From 95bddb930aa72edd40fdff52cf447202995b0dce Mon Sep 17 00:00:00 2001 From: dergoegge Date: Fri, 19 Jan 2024 11:49:48 +0000 Subject: [PATCH 1/9] [validation] Isolate merkle root checks --- src/validation.cpp | 90 ++++++++++++++++++++++++++-------------------- 1 file changed, 52 insertions(+), 38 deletions(-) diff --git a/src/validation.cpp b/src/validation.cpp index caa4ff3115c5f..98383cd13305a 100644 --- a/src/validation.cpp +++ b/src/validation.cpp @@ -3639,6 +3639,54 @@ static bool CheckBlockHeader(const CBlockHeader& block, BlockValidationState& st return true; } +static bool CheckMerkleRoot(const CBlock& block, BlockValidationState& state) +{ + bool mutated; + uint256 hashMerkleRoot2 = BlockMerkleRoot(block, &mutated); + if (block.hashMerkleRoot != hashMerkleRoot2) + return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-txnmrklroot", "hashMerkleRoot mismatch"); + + // Check for merkle tree malleability (CVE-2012-2459): repeating sequences + // of transactions in a block without affecting the merkle root of a block, + // while still invalidating it. + if (mutated) + return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-txns-duplicate", "duplicate transaction"); + + return true; +} + +static bool CheckWitnessMalleation(const CBlock& block, bool expect_witness_commitment, BlockValidationState& state) +{ + if (expect_witness_commitment) { + int commitpos = GetWitnessCommitmentIndex(block); + if (commitpos != NO_WITNESS_COMMITMENT) { + bool malleated = false; + uint256 hashWitness = BlockWitnessMerkleRoot(block, &malleated); + // The malleation check is ignored; as the transaction tree itself + // already does not permit it, it is impossible to trigger in the + // witness tree. + if (block.vtx[0]->vin[0].scriptWitness.stack.size() != 1 || block.vtx[0]->vin[0].scriptWitness.stack[0].size() != 32) { + return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-witness-nonce-size", strprintf("%s : invalid witness reserved value size", __func__)); + } + CHash256().Write(hashWitness).Write(block.vtx[0]->vin[0].scriptWitness.stack[0]).Finalize(hashWitness); + if (memcmp(hashWitness.begin(), &block.vtx[0]->vout[commitpos].scriptPubKey[6], 32)) { + return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-witness-merkle-match", strprintf("%s : witness merkle commitment mismatch", __func__)); + } + + return true; + } + } + + // No witness data is allowed in blocks that don't commit to witness data, as this would otherwise leave room for spam + for (const auto& tx : block.vtx) { + if (tx->HasWitness()) { + return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "unexpected-witness", strprintf("%s : unexpected witness data found", __func__)); + } + } + + return true; +} + bool CheckBlock(const CBlock& block, BlockValidationState& state, const Consensus::Params& consensusParams, bool fCheckPOW, bool fCheckMerkleRoot) { // These are checks that are independent of context. @@ -3657,17 +3705,8 @@ bool CheckBlock(const CBlock& block, BlockValidationState& state, const Consensu } // Check the merkle root. - if (fCheckMerkleRoot) { - bool mutated; - uint256 hashMerkleRoot2 = BlockMerkleRoot(block, &mutated); - if (block.hashMerkleRoot != hashMerkleRoot2) - return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-txnmrklroot", "hashMerkleRoot mismatch"); - - // Check for merkle tree malleability (CVE-2012-2459): repeating sequences - // of transactions in a block without affecting the merkle root of a block, - // while still invalidating it. - if (mutated) - return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-txns-duplicate", "duplicate transaction"); + if (fCheckMerkleRoot && !CheckMerkleRoot(block, state)) { + return false; } // All potential-corruption validation must be done before we do any @@ -3866,33 +3905,8 @@ static bool ContextualCheckBlock(const CBlock& block, BlockValidationState& stat // * There must be at least one output whose scriptPubKey is a single 36-byte push, the first 4 bytes of which are // {0xaa, 0x21, 0xa9, 0xed}, and the following 32 bytes are SHA256^2(witness root, witness reserved value). In case there are // multiple, the last one is used. - bool