Channel establishment v2 (dual funding)

smite-ir-mutator/src/lib.rs

@@ -17,6 +17,13 @@
 //!   bypasses our custom mutators. This was an AFL++ bug fixed upstream in
 //!   commit eddb2701b022351fb34b696ccf923bb856e9d953.
 //!
+//! Optionally:
+//! - `SMITE_IR_GENERATORS=v1|v2|all` -- which generators to draw from. BOLT 2
+//!   makes the two channel establishment flows mutually exclusive on one
+//!   connection, so a campaign against an `ir` scenario wants `v1` and one
+//!   against `ir_v2` wants `v2`; the other flow's programs would only ever be
+//!   rejected. Defaults to `all`, which draws from both.
+//!
 //! # Logging
 //!
 //! Logging is opt-in: [`afl_custom_init`] installs a logger only when
@@ -60,6 +67,24 @@ struct MutatorState {
     /// Sequence of actions taken in the last [`afl_custom_fuzz`] call, used by
     /// [`afl_custom_describe`] to name queue entries.
     last_sequence: Vec<&'static str>,
+    /// Generators this campaign draws from, selected by `SMITE_IR_GENERATORS`.
+    generators: &'static [AnyGenerator],
+}
+
+/// Reads `SMITE_IR_GENERATORS` and returns the generator set it names,
+/// defaulting to all of them.
+fn generators_from_env() -> &'static [AnyGenerator] {
+    match std::env::var("SMITE_IR_GENERATORS").as_deref() {
+        Ok("v1") => AnyGenerator::V1,
+        Ok("v2") => AnyGenerator::V2,
+        Ok("all") | Err(_) => AnyGenerator::ALL,
+        Ok(other) => {
+            eprintln!(
+                "[smite-ir-mutator] WARNING: unknown SMITE_IR_GENERATORS={other:?}, using all",
+            );
+            AnyGenerator::ALL
+        }
+    }
 }
 
 impl MutatorState {
@@ -69,17 +94,18 @@ impl MutatorState {
             out_buf: Vec::new(),
             description: Vec::new(),
             last_sequence: vec!["init"],
+            generators: generators_from_env(),
         }
     }
 
     /// Generates a fresh program from scratch by randomly delegating to one of
     /// the registered generators.
     fn generate_fresh(&mut self) -> Program {
         let mut builder = ProgramBuilder::new();
-        AnyGenerator::ALL
+        self.generators
             .iter()
             .choose(&mut self.rng)
-            .expect("AnyGenerator::ALL is non-empty")
+            .expect("the generator set is non-empty")
             .generate(&mut builder, &mut self.rng);
         self.last_sequence.clear();
         self.last_sequence.push("fresh");
@@ -114,10 +140,11 @@ impl MutatorState {
                     "instr-reorder"
                 }
                 4 => {
-                    let generator = *AnyGenerator::ALL
+                    let generator = *self
+                        .generators
                         .iter()
                         .choose(&mut self.rng)
-                        .expect("AnyGenerator::ALL is non-empty");
+                        .expect("the generator set is non-empty");
                     let mutator = GeneratorInsertionMutator::new(generator);
                     mutator.mutate(program, &mut self.rng);
                     "gen-insert"

smite-ir/src/builder.rs

@@ -222,12 +222,27 @@ impl ProgramBuilder {
             VariableType::AcceptChannel => {
                 panic!("cannot generate fresh AcceptChannel: requires protocol interaction")
             }
+            VariableType::OpenChannel2Message => {
+                panic!("cannot generate fresh OpenChannel2Message: requires composed inputs")
+            }
+            VariableType::AcceptChannel2 => {
+                panic!("cannot generate fresh AcceptChannel2: requires protocol interaction")
+            }
             VariableType::FundingTransaction => {
                 panic!("cannot generate fresh FundingTransaction: requires composed inputs")
             }
             VariableType::SentOpenChannel => {
                 panic!("cannot generate fresh SentOpenChannel: affine type")
             }
+            VariableType::SentOpenChannel2 => {
+                panic!("cannot generate fresh SentOpenChannel2: affine type")
+            }
+            VariableType::SentInteractiveTx => {
+                panic!("cannot generate fresh SentInteractiveTx: affine type")
+            }
+            VariableType::SentCommitmentSigned => {
+                panic!("cannot generate fresh SentCommitmentSigned: affine type")
+            }
             VariableType::SentFundingCreated => {
                 panic!("cannot generate fresh SentFundingCreated: affine type")
             }

