Require callers of AcceptBlockHeader() to perform anti-dos checks

In order to prevent memory DoS, we must ensure that we don't accept a new
header into memory until we've performed anti-DoS checks, such as verifying
that the header is part of a sufficiently high work chain. This commit adds a
new argument to AcceptBlockHeader() so that we can ensure that all call-sites
which might cause a new header to be accepted into memory have to grapple with
the question of whether the header is safe to accept, or needs further
validation.

This patch also fixes two places where low-difficulty-headers could have been
processed without such validation (processing an unrequested block from the
network, and processing a compact block).

Credit to Niklas Gögge for noticing this issue, and thanks to Sjors Provoost
for test code.

14 files changed, 76 insertions, 41 deletions

diff --git a/src/bitcoin-chainstate.cpp b/src/bitcoin-chainstate.cpp
index 7312ae45d4..f3bd543de8 100644
--- a/src/bitcoin-chainstate.cpp
+++ b/src/bitcoin-chainstate.cpp
@@ -195,7 +195,7 @@ int main(int argc, char* argv[])
         bool new_block;
         auto sc = std::make_shared<submitblock_StateCatcher>(block.GetHash());
         RegisterSharedValidationInterface(sc);
-        bool accepted = chainman.ProcessNewBlock(blockptr, /*force_processing=*/true, /*new_block=*/&new_block);
+        bool accepted = chainman.ProcessNewBlock(blockptr, /*force_processing=*/true, /*min_pow_checked=*/true, /*new_block=*/&new_block);
         UnregisterSharedValidationInterface(sc);
         if (!new_block && accepted) {
             std::cerr << "duplicate" << std::endl;
@@ -210,6 +210,9 @@ int main(int argc, char* argv[])
         case BlockValidationResult::BLOCK_RESULT_UNSET:
             std::cerr << "initial value. Block has not yet been rejected" << std::endl;
             break;
+        case BlockValidationResult::BLOCK_HEADER_LOW_WORK:
+            std::cerr << "the block header may be on a too-little-work chain" << std::endl;
+            break;
         case BlockValidationResult::BLOCK_CONSENSUS:
             std::cerr << "invalid by consensus rules (excluding any below reasons)" << std::endl;
             break;
diff --git a/src/consensus/validation.h b/src/consensus/validation.h
index 6027bb9aeb..9c0aa09356 100644
--- a/src/consensus/validation.h
+++ b/src/consensus/validation.h
@@ -79,6 +79,7 @@ enum class BlockValidationResult {
     BLOCK_INVALID_PREV,      //!< A block this one builds on is invalid
     BLOCK_TIME_FUTURE,       //!< block timestamp was > 2 hours in the future (or our clock is bad)
     BLOCK_CHECKPOINT,        //!< the block failed to meet one of our checkpoints
+    BLOCK_HEADER_LOW_WORK    //!< the block header may be on a too-little-work chain
 };
 
 
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 2b899fdc2b..a0fe9d52b3 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -875,7 +875,7 @@ private:
         EXCLUSIVE_LOCKS_REQUIRED(!m_most_recent_block_mutex, peer.m_getdata_requests_mutex) LOCKS_EXCLUDED(::cs_main);
 
     /** Process a new block. Perform any post-processing housekeeping */
-    void ProcessBlock(CNode& node, const std::shared_ptr<const CBlock>& block, bool force_processing);
+    void ProcessBlock(CNode& node, const std::shared_ptr<const CBlock>& block, bool force_processing, bool min_pow_checked);
 
     /** Relay map (txid or wtxid -> CTransactionRef) */
     typedef std::map<uint256, CTransactionRef> MapRelay;
@@ -1603,6 +1603,10 @@ bool PeerManagerImpl::MaybePunishNodeForBlock(NodeId nodeid, const BlockValidati
     switch (state.GetResult()) {
     case BlockValidationResult::BLOCK_RESULT_UNSET:
         break;
+    case BlockValidationResult::BLOCK_HEADER_LOW_WORK:
+        // We didn't try to process the block because the header chain may have
+        // too little work.
+        break;
     // The node is providing invalid data:
     case BlockValidationResult::BLOCK_CONSENSUS:
     case BlockValidationResult::BLOCK_MUTATED:
@@ -2758,7 +2762,7 @@ void PeerManagerImpl::ProcessHeadersMessage(CNode& pfrom, Peer& peer,
 
