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Merge bitcoin/bitcoin#26933: mempool: disallow txns under min relay fee, even in packages

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bf77fc9cb4 [test] mempool full in package accept (glozow)
b51ebccc28 [validation] set PackageValidationState when mempool full (glozow)
563a2ee4f5 [policy] disallow transactions under min relay fee, even in packages (glozow)
c4554fe894 [test] package cpfp bumps parents <mempoolminfee but >=minrelaytxfee (glozow)
ac463e87df [test util] mock mempool minimum feerate (glozow)

Pull request description:

  Part of package relay, see #27463.

  Note that this still allows packages to bump transactions that are below the dynamic mempool minimum feerate, which means this still solves the "mempool is congested and my presigned 1sat/vB tx is screwed" problem for all transactions.

  On master, the package policy (only accessible through regtest-only RPC submitpackage) allows 0-fee (or otherwise below min relay feerate) transactions if they are bumped by a child. However, with default package limits, we don't yet have a DoS-resistant way of ensuring these transactions remain bumped throughout their time in the mempool. Primarily, the fee-bumping child may later be replaced by another transaction that doesn't bump the parent(s). The parent(s) could potentially stay bumped by other transactions, but not enough to ever be selected by the `BlockAssembler` (due to `blockmintxfee`).

  For example, (tested [here](https://github.com/glozow/bitcoin/commits/26933-motivation)):
  - The mempool accepts 24 below-minrelayfeerate transactions ("0-fee parents"), all bumped by a single high-fee transaction ("the fee-bumping child"). The fee-bumping child also spends a confirmed UTXO.
  - Two additional children are added to each 0-fee parent. These children each pay a feerate slightly above the minimum relay feerate (e.g. 1.9sat/vB) such that, for each 0-fee parent, the total fees of its two children divided by the total size of the children and parent is above the minimum relay feerate.
  - If a block template is built now, all transactions would be selected.
  - A transaction replaces the the fee-bumping child, spending only the confirmed UTXO and not any of the outputs from the 0-fee parents.
   - The 0-fee parents now each have 2 children. Their descendant feerates are above minrelayfeerate, which means that they remain in the mempool, even if the mempool evicts all below-minrelayfeerate packages.
   - If a block template is built now, none of the 0-fee parents or their children would be selected.
   - Even more low-feerate descendants can be added to these below-minrelayfeerate packages and they will not be evicted until they expire or the mempool reaches capacity.

  Unless we have a DoS-resistant way of ensuring package CPFP-bumped transactions are always bumped, allowing package CPFP to bump below-minrelayfeerate transactions can result in these problematic situations. See #27018 which proposes a partial solution with some limitations, and contains discussion about potential improvements to eviction strategy. While no adequate solution exists, for now, avoid these situations by requiring all transactions to meet min relay feerate.

ACKs for top commit:
  ajtowns:
    reACK bf77fc9cb4
  instagibbs:
    re-ACK bf77fc9cb4

Tree-SHA512: 28940f41493a9e280b010284316fb8caf1ed7b2090ba9a4ef8a3b2eafc5933601074b142f4f7d4e3c6c4cce99d3146f5c8e1393d9406c6f2070dd41c817985c9
This commit is contained in:
glozow
2023-04-26 11:17:46 +01:00
parent 2cc43de69b bf77fc9cb4
commit bdfe27c9d2
7 changed files with 192 additions and 85 deletions
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72
src/test/txpackage_tests.cpp
View File