fHaveWitness = false; - if (DeploymentActiveAfter(pindexPrev, chainman, Consensus::DEPLOYMENT_SEGWIT)) { - int commitpos = GetWitnessCommitmentIndex(block); - if (commitpos != NO_WITNESS_COMMITMENT) { - bool malleated = false; - uint256 hashWitness = BlockWitnessMerkleRoot(block, &malleated); - // The malleation check is ignored; as the transaction tree itself - // already does not permit it, it is impossible to trigger in the - // witness tree. - if (block.vtx[0]->vin[0].scriptWitness.stack.size() != 1 || block.vtx[0]->vin[0].scriptWitness.stack[0].size() != 32) { - return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-witness-nonce-size", strprintf("%s : invalid witness reserved value size", __func__)); - } - CHash256().Write(hashWitness).Write(block.vtx[0]->vin[0].scriptWitness.stack[0]).Finalize(hashWitness); - if (memcmp(hashWitness.begin(), &block.vtx[0]->vout[commitpos].scriptPubKey[6], 32)) { - return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-witness-merkle-match", strprintf("%s : witness merkle commitment mismatch", __func__)); - } - fHaveWitness = true; - } - } - - // No witness data is allowed in blocks that don't commit to witness data, as this would otherwise leave room for spam - if (!fHaveWitness) { - for (const auto& tx : block.vtx) { - if (tx->HasWitness()) { - return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "unexpected-witness", strprintf("%s : unexpected witness data found", __func__)); - } - } + if (!CheckWitnessMalleation(block, DeploymentActiveAfter(pindexPrev, chainman, Consensus::DEPLOYMENT_SEGWIT), state)) { + return false; } // After the coinbase witness reserved value and commitment are verified, From e7669e1343aec4298fd30d539847963e6fa5619c Mon Sep 17 00:00:00 2001 From: dergoegge Date: Thu, 22 Feb 2024 11:27:49 +0000 Subject: [PATCH 2/9] [refactor] Cleanup merkle root checks --- src/validation.cpp | 55 ++++++++++++++++++++++++++++++++++------------ 1 file changed, 41 insertions(+), 14 deletions(-) diff --git a/src/validation.cpp b/src/validation.cpp index 98383cd13305a..e02ce2ad1da80 100644 --- a/src/validation.cpp +++ b/src/validation.cpp @@ -3642,35 +3642,59 @@ static bool CheckBlockHeader(const CBlockHeader& block, BlockValidationState& st static bool CheckMerkleRoot(const CBlock& block, BlockValidationState& state) { bool mutated; - uint256 hashMerkleRoot2 = BlockMerkleRoot(block, &mutated); - if (block.hashMerkleRoot != hashMerkleRoot2) - return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-txnmrklroot", "hashMerkleRoot mismatch"); + uint256 merkle_root = BlockMerkleRoot(block, &mutated); + if (block.hashMerkleRoot != merkle_root) { + return state.Invalid( + /*result=*/BlockValidationResult::BLOCK_MUTATED, + /*reject_reason=*/"bad-txnmrklroot", + /*debug_message=*/"hashMerkleRoot mismatch"); + } // Check for merkle tree malleability (CVE-2012-2459): repeating sequences // of transactions in a block without affecting the merkle root of a block, // while still invalidating it. - if (mutated) - return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-txns-duplicate", "duplicate transaction"); + if (mutated) { + return state.Invalid( + /*result=*/BlockValidationResult::BLOCK_MUTATED, + /*reject_reason=*/"bad-txns-duplicate", + /*debug_message=*/"duplicate transaction"); + } return true; } +/** CheckWitnessMalleation performs checks for block malleation with regard to + * its witnesses. + * + * Note: If the witness commitment is expected (i.e. `expect_witness_commitment + * = true`), then the block is required to have at least one transaction and the + * first transaction needs to have at least one input. */ static bool CheckWitnessMalleation(const CBlock& block, bool expect_witness_commitment, BlockValidationState& state) { if (expect_witness_commitment) { int commitpos = GetWitnessCommitmentIndex(block); if (commitpos != NO_WITNESS_COMMITMENT) { - bool malleated = false; - uint256 hashWitness = BlockWitnessMerkleRoot(block, &malleated); + assert(!block.vtx.empty() && !block.vtx[0]->vin.empty()); + const auto& witness_stack{block.vtx[0]->vin[0].scriptWitness.stack}; + + if (witness_stack.size() != 1 || witness_stack[0].size() != 