     // Now process all the headers.
     BlockValidationState state;
-    if (!m_chainman.ProcessNewBlockHeaders(headers, state, &pindexLast)) {
+    if (!m_chainman.ProcessNewBlockHeaders(headers, /*min_pow_checked=*/true, state, &pindexLast)) {
         if (state.IsInvalid()) {
             MaybePunishNodeForBlock(pfrom.GetId(), state, via_compact_block, "invalid header received");
             return;
@@ -3030,10 +3034,10 @@ void PeerManagerImpl::ProcessGetCFCheckPt(CNode& node, Peer& peer, CDataStream&
     m_connman.PushMessage(&node, std::move(msg));
 }
 
-void PeerManagerImpl::ProcessBlock(CNode& node, const std::shared_ptr<const CBlock>& block, bool force_processing)
+void PeerManagerImpl::ProcessBlock(CNode& node, const std::shared_ptr<const CBlock>& block, bool force_processing, bool min_pow_checked)
 {
     bool new_block{false};
-    m_chainman.ProcessNewBlock(block, force_processing, &new_block);
+    m_chainman.ProcessNewBlock(block, force_processing, min_pow_checked, &new_block);
     if (new_block) {
         node.m_last_block_time = GetTime<std::chrono::seconds>();
     } else {
@@ -4008,12 +4012,17 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
         {
         LOCK(cs_main);
 
-        if (!m_chainman.m_blockman.LookupBlockIndex(cmpctblock.header.hashPrevBlock)) {
+        const CBlockIndex* prev_block = m_chainman.m_blockman.LookupBlockIndex(cmpctblock.header.hashPrevBlock);
+        if (!prev_block) {
             // Doesn't connect (or is genesis), instead of DoSing in AcceptBlockHeader, request deeper headers
             if (!m_chainman.ActiveChainstate().IsInitialBlockDownload()) {
                 MaybeSendGetHeaders(pfrom, GetLocator(m_chainman.m_best_header), *peer);
             }
             return;
+        } else if (prev_block->nChainWork + CalculateHeadersWork({cmpctblock.header}) < GetAntiDoSWorkThreshold()) {
+            // If we get a low-work header in a compact block, we can ignore it.
+            LogPrint(BCLog::NET, "Ignoring low-work compact block from peer %d\n", pfrom.GetId());
+            return;
         }
 
         if (!m_chainman.m_blockman.LookupBlockIndex(cmpctblock.header.GetHash())) {
@@ -4023,7 +4032,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
 
         const CBlockIndex *pindex = nullptr;
         BlockValidationState state;
-        if (!m_chainman.ProcessNewBlockHeaders({cmpctblock.header}, state, &pindex)) {
+        if (!m_chainman.ProcessNewBlockHeaders({cmpctblock.header}, /*min_pow_checked=*/true, state, &pindex)) {
             if (state.IsInvalid()) {
                 MaybePunishNodeForBlock(pfrom.GetId(), state, /*via_compact_block=*/true, "invalid header via cmpctblock");
                 return;
@@ -4190,7 +4199,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
             // we have a chain with at least nMinimumChainWork), and we ignore
             // compact blocks with less work than our tip, it is safe to treat
             // reconstructed compact blocks as having been requested.
-            ProcessBlock(pfrom, pblock, /*force_processing=*/true);
+            ProcessBlock(pfrom, pblock, /*force_processing=*/true, /*min_pow_checked=*/true);
             LOCK(cs_main); // hold cs_main for CBlockIndex::IsValid()
             if (pindex->IsValid(BLOCK_VALID_TRANSACTIONS)) {
                 // Clear download state for this block, which is in
@@ -4273,7 +4282,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
             // disk-space attacks), but this should be safe due to the
             // protections in the compact block handler -- see related comment
             // in compact block optimistic reconstruction handling.
-            ProcessBlock(pfrom, pblock, /*force_processing=*/true);
+            ProcessBlock(pfrom, pblock, /*force_processing=*/true, /*min_pow_checked=*/true);
         }
         return;
     }
@@ -4322,6 +4331,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
 
         bool forceProcessing = false;
         const uint256 hash(pblock->GetHash());
+        bool min_pow_checked = false;
         {
             LOCK(cs_main);
             // Always process the block if we requested it, since we may
@@ -4332,8 +4342,14 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
             // which peers send us compact blocks, so the race between here and
             // cs_main in ProcessNewBlock is fine.
             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;
+            }
         }
-        ProcessBlock(pfrom, pblock, forceProcessing);
+        ProcessBlock(pfrom, pblock, forceProcessing, min_pow_checked);
         return;
     }
 