@@ -16,6 +16,9 @@
#include <boost/test/unit_test.hpp>
BOOST_AUTO_TEST_SUITE(txpackage_tests)
// A fee amount that is above 1sat/vB but below 5sat/vB for most transactions created within these
// unit tests.
static const CAmount low_fee_amt{200};
// Create placeholder transactions that have no meaning.
inline CTransactionRef create_placeholder_tx(size_t num_inputs, size_t num_outputs)
@@ -373,6 +376,7 @@ BOOST_FIXTURE_TEST_CASE(package_witness_swap_tests, TestChain100Setup)
{
// Mine blocks to mature coinbases.
mineBlocks(5);
MockMempoolMinFee(CFeeRate(5000));
LOCK(cs_main);
// Transactions with a same-txid-different-witness transaction in the mempool should be ignored,
@@ -560,13 +564,15 @@ BOOST_FIXTURE_TEST_CASE(package_witness_swap_tests, TestChain100Setup)
BOOST_CHECK(parent2_v2_result.m_result_type == MempoolAcceptResult::ResultType::VALID);
package_mixed.push_back(ptx_parent2_v1);
// parent3 will be a new transaction. Put 0 fees on it to make it invalid on its own.
// parent3 will be a new transaction. Put a low feerate to make it invalid on its own.
auto mtx_parent3 = CreateValidMempoolTransaction(/*input_transaction=*/m_coinbase_txns[3], /*input_vout=*/0,
/*input_height=*/0, /*input_signing_key=*/coinbaseKey,
/*output_destination=*/acs_spk,
/*output_amount=*/CAmount(50 * COIN), /*submit=*/false);
/*output_amount=*/CAmount(50 * COIN - low_fee_amt), /*submit=*/false);
CTransactionRef ptx_parent3 = MakeTransactionRef(mtx_parent3);
package_mixed.push_back(ptx_parent3);
BOOST_CHECK(m_node.mempool->GetMinFee().GetFee(GetVirtualTransactionSize(*ptx_parent3)) > low_fee_amt);
BOOST_CHECK(m_node.mempool->m_min_relay_feerate.GetFee(GetVirtualTransactionSize(*ptx_parent3)) <= low_fee_amt);
// child spends parent1, parent2, and parent3
CKey mixed_grandchild_key;
@@ -627,6 +633,7 @@ BOOST_FIXTURE_TEST_CASE(package_witness_swap_tests, TestChain100Setup)
BOOST_FIXTURE_TEST_CASE(package_cpfp_tests, TestChain100Setup)
{
mineBlocks(5);
MockMempoolMinFee(CFeeRate(5000));
LOCK(::cs_main);
size_t expected_pool_size = m_node.mempool->size();
CKey child_key;
@@ -636,9 +643,9 @@ BOOST_FIXTURE_TEST_CASE(package_cpfp_tests, TestChain100Setup)
grandchild_key.MakeNewKey(true);
CScript child_spk = GetScriptForDestination(WitnessV0KeyHash(grandchild_key.GetPubKey()));
// zero-fee parent and high-fee child package
// low-fee parent and high-fee child package
const CAmount coinbase_value{50 * COIN};
const CAmount parent_value{coinbase_value - 0};
const CAmount parent_value{coinbase_value - low_fee_amt};
const CAmount child_value{parent_value - COIN};
Package package_cpfp;
@@ -657,17 +664,20 @@ BOOST_FIXTURE_TEST_CASE(package_cpfp_tests, TestChain100Setup)
package_cpfp.push_back(tx_child);
// Package feerate is calculated using modified fees, and prioritisetransaction accepts negative
// fee deltas. This should be taken into account. De-prioritise the parent transaction by -1BTC,
// bringing the package feerate to 0.
m_node.mempool->PrioritiseTransaction(tx_parent->GetHash(), -1 * COIN);
// fee deltas. This should be taken into account. De-prioritise the parent transaction
// to bring the package feerate to 0.
m_node.mempool->PrioritiseTransaction(tx_parent->GetHash(), child_value - coinbase_value);
{
BOOST_CHECK_EQUAL(m_node.mempool->size(), expected_pool_size);
const auto submit_cpfp_deprio = ProcessNewPackage(m_node.chainman->ActiveChainstate(), *m_node.mempool,
package_cpfp, /*test_accept=*/ false);
BOOST_CHECK_EQUAL(submit_cpfp_deprio.m_state.GetResult(), PackageValidationResult::PCKG_POLICY);
BOOST_CHECK_MESSAGE(submit_cpfp_deprio.m_state.IsInvalid(),
"Package validation unexpectedly succeeded: " << submit_cpfp_deprio.m_state.GetRejectReason());
BOOST_CHECK(submit_cpfp_deprio.m_tx_results.empty());
BOOST_CHECK_EQUAL(submit_cpfp_deprio.m_state.GetResult(), PackageValidationResult::PCKG_TX);
BOOST_CHECK(submit_cpfp_deprio.m_state.IsInvalid());
BOOST_CHECK_EQUAL(submit_cpfp_deprio.m_tx_results.find(tx_parent->GetWitnessHash())->second.m_state.GetResult(),
TxValidationResult::TX_MEMPOOL_POLICY);
