Limit index lookups to prevent DoS for "popular" addresses

internal/config_specification.toml

@@ -86,7 +86,7 @@ name = "ignore_mempool"
 doc = "Don't sync mempool - queries will show only confirmed transactions."
 
 [[param]]
-name = "txid_limit"
+name = "index_lookup_limit"
 type = "usize"
 doc = "Number of transactions to lookup before returning an error, to prevent 'too popular' addresses from causing the RPC server to get stuck (0 - disable the limit)"
 default = "100"

src/config.rs

@@ -130,6 +130,7 @@ pub struct Config {
     pub monitoring_addr: SocketAddr,
     pub wait_duration: Duration,
     pub index_batch_size: usize,
+    pub index_lookup_limit: Option<usize>,
     pub ignore_mempool: bool,
     pub server_banner: String,
     pub args: Vec<String>,
@@ -275,6 +276,10 @@ impl Config {
             _ => log::LevelFilter::Trace,
         };
 
+        let index_lookup_limit = match config.index_lookup_limit {
+            0 => None,
+            _ => Some(config.index_lookup_limit),
+        };
         let config = Config {
             network: config.network,
             db_path: config.db_dir,
@@ -286,6 +291,7 @@ impl Config {
             monitoring_addr,
             wait_duration: Duration::from_secs(config.wait_duration_secs),
             index_batch_size: config.index_batch_size,
+            index_lookup_limit,
             ignore_mempool: config.ignore_mempool,
             server_banner: config.server_banner,
             args: args.map(|a| a.into_string().unwrap()).collect(),

src/index.rs

@@ -85,12 +85,18 @@ impl IndexResult {
 /// Confirmed transactions' address index
 pub struct Index {
     store: DBStore,
+    lookup_limit: Option<usize>,
     chain: Chain,
     stats: Stats,
 }
 
 impl Index {
-    pub(crate) fn load(store: DBStore, mut chain: Chain, metrics: &Metrics) -> Result<Self> {
+    pub(crate) fn load(
+        store: DBStore,
+        mut chain: Chain,
+        metrics: &Metrics,
+        lookup_limit: Option<usize>,
+    ) -> Result<Self> {
         if let Some(row) = store.get_tip() {
             let tip = deserialize(&row).expect("invalid tip");
             let headers = store
@@ -103,6 +109,7 @@ impl Index {
 
         Ok(Index {
             store,
+            lookup_limit,
             chain,
             stats: Stats::new(metrics),
         })
@@ -112,6 +119,18 @@ impl Index {
         &self.chain
     }
 
+    pub(crate) fn limit_result<T>(&self, entries: impl Iterator<Item = T>) -> Result<Vec<T>> {
+        let mut entries = entries.fuse();
+        let result: Vec<T> = match self.lookup_limit {
+            Some(lookup_limit) => entries.by_ref().take(lookup_limit).collect(),
+            None => entries.by_ref().collect(),
+        };
+        if entries.next().is_some() {
+            bail!(">{} index entries, query may take too long", result.len())
+        }
+        Ok(result)
+    }
+
     pub(crate) fn filter_by_txid(&self, txid: Txid) -> impl Iterator<Item = BlockHash> + '_ {
         self.store
             .iter_txid(TxidRow::scan_prefix(txid))

src/status.rs

@@ -288,7 +288,7 @@ impl ScriptHashStatus {
         type PosTxid = (u32, Txid);
         let mut result = HashMap::<BlockHash, HashMap<PosTxid, Entry>>::new();
 
-        let funding_blockhashes = index.filter_by_funding(self.scripthash);
+        let funding_blockhashes = index.limit_result(index.filter_by_funding(self.scripthash))?;
         self.for_new_blocks(funding_blockhashes, daemon, |blockhash, block| {
             let txids: Vec<Txid> = block.txdata.iter().map(|tx| tx.txid()).collect();
             for (pos, (tx, txid)) in block.txdata.into_iter().zip(txids.iter()).enumerate() {

src/tracker.rs

@@ -31,7 +31,8 @@ impl Tracker {
         let store = DBStore::open(Path::new(&config.db_path))?;
         let chain = Chain::new(config.network);
         Ok(Self {
-            index: Index::load(store, chain, &metrics).context("failed to open index")?,
+            index: Index::load(store, chain, &metrics, config.index_lookup_limit)
+                .context("failed to open index")?,
             mempool: Mempool::new(),
             metrics,
             index_batch_size: config.index_batch_size,

tests/run.sh

@@ -40,7 +40,12 @@ echo `$BTC getblockchaininfo | jq -r '"Generated \(.blocks) regtest blocks (\(.s
 TIP=`$BTC getbestblockhash`
 
 export RUST_LOG=electrs=debug
-electrs --db-dir=data/electrs --daemon-dir=data/bitcoin --network=regtest 2> data/electrs/regtest-debug.log &
+electrs \
+  --index-lookup-limit 200 \
+  --db-dir=data/electrs \
+  --daemon-dir=data/bitcoin \
+  --network=regtest \
+  2> data/electrs/regtest-debug.log &
 ELECTRS_PID=$!
 tail_log data/electrs/regtest-debug.log | grep -m1 "serving Electrum RPC"