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
index 91feb2c24b..1ad704a490 100644
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -132,7 +132,7 @@ static bool GenerateBlock(ChainstateManager& chainman, CBlock& block, uint64_t&
     }
 
     std::shared_ptr<const CBlock> shared_pblock = std::make_shared<const CBlock>(block);
-    if (!chainman.ProcessNewBlock(shared_pblock, true, nullptr)) {
+    if (!chainman.ProcessNewBlock(shared_pblock, /*force_processing=*/true, /*min_pow_checked=*/true, nullptr)) {
         throw JSONRPCError(RPC_INTERNAL_ERROR, "ProcessNewBlock, block not accepted");
     }
 
@@ -981,7 +981,7 @@ static RPCHelpMan submitblock()
     bool new_block;
     auto sc = std::make_shared<submitblock_StateCatcher>(block.GetHash());
     RegisterSharedValidationInterface(sc);
-    bool accepted = chainman.ProcessNewBlock(blockptr, /*force_processing=*/true, /*new_block=*/&new_block);
+    bool accepted = chainman.ProcessNewBlock(blockptr, /*force_processing=*/true, /*min_pow_checked=*/true, /*new_block=*/&new_block);
     UnregisterSharedValidationInterface(sc);
     if (!new_block && accepted) {
         return "duplicate";
@@ -1023,7 +1023,7 @@ static RPCHelpMan submitheader()
     }
 
     BlockValidationState state;
-    chainman.ProcessNewBlockHeaders({h}, state);
+    chainman.ProcessNewBlockHeaders({h}, /*min_pow_checked=*/true, state);
     if (state.IsValid()) return UniValue::VNULL;
     if (state.IsError()) {
         throw JSONRPCError(RPC_VERIFY_ERROR, state.ToString());
diff --git a/src/test/blockfilter_index_tests.cpp b/src/test/blockfilter_index_tests.cpp
index 1a182209b8..2798e998af 100644
--- a/src/test/blockfilter_index_tests.cpp
+++ b/src/test/blockfilter_index_tests.cpp
@@ -101,7 +101,7 @@ bool BuildChainTestingSetup::BuildChain(const CBlockIndex* pindex,
         CBlockHeader header = block->GetBlockHeader();
 
         BlockValidationState state;
-        if (!Assert(m_node.chainman)->ProcessNewBlockHeaders({header}, state, &pindex)) {
+        if (!Assert(m_node.chainman)->ProcessNewBlockHeaders({header}, true, state, &pindex)) {
             return false;
         }
     }
@@ -178,7 +178,7 @@ BOOST_FIXTURE_TEST_CASE(blockfilter_index_initial_sync, BuildChainTestingSetup)
     uint256 chainA_last_header = last_header;
     for (size_t i = 0; i < 2; i++) {
         const auto& block = chainA[i];
-        BOOST_REQUIRE(Assert(m_node.chainman)->ProcessNewBlock(block, true, nullptr));
+        BOOST_REQUIRE(Assert(m_node.chainman)->ProcessNewBlock(block, true, true, nullptr));
     }
     for (size_t i = 0; i < 2; i++) {
         const auto& block = chainA[i];
@@ -196,7 +196,7 @@ BOOST_FIXTURE_TEST_CASE(blockfilter_index_initial_sync, BuildChainTestingSetup)
     uint256 chainB_last_header = last_header;
     for (size_t i = 0; i < 3; i++) {
         const auto& block = chainB[i];
-        BOOST_REQUIRE(Assert(m_node.chainman)->ProcessNewBlock(block, true, nullptr));
+        BOOST_REQUIRE(Assert(m_node.chainman)->ProcessNewBlock(block, true, true, nullptr));
     }
     for (size_t i = 0; i < 3; i++) {
         const auto& block = chainB[i];
@@ -227,7 +227,7 @@ BOOST_FIXTURE_TEST_CASE(blockfilter_index_initial_sync, BuildChainTestingSetup)
     // Reorg back to chain A.
      for (size_t i = 2; i < 4; i++) {
          const auto& block = chainA[i];
-         BOOST_REQUIRE(Assert(m_node.chainman)->ProcessNewBlock(block, true, nullptr));
+         BOOST_REQUIRE(Assert(m_node.chainman)->ProcessNewBlock(block, true, true, nullptr));
      }
 