BOOST_CHECK_EQUAL(submit_cpfp_deprio.m_tx_results.find(tx_child->GetWitnessHash())->second.m_state.GetResult(),
TxValidationResult::TX_MISSING_INPUTS);
BOOST_CHECK(submit_cpfp_deprio.m_tx_results.find(tx_parent->GetWitnessHash())->second.m_state.GetRejectReason() == "min relay fee not met");
BOOST_CHECK_EQUAL(m_node.mempool->size(), expected_pool_size);
const CFeeRate expected_feerate(0, GetVirtualTransactionSize(*tx_parent) + GetVirtualTransactionSize(*tx_child));
}
@@ -675,8 +685,8 @@ BOOST_FIXTURE_TEST_CASE(package_cpfp_tests, TestChain100Setup)
// Clear the prioritisation of the parent transaction.
WITH_LOCK(m_node.mempool->cs, m_node.mempool->ClearPrioritisation(tx_parent->GetHash()));
// Package CPFP: Even though the parent pays 0 absolute fees, the child pays 1 BTC which is
// enough for the package feerate to meet the threshold.
// Package CPFP: Even though the parent's feerate is below the mempool minimum feerate, the
// child pays enough for the package feerate to meet the threshold.
{
BOOST_CHECK_EQUAL(m_node.mempool->size(), expected_pool_size);
const auto submit_cpfp = ProcessNewPackage(m_node.chainman->ActiveChainstate(), *m_node.mempool,
@@ -689,7 +699,7 @@ BOOST_FIXTURE_TEST_CASE(package_cpfp_tests, TestChain100Setup)
auto it_child = submit_cpfp.m_tx_results.find(tx_child->GetWitnessHash());
BOOST_CHECK(it_parent != submit_cpfp.m_tx_results.end());
BOOST_CHECK(it_parent->second.m_result_type == MempoolAcceptResult::ResultType::VALID);
BOOST_CHECK(it_parent->second.m_base_fees.value() == 0);
BOOST_CHECK(it_parent->second.m_base_fees.value() == coinbase_value - parent_value);
BOOST_CHECK(it_child != submit_cpfp.m_tx_results.end());
BOOST_CHECK(it_child->second.m_result_type == MempoolAcceptResult::ResultType::VALID);
BOOST_CHECK(it_child->second.m_base_fees.value() == COIN);
@@ -709,22 +719,28 @@ BOOST_FIXTURE_TEST_CASE(package_cpfp_tests, TestChain100Setup)
}
// Just because we allow low-fee parents doesn't mean we allow low-feerate packages.
// This package just pays 200 satoshis total. This would be enough to pay for the child alone,
// but isn't enough for the entire package to meet the 1sat/vbyte minimum.
// The mempool minimum feerate is 5sat/vB, but this package just pays 800 satoshis total.
// The child fees would be able to pay for itself, but isn't enough for the entire package.
Package package_still_too_low;
const CAmount parent_fee{200};
const CAmount child_fee{600};
auto mtx_parent_cheap = CreateValidMempoolTransaction(/*input_transaction=*/m_coinbase_txns[1], /*input_vout=*/0,
/*input_height=*/0, /*input_signing_key=*/coinbaseKey,
/*output_destination=*/parent_spk,
/*output_amount=*/coinbase_value, /*submit=*/false);
/*output_amount=*/coinbase_value - parent_fee, /*submit=*/false);
CTransactionRef tx_parent_cheap = MakeTransactionRef(mtx_parent_cheap);
package_still_too_low.push_back(tx_parent_cheap);
BOOST_CHECK(m_node.mempool->GetMinFee().GetFee(GetVirtualTransactionSize(*tx_parent_cheap)) > parent_fee);
BOOST_CHECK(m_node.mempool->m_min_relay_feerate.GetFee(GetVirtualTransactionSize(*tx_parent_cheap)) <= parent_fee);
auto mtx_child_cheap = CreateValidMempoolTransaction(/*input_transaction=*/tx_parent_cheap, /*input_vout=*/0,
/*input_height=*/101, /*input_signing_key=*/child_key,
/*output_destination=*/child_spk,
/*output_amount=*/coinbase_value - 200, /*submit=*/false);
/*output_amount=*/coinbase_value - parent_fee - child_fee, /*submit=*/false);
CTransactionRef tx_child_cheap = MakeTransactionRef(mtx_child_cheap);
package_still_too_low.push_back(tx_child_cheap);
BOOST_CHECK(m_node.mempool->GetMinFee().GetFee(GetVirtualTransactionSize(*tx_child_cheap)) <= child_fee);
BOOST_CHECK(m_node.mempool->GetMinFee().GetFee(GetVirtualTransactionSize(*tx_parent_cheap) + GetVirtualTransactionSize(*tx_child_cheap)) > parent_fee + child_fee);
// Cheap package should fail with package-fee-too-low.
{
@@ -735,11 +751,6 @@ BOOST_FIXTURE_TEST_CASE(package_cpfp_tests, TestChain100Setup)
BOOST_CHECK_EQUAL(submit_package_too_low.m_state.GetResult(), PackageValidationResult::PCKG_POLICY);
