fix: limit total number of filters that can be created (#661)

* Problem: No way to limit total number of filters that can be created

Solution: Add a config parameter to set the total number of filters that can be created

* Add defer statement for releasing locks

* Change default value for filter cap to 200

* Changed data type of filter cap to int32

* Add changelog entry

* Update CHANGELOG.md

* Fix struct alignment

Co-authored-by: Federico Kunze Küllmer <31522760+fedekunze@users.noreply.github.com>

CHANGELOG.md

@@ -51,7 +51,8 @@ Ref: https://keepachangelog.com/en/1.0.0/
 * (deps) [tharsis#655](https://github.com/tharsis/ethermint/pull/665) Bump Cosmos SDK version to [`v0.44.2`](https://github.com/cosmos/cosmos-sdk/releases/tag/v0.44.2).
 * (evm) [tharsis#650](https://github.com/tharsis/ethermint/pull/650) Fix panic when flattening the cache context in case transaction is reverted.
 * (rpc, test) [tharsis#608](https://github.com/tharsis/ethermint/pull/608) Fix rpc test.
-* (evm) [tharsis#660](https://github.com/tharsis/ethermint/pull/660) Fix nil pointer panic in ApplyNativeMessage.
+* (rpc) [tharsis#661](https://github.com/tharsis/ethermint/pull/661) Fix OOM bug when creating too many filters using JSON-RPC.
+* (evm) [tharsis#660](https://github.com/tharsis/ethermint/pull/660) Fix `nil` pointer panic in `ApplyNativeMessage`.
 
 ## [v0.7.0] - 2021-10-07
 

rpc/ethereum/backend/backend.go

@@ -765,6 +765,11 @@ func (e *EVMBackend) RPCGasCap() uint64 {
 	return e.cfg.JSONRPC.GasCap
 }
 
+// RPCFilterCap is the limit for total number of filters that can be created
+func (e *EVMBackend) RPCFilterCap() int32 {
+	return e.cfg.JSONRPC.FilterCap
+}
+
 // RPCMinGasPrice returns the minimum gas price for a transaction obtained from
 // the node config. If set value is 0, it will default to 20.
 

rpc/ethereum/namespaces/eth/filters/api.go

@@ -36,6 +36,8 @@ type Backend interface {
 	BloomStatus() (uint64, uint64)
 
 	GetFilteredBlocks(from int64, to int64, bloomIndexes [][]BloomIV, filterAddresses bool) ([]int64, error)
+
+	RPCFilterCap() int32
 }
 
 // consider a filter inactive if it has not been polled for within deadline
@@ -107,15 +109,20 @@ func (api *PublicFilterAPI) timeoutLoop() {
 //
 // https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_newPendingTransactionFilter
 func (api *PublicFilterAPI) NewPendingTransactionFilter() rpc.ID {
+	api.filtersMu.Lock()
+	defer api.filtersMu.Unlock()
+
+	if len(api.filters) >= int(api.backend.RPCFilterCap()) {
+		return rpc.ID("error creating pending tx filter: max limit reached")
+	}
+
 	pendingTxSub, cancelSubs, err := api.events.SubscribePendingTxs()
 	if err != nil {
 		// wrap error on the ID
 		return rpc.ID(fmt.Sprintf("error creating pending tx filter: %s", err.Error()))
 	}
 
-	api.filtersMu.Lock()
 	api.filters[pendingTxSub.ID()] = &filter{typ: filters.PendingTransactionsSubscription, deadline: time.NewTimer(deadline), hashes: make([]common.Hash, 0), s: pendingTxSub}
-	api.filtersMu.Unlock()
 
 	go func(txsCh <-chan coretypes.ResultEvent, errCh <-chan error) {
 		defer cancelSubs()
@@ -219,6 +226,13 @@ func (api *PublicFilterAPI) NewPendingTransactions(ctx context.Context) (*rpc.Su
 //
 // https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_newblockfilter
 func (api *PublicFilterAPI) NewBlockFilter() rpc.ID {
+	api.filtersMu.Lock()
+	defer api.filtersMu.Unlock()
+
+	if len(api.filters) >= int(api.backend.RPCFilterCap()) {
+		return rpc.ID("error creating block filter: max limit reached")
+	}
+
 	headerSub, cancelSubs, err := api.events.SubscribeNewHeads()
 	if err != nil {
 		// wrap error on the ID
@@ -228,9 +242,7 @@ func (api *PublicFilterAPI) NewBlockFilter() rpc.ID {
 	// TODO: use events to get the base fee amount
 	baseFee := big.NewInt(params.InitialBaseFee)
 
-	api.filtersMu.Lock()
 	api.filters[headerSub.ID()] = &filter{typ: filters.BlocksSubscription, deadline: time.NewTimer(deadline), hashes: []common.Hash{}, s: headerSub}
-	api.filtersMu.Unlock()
 
 	go func(headersCh <-chan coretypes.ResultEvent, errCh <-chan error) {
 		defer cancelSubs()
@@ -404,6 +416,13 @@ func (api *PublicFilterAPI) Logs(ctx context.Context, crit filters.FilterCriteri
 //
 // https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_newfilter
 func (api *PublicFilterAPI) NewFilter(criteria filters.FilterCriteria) (rpc.ID, error) {
+	api.filtersMu.Lock()
+	defer api.filtersMu.Unlock()
+
+	if len(api.filters) >= int(api.backend.RPCFilterCap()) {
+		return rpc.ID(""), fmt.Errorf("error creating filter: max limit reached")
+	}
+
 	var (
 		filterID = rpc.ID("")
 		err      error
@@ -416,9 +435,7 @@ func (api *PublicFilterAPI) NewFilter(criteria filters.FilterCriteria) (rpc.ID,
 
 	filterID = logsSub.ID()
 