32) { + return state.Invalid( + /*result=*/BlockValidationResult::BLOCK_MUTATED, + /*reject_reason=*/"bad-witness-nonce-size", + /*debug_message=*/strprintf("%s : invalid witness reserved value size", __func__)); + } + // The malleation check is ignored; as the transaction tree itself // already does not permit it, it is impossible to trigger in the // witness tree. - if (block.vtx[0]->vin[0].scriptWitness.stack.size() != 1 || block.vtx[0]->vin[0].scriptWitness.stack[0].size() != 32) { - return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-witness-nonce-size", strprintf("%s : invalid witness reserved value size", __func__)); - } - CHash256().Write(hashWitness).Write(block.vtx[0]->vin[0].scriptWitness.stack[0]).Finalize(hashWitness); - if (memcmp(hashWitness.begin(), &block.vtx[0]->vout[commitpos].scriptPubKey[6], 32)) { - return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "bad-witness-merkle-match", strprintf("%s : witness merkle commitment mismatch", __func__)); + uint256 hash_witness = BlockWitnessMerkleRoot(block, /*mutated=*/nullptr); + + CHash256().Write(hash_witness).Write(witness_stack[0]).Finalize(hash_witness); + if (memcmp(hash_witness.begin(), &block.vtx[0]->vout[commitpos].scriptPubKey[6], 32)) { + return state.Invalid( + /*result=*/BlockValidationResult::BLOCK_MUTATED, + /*reject_reason=*/"bad-witness-merkle-match", + /*debug_message=*/strprintf("%s : witness merkle commitment mismatch", __func__)); } return true; @@ -3680,7 +3704,10 @@ static bool CheckWitnessMalleation(const CBlock& block, bool expect_witness_comm // No witness data is allowed in blocks that don't commit to witness data, as this would otherwise leave room for spam for (const auto& tx : block.vtx) { if (tx->HasWitness()) { - return state.Invalid(BlockValidationResult::BLOCK_MUTATED, "unexpected-witness", strprintf("%s : unexpected witness data found", __func__)); + return state.Invalid( + /*result=*/BlockValidationResult::BLOCK_MUTATED, + /*reject_reason=*/"unexpected-witness", + /*debug_message=*/strprintf("%s : unexpected witness data found", __func__)); } } From 66abce1d98115e41f394bc4f4f52341960ddc839 Mon Sep 17 00:00:00 2001 From: dergoegge Date: Fri, 19 Jan 2024 15:09:28 +0000 Subject: [PATCH 3/9] [validation] Introduce IsBlockMutated --- src/validation.cpp | 20 ++++++++++++++++++++ src/validation.h | 3 +++ 2 files changed, 23 insertions(+) diff --git a/src/validation.cpp b/src/validation.cpp index e02ce2ad1da80..e1133138df392 100644 --- a/src/validation.cpp +++ b/src/validation.cpp @@ -3824,6 +3824,26 @@ bool HasValidProofOfWork(const std::vector& headers, const Consens [&](const auto& header) { return CheckProofOfWork(header.GetHash(), header.nBits, consensusParams);}); } +bool IsBlockMutated(const CBlock& block, bool check_witness_root) +{ + BlockValidationState state; + if (!CheckMerkleRoot(block, state)) { + LogDebug(BCLog::VALIDATION, "Block mutated: %s\n", state.ToString()); + return true; + } + + if (block.vtx.empty() || !block.vtx[0]->IsCoinBase()) { + return false; + } + + if (!CheckWitnessMalleation(block, check_witness_root, state)) { + LogDebug(BCLog::VALIDATION, "Block mutated: %s\n", state.ToString()); + return true; + } + + return false; +} + arith_uint256 CalculateHeadersWork(const std::vector& headers) { arith_uint256 total_work{0}; diff --git a/src/validation.h b/src/validation.h index fd9b53df8f2d7..566153c15011a 100644 --- a/src/validation.h +++ b/src/validation.h @@ -383,6 +383,9 @@ bool TestBlockValidity(BlockValidationState& state, /** Check with the proof of work on each blockheader matches the value in nBits */ bool HasValidProofOfWork(const std::vector& headers, const Consensus::Params& consensusParams); +/** Check if a block has been mutated (with respect to its merkle root and witness commitments). */ +bool IsBlockMutated(const CBlock& block, bool check_witness_root); + /** Return the sum of the work on a given set of headers */ arith_uint256 CalculateHeadersWork(const std::vector& headers); From 2d8495e0800f5332748cd50eaad801ff77671bba Mon Sep 17 00:00:00 2001 From: dergoegge Date: Tue, 6 Feb 2024 17:07:48 +0000 Subject: [PATCH 4/9] [validation] Merkle