BOOST_CHECK_EQUAL(submit_package_too_low.m_state.GetRejectReason(), "package-fee-too-low");
BOOST_CHECK_EQUAL(m_node.mempool->size(), expected_pool_size);
const CFeeRate child_feerate(200, GetVirtualTransactionSize(*tx_child_cheap));
BOOST_CHECK(child_feerate.GetFeePerK() > 1000);
const CFeeRate expected_feerate(200,
GetVirtualTransactionSize(*tx_parent_cheap) + GetVirtualTransactionSize(*tx_child_cheap));
BOOST_CHECK(expected_feerate.GetFeePerK() < 1000);
}
// Package feerate includes the modified fees of the transactions.
@@ -752,18 +763,18 @@ BOOST_FIXTURE_TEST_CASE(package_cpfp_tests, TestChain100Setup)
expected_pool_size += 2;
BOOST_CHECK_MESSAGE(submit_prioritised_package.m_state.IsValid(),
"Package validation unexpectedly failed" << submit_prioritised_package.m_state.GetRejectReason());
const CFeeRate expected_feerate(1 * COIN + 200,
const CFeeRate expected_feerate(1 * COIN + parent_fee + child_fee,
GetVirtualTransactionSize(*tx_parent_cheap) + GetVirtualTransactionSize(*tx_child_cheap));
BOOST_CHECK_EQUAL(submit_prioritised_package.m_tx_results.size(), package_still_too_low.size());
auto it_parent = submit_prioritised_package.m_tx_results.find(tx_parent_cheap->GetWitnessHash());
auto it_child = submit_prioritised_package.m_tx_results.find(tx_child_cheap->GetWitnessHash());
BOOST_CHECK(it_parent != submit_prioritised_package.m_tx_results.end());
BOOST_CHECK(it_parent->second.m_result_type == MempoolAcceptResult::ResultType::VALID);
BOOST_CHECK(it_parent->second.m_base_fees.value() == 0);
BOOST_CHECK(it_parent->second.m_base_fees.value() == parent_fee);
BOOST_CHECK(it_parent->second.m_effective_feerate.value() == expected_feerate);
BOOST_CHECK(it_child != submit_prioritised_package.m_tx_results.end());
BOOST_CHECK(it_child->second.m_result_type == MempoolAcceptResult::ResultType::VALID);
BOOST_CHECK(it_child->second.m_base_fees.value() == 200);
BOOST_CHECK(it_child->second.m_base_fees.value() == child_fee);
BOOST_CHECK(it_child->second.m_effective_feerate.value() == expected_feerate);
std::vector<uint256> expected_wtxids({tx_parent_cheap->GetWitnessHash(), tx_child_cheap->GetWitnessHash()});
BOOST_CHECK(it_parent->second.m_wtxids_fee_calculations.value() == expected_wtxids);
@@ -800,8 +811,8 @@ BOOST_FIXTURE_TEST_CASE(package_cpfp_tests, TestChain100Setup)
BOOST_CHECK_MESSAGE(submit_rich_parent.m_state.IsInvalid(), "Package validation unexpectedly succeeded");
// The child would have been validated on its own and failed, then submitted as a "package" of 1.
BOOST_CHECK_EQUAL(submit_rich_parent.m_state.GetResult(), PackageValidationResult::PCKG_POLICY);
BOOST_CHECK_EQUAL(submit_rich_parent.m_state.GetRejectReason(), "package-fee-too-low");
BOOST_CHECK_EQUAL(submit_rich_parent.m_state.GetResult(), PackageValidationResult::PCKG_TX);
BOOST_CHECK_EQUAL(submit_rich_parent.m_state.GetRejectReason(), "transaction failed");
auto it_parent = submit_rich_parent.m_tx_results.find(tx_parent_rich->GetWitnessHash());
BOOST_CHECK(it_parent != submit_rich_parent.m_tx_results.end());
@@ -810,6 +821,11 @@ BOOST_FIXTURE_TEST_CASE(package_cpfp_tests, TestChain100Setup)
BOOST_CHECK_MESSAGE(it_parent->second.m_base_fees.value() == high_parent_fee,
strprintf("rich parent: expected fee %s, got %s", high_parent_fee, it_parent->second.m_base_fees.value()));
BOOST_CHECK(it_parent->second.m_effective_feerate == CFeeRate(high_parent_fee, GetVirtualTransactionSize(*tx_parent_rich)));
auto it_child = submit_rich_parent.m_tx_results.find(tx_child_poor->GetWitnessHash());
BOOST_CHECK(it_child != submit_rich_parent.m_tx_results.end());
BOOST_CHECK_EQUAL(it_child->second.m_result_type, MempoolAcceptResult::ResultType::INVALID);
BOOST_CHECK_EQUAL(it_child->second.m_state.GetResult(), TxValidationResult::TX_MEMPOOL_POLICY);
BOOST_CHECK(it_child->second.m_state.GetRejectReason() == "min relay fee not met");
BOOST_CHECK_EQUAL(m_node.mempool->size(), expected_pool_size);
BOOST_CHECK(m_node.mempool->exists(GenTxid::Txid(tx_parent_rich->GetHash())));