-	api.filtersMu.Lock()
 	api.filters[filterID] = &filter{typ: filters.LogsSubscription, deadline: time.NewTimer(deadline), hashes: []common.Hash{}, s: logsSub}
-	api.filtersMu.Unlock()
 
 	go func(eventCh <-chan coretypes.ResultEvent) {
 		defer cancelSubs()

server/config/config.go

@@ -28,6 +28,8 @@ const (
 	DefaultEVMTracer = "json"
 
 	DefaultGasCap uint64 = 25000000
+
+	DefaultFilterCap int32 = 200
 )
 
 var evmTracers = []string{DefaultEVMTracer, "markdown", "struct", "access_list"}
@@ -51,16 +53,18 @@ type EVMConfig struct {
 
 // JSONRPCConfig defines configuration for the EVM RPC server.
 type JSONRPCConfig struct {
+	// API defines a list of JSON-RPC namespaces that should be enabled
+	API []string `mapstructure:"api"`
 	// Address defines the HTTP server to listen on
 	Address string `mapstructure:"address"`
 	// WsAddress defines the WebSocket server to listen on
 	WsAddress string `mapstructure:"ws-address"`
-	// API defines a list of JSON-RPC namespaces that should be enabled
-	API []string `mapstructure:"api"`
-	// Enable defines if the EVM RPC server should be enabled.
-	Enable bool `mapstructure:"enable"`
 	// GasCap is the global gas cap for eth-call variants.
 	GasCap uint64 `mapstructure:"gas-cap"`
+	// FilterCap is the global cap for total number of filters that can be created.
+	FilterCap int32 `mapstructure:"filter-cap"`
+	// Enable defines if the EVM RPC server should be enabled.
+	Enable bool `mapstructure:"enable"`
 }
 
 // TLSConfig defines the certificate and matching private key for the server.
@@ -145,6 +149,7 @@ func DefaultJSONRPCConfig() *JSONRPCConfig {
 		Address:   DefaultJSONRPCAddress,
 		WsAddress: DefaultJSONRPCWsAddress,
 		GasCap:    DefaultGasCap,
+		FilterCap: DefaultFilterCap,
 	}
 }
 
@@ -154,6 +159,10 @@ func (c JSONRPCConfig) Validate() error {
 		return errors.New("cannot enable JSON-RPC without defining any API namespace")
 	}
 
+	if c.FilterCap < 0 {
+		return errors.New("JSON-RPC filter-cap cannot be negative")
+	}
+
 	// TODO: validate APIs
 	seenAPIs := make(map[string]bool)
 	for _, api := range c.API {
@@ -207,6 +216,7 @@ func GetConfig(v *viper.Viper) Config {
 			Address:   v.GetString("json-rpc.address"),
 			WsAddress: v.GetString("json-rpc.ws-address"),
 			GasCap:    v.GetUint64("json-rpc.gas-cap"),
+			FilterCap: v.GetInt32("json-rpc.filter-cap"),
 		},
 		TLS: TLSConfig{
 			CertificatePath: v.GetString("tls.certificate-path"),

server/config/toml.go

@@ -35,6 +35,9 @@ api = "{{range $index, $elmt := .JSONRPC.API}}{{if $index}},{{$elmt}}{{else}}{{$
 # GasCap sets a cap on gas that can be used in eth_call/estimateGas (0=infinite). Default: 25,000,000.
 gas-cap = {{ .JSONRPC.GasCap }}
 
+# FilterCap sets the global cap for total number of filters that can be created
+filter-cap = {{ .JSONRPC.FilterCap }}
+
 ###############################################################################
 ###                             TLS Configuration                           ###
 ###############################################################################

server/flags/flags.go

@@ -31,6 +31,7 @@ const (
 	JSONRPCAddress   = "json-rpc.address"
 	JSONWsAddress    = "json-rpc.ws-address"
 	JSONRPCGasCap    = "json-rpc.gas-cap"
+	JSONRPCFilterCap = "json-rpc.filter-cap"
 )
 
 // EVM flags

server/start.go

@@ -156,6 +156,7 @@ which accepts a path for the resulting pprof file.
 	cmd.Flags().String(srvflags.JSONRPCAddress, config.DefaultJSONRPCAddress, "the JSON-RPC server address to listen on")
 	cmd.Flags().String(srvflags.JSONWsAddress, config.DefaultJSONRPCWsAddress, "the JSON-RPC WS server address to listen on")
 	cmd.Flags().Uint64(srvflags.JSONRPCGasCap, config.DefaultGasCap, "Sets a cap on gas that can be used in eth_call/estimateGas (0=infinite)")
+	cmd.Flags().Int32(srvflags.JSONRPCFilterCap, config.DefaultFilterCap, "Sets the global cap for total number of filters that can be created")
 
 	cmd.Flags().String(srvflags.EVMTracer, config.DefaultEVMTracer, "the EVM tracer type to collect execution traces from the EVM transaction execution (json|struct|access_list|markdown)")