Merge bitcoin/bitcoin#32646: p2p: Add witness mutation check inside FillBlock

28299ce p2p: remove vestigial READ_STATUS_CHECKBLOCK_FAILED (Greg Sanders)
bac9ee4 p2p: Add witness mutation check inside FillBlock (Greg Sanders)

Pull request description:

  Since #29412, we have not allowed mutated blocks to continue being processed immediately the block is received, but this is only done for the legacy BLOCK message.

  Extend these checks as belt-and-suspenders to not allow similar mutation strategies to affect relay by honest peers by applying the check inside `PartiallyDownloadedBlock::FillBlock`, immediately before returning `READ_STATUS_OK`.

ACKs for top commit:
  Crypt-iQ:
    ACK 28299ce
  achow101:
    ACK 28299ce
  stratospher:
    ACK 28299ce.
  dergoegge:
    Code review ACK 28299ce

Tree-SHA512: 883d7c12ca096234b425e6fe12e46b0611607600916e6ac8d1c8112224aa76924b7b074754910163ac2ec15379075d618a9ece3642649ac7629cddb0d4e432ea

Author: glozow

src/blockencodings.cpp

@@ -179,7 +179,7 @@ bool PartiallyDownloadedBlock::IsTxAvailable(size_t index) const
     return txn_available[index] != nullptr;
 }
 
-ReadStatus PartiallyDownloadedBlock::FillBlock(CBlock& block, const std::vector<CTransactionRef>& vtx_missing)
+ReadStatus PartiallyDownloadedBlock::FillBlock(CBlock& block, const std::vector<CTransactionRef>& vtx_missing, bool segwit_active)
 {
     if (header.IsNull()) return READ_STATUS_INVALID;
 
@@ -206,16 +206,11 @@ ReadStatus PartiallyDownloadedBlock::FillBlock(CBlock& block, const std::vector<
     if (vtx_missing.size() != tx_missing_offset)
         return READ_STATUS_INVALID;
 
-    BlockValidationState state;
-    CheckBlockFn check_block = m_check_block_mock ? m_check_block_mock : CheckBlock;
-    if (!check_block(block, state, Params().GetConsensus(), /*fCheckPoW=*/true, /*fCheckMerkleRoot=*/true)) {
-        // TODO: We really want to just check merkle tree manually here,
-        // but that is expensive, and CheckBlock caches a block's
-        // "checked-status" (in the CBlock?). CBlock should be able to
-        // check its own merkle root and cache that check.
-        if (state.GetResult() == BlockValidationResult::BLOCK_MUTATED)
-            return READ_STATUS_FAILED; // Possible Short ID collision
-        return READ_STATUS_CHECKBLOCK_FAILED;
+    // Check for possible mutations early now that we have a seemingly good block
+    IsBlockMutatedFn check_mutated{m_check_block_mutated_mock ? m_check_block_mutated_mock : IsBlockMutated};
+    if (check_mutated(/*block=*/block,
+                       /*check_witness_root=*/segwit_active)) {
+        return READ_STATUS_FAILED; // Possible Short ID collision
     }
 
     LogDebug(BCLog::CMPCTBLOCK, "Successfully reconstructed block %s with %u txn prefilled, %u txn from mempool (incl at least %u from extra pool) and %u txn (%u bytes) requested\n", hash.ToString(), prefilled_count, mempool_count, extra_count, vtx_missing.size(), tx_missing_size);

src/blockencodings.h

@@ -84,8 +84,6 @@ typedef enum ReadStatus_t
     READ_STATUS_OK,
     READ_STATUS_INVALID, // Invalid object, peer is sending bogus crap
     READ_STATUS_FAILED, // Failed to process object
-    READ_STATUS_CHECKBLOCK_FAILED, // Used only by FillBlock to indicate a
-                                   // failure in CheckBlock.
 } ReadStatus;
 
 class CBlockHeaderAndShortTxIDs {
@@ -141,15 +139,16 @@ class PartiallyDownloadedBlock {
     CBlockHeader header;
 