smite-ir/src/generators.rs

@@ -8,6 +8,7 @@
 mod channel_announcement;
 mod channel_ready;
 mod channel_update;
+mod dual_funding_flow;
 mod funding_created;
 mod funding_flow;
 mod node_announcement;
@@ -16,6 +17,7 @@ mod open_channel;
 pub use channel_announcement::ChannelAnnouncementGenerator;
 pub use channel_ready::ChannelReadyGenerator;
 pub use channel_update::ChannelUpdateGenerator;
+pub use dual_funding_flow::DualFundingFlowGenerator;
 pub use funding_created::FundingCreatedGenerator;
 pub use funding_flow::FundingFlowGenerator;
 pub use node_announcement::NodeAnnouncementGenerator;
@@ -42,9 +44,37 @@ pub enum AnyGenerator {
     FundingCreated(FundingCreatedGenerator),
     ChannelReady(ChannelReadyGenerator),
     FundingFlow(FundingFlowGenerator),
+    DualFundingFlow(DualFundingFlowGenerator),
 }
 
 impl AnyGenerator {
+    /// Generators for the v1 (single-funded) channel establishment flow, plus
+    /// the gossip generators, which are flow-independent.
+    ///
+    /// BOLT 2 makes the two establishment flows mutually exclusive on one
+    /// connection, so a campaign negotiating `option_dual_fund` can only ever
+    /// have the v1 generators rejected, and vice versa. Splitting them lets a
+    /// campaign spend its executions on programs its target can act on.
+    pub const V1: &[Self] = &[
+        Self::ChannelAnnouncement(ChannelAnnouncementGenerator),
+        Self::ChannelUpdate(ChannelUpdateGenerator),
+        Self::NodeAnnouncement(NodeAnnouncementGenerator),
+        Self::OpenChannel(OpenChannelGenerator),
+        Self::FundingCreated(FundingCreatedGenerator),
+        Self::ChannelReady(ChannelReadyGenerator),
+        Self::FundingFlow(FundingFlowGenerator),
+    ];
+
+    /// Generators for the v2 (dual-funded) channel establishment flow, plus the
+    /// gossip generators. See [`Self::V1`].
+    pub const V2: &[Self] = &[
+        Self::ChannelAnnouncement(ChannelAnnouncementGenerator),
+        Self::ChannelUpdate(ChannelUpdateGenerator),
+        Self::NodeAnnouncement(NodeAnnouncementGenerator),
+        Self::ChannelReady(ChannelReadyGenerator),
+        Self::DualFundingFlow(DualFundingFlowGenerator),
+    ];
+
     /// All variants. Keep in sync with the enum definition.
     pub const ALL: &[Self] = &[
         Self::ChannelAnnouncement(ChannelAnnouncementGenerator),
@@ -54,6 +84,7 @@ impl AnyGenerator {
         Self::FundingCreated(FundingCreatedGenerator),
         Self::ChannelReady(ChannelReadyGenerator),
         Self::FundingFlow(FundingFlowGenerator),
+        Self::DualFundingFlow(DualFundingFlowGenerator),
     ];
 }
 
@@ -67,6 +98,7 @@ impl Generator for AnyGenerator {
             Self::FundingCreated(generator) => generator.generate(builder, rng),
             Self::ChannelReady(generator) => generator.generate(builder, rng),
             Self::FundingFlow(generator) => generator.generate(builder, rng),
+            Self::DualFundingFlow(generator) => generator.generate(builder, rng),
         }
     }
 }

