Consensus: fix panic in batch verifier (#152)

* fix panic in batch verifier

* docs

* review comments

* Update consensus/rules/src/batch_verifier.rs

Co-authored-by: hinto-janai <hinto.janai@protonmail.com>

---------

Co-authored-by: hinto-janai <hinto.janai@protonmail.com>

Cargo.lock

@@ -50,6 +50,16 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "async-buffer"
+version = "0.1.0"
+dependencies = [
+ "futures",
+ "pin-project",
+ "thiserror",
+ "tokio",
+]
+
 [[package]]
 name = "async-lock"
 version = "3.3.0"
@@ -525,6 +535,7 @@ dependencies = [
  "tokio-util",
  "tower",
  "tracing",
+ "tracing-subscriber",
 ]
 
 [[package]]
@@ -613,7 +624,7 @@ dependencies = [
 ]
 
 [[package]]
-name = "dandelion_tower"
+name = "dandelion-tower"
 version = "0.1.0"
 dependencies = [
  "futures",
@@ -1463,6 +1474,16 @@ dependencies = [
  "zeroize",
 ]
 
+[[package]]
+name = "nu-ansi-term"
+version = "0.46.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "77a8165726e8236064dbb45459242600304b42a5ea24ee2948e18e023bf7ba84"
+dependencies = [
+ "overload",
+ "winapi",
+]
+
 [[package]]
 name = "num-traits"
 version = "0.2.18"
@@ -1510,6 +1531,12 @@ version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "04744f49eae99ab78e0d5c0b603ab218f515ea8cfe5a456d7629ad883a3b6e7d"
 
+[[package]]
+name = "overload"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b15813163c1d831bf4a13c3610c05c0d03b39feb07f7e09fa234dac9b15aaf39"
+
 [[package]]
 name = "page_size"
 version = "0.6.0"
@@ -2136,6 +2163,15 @@ dependencies = [
  "keccak",
 ]
 
+[[package]]
+name = "sharded-slab"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f40ca3c46823713e0d4209592e8d6e826aa57e928f09752619fc696c499637f6"
+dependencies = [
+ "lazy_static",
+]
+
 [[package]]
 name = "signal-hook-registry"
 version = "1.4.2"
@@ -2476,6 +2512,18 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c06d3da6113f116aaee68e4d601191614c9053067f9ab7f6edbcb161237daa54"
 dependencies = [
  "once_cell",
+ "valuable",
+]
+
+[[package]]
+name = "tracing-log"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ee855f1f400bd0e5c02d150ae5de3840039a3f54b025156404e34c23c03f47c3"
+dependencies = [
+ "log",
+ "once_cell",
+ "tracing-core",
 ]
 
 [[package]]
@@ -2484,7 +2532,12 @@ version = "0.3.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ad0f048c97dbd9faa9b7df56362b8ebcaa52adb06b498c050d2f4e32f90a7a8b"
 dependencies = [
+ "nu-ansi-term",
+ "sharded-slab",
+ "smallvec",
+ "thread_local",
  "tracing-core",
+ "tracing-log",
 ]
 
 [[package]]
@@ -2543,6 +2596,12 @@ dependencies = [
  "percent-encoding",
 ]
 
+[[package]]
+name = "valuable"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "830b7e5d4d90034032940e4ace0d9a9a057e7a45cd94e6c007832e39edb82f6d"
+
 [[package]]
 name = "version_check"
 version = "0.9.4"

