool struct{}
 func (m MockEvidencePool) PendingEvidence(int64) []types.Evidence { return nil }
 func (m MockEvidencePool) AddEvidence(types.Evidence) error       { return nil }
 func (m MockEvidencePool) Update(*types.Block, State)             {}
+func (m MockEvidencePool) IsCommitted(types.Evidence) bool        { return false }

state/validation.go

@@ -13,7 +13,7 @@ import (
 //-----------------------------------------------------
 // Validate block
 
-func validateBlock(stateDB dbm.DB, state State, block *types.Block) error {
+func validateBlock(evidencePool EvidencePool, stateDB dbm.DB, state State, block *types.Block) error {
 	// Validate internal consistency.
 	if err := block.ValidateBasic(); err != nil {
 		return err
@@ -145,6 +145,9 @@ func validateBlock(stateDB dbm.DB, state State, block *types.Block) error {
 		if err := VerifyEvidence(stateDB, state, ev); err != nil {
 			return types.NewErrEvidenceInvalid(ev, err)
 		}
+		if evidencePool != nil && evidencePool.IsCommitted(ev) {
+			return types.NewErrEvidenceInvalid(ev, errors.New("evidence was already committed"))
+		}
 	}
 
 	// NOTE: We can't actually verify it's the right proposer because we dont

state/validation_test.go

@@ -121,6 +121,31 @@ func TestValidateBlockEvidence(t *testing.T) {
 	require.True(t, ok)
 }
 
+// always returns true if asked if any evidence was already committed.
+type mockEvPoolAlwaysCommitted struct{}
+
+func (m mockEvPoolAlwaysCommitted) PendingEvidence(int64) []types.Evidence { return nil }
+func (m mockEvPoolAlwaysCommitted) AddEvidence(types.Evidence) error       { return nil }
+func (m mockEvPoolAlwaysCommitted) Update(*types.Block, State)             {}
+func (m mockEvPoolAlwaysCommitted) IsCommitted(types.Evidence) bool        { return true }
+
+func TestValidateFailBlockOnCommittedEvidence(t *testing.T) {
+	var height int64 = 1
+	state, stateDB := state(1, int(height))
+
+	blockExec := NewBlockExecutor(stateDB, log.TestingLogger(), nil, nil, mockEvPoolAlwaysCommitted{})
+	// A block with a couple pieces of evidence passes.
+	block := makeBlock(state, height)
+	addr, _ := state.Validators.GetByIndex(0)
+	alreadyCommittedEvidence := types.NewMockGoodEvidence(height, 0, addr)
+	block.Evidence.Evidence = []types.Evidence{alreadyCommittedEvidence}
+	block.EvidenceHash = block.Evidence.Hash()
+	err := blockExec.ValidateBlock(state, block)
+
+	require.Error(t, err)
+	require.IsType(t, err, &types.ErrEvidenceInvalid{})
+}
+
 /*
 	TODO(#2589):
 	- test unmarshalling BlockParts that are too big into a Block that