smite-ir/src/generators/dual_funding_flow.rs

@@ -0,0 +1,223 @@
+//! Generator for the complete channel establishment v2 (dual-funded) flow.
+
+use rand::seq::IndexedRandom;
+use rand::{Rng, RngExt};
+
+use super::Generator;
+use crate::builder::ProgramBuilder;
+use crate::operation::{
+    AcceptChannel2Field, ChannelTypeVariant, ShutdownScriptVariant, TxOutputRole,
+};
+use crate::{Operation, VariableType};
+
+/// `serial_id` of the funding output we contribute. BOLT 2 requires the
+/// initiator to use even ids; picking these from a high range keeps them clear
+/// of the ones assigned to inputs.
+const FUNDING_OUTPUT_SERIAL_ID: u64 = 2000;
+
+/// `serial_id` of our change output.
+const CHANGE_OUTPUT_SERIAL_ID: u64 = 2002;
+
+/// `nSequence` for the inputs we contribute. BOLT 2 caps it at `0xfffffffd` so
+/// every input signals replaceability, and recommends one shared value across
+/// implementations to avoid fingerprinting.
+const SEQUENCE: u32 = 0xffff_fffd;
+
+/// Channel types most likely to be accepted, so the flow reaches its later
+/// steps often enough to cover them. `LoadChannelType` is mutable, so the
+/// mutator still reaches the rest.
+const LIKELY_CHANNEL_TYPES: &[ChannelTypeVariant] = &[
+    ChannelTypeVariant::Anchors,
+    ChannelTypeVariant::StaticRemoteKey,
+];
+
+/// Generates the complete channel establishment v2 flow.
+///
+/// Emits instructions to:
+/// 1. Build and send `open_channel2`, then receive `accept_channel2`
+/// 2. Contribute inputs, the funding output and a change output through
+///    interactive transaction construction, concluding with `tx_complete`
+/// 3. Exchange `commitment_signed`, then `tx_signatures`
+/// 4. Broadcast and confirm the funding transaction
+/// 5. Complete the `channel_ready` exchange
+#[derive(Clone, Copy)]
+pub struct DualFundingFlowGenerator;
+
+impl Generator for DualFundingFlowGenerator {
+    // One linear protocol script, from open_channel2 through channel_ready.
+    // Splitting it would scatter a sequence that reads best in wire order.
+    #[allow(clippy::too_many_lines)]
+    fn generate(&self, builder: &mut ProgramBuilder, rng: &mut impl Rng) {
+        // Keys are generated fresh to ensure they're distinct.
+        let funding_privkey = builder.generate_fresh(VariableType::PrivateKey, rng);
+        let funding_pubkey = builder.append(Operation::DerivePoint, &[funding_privkey]);
+        let revocation_basepoint = builder.generate_fresh(VariableType::Point, rng);
+        let payment_basepoint = builder.generate_fresh(VariableType::Point, rng);
+        let delayed_payment_basepoint = builder.generate_fresh(VariableType::Point, rng);
+        let htlc_basepoint = builder.generate_fresh(VariableType::Point, rng);
+        let first_per_commitment_point = builder.generate_fresh(VariableType::Point, rng);
+        let second_per_commitment_point = builder.generate_fresh(VariableType::Point, rng);
+
+        // BOLT 2 derives the v2 temporary_channel_id from our revocation
+        // basepoint with a zeroed one standing in for the peer.
+        let temporary_channel_id = builder.append(
+            Operation::DeriveTemporaryChannelIdV2,
+            &[revocation_basepoint],
+        );
+
+        let chain_hash = builder.pick_variable(VariableType::ChainHash, rng);
+        let funding_satoshis = builder.append(
+            Operation::LoadAmount(rng.random_range(100_000..=1_000_000)),
+            &[],
+        );
+        let funding_feerate_perkw = builder.append(
+            Operation::LoadFeeratePerKw(rng.random_range(253..=2_000)),
+            &[],
+        );
+        let commitment_feerate_perkw = builder.append(
+            Operation::LoadFeeratePerKw(rng.random_range(253..=5_000)),
+            &[],
+        );
+        let dust_limit_satoshis = builder.append(Operation::LoadAmount(546), &[]);
+        let max_htlc_value_in_flight_msat = builder.append(Operation::LoadAmount(100_000_000), &[]);
+        let htlc_minimum_msat = builder.append(Operation::LoadAmount(1), &[]);
+        let to_self_delay = builder.append(Operation::LoadU16(144), &[]);
+        let max_accepted_htlcs = builder.append(Operation::LoadU16(483), &[]);
+        let locktime = builder.append(Operation::LoadBlockHeight(0), &[]);
+        let channel_flags = builder.append(Operation::LoadU8(u8::from(rng.random::<bool>())), &[]);
+        let upfront_shutdown_script = builder.append(
+            Operation::LoadShutdownScript(ShutdownScriptVariant::Empty),
+            &[],
+        );
+        let channel_type_variant = if rng.random_range(0..4) == 0 {
+            *ChannelTypeVariant::ALL
+                .choose(rng)
+                .expect("ChannelTypeVariant::ALL is non-empty")
+        } else {
+            *LIKELY_CHANNEL_TYPES
+                .choose(rng)
+                .expect("LIKELY_CHANNEL_TYPES is non-empty")
+        };
+        let channel_type = builder.append(Operation::LoadChannelType(channel_type_variant), &[]);
+
+        // Build and send open_channel2.
+        let open_channel2_msg = builder.append(
+            Operation::BuildOpenChannel2 {
+                require_confirmed_inputs: rng.random_range(0..8) == 0,
+            },