27
src/test/util/setup_common.cpp
View File

@@ -433,6 +433,33 @@ std::vector<CTransactionRef> TestChain100Setup::PopulateMempool(FastRandomContex
return mempool_transactions;
}
void TestChain100Setup::MockMempoolMinFee(const CFeeRate& target_feerate)
{
LOCK2(cs_main, m_node.mempool->cs);
// Transactions in the mempool will affect the new minimum feerate.
assert(m_node.mempool->size() == 0);
// The target feerate cannot be too low...
// ...otherwise the transaction's feerate will need to be negative.
assert(target_feerate > m_node.mempool->m_incremental_relay_feerate);
// ...otherwise this is not meaningful. The feerate policy uses the maximum of both feerates.
assert(target_feerate > m_node.mempool->m_min_relay_feerate);
// Manually create an invalid transaction. Manually set the fee in the CTxMemPoolEntry to
// achieve the exact target feerate.
CMutableTransaction mtx = CMutableTransaction();
mtx.vin.push_back(CTxIn{COutPoint{g_insecure_rand_ctx.rand256(), 0}});
mtx.vout.push_back(CTxOut(1 * COIN, GetScriptForDestination(WitnessV0ScriptHash(CScript() << OP_TRUE))));
const auto tx{MakeTransactionRef(mtx)};
LockPoints lp;
// The new mempool min feerate is equal to the removed package's feerate + incremental feerate.
const auto tx_fee = target_feerate.GetFee(GetVirtualTransactionSize(*tx)) -
m_node.mempool->m_incremental_relay_feerate.GetFee(GetVirtualTransactionSize(*tx));
m_node.mempool->addUnchecked(CTxMemPoolEntry(tx, /*fee=*/tx_fee,
/*time=*/0, /*entry_height=*/1,
/*spends_coinbase=*/true, /*sigops_cost=*/1, lp));
m_node.mempool->TrimToSize(0);
assert(m_node.mempool->GetMinFee() == target_feerate);
}
/**
* @returns a real block (0000000000013b8ab2cd513b0261a14096412195a72a0c4827d229dcc7e0f7af)
* with 9 txs.