root malleation should be caught by IsBlockMutated --- src/test/validation_tests.cpp | 5 +++++ src/validation.cpp | 13 ++++++++++++- 2 files changed, 17 insertions(+), 1 deletion(-) diff --git a/src/test/validation_tests.cpp b/src/test/validation_tests.cpp index 14440571eb680..cb7d1a312f071 100644 --- a/src/test/validation_tests.cpp +++ b/src/test/validation_tests.cpp @@ -4,12 +4,17 @@ #include #include +#include +#include +#include #include #include #include #include #include +#include + #include #include diff --git a/src/validation.cpp b/src/validation.cpp index e1133138df392..120663bfc0ba0 100644 --- a/src/validation.cpp +++ b/src/validation.cpp @@ -3833,7 +3833,18 @@ bool IsBlockMutated(const CBlock& block, bool check_witness_root) } if (block.vtx.empty() || !block.vtx[0]->IsCoinBase()) { - return false; + // Consider the block mutated if any transaction is 64 bytes in size (see 3.1 + // in "Weaknesses in Bitcoin’s Merkle Root Construction": + // https://lists.linuxfoundation.org/pipermail/bitcoin-dev/attachments/20190225/a27d8837/attachment-0001.pdf). + // + // Note: This is not a consensus change as this only applies to blocks that + // don't have a coinbase transaction and would therefore already be invalid. + return std::any_of(block.vtx.begin(), block.vtx.end(), + [](auto& tx) { return GetSerializeSize(TX_NO_WITNESS(tx)) == 64; }); + } else { + // Theoretically it is still possible for a block with a 64 byte + // coinbase transaction to be mutated but we neglect that possibility + // here as it requires at least 224 bits of work. } if (!CheckWitnessMalleation(block, check_witness_root, state)) { From 49257c0304828a185c273fcb99742c54bbef0c8e Mon Sep 17 00:00:00 2001 From: dergoegge Date: Fri, 19 Jan 2024 15:25:01 +0000 Subject: [PATCH 5/9] [net processing] Don't process mutated blocks We preemptively perform a block mutation check before further processing a block message (similar to early sanity checks on other messsage types). The main reasons for this change are as follows: - `CBlock::GetHash()` is a foot-gun without a prior mutation check, as the hash returned only commits to the header but not to the actual transactions (`CBlock::vtx`) contained in the block. - We have observed attacks that abused mutated blocks in the past, which could have been prevented by simply not processing mutated blocks (e.g. https://github.com/bitcoin/bitcoin/pull/27608). --- src/net_processing.cpp | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/src/net_processing.cpp b/src/net_processing.cpp index c8da927763443..5c3ec5f7006d0 100644 --- a/src/net_processing.cpp +++ b/src/net_processing.cpp @@ -4719,6 +4719,16 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type, LogPrint(BCLog::NET, "received block %s peer=%d\n", pblock->GetHash().ToString(), pfrom.GetId()); + const CBlockIndex* prev_block{WITH_LOCK(m_chainman.GetMutex(), return m_chainman.m_blockman.LookupBlockIndex(pblock->hashPrevBlock))}; + + if (IsBlockMutated(/*block=*/*pblock, + /*check_witness_root=*/DeploymentActiveAfter(prev_block, m_chainman, Consensus::DEPLOYMENT_SEGWIT))) { + LogDebug(BCLog::NET, "Received mutated block from peer=%d\n", peer->m_id); + Misbehaving(*peer, 100, "mutated block"); + WITH_LOCK(cs_main, RemoveBlockRequest(pblock->GetHash(), peer->m_id)); + return; + } + bool forceProcessing = false; const uint256 hash(pblock->GetHash()); bool min_pow_checked = false; @@ -4734,7 +4744,6 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type, mapBlockSource.emplace(hash, std::make_pair(pfrom.GetId(), true)); // Check work on this block against our anti-dos thresholds. - const CBlockIndex* prev_block = m_chainman.m_blockman.LookupBlockIndex(pblock->hashPrevBlock); if (prev_block && prev_block->nChainWork + CalculateHeadersWork({pblock->GetBlockHeader()}) >= GetAntiDoSWorkThreshold()) { min_pow_checked = true; } From 5bf4f5ba32da4627f152b54d266df9b2aa930457 Mon Sep 17 00:00:00 2001 From: dergoegge Date: Fri, 2 Feb 2024 16:16:55 +0000 Subject: [PATCH 6/9] [test] Add regression test for #27608 --- test/functional/p2p_mutated_blocks.py | 96 +++++++++++++++++++++++++++ test/functional/test_runner.py | 1 + 2 files changed, 97 insertions(+) create mode 100755 test/functional/p2p_mutated_blocks.py diff --git a/test/functional/p2p_mutated_blocks.py b/test/functional/p2p_mutated_blocks.py new file mode 100755 index 0000000000000..20f618dc6e164 --- /dev/null +++ b/test/functional/p2p_mutated_blocks.py @@ -0,0 +1,96 @@ +#!