+            &[
+                chain_hash,
+                temporary_channel_id,
+                funding_feerate_perkw,
+                commitment_feerate_perkw,
+                funding_satoshis,
+                dust_limit_satoshis,
+                max_htlc_value_in_flight_msat,
+                htlc_minimum_msat,
+                to_self_delay,
+                max_accepted_htlcs,
+                locktime,
+                funding_pubkey,
+                revocation_basepoint,
+                payment_basepoint,
+                delayed_payment_basepoint,
+                htlc_basepoint,
+                first_per_commitment_point,
+                second_per_commitment_point,
+                channel_flags,
+                upfront_shutdown_script,
+                channel_type,
+            ],
+        );
+        let sent_open_channel2 = builder.append(Operation::SendOpenChannel2, &[open_channel2_msg]);
+
+        // Receive accept_channel2, which reveals the peer's revocation
+        // basepoint and so the channel_id every later message carries.
+        let accept_channel2 = builder.append(Operation::RecvAcceptChannel2, &[sent_open_channel2]);
+        let peer_revocation_basepoint = builder.append(
+            Operation::ExtractAcceptChannel2(AcceptChannel2Field::RevocationBasepoint),
+            &[accept_channel2],
+        );
+        let channel_id = builder.append(
+            Operation::DeriveChannelIdV2,
+            &[revocation_basepoint, peer_revocation_basepoint],
+        );
+
+        // Interactive transaction construction. The protocol is turn-based, so
+        // every contribution we send is followed by the peer's reply.
+        for i in 0..rng.random_range(1u8..=3) {
+            let sent = builder.append(
+                Operation::SendTxAddInput {
+                    // Even ids, as BOLT 2 requires of the initiator.
+                    serial_id: 2 * (u64::from(i) + 1),
+                    utxo_index: i,
+                    sequence: SEQUENCE,
+                },
+                &[channel_id],
+            );
+            builder.append(Operation::RecvInteractiveTx, &[sent]);
+        }
+
+        // The opener must contribute the funding output, and pays its fees.
+        for (serial_id, role) in [
+            (FUNDING_OUTPUT_SERIAL_ID, TxOutputRole::Funding),
+            (CHANGE_OUTPUT_SERIAL_ID, TxOutputRole::Change),
+        ] {
+            let sent = builder.append(
+                Operation::SendTxAddOutput { serial_id, role },
+                // The value and script are derived from the negotiation for
+                // both roles here; they matter only once a mutator switches
+                // the role to `Explicit`.
+                &[channel_id, funding_satoshis, upfront_shutdown_script],
+            );
+            builder.append(Operation::RecvInteractiveTx, &[sent]);
+        }
+
+        // The exchange ends once both sides have sent `tx_complete` back to
+        // back. If the peer already sent one, ours ends it and nothing more
+        // arrives. If the peer contributed instead, it still has to answer
+        // ours with its own `tx_complete`. The executor tells the two cases
+        // apart at runtime, so this receive reads only when a reply is owed.
+        let sent_tx_complete = builder.append(Operation::SendTxComplete, &[channel_id]);
+        builder.append(Operation::RecvInteractiveTx, &[sent_tx_complete]);
+
+        // Exchange commitment signatures over the negotiated transaction.
+        let funding_transaction =
+            builder.append(Operation::BuildFundingTransactionV2, &[channel_id]);
+        let sent_commitment_signed = builder.append(
+            Operation::SendCommitmentSigned,
+            &[funding_transaction, funding_privkey, channel_id],
+        );
+        let funded_channel_id =
+            builder.append(Operation::RecvCommitmentSigned, &[sent_commitment_signed]);
+
+        // We contribute every input, so BOLT 2 has the peer send its
+        // tx_signatures first.
+        builder.append(Operation::RecvTxSignatures, &[channel_id]);
+        builder.append(
+            Operation::SendTxSignatures,
+            &[channel_id, funding_transaction],
+        );
+        builder.append(Operation::RecvTxSignatures, &[channel_id]);
+
+        builder.append(Operation::BroadcastTransaction, &[funding_transaction]);
+        builder.append(Operation::MineBlocks(rng.random_range(1..=16)), &[]);
+
+        // Reuse the second_per_commitment_point already committed to in
+        // open_channel2: implementations may cross-check the two, and feeding
+        // an unrelated point would fail channel_ready for a reason that has
+        // nothing to do with the flow under test.
+        let short_channel_id = builder.generate_fresh(VariableType::ShortChannelId, rng);
+        builder.append(
+            Operation::SendChannelReady {
+                include_alias: rng.random(),
+            },
+            &[
+                funded_channel_id,
+                second_per_commitment_point,
+                short_channel_id,
+            ],
+        );
+        builder.append(Operation::RecvChannelReady, &[]);
+    }
+}