consensus/rules/src/batch_verifier.rs

@@ -0,0 +1,29 @@
+use multiexp::BatchVerifier as InternalBatchVerifier;
+
+/// This trait represents a batch verifier.
+///
+/// A batch verifier is used to speed up verification by verifying multiple transactions together.
+///
+/// Not all proofs can be batched and at its core it's intended to verify a series of statements are
+/// each equivalent to zero.
+pub trait BatchVerifier {
+    /// Queue a statement for batch verification.
+    ///
+    /// # Panics
+    /// This function may panic if `stmt` contains calls to `rayon`'s parallel iterators, e.g. `par_iter()`.
+    // TODO: remove the panics by adding a generic API upstream.
+    fn queue_statement<R>(
+        &mut self,
+        stmt: impl FnOnce(&mut InternalBatchVerifier<(), dalek_ff_group::EdwardsPoint>) -> R,
+    ) -> R;
+}
+
+// impl this for a single threaded batch verifier.
+impl BatchVerifier for &'_ mut InternalBatchVerifier<(), dalek_ff_group::EdwardsPoint> {
+    fn queue_statement<R>(
+        &mut self,
+        stmt: impl FnOnce(&mut InternalBatchVerifier<(), dalek_ff_group::EdwardsPoint>) -> R,
+    ) -> R {
+        stmt(self)
+    }
+}

consensus/rules/src/lib.rs

@@ -1,5 +1,6 @@
 use std::time::{SystemTime, UNIX_EPOCH};
 
+pub mod batch_verifier;
 pub mod blocks;
 mod decomposed_amount;
 pub mod genesis;

consensus/rules/src/transactions.rs

@@ -3,10 +3,10 @@ use std::cmp::Ordering;
 use monero_serai::ringct::RctType;
 
 use monero_serai::transaction::{Input, Output, Timelock, Transaction};
-use multiexp::BatchVerifier;
 
 use crate::{
-    blocks::penalty_free_zone, check_point_canonically_encoded, is_decomposed_amount, HardFork,
+    batch_verifier::BatchVerifier, blocks::penalty_free_zone, check_point_canonically_encoded,
+    is_decomposed_amount, HardFork,
 };
 
 mod contextual_data;
@@ -606,7 +606,7 @@ pub fn check_transaction_semantic(
     tx_weight: usize,
     tx_hash: &[u8; 32],
     hf: &HardFork,
-    verifier: &mut BatchVerifier<(), dalek_ff_group::EdwardsPoint>,
+    verifier: impl BatchVerifier,
 ) -> Result<u64, TransactionError> {
     // <https://monero-book.cuprate.org/consensus_rules/transactions.html#transaction-size>
     if tx_blob_size > MAX_TX_BLOB_SIZE

consensus/rules/src/transactions/ring_ct.rs

@@ -9,12 +9,11 @@ use monero_serai::{
     transaction::{Input, Transaction},
     H,
 };
-use multiexp::BatchVerifier;
 use rand::thread_rng;
 #[cfg(feature = "rayon")]
 use rayon::prelude::*;
 
-use crate::{transactions::Rings, try_par_iter, HardFork};
+use crate::{batch_verifier::BatchVerifier, transactions::Rings, try_par_iter, HardFork};
 
 /// This constant contains the IDs of 2 transactions that should be allowed after the fork the ringCT
 /// type they used should be banned.
@@ -91,7 +90,7 @@ fn simple_type_balances(rct_sig: &RctSignatures) -> Result<(), RingCTError> {
 /// <https://monero-book.cuprate.org/consensus_rules/ring_ct/bulletproofs+.html>
 fn check_output_range_proofs(
     rct_sig: &RctSignatures,
-    verifier: &mut BatchVerifier<(), dalek_ff_group::EdwardsPoint>,
+    mut verifier: impl BatchVerifier,
 ) -> Result<(), RingCTError> {
     let commitments = &rct_sig.base.commitments;
 
@@ -109,7 +108,9 @@ fn check_output_range_proofs(
             }),
         RctPrunable::MlsagBulletproofs { bulletproofs, .. }
         | RctPrunable::Clsag { bulletproofs, .. } => {
-            if bulletproofs.batch_verify(&mut thread_rng(), verifier, (), commitments) {
+            if verifier.queue_statement(|verifier| {
+                bulletproofs.batch_verify(&mut thread_rng(), verifier, (), commitments)
+            }) {
                 Ok(())
             } else {
                 Err(RingCTError::BulletproofsRangeInvalid)
@@ -121,7 +122,7 @@ fn check_output_range_proofs(
 pub(crate) fn ring_ct_semantic_checks(
     tx: &Transaction,
     tx_hash: &[u8; 32],
-    verifier: &mut BatchVerifier<(), dalek_ff_group::EdwardsPoint>,
+    verifier: impl BatchVerifier,
     hf: &HardFork,
 ) -> Result<(), RingCTError> {
     let rct_type = tx.rct_signatures.rct_type();

consensus/src/batch_verifier.rs

@@ -4,8 +4,6 @@ use multiexp::BatchVerifier as InternalBatchVerifier;
 use rayon::prelude::*;
 use thread_local::ThreadLocal;
 
-use crate::ConsensusError;
-
 /// A multithreaded batch verifier.
 pub struct MultiThreadedBatchVerifier {
     internal: ThreadLocal<RefCell<InternalBatchVerifier<(), dalek_ff_group::EdwardsPoint>>>,
@@ -19,19 +17,6 @@ impl MultiThreadedBatchVerifier {
         }
     }
 
-    pub fn queue_statement<R>(
-        &self,
-        stmt: impl FnOnce(
-            &mut InternalBatchVerifier<(), dalek_ff_group::EdwardsPoint>,
-        ) -> Result<R, ConsensusError>,
-    ) -> Result<R, ConsensusError> {
-        let verifier_cell = self
-            .internal
-            .get_or(|| RefCell::new(InternalBatchVerifier::new(8)));
-        // TODO: this is not ok as a rayon par_iter could be called in stmt.
-        stmt(verifier_cell.borrow_mut().deref_mut())
-    }
-
     pub fn verify(self) -> bool {
         self.internal
             .into_iter()
@@ -41,3 +26,17 @@ impl MultiThreadedBatchVerifier {
             .is_none()
     }
 }
+
+impl cuprate_consensus_rules::batch_verifier::BatchVerifier for &'_ MultiThreadedBatchVerifier {
+    fn queue_statement<R>(
+        &mut self,
+        stmt: impl FnOnce(&mut InternalBatchVerifier<(), dalek_ff_group::EdwardsPoint>) -> R,
+    ) -> R {
+        let mut verifier = self
+            .internal
+            .get_or(|| RefCell::new(InternalBatchVerifier::new(32)))
+            .borrow_mut();
+
+        stmt(verifier.deref_mut())
+    }
+}

consensus/src/transactions.rs

@@ -484,26 +484,23 @@ where
         batch_get_ring_member_info(txs.iter().map(|(tx, _)| tx), &hf, database).await?;
 
     rayon_spawn_async(move || {
-        let batch_veriifier = MultiThreadedBatchVerifier::new(rayon::current_num_threads());
+        let batch_verifier = MultiThreadedBatchVerifier::new(rayon::current_num_threads());
 
         txs.par_iter()
             .zip(txs_ring_member_info.par_iter())
             .try_for_each(|((tx, verification_needed), ring)| {
                 // do semantic validation if needed.
                 if *verification_needed == VerificationNeeded::SemanticAndContextual {
-                    batch_veriifier.queue_statement(|verifier| {
-                        let fee = check_transaction_semantic(
-                            &tx.tx,
-                            tx.tx_blob.len(),
-                            tx.tx_weight,
-                            &tx.tx_hash,
-                            &hf,
-                            verifier,
-                        )?;
-                        // make sure monero-serai calculated the same fee.
-                        assert_eq!(fee, tx.fee);
-                        Ok(())
-                    })?;
+                    let fee = check_transaction_semantic(
+                        &tx.tx,
+                        tx.tx_blob.len(),
+                        tx.tx_weight,
+                        &tx.tx_hash,
+                        &hf,
+                        &batch_verifier,
+                    )?;
+                    // make sure monero-serai calculated the same fee.
+                    assert_eq!(fee, tx.fee);
                 }
 
                 // Both variants of `VerificationNeeded` require contextual validation.
@@ -518,7 +515,7 @@ where
                 Ok::<_, ConsensusError>(())
             })?;
 
-        if !batch_veriifier.verify() {
+        if !batch_verifier.verify() {
             return Err(ExtendedConsensusError::OneOrMoreBatchVerificationStatementsInvalid);
         }