     // Can be overridden for testing
-    using CheckBlockFn = std::function<bool(const CBlock&, BlockValidationState&, const Consensus::Params&, bool, bool)>;
-    CheckBlockFn m_check_block_mock{nullptr};
+    using IsBlockMutatedFn = std::function<bool(const CBlock&, bool)>;
+    IsBlockMutatedFn m_check_block_mutated_mock{nullptr};
 
     explicit PartiallyDownloadedBlock(CTxMemPool* poolIn) : pool(poolIn) {}
 
     // extra_txn is a list of extra orphan/conflicted/etc transactions to look at
     ReadStatus InitData(const CBlockHeaderAndShortTxIDs& cmpctblock, const std::vector<CTransactionRef>& extra_txn);
     bool IsTxAvailable(size_t index) const;
-    ReadStatus FillBlock(CBlock& block, const std::vector<CTransactionRef>& vtx_missing);
+    // segwit_active enforces witness mutation checks just before reporting a healthy status
+    ReadStatus FillBlock(CBlock& block, const std::vector<CTransactionRef>& vtx_missing, bool segwit_active);
 };
 
 #endif // BITCOIN_BLOCKENCODINGS_H

src/net_processing.cpp

@@ -3360,7 +3360,11 @@ void PeerManagerImpl::ProcessCompactBlockTxns(CNode& pfrom, Peer& peer, const Bl
         }
 
         PartiallyDownloadedBlock& partialBlock = *range_flight.first->second.second->partialBlock;
-        ReadStatus status = partialBlock.FillBlock(*pblock, block_transactions.txn);
+
+        // We should not have gotten this far in compact block processing unless it's attached to a known header
+        const CBlockIndex* prev_block{Assume(m_chainman.m_blockman.LookupBlockIndex(partialBlock.header.hashPrevBlock))};
+        ReadStatus status = partialBlock.FillBlock(*pblock, block_transactions.txn,
+                                                   /*segwit_active=*/DeploymentActiveAfter(prev_block, m_chainman, Consensus::DEPLOYMENT_SEGWIT));
         if (status == READ_STATUS_INVALID) {
             RemoveBlockRequest(block_transactions.blockhash, pfrom.GetId()); // Reset in-flight state in case Misbehaving does not result in a disconnect
             Misbehaving(peer, "invalid compact block/non-matching block transactions");
@@ -3377,23 +3381,7 @@ void PeerManagerImpl::ProcessCompactBlockTxns(CNode& pfrom, Peer& peer, const Bl
                 return;
             }
         } else {
-            // Block is either okay, or possibly we received
-            // READ_STATUS_CHECKBLOCK_FAILED.
-            // Note that CheckBlock can only fail for one of a few reasons:
-            // 1. bad-proof-of-work (impossible here, because we've already
-            //    accepted the header)
-            // 2. merkleroot doesn't match the transactions given (already
-            //    caught in FillBlock with READ_STATUS_FAILED, so
-            //    impossible here)
-            // 3. the block is otherwise invalid (eg invalid coinbase,
-            //    block is too big, too many legacy sigops, etc).
-            // So if CheckBlock failed, #3 is the only possibility.
-            // Under BIP 152, we don't discourage the peer unless proof of work is
-            // invalid (we don't require all the stateless checks to have
-            // been run).  This is handled below, so just treat this as
-            // though the block was successfully read, and rely on the
-            // handling in ProcessNewBlock to ensure the block index is
-            // updated, etc.
+            // Block is okay for further processing
             RemoveBlockRequest(block_transactions.blockhash, pfrom.GetId()); // it is now an empty pointer
             fBlockRead = true;
             // mapBlockSource is used for potentially punishing peers and
@@ -4529,7 +4517,9 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
                     return;
                 }
                 std::vector<CTransactionRef> dummy;
-                status = tempBlock.FillBlock(*pblock, dummy);
+                const CBlockIndex* prev_block{Assume(m_chainman.m_blockman.LookupBlockIndex(cmpctblock.header.hashPrevBlock))};
+                status = tempBlock.FillBlock(*pblock, dummy,
+                                             /*segwit_active=*/DeploymentActiveAfter(prev_block, m_chainman, Consensus::DEPLOYMENT_SEGWIT));
                 if (status == READ_STATUS_OK) {
                     fBlockReconstructed = true;
                 }