      // Check that chain A and B blocks can be retrieved.
diff --git a/src/test/coinstatsindex_tests.cpp b/src/test/coinstatsindex_tests.cpp
index c93d05a93b..132c4e53e7 100644
--- a/src/test/coinstatsindex_tests.cpp
+++ b/src/test/coinstatsindex_tests.cpp
@@ -102,7 +102,7 @@ BOOST_FIXTURE_TEST_CASE(coinstatsindex_unclean_shutdown, TestChain100Setup)
             LOCK(cs_main);
             BlockValidationState state;
             BOOST_CHECK(CheckBlock(block, state, params.GetConsensus()));
-            BOOST_CHECK(chainstate.AcceptBlock(new_block, state, &new_block_index, true, nullptr, nullptr));
+            BOOST_CHECK(chainstate.AcceptBlock(new_block, state, &new_block_index, true, nullptr, nullptr, true));
             CCoinsViewCache view(&chainstate.CoinsTip());
             BOOST_CHECK(chainstate.ConnectBlock(block, state, new_block_index, view));
         }
diff --git a/src/test/fuzz/utxo_snapshot.cpp b/src/test/fuzz/utxo_snapshot.cpp
index 0b596492be..8abb943266 100644
--- a/src/test/fuzz/utxo_snapshot.cpp
+++ b/src/test/fuzz/utxo_snapshot.cpp
@@ -58,7 +58,7 @@ FUZZ_TARGET_INIT(utxo_snapshot, initialize_chain)
     if (fuzzed_data_provider.ConsumeBool()) {
         for (const auto& block : *g_chain) {
             BlockValidationState dummy;
-            bool processed{chainman.ProcessNewBlockHeaders({*block}, dummy)};
+            bool processed{chainman.ProcessNewBlockHeaders({*block}, true, dummy)};
             Assert(processed);
             const auto* index{WITH_LOCK(::cs_main, return chainman.m_blockman.LookupBlockIndex(block->GetHash()))};
             Assert(index);
diff --git a/src/test/miner_tests.cpp b/src/test/miner_tests.cpp
index d88aed7d4a..9f5fb17b60 100644
--- a/src/test/miner_tests.cpp
+++ b/src/test/miner_tests.cpp
@@ -588,7 +588,7 @@ BOOST_AUTO_TEST_CASE(CreateNewBlock_validity)
             pblock->nNonce = bi.nonce;
         }
         std::shared_ptr<const CBlock> shared_pblock = std::make_shared<const CBlock>(*pblock);
-        BOOST_CHECK(Assert(m_node.chainman)->ProcessNewBlock(shared_pblock, true, nullptr));
+        BOOST_CHECK(Assert(m_node.chainman)->ProcessNewBlock(shared_pblock, true, true, nullptr));
         pblock->hashPrevBlock = pblock->GetHash();
     }
 
diff --git a/src/test/util/mining.cpp b/src/test/util/mining.cpp
index 88cf9647e7..faa0b2878c 100644
--- a/src/test/util/mining.cpp
+++ b/src/test/util/mining.cpp
@@ -68,7 +68,7 @@ CTxIn MineBlock(const NodeContext& node, const CScript& coinbase_scriptPubKey)
         assert(block->nNonce);
     }
 
-    bool processed{Assert(node.chainman)->ProcessNewBlock(block, true, nullptr)};
+    bool processed{Assert(node.chainman)->ProcessNewBlock(block, true, true, nullptr)};
     assert(processed);
 
     return CTxIn{block->vtx[0]->GetHash(), 0};
diff --git a/src/test/util/setup_common.cpp b/src/test/util/setup_common.cpp
index 30d26ecf79..8a0b03c9d1 100644
--- a/src/test/util/setup_common.cpp
+++ b/src/test/util/setup_common.cpp
@@ -321,7 +321,7 @@ CBlock TestChain100Setup::CreateAndProcessBlock(
 
     const CBlock block = this->CreateBlock(txns, scriptPubKey, *chainstate);
     std::shared_ptr<const CBlock> shared_pblock = std::make_shared<const CBlock>(block);
-    Assert(m_node.chainman)->ProcessNewBlock(shared_pblock, true, nullptr);
+    Assert(m_node.chainman)->ProcessNewBlock(shared_pblock, true, true, nullptr);
 