/usr/bin/env python3 +# Copyright (c) The Bitcoin Core developers +# Distributed under the MIT software license, see the accompanying +# file COPYING or http://www.opensource.org/licenses/mit-license.php. + +""" +Test that an attacker can't degrade compact block relay by sending unsolicited +mutated blocks to clear in-flight blocktxn requests from other honest peers. +""" + +from test_framework.p2p import P2PInterface +from test_framework.messages import ( + BlockTransactions, + msg_cmpctblock, + msg_block, + msg_blocktxn, + HeaderAndShortIDs, +) +from test_framework.test_framework import BitcoinTestFramework +from test_framework.blocktools import ( + COINBASE_MATURITY, + create_block, + add_witness_commitment, + NORMAL_GBT_REQUEST_PARAMS, +) +from test_framework.util import assert_equal +from test_framework.wallet import MiniWallet +import copy + +class MutatedBlocksTest(BitcoinTestFramework): + def set_test_params(self): + self.setup_clean_chain = True + self.num_nodes = 1 + + def run_test(self): + self.wallet = MiniWallet(self.nodes[0]) + self.generate(self.wallet, COINBASE_MATURITY) + + honest_relayer = self.nodes[0].add_outbound_p2p_connection(P2PInterface(), p2p_idx=0, connection_type="outbound-full-relay") + attacker = self.nodes[0].add_p2p_connection(P2PInterface()) + + # Create new block with two transactions (coinbase + 1 self-transfer). + # The self-transfer transaction is needed to trigger a compact block + # `getblocktxn` roundtrip. + tx = self.wallet.create_self_transfer()["tx"] + block = create_block(tmpl=self.nodes[0].getblocktemplate(NORMAL_GBT_REQUEST_PARAMS), txlist=[tx]) + add_witness_commitment(block) + block.solve() + + # Create mutated version of the block by changing the transaction + # version on the self-transfer. + mutated_block = copy.deepcopy(block) + mutated_block.vtx[1].nVersion = 4 + + # Announce the new block via a compact block through the honest relayer + cmpctblock = HeaderAndShortIDs() + cmpctblock.initialize_from_block(block, use_witness=True) + honest_relayer.send_message(msg_cmpctblock(cmpctblock.to_p2p())) + + # Wait for a `getblocktxn` that attempts to fetch the self-transfer + def self_transfer_requested(): + if not honest_relayer.last_message.get('getblocktxn'): + return False + + get_block_txn = honest_relayer.last_message['getblocktxn'] + return get_block_txn.block_txn_request.blockhash == block.sha256 and \ + get_block_txn.block_txn_request.indexes == [1] + honest_relayer.wait_until(self_transfer_requested, timeout=5) + + # Block at height 101 should be the only one in flight from peer 0 + peer_info_prior_to_attack = self.nodes[0].getpeerinfo() + assert_equal(peer_info_prior_to_attack[0]['id'], 0) + assert_equal([101], peer_info_prior_to_attack[0]["inflight"]) + + # Attempt to clear the honest relayer's download request by sending the + # mutated block (as the attacker). + with self.nodes[0].assert_debug_log(expected_msgs=["bad-txnmrklroot, hashMerkleRoot mismatch"]): + attacker.send_message(msg_block(mutated_block)) + # Attacker should get disconnected for sending a mutated block + attacker.wait_for_disconnect(timeout=5) + + # Block at height 101 should *still* be the only block in-flight from + # peer 0 + peer_info_after_attack = self.nodes[0].getpeerinfo() + assert_equal(peer_info_after_attack[0]['id'], 0) + assert_equal([101], peer_info_after_attack[0]["inflight"]) + + # The honest relayer should be able to complete relaying the block by + # sending the blocktxn that was requested. + block_txn = msg_blocktxn() + block_txn.block_transactions = BlockTransactions(blockhash=block.sha256, transactions=[tx]) + honest_relayer.send_and_ping(block_txn) + assert_equal(self.nodes[0].getbestblockhash(), block.hash) + +if __name__ == '__main__': + MutatedBlocksTest().main() diff --git a/test/functional/test_runner.py b/test/functional/test_runner.py