src/test/blockencodings_tests.cpp

@@ -95,21 +95,21 @@ BOOST_AUTO_TEST_CASE(SimpleRoundTripTest)
         CBlock block2;
         {
             PartiallyDownloadedBlock tmp = partialBlock;
-            BOOST_CHECK(partialBlock.FillBlock(block2, {}) == READ_STATUS_INVALID); // No transactions
+            BOOST_CHECK(partialBlock.FillBlock(block2, {}, /*segwit_active=*/true) == READ_STATUS_INVALID); // No transactions
             partialBlock = tmp;
         }
 
         // Wrong transaction
         {
             PartiallyDownloadedBlock tmp = partialBlock;
-            partialBlock.FillBlock(block2, {block.vtx[2]}); // Current implementation doesn't check txn here, but don't require that
+            partialBlock.FillBlock(block2, {block.vtx[2]}, /*segwit_active=*/true); // Current implementation doesn't check txn here, but don't require that
             partialBlock = tmp;
         }
         bool mutated;
         BOOST_CHECK(block.hashMerkleRoot != BlockMerkleRoot(block2, &mutated));
 
         CBlock block3;
-        BOOST_CHECK(partialBlock.FillBlock(block3, {block.vtx[1]}) == READ_STATUS_OK);
+        BOOST_CHECK(partialBlock.FillBlock(block3, {block.vtx[1]}, /*segwit_active=*/true) == READ_STATUS_OK);
         BOOST_CHECK_EQUAL(block.GetHash().ToString(), block3.GetHash().ToString());
         BOOST_CHECK_EQUAL(block.hashMerkleRoot.ToString(), BlockMerkleRoot(block3, &mutated).ToString());
         BOOST_CHECK(!mutated);
@@ -182,14 +182,14 @@ BOOST_AUTO_TEST_CASE(NonCoinbasePreforwardRTTest)
         CBlock block2;
         {
             PartiallyDownloadedBlock tmp = partialBlock;
-            BOOST_CHECK(partialBlock.FillBlock(block2, {}) == READ_STATUS_INVALID); // No transactions
+            BOOST_CHECK(partialBlock.FillBlock(block2, {}, /*segwit_active=*/true) == READ_STATUS_INVALID); // No transactions
             partialBlock = tmp;
         }
 
         // Wrong transaction
         {
             PartiallyDownloadedBlock tmp = partialBlock;
-            partialBlock.FillBlock(block2, {block.vtx[1]}); // Current implementation doesn't check txn here, but don't require that
+            partialBlock.FillBlock(block2, {block.vtx[1]}, /*segwit_active=*/true); // Current implementation doesn't check txn here, but don't require that
             partialBlock = tmp;
         }
         BOOST_CHECK_EQUAL(pool.get(block.vtx[2]->GetHash()).use_count(), SHARED_TX_OFFSET + 2); // +2 because of partialBlock and block2
@@ -198,7 +198,7 @@ BOOST_AUTO_TEST_CASE(NonCoinbasePreforwardRTTest)
 
         CBlock block3;
         PartiallyDownloadedBlock partialBlockCopy = partialBlock;
-        BOOST_CHECK(partialBlock.FillBlock(block3, {block.vtx[0]}) == READ_STATUS_OK);
+        BOOST_CHECK(partialBlock.FillBlock(block3, {block.vtx[0]}, /*segwit_active=*/true) == READ_STATUS_OK);
         BOOST_CHECK_EQUAL(block.GetHash().ToString(), block3.GetHash().ToString());
         BOOST_CHECK_EQUAL(block.hashMerkleRoot.ToString(), BlockMerkleRoot(block3, &mutated).ToString());
         BOOST_CHECK(!mutated);
@@ -252,7 +252,7 @@ BOOST_AUTO_TEST_CASE(SufficientPreforwardRTTest)
 