     return block;
 }
diff --git a/src/test/validation_block_tests.cpp b/src/test/validation_block_tests.cpp
index 1c5ca18759..bb1ade153a 100644
--- a/src/test/validation_block_tests.cpp
+++ b/src/test/validation_block_tests.cpp
@@ -100,7 +100,7 @@ std::shared_ptr<CBlock> MinerTestingSetup::FinalizeBlock(std::shared_ptr<CBlock>
     // submit block header, so that miner can get the block height from the
     // global state and the node has the topology of the chain
     BlockValidationState ignored;
-    BOOST_CHECK(Assert(m_node.chainman)->ProcessNewBlockHeaders({pblock->GetBlockHeader()}, ignored));
+    BOOST_CHECK(Assert(m_node.chainman)->ProcessNewBlockHeaders({pblock->GetBlockHeader()}, true, ignored));
 
     return pblock;
 }
@@ -157,7 +157,7 @@ BOOST_AUTO_TEST_CASE(processnewblock_signals_ordering)
 
     bool ignored;
     // Connect the genesis block and drain any outstanding events
-    BOOST_CHECK(Assert(m_node.chainman)->ProcessNewBlock(std::make_shared<CBlock>(Params().GenesisBlock()), true, &ignored));
+    BOOST_CHECK(Assert(m_node.chainman)->ProcessNewBlock(std::make_shared<CBlock>(Params().GenesisBlock()), true, true, &ignored));
     SyncWithValidationInterfaceQueue();
 
     // subscribe to events (this subscriber will validate event ordering)
@@ -179,13 +179,13 @@ BOOST_AUTO_TEST_CASE(processnewblock_signals_ordering)
             FastRandomContext insecure;
             for (int i = 0; i < 1000; i++) {
                 auto block = blocks[insecure.randrange(blocks.size() - 1)];
-                Assert(m_node.chainman)->ProcessNewBlock(block, true, &ignored);
+                Assert(m_node.chainman)->ProcessNewBlock(block, true, true, &ignored);
             }
 
             // to make sure that eventually we process the full chain - do it here
             for (const auto& block : blocks) {
                 if (block->vtx.size() == 1) {
-                    bool processed = Assert(m_node.chainman)->ProcessNewBlock(block, true, &ignored);
+                    bool processed = Assert(m_node.chainman)->ProcessNewBlock(block, true, true, &ignored);
                     assert(processed);
                 }
             }
@@ -224,7 +224,7 @@ BOOST_AUTO_TEST_CASE(mempool_locks_reorg)
 {
     bool ignored;
     auto ProcessBlock = [&](std::shared_ptr<const CBlock> block) -> bool {
-        return Assert(m_node.chainman)->ProcessNewBlock(block, /*force_processing=*/true, /*new_block=*/&ignored);
+        return Assert(m_node.chainman)->ProcessNewBlock(block, /*force_processing=*/true, /*min_pow_checked=*/true, /*new_block=*/&ignored);
     };
 
     // Process all mined blocks
diff --git a/src/test/validation_chainstate_tests.cpp b/src/test/validation_chainstate_tests.cpp
index ee60f9aa4d..98294b9028 100644
--- a/src/test/validation_chainstate_tests.cpp
+++ b/src/test/validation_chainstate_tests.cpp
@@ -132,7 +132,7 @@ BOOST_FIXTURE_TEST_CASE(chainstate_update_tip, TestChain100Setup)
         bool checked = CheckBlock(*pblock, state, chainparams.GetConsensus());
         BOOST_CHECK(checked);
         bool accepted = background_cs.AcceptBlock(
-            pblock, state, &pindex, true, nullptr, &newblock);
+            pblock, state, &pindex, true, nullptr, &newblock, true);
         BOOST_CHECK(accepted);
     }
     // UpdateTip is called here
diff --git a/src/validation.cpp b/src/validation.cpp
index cb8ac664d8..dda575fede 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -3588,9 +3588,10 @@ static bool ContextualCheckBlock(const CBlock& block, BlockValidationState& stat
     return true;
 }
 
-bool ChainstateManager::AcceptBlockHeader(const CBlockHeader& block, BlockValidationState& state, CBlockIndex** ppindex)
+bool ChainstateManager::AcceptBlockHeader(const CBlockHeader& block, BlockValidationState& state, CBlockