Check filter header checkpoints against hardcoded list

blockmanager.go

@@ -21,6 +21,7 @@ import (
 	"github.com/btcsuite/btcutil/gcs"
 	"github.com/btcsuite/btcutil/gcs/builder"
 	"github.com/lightninglabs/neutrino/blockntfns"
+	"github.com/lightninglabs/neutrino/chainsync"
 	"github.com/lightninglabs/neutrino/headerfs"
 	"github.com/lightninglabs/neutrino/headerlist"
 )
@@ -1236,6 +1237,37 @@ func (b *blockManager) resolveConflict(
 	store *headerfs.FilterHeaderStore, fType wire.FilterType) (
 	[]*chainhash.Hash, error) {
 
+	// First check the served checkpoints against the hardcoded ones.
+	for peer, cp := range checkpoints {
+		for i, header := range cp {
+			height := uint32((i + 1) * wire.CFCheckptInterval)
+			err := chainsync.ControlCFHeader(
+				b.server.chainParams, fType, height, header,
+			)
+			if err == chainsync.ErrCheckpointMismatch {
+				log.Warnf("Banning peer=%v since served "+
+					"checkpoints didn't match our "+
+					"checkpoint at height %d", peer, height)
+
+				sp := b.server.PeerByAddr(peer)
+				if sp != nil {
+					b.server.BanPeer(sp)
+					sp.Disconnect()
+				}
+				delete(checkpoints, peer)
+				break
+			} else if err != nil {
+				return nil, err
+			}
+		}
+	}
+
+	if len(checkpoints) == 0 {
+		return nil, fmt.Errorf("no peer is serving good cfheader " +
+			"checkpoints")
+	}
+
+	// Check if the remaining checkpoints are sane.
 	heightDiff, err := checkCFCheckptSanity(checkpoints, store)
 	if err != nil {
 		return nil, err

chainsync/filtercontrol.go

@@ -0,0 +1,56 @@
+package chainsync
+
+import (
+	"fmt"
+
+	"github.com/btcsuite/btcd/chaincfg"
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/btcsuite/btcd/wire"
+)
+
+// ErrCheckpointMismatch is returned if given filter headers don't pass our
+// control check.
+var ErrCheckpointMismatch = fmt.Errorf("checkpoint doesn't match")
+
+// filterHeaderCheckpoints holds a mapping from heights to filter headers for
+// various heights. We use them to check whether peers are serving us the
+// expected filter headers.
+var filterHeaderCheckpoints = map[wire.BitcoinNet]map[uint32]*chainhash.Hash{
+	// Mainnet filter header checkpoints.
+	chaincfg.MainNetParams.Net: map[uint32]*chainhash.Hash{},
+
+	// Testnet filter header checkpoints.
+	chaincfg.TestNet3Params.Net: map[uint32]*chainhash.Hash{},
+}
+
+// ControlCFHeader controls the given filter header against our list of
+// checkpoints. It returns ErrCheckpointMismatch if we have a checkpoint at the
+// given height, and it doesn't match.
+func ControlCFHeader(params chaincfg.Params, fType wire.FilterType,
+	height uint32, filterHeader *chainhash.Hash) error {
+
+	if fType != wire.GCSFilterRegular {
+		return fmt.Errorf("unsupported filter type %v", fType)
+	}
+
+	control, ok := filterHeaderCheckpoints[params.Net]
+	if !ok {
+		return nil
+	}
+
+	hash, ok := control[height]
+	if !ok {
+		return nil
+	}
+
+	if *filterHeader != *hash {
+		return ErrCheckpointMismatch
+	}
+
+	return nil
+}
+
+func hashFromStr(hexStr string) *chainhash.Hash {
+	hash, _ := chainhash.NewHashFromStr(hexStr)
+	return hash
+}

chainsync/filtercontrol_test.go

@@ -0,0 +1,52 @@
+package chainsync
+
+import (
+	"testing"
+
+	"github.com/btcsuite/btcd/chaincfg"
+	"github.com/btcsuite/btcd/chaincfg/chainhash"
+	"github.com/btcsuite/btcd/wire"
+)
+
+func TestControlCFHeader(t *testing.T) {
+	t.Parallel()
+
+	// We'll modify our backing list of checkpoints for this test.
+	height := uint32(999)
+	header := hashFromStr(
+		"4a242283a406a7c089f671bb8df7671e5d5e9ba577cea1047d30a7f4919df193",
+	)
+	filterHeaderCheckpoints = map[wire.BitcoinNet]map[uint32]*chainhash.Hash{
+		chaincfg.MainNetParams.Net: map[uint32]*chainhash.Hash{
+			height: header,
+		},
+	}
+
+	// Expect the control at height to succeed.
+	err := ControlCFHeader(
+		chaincfg.MainNetParams, wire.GCSFilterRegular, height, header,
+	)
+	if err != nil {
+		t.Fatalf("error checking height: %v", err)
+	}
+
+	// Pass an invalid header, this should return an error.
+	header = hashFromStr(
+		"000000000006a7c089f671bb8df7671e5d5e9ba577cea1047d30a7f4919df193",
+	)
+	err = ControlCFHeader(
+		chaincfg.MainNetParams, wire.GCSFilterRegular, height, header,
+	)
+	if err != ErrCheckpointMismatch {
+		t.Fatalf("expected ErrCheckpointMismatch, got %v", err)
+	}
+
+	// Finally, control an unknown height. This should also pass since we
+	// don't have the checkpoint stored.
+	err = ControlCFHeader(
+		chaincfg.MainNetParams, wire.GCSFilterRegular, 99, header,
+	)
+	if err != nil {
+		t.Fatalf("error checking height: %v", err)
+	}
+}