         CBlock block2;
         PartiallyDownloadedBlock partialBlockCopy = partialBlock;
-        BOOST_CHECK(partialBlock.FillBlock(block2, {}) == READ_STATUS_OK);
+        BOOST_CHECK(partialBlock.FillBlock(block2, {}, /*segwit_active=*/true) == READ_STATUS_OK);
         BOOST_CHECK_EQUAL(block.GetHash().ToString(), block2.GetHash().ToString());
         bool mutated;
         BOOST_CHECK_EQUAL(block.hashMerkleRoot.ToString(), BlockMerkleRoot(block2, &mutated).ToString());
@@ -300,7 +300,7 @@ BOOST_AUTO_TEST_CASE(EmptyBlockRoundTripTest)
 
         CBlock block2;
         std::vector<CTransactionRef> vtx_missing;
-        BOOST_CHECK(partialBlock.FillBlock(block2, vtx_missing) == READ_STATUS_OK);
+        BOOST_CHECK(partialBlock.FillBlock(block2, vtx_missing, /*segwit_active=*/true) == READ_STATUS_OK);
         BOOST_CHECK_EQUAL(block.GetHash().ToString(), block2.GetHash().ToString());
         BOOST_CHECK_EQUAL(block.hashMerkleRoot.ToString(), BlockMerkleRoot(block2, &mutated).ToString());
         BOOST_CHECK(!mutated);

src/test/fuzz/partially_downloaded_block.cpp

@@ -36,14 +36,10 @@ void initialize_pdb()
     g_setup = testing_setup.get();
 }
 
-PartiallyDownloadedBlock::CheckBlockFn FuzzedCheckBlock(std::optional<BlockValidationResult> result)
+PartiallyDownloadedBlock::IsBlockMutatedFn FuzzedIsBlockMutated(bool result)
 {
-    return [result](const CBlock&, BlockValidationState& state, const Consensus::Params&, bool, bool) {
-        if (result) {
-            return state.Invalid(*result);
-        }
-
-        return true;
+    return [result](const CBlock& block, bool) {
+        return result;
     };
 }
 
@@ -115,35 +111,22 @@ FUZZ_TARGET(partially_downloaded_block, .init = initialize_pdb)
         skipped_missing |= (!pdb.IsTxAvailable(i) && skip);
     }
 
-    // Mock CheckBlock
-    bool fail_check_block{fuzzed_data_provider.ConsumeBool()};
-    auto validation_result =
-        fuzzed_data_provider.PickValueInArray(
-            {BlockValidationResult::BLOCK_RESULT_UNSET,
-             BlockValidationResult::BLOCK_CONSENSUS,
-             BlockValidationResult::BLOCK_CACHED_INVALID,
-             BlockValidationResult::BLOCK_INVALID_HEADER,
-             BlockValidationResult::BLOCK_MUTATED,
-             BlockValidationResult::BLOCK_MISSING_PREV,
-             BlockValidationResult::BLOCK_INVALID_PREV,
-             BlockValidationResult::BLOCK_TIME_FUTURE,
-             BlockValidationResult::BLOCK_HEADER_LOW_WORK});
-    pdb.m_check_block_mock = FuzzedCheckBlock(
-        fail_check_block ?
-            std::optional<BlockValidationResult>{validation_result} :
-            std::nullopt);
+    bool segwit_active{fuzzed_data_provider.ConsumeBool()};
+
+    // Mock IsBlockMutated
+    bool fail_block_mutated{fuzzed_data_provider.ConsumeBool()};
+    pdb.m_check_block_mutated_mock = FuzzedIsBlockMutated(fail_block_mutated);
 
     CBlock reconstructed_block;
-    auto fill_status{pdb.FillBlock(reconstructed_block, missing)};
+    auto fill_status{pdb.FillBlock(reconstructed_block, missing, segwit_active)};
     switch (fill_status) {
     case READ_STATUS_OK:
         assert(!skipped_missing);
-        assert(!fail_check_block);
+        assert(!fail_block_mutated);
         assert(block->GetHash() == reconstructed_block.GetHash());
         break;
-    case READ_STATUS_CHECKBLOCK_FAILED: [[fallthrough]];
     case READ_STATUS_FAILED:
-        assert(fail_check_block);
+        assert(fail_block_mutated);
         break;
     case READ_STATUS_INVALID:
         break;