index 9bfc9aa7d4b17..a852a0d65cdcd 100755 --- a/test/functional/test_runner.py +++ b/test/functional/test_runner.py @@ -306,6 +306,7 @@ 'wallet_crosschain.py', 'mining_basic.py', 'feature_signet.py', + 'p2p_mutated_blocks.py', 'wallet_implicitsegwit.py --legacy-wallet', 'rpc_named_arguments.py', 'feature_startupnotify.py', From 1ec6bbeb8d27d31647d1433ccb87b362f6d81f90 Mon Sep 17 00:00:00 2001 From: dergoegge Date: Tue, 6 Feb 2024 10:07:18 +0000 Subject: [PATCH 7/9] [validation] Cache merkle root and witness commitment checks Slight performance improvement by avoiding duplicate work. --- src/primitives/block.h | 8 ++++++-- src/validation.cpp | 6 ++++++ 2 files changed, 12 insertions(+), 2 deletions(-) diff --git a/src/primitives/block.h b/src/primitives/block.h index 99accfc7dd90f..832f8a03f74a7 100644 --- a/src/primitives/block.h +++ b/src/primitives/block.h @@ -71,8 +71,10 @@ class CBlock : public CBlockHeader // network and disk std::vector vtx; - // memory only - mutable bool fChecked; + // Memory-only flags for caching expensive checks + mutable bool fChecked; // CheckBlock() + mutable bool m_checked_witness_commitment{false}; // CheckWitnessCommitment() + mutable bool m_checked_merkle_root{false}; // CheckMerkleRoot() CBlock() { @@ -95,6 +97,8 @@ class CBlock : public CBlockHeader CBlockHeader::SetNull(); vtx.clear(); fChecked = false; + m_checked_witness_commitment = false; + m_checked_merkle_root = false; } CBlockHeader GetBlockHeader() const diff --git a/src/validation.cpp b/src/validation.cpp index 120663bfc0ba0..b03cc7f78a889 100644 --- a/src/validation.cpp +++ b/src/validation.cpp @@ -3641,6 +3641,8 @@ static bool CheckBlockHeader(const CBlockHeader& block, BlockValidationState& st static bool CheckMerkleRoot(const CBlock& block, BlockValidationState& state) { + if (block.m_checked_merkle_root) return true; + bool mutated; uint256 merkle_root = BlockMerkleRoot(block, &mutated); if (block.hashMerkleRoot != merkle_root) { @@ -3660,6 +3662,7 @@ static bool CheckMerkleRoot(const CBlock& block, BlockValidationState& state) /*debug_message=*/"duplicate transaction"); } + block.m_checked_merkle_root = true; return true; } @@ -3672,6 +3675,8 @@ static bool CheckMerkleRoot(const CBlock& block, BlockValidationState& state) static bool CheckWitnessMalleation(const CBlock& block, bool expect_witness_commitment, BlockValidationState& state) { if (expect_witness_commitment) { + if (block.m_checked_witness_commitment) return true; + int commitpos = GetWitnessCommitmentIndex(block); if (commitpos != NO_WITNESS_COMMITMENT) { assert(!block.vtx.empty() && !block.vtx[0]->vin.empty()); @@ -3697,6 +3702,7 @@ static bool CheckWitnessMalleation(const CBlock& block, bool expect_witness_comm /*debug_message=*/strprintf("%s : witness merkle commitment mismatch", __func__)); } + block.m_checked_witness_commitment = true; return true; } } From 1ed2c9829700054526156297552bb47230406098 Mon Sep 17 00:00:00 2001 From: dergoegge Date: Tue, 27 Feb 2024 11:57:26 +0000 Subject: [PATCH 8/9] Add transaction_identifier::size to allow Span conversion --- src/util/transaction_identifier.h | 1 + 1 file changed, 1 insertion(+) diff --git a/src/util/transaction_identifier.h b/src/util/transaction_identifier.h index 89e10dee0175a..d4a0ede25aad5 100644 --- a/src/util/transaction_identifier.h +++ b/src/util/transaction_identifier.h @@ -44,6 +44,7 @@ class transaction_identifier constexpr void SetNull() { m_wrapped.SetNull(); } std::string GetHex() const { return m_wrapped.GetHex(); } std::string ToString() const { return m_wrapped.ToString(); } + static constexpr auto size() { return decltype(m_wrapped)::size(); } constexpr const std::byte* data() const { return reinterpret_cast(m_wrapped.data()); } constexpr const std::byte* begin() const { return reinterpret_cast(m_wrapped.begin()); } constexpr const std::byte* end() const { return reinterpret_cast(m_wrapped.end()); } From d8087adc7ebd4ea05dd3843e5a92e8115fd7bbcc Mon Sep 17 00:00:00 2001 From: dergoegge Date: Fri, 23 Feb 2024 15:50:36 +0000 Subject: [PATCH 9/9] [test] IsBlockMutated unit tests --- src/test/validation_tests.cpp | 211 ++++++++++++++++++++++++++++++++++ 1 file changed, 211 insertions(+) diff --git a/src/test/validation_tests.cpp b/src/test/validation_tests.cpp index cb7d1a312f071..c6f6ac3bdb442 100644 --- a/src/test/validation_tests.cpp +++ b/src/test/validation_tests.cpp @@ -150,4 +150,215 @@ BOOST_AUTO_TEST_CASE(test_assumeutxo) BOOST_CHECK_EQUAL(out110_2.nChainTx, 111U); } +BOOST_AUTO_TEST_CASE(block_malleation) +{ + // Test utilities that calls `IsBlockMutated` and then clears the validity + // cache flags on `CBlock`. + auto is_mutated = [](CBlock& block, bool check_witness_root) { + bool mutated{IsBlockMutated(block, check_witness_root)}; + block.fChecked = false; + block.m_checked_witness_commitment = false; + block.m_checked_merkle_root = false; + return mutated; + }; + auto is_not_mutated = [&is_mutated](CBlock& block, bool check_witness_root) { + return !is_mutated(block, check_witness_root); + }; + + // Test utilities to create coinbase transactions and insert witness + // commitments. + // + // Note: this will not include the witness stack by default to avoid + // triggering the "no witnesses allowed for blocks that don't commit to + // witnesses" rule when testing other malleation vectors. + auto create_coinbase_tx = [](bool include_witness = false) { + CMutableTransaction coinbase; + coinbase.vin.resize(1); + if (include_witness) { + coinbase.vin[0].scriptWitness.stack.resize(1); + coinbase.vin[0].scriptWitness.stack[0] = std::vector(32, 0x00); + } + + coinbase.vout.resize(1); + coinbase.vout[0].scriptPubKey.resize(MINIMUM_WITNESS_COMMITMENT); + coinbase.vout[0].scriptPubKey[0] = OP_RETURN; + coinbase.vout[0].scriptPubKey[1] = 0x24; + coinbase.vout[0].scriptPubKey[2] = 0xaa; + coinbase.vout[0].scriptPubKey[3] = 0x21; + coinbase.vout[0].scriptPubKey[4] = 0xa9; + coinbase.vout[0].scriptPubKey[5] = 0xed; + + auto tx = MakeTransactionRef(coinbase); + assert(tx->IsCoinBase()); + return tx; + }; + auto insert_witness_commitment = [](CBlock& block, uint256 commitment) { + assert(!block.vtx.empty() && block.vtx[0]->IsCoinBase() && !block.vtx[0]->vout.empty()); + + CMutableTransaction mtx{*block.vtx[0]}; + CHash256().Write(commitment).Write(std::vector(32, 0x00)).Finalize(commitment); + memcpy(&mtx.vout[0].scriptPubKey[6], commitment.begin(), 32); + block.vtx[0] = MakeTransactionRef(mtx); + }; + + { + CBlock block; + + // Empty block is expected to have merkle root of 0x0. + BOOST_CHECK(block.vtx.empty()); + block.hashMerkleRoot = uint256{1}; + BOOST_CHECK(is_mutated(block, /*check_witness_root=*/false)); + block.hashMerkleRoot = uint256{}; + BOOST_CHECK(is_not_mutated(block, /*check_witness_root=*/false)); + + // Block with a single coinbase tx is mutated if the merkle root is not + // equal to the coinbase tx's hash. + block.vtx.push_back(create_coinbase_tx()); + BOOST_CHECK(block.vtx[0]->GetHash() != block.hashMerkleRoot); + BOOST_CHECK(is_mutated(block, /*check_witness_root=*/false)); + block.hashMerkleRoot = block.vtx[0]->GetHash(); + BOOST_CHECK(is_not_mutated(block, /*check_witness_root=*/false)); + + // Block with two transactions is mutated if the merkle root does not + // match the double sha256 of the concatenation of the two transaction + // hashes. + block.vtx.push_back(MakeTransactionRef(CMutableTransaction{})); + BOOST_CHECK(is_mutated(block, /*check_witness_root=*/false)); + HashWriter hasher; + hasher.write(block.vtx[0]->GetHash()); + hasher.write(block.vtx[1]->GetHash()); + block.hashMerkleRoot = hasher.GetHash(); + BOOST_CHECK(is_not_mutated(block, /*check_witness_root=*/false)); + + // Block with two transactions is mutated if any node is duplicate. + { + block.vtx[1] = block.vtx[0]; + BOOST_CHECK(is_mutated(block, /*check_witness_root=*/false)); + HashWriter hasher; + hasher.write(block.vtx[0]->GetHash()); + hasher.write(block.vtx[1]->GetHash()); + block.hashMerkleRoot = hasher.GetHash(); + BOOST_CHECK(is_mutated(block, /*check_witness_root=*/false)); + } + + // Blocks with 64-byte coinbase transactions are not considered mutated + block.vtx.clear(); + { + CMutableTransaction mtx; + mtx.vin.resize(1); + mtx.vout.resize(1); + mtx.vout[0].scriptPubKey.resize(4); + block.vtx.push_back(MakeTransactionRef(mtx)); + block.hashMerkleRoot = block.vtx.back()->GetHash(); + assert(block.vtx.back()->IsCoinBase()); + assert(GetSerializeSize(TX_NO_WITNESS(block.vtx.back())) == 64); + } + BOOST_CHECK(is_not_mutated(block, /*check_witness_root=*/false)); + } + + { + // Test merkle root malleation + + // Pseudo code to mine transactions tx{1,2,3}: + // + // ``` + // loop { + // tx1 = random_tx() + // tx2 = random_tx() + // tx3 = deserialize_tx(txid(tx1) || txid(tx2)); + // if serialized_size_without_witness(tx3) == 64 { + // print(hex(tx3)) + // break + // } + // } + // ``` + // + // The `random_tx` function used to mine the txs below simply created + // empty transactions with a random version field. + CMutableTransaction tx1; + BOOST_CHECK(DecodeHexTx(tx1, "ff204bd0000000000000", /*try_no_witness=*/true, /*try_witness=*/false)); + CMutableTransaction tx2; + BOOST_CHECK(DecodeHexTx(tx2, "8ae53c92000000000000", /*try_no_witness=*/true, /*try_witness=*/false)); + CMutableTransaction tx3; + BOOST_CHECK(DecodeHexTx(tx3, "cdaf22d00002c6a7f848f8ae4d30054e61dcf3303d6fe01d282163341f06feecc10032b3160fcab87bdfe3ecfb769206ef2d991b92f8a268e423a6ef4d485f06", /*try_no_witness=*/true, /*try_witness=*/false)); + { + // Verify that double_sha256(txid1||txid2) == txid3 + HashWriter hasher; + hasher.write(tx1.GetHash()); + hasher.write(tx2.GetHash()); + assert(hasher.GetHash() == tx3.GetHash()); + // Verify that tx3 is 64 bytes in size (without witness). + assert(GetSerializeSize(TX_NO_WITNESS(tx3)) == 64); + } + + CBlock block; + block.vtx.push_back(MakeTransactionRef(tx1)); + block.vtx.push_back(MakeTransactionRef(tx2)); + uint256 merkle_root = block.hashMerkleRoot = BlockMerkleRoot(block); + BOOST_CHECK(is_not_mutated(block, /*check_witness_root=*/false)); + + // Mutate the block by replacing the two transactions with one 64-byte + // transaction that serializes into the concatenation of the txids of + // the transactions in the unmutated block. + block.vtx.clear(); + block.vtx.push_back(MakeTransactionRef(tx3)); + BOOST_CHECK(!block.vtx.back()->IsCoinBase()); + BOOST_CHECK(BlockMerkleRoot(block) == merkle_root); + BOOST_CHECK(is_mutated(block, /*check_witness_root=*/false)); + } + + { + CBlock block; + block.vtx.push_back(create_coinbase_tx(/*include_witness=*/true)); + { + CMutableTransaction mtx; + mtx.vin.resize(1); + mtx.vin[0].scriptWitness.stack.resize(1); + mtx.vin[0].scriptWitness.stack[0] = {0}; + block.vtx.push_back(MakeTransactionRef(mtx)); + } + block.hashMerkleRoot = BlockMerkleRoot(block); + // Block with witnesses is considered mutated if the witness commitment + // is not validated. + BOOST_CHECK(is_mutated(block, /*check_witness_root=*/false)); + // Block with invalid witness commitment is considered mutated. + BOOST_CHECK(is_mutated(block, /*check_witness_root=*/true)); + + // Block with valid commitment is not mutated + { + auto commitment{BlockWitnessMerkleRoot(block)}; + insert_witness_commitment(block, commitment); + block.hashMerkleRoot = BlockMerkleRoot(block); + } + BOOST_CHECK(is_not_mutated(block, /*check_witness_root=*/true)); + + // Malleating witnesses should be caught by `IsBlockMutated`. + { + CMutableTransaction mtx{*block.vtx[1]}; + assert(!mtx.vin[0].scriptWitness.stack[0].empty()); + ++mtx.vin[0].scriptWitness.stack[0][0]; + block.vtx[1] = MakeTransactionRef(mtx); + } + // Without also updating the witness commitment, the merkle root should + // not change when changing one of the witnesses. + BOOST_CHECK(block.hashMerkleRoot == BlockMerkleRoot(block)); + BOOST_CHECK(is_mutated(block, /*check_witness_root=*/true)); + { + auto commitment{BlockWitnessMerkleRoot(block)}; + insert_witness_commitment(block, commitment); + block.hashMerkleRoot = BlockMerkleRoot(block); + } + BOOST_CHECK(is_not_mutated(block, /*check_witness_root=*/true)); + + // Test malleating the coinbase witness reserved value + { + CMutableTransaction mtx{*block.vtx[0]}; + mtx.vin[0].scriptWitness.stack.resize(0); + block.vtx[0] = MakeTransactionRef(mtx); + block.hashMerkleRoot = BlockMerkleRoot(block); + } + BOOST_CHECK(is_mutated(block, /*check_witness_root=*/true)); + } +} + BOOST_AUTO_TEST_SUITE_END()