12
src/test/util/setup_common.h
View File

@@ -23,6 +23,7 @@
#include <type_traits>
#include <vector>
class CFeeRate;
class Chainstate;
/** This is connected to the logger. Can be used to redirect logs to any other log */
@@ -185,6 +186,17 @@ struct TestChain100Setup : public TestingSetup {
*/
std::vector<CTransactionRef> PopulateMempool(FastRandomContext& det_rand, size_t num_transactions, bool submit);
/** Mock the mempool minimum feerate by adding a transaction and calling TrimToSize(0),
* simulating the mempool "reaching capacity" and evicting by descendant feerate. Note that
* this clears the mempool, and the new minimum feerate will depend on the maximum feerate of
* transactions removed, so this must be called while the mempool is empty.
*
* @param target_feerate The new mempool minimum feerate after this function returns.
* Must be above max(incremental feerate, min relay feerate),
* or 1sat/vB with default settings.
*/
void MockMempoolMinFee(const CFeeRate& target_feerate);
std::vector<CTransactionRef> m_coinbase_txns; // For convenience, coinbase transactions
CKey coinbaseKey; // private/public key needed to spend coinbase transactions
};

16
src/validation.cpp
View File

@@ -846,9 +846,18 @@ bool MemPoolAccept::PreChecks(ATMPArgs& args, Workspace& ws)
return state.Invalid(TxValidationResult::TX_NOT_STANDARD, "bad-txns-too-many-sigops",
strprintf("%d", nSigOpsCost));
// No individual transactions are allowed below the min relay feerate and mempool min feerate except from
// disconnected blocks and transactions in a package. Package transactions will be checked using
// package feerate later.
// No individual transactions are allowed below the min relay feerate except from disconnected blocks.
// This requirement, unlike CheckFeeRate, cannot be bypassed using m_package_feerates because,
// while a tx could be package CPFP'd when entering the mempool, we do not have a DoS-resistant
// method of ensuring the tx remains bumped. For example, the fee-bumping child could disappear
// due to a replacement.
if (!bypass_limits && ws.m_modified_fees < m_pool.m_min_relay_feerate.GetFee(ws.m_vsize)) {
return state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "min relay fee not met",
strprintf("%d < %d", ws.m_modified_fees, m_pool.m_min_relay_feerate.GetFee(ws.m_vsize)));
}
// No individual transactions are allowed below the mempool min feerate except from disconnected
// blocks and transactions in a package. Package transactions will be checked using package
// feerate later.
if (!bypass_limits && !args.m_package_feerates && !CheckFeeRate(ws.m_vsize, ws.m_modified_fees, state)) return false;
ws.m_iters_conflicting = m_pool.GetIterSet(ws.m_conflicts);
@@ -1192,6 +1201,7 @@ bool MemPoolAccept::SubmitPackage(const ATMPArgs& args, std::vector<Workspace>&
} else {
all_submitted = false;
ws.m_state.Invalid(TxValidationResult::TX_MEMPOOL_POLICY, "mempool full");
package_state.Invalid(PackageValidationResult::PCKG_TX, "transaction failed");
results.emplace(ws.m_ptx->GetWitnessHash(), MempoolAcceptResult::Failure(ws.m_state));
}
}