consensus/beacon: check that only the latest pow block is valid ttd block (#25187)

* consensus/beacon: check that only the latest pow block is valid ttd block

* consensus/beacon: move verification to async function

* consensus/beacon: fix verifyTerminalPoWBlock, add test cases

* consensus/beacon: cosmetic changes

* consensus/beacon: apply karalabe's fixes

consensus/beacon/consensus.go

@@ -112,10 +112,12 @@ func (beacon *Beacon) VerifyHeaders(chain consensus.ChainHeaderReader, headers [
 			break
 		}
 	}
+
 	// All the headers have passed the transition point, use new rules.
 	if len(preHeaders) == 0 {
 		return beacon.verifyHeaders(chain, headers, nil)
 	}
+
 	// The transition point exists in the middle, separate the headers
 	// into two batches and apply different verification rules for them.
 	var (
@@ -130,6 +132,14 @@ func (beacon *Beacon) VerifyHeaders(chain consensus.ChainHeaderReader, headers [
 			oldDone, oldResult = beacon.ethone.VerifyHeaders(chain, preHeaders, preSeals)
 			newDone, newResult = beacon.verifyHeaders(chain, postHeaders, preHeaders[len(preHeaders)-1])
 		)
+		// Verify that pre-merge headers don't overflow the TTD
+		if index, err := verifyTerminalPoWBlock(chain, preHeaders); err != nil {
+			// Mark all subsequent pow headers with the error.
+			for i := index; i < len(preHeaders); i++ {
+				errors[i], done[i] = err, true
+			}
+		}
+		// Collect the results
 		for {
 			for ; done[out]; out++ {
 				results <- errors[out]
@@ -139,7 +149,9 @@ func (beacon *Beacon) VerifyHeaders(chain consensus.ChainHeaderReader, headers [
 			}
 			select {
 			case err := <-oldResult:
+				if !done[old] { // skip TTD-verified failures
 					errors[old], done[old] = err, true
+				}
 				old++
 			case err := <-newResult:
 				errors[new], done[new] = err, true
@@ -154,6 +166,32 @@ func (beacon *Beacon) VerifyHeaders(chain consensus.ChainHeaderReader, headers [
 	return abort, results
 }
 
+// verifyTerminalPoWBlock verifies that the preHeaders confirm to the specification
+// wrt. their total difficulty.
+// It expects:
+// - preHeaders to be at least 1 element
+// - the parent of the header element to be stored in the chain correctly
+// - the preHeaders to have a set difficulty
+// - the last element to be the terminal block
+func verifyTerminalPoWBlock(chain consensus.ChainHeaderReader, preHeaders []*types.Header) (int, error) {
+	td := chain.GetTd(preHeaders[0].ParentHash, preHeaders[0].Number.Uint64()-1)
+	if td == nil {
+		return 0, consensus.ErrUnknownAncestor
+	}
+	// Check that all blocks before the last one are below the TTD
+	for i, head := range preHeaders {
+		if td.Cmp(chain.Config().TerminalTotalDifficulty) >= 0 {
+			return i, consensus.ErrInvalidTerminalBlock
+		}
+		td.Add(td, head.Difficulty)
+	}
+	// Check that the last block is the terminal block
+	if td.Cmp(chain.Config().TerminalTotalDifficulty) < 0 {
+		return len(preHeaders) - 1, consensus.ErrInvalidTerminalBlock
+	}
+	return 0, nil
+}
+
 // VerifyUncles verifies that the given block's uncles conform to the consensus
 // rules of the Ethereum consensus engine.
 func (beacon *Beacon) VerifyUncles(chain consensus.ChainReader, block *types.Block) error {

consensus/beacon/consensus_test.go

@@ -0,0 +1,137 @@
+package beacon
+
+import (
+	"fmt"
+	"math/big"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/consensus"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/params"
+)
+
+type mockChain struct {
+	config *params.ChainConfig
+	tds    map[uint64]*big.Int
+}
+
+func newMockChain() *mockChain {
+	return &mockChain{
+		config: new(params.ChainConfig),
+		tds:    make(map[uint64]*big.Int),
+	}
+}
+
+func (m *mockChain) Config() *params.ChainConfig {
+	return m.config
+}
+
+func (m *mockChain) CurrentHeader() *types.Header { panic("not implemented") }
+
+func (m *mockChain) GetHeader(hash common.Hash, number uint64) *types.Header {
+	panic("not implemented")
+}
+
+func (m *mockChain) GetHeaderByNumber(number uint64) *types.Header { panic("not implemented") }
+
+func (m *mockChain) GetHeaderByHash(hash common.Hash) *types.Header { panic("not implemented") }
+
+func (m *mockChain) GetTd(hash common.Hash, number uint64) *big.Int {
+	num, ok := m.tds[number]
+	if ok {
+		return new(big.Int).Set(num)
+	}
+	return nil
+}
+
+func TestVerifyTerminalBlock(t *testing.T) {
+	chain := newMockChain()
+	chain.tds[0] = big.NewInt(10)
+	chain.config.TerminalTotalDifficulty = big.NewInt(50)
+
+	tests := []struct {
+		preHeaders []*types.Header
+		ttd        *big.Int
+		err        error
+		index      int
+	}{
+		// valid ttd
+		{
+			preHeaders: []*types.Header{
+				{Number: big.NewInt(1), Difficulty: big.NewInt(10)},
+				{Number: big.NewInt(2), Difficulty: big.NewInt(10)},
+				{Number: big.NewInt(3), Difficulty: big.NewInt(10)},
+				{Number: big.NewInt(4), Difficulty: big.NewInt(10)},
+			},
+			ttd: big.NewInt(50),
+		},
+		// last block doesn't reach ttd
+		{
+			preHeaders: []*types.Header{
+				{Number: big.NewInt(1), Difficulty: big.NewInt(10)},
+				{Number: big.NewInt(2), Difficulty: big.NewInt(10)},
+				{Number: big.NewInt(3), Difficulty: big.NewInt(10)},
+				{Number: big.NewInt(4), Difficulty: big.NewInt(9)},
+			},
+			ttd:   big.NewInt(50),
+			err:   consensus.ErrInvalidTerminalBlock,
+			index: 3,
+		},
+		// two blocks reach ttd
+		{
+			preHeaders: []*types.Header{
+				{Number: big.NewInt(1), Difficulty: big.NewInt(10)},
+				{Number: big.NewInt(2), Difficulty: big.NewInt(10)},
+				{Number: big.NewInt(3), Difficulty: big.NewInt(20)},
+				{Number: big.NewInt(4), Difficulty: big.NewInt(10)},
+			},
+			ttd:   big.NewInt(50),
+			err:   consensus.ErrInvalidTerminalBlock,
+			index: 3,
+		},
+		// three blocks reach ttd
+		{
+			preHeaders: []*types.Header{
+				{Number: big.NewInt(1), Difficulty: big.NewInt(10)},
+				{Number: big.NewInt(2), Difficulty: big.NewInt(10)},
+				{Number: big.NewInt(3), Difficulty: big.NewInt(20)},
+				{Number: big.NewInt(4), Difficulty: big.NewInt(10)},
+				{Number: big.NewInt(4), Difficulty: big.NewInt(10)},
+			},
+			ttd:   big.NewInt(50),
+			err:   consensus.ErrInvalidTerminalBlock,
+			index: 3,
+		},
+		// parent reached ttd
+		{
+			preHeaders: []*types.Header{
+				{Number: big.NewInt(1), Difficulty: big.NewInt(10)},
+			},
+			ttd:   big.NewInt(9),
+			err:   consensus.ErrInvalidTerminalBlock,
+			index: 0,
+		},
+		// unknown parent
+		{
+			preHeaders: []*types.Header{
+				{Number: big.NewInt(4), Difficulty: big.NewInt(10)},
+			},
+			ttd:   big.NewInt(9),
+			err:   consensus.ErrUnknownAncestor,
+			index: 0,
+		},
+	}
+
+	for i, test := range tests {
+		fmt.Printf("Test: %v\n", i)
+		chain.config.TerminalTotalDifficulty = test.ttd
+		index, err := verifyTerminalPoWBlock(chain, test.preHeaders)
+		if err != test.err {
+			t.Fatalf("Invalid error encountered, expected %v got %v", test.err, err)
+		}
+		if index != test.index {
+			t.Fatalf("Invalid index, expected %v got %v", test.index, index)
+		}
+	}
+}

consensus/errors.go

@@ -34,4 +34,8 @@ var (
 	// ErrInvalidNumber is returned if a block's number doesn't equal its parent's
 	// plus one.
 	ErrInvalidNumber = errors.New("invalid block number")
+
+	// ErrInvalidTerminalBlock is returned if a block is invalid wrt. the terminal
+	// total difficulty.
+	ErrInvalidTerminalBlock = errors.New("invalid terminal block")
 )

core/block_validator_test.go

@@ -108,6 +108,7 @@ func testHeaderVerificationForMerging(t *testing.T, isClique bool) {
 				addr: {Balance: big.NewInt(1)},
 			},
 			BaseFee:    big.NewInt(params.InitialBaseFee),
+			Difficulty: new(big.Int),
 		}
 		copy(genspec.ExtraData[32:], addr[:])
 		genesis := genspec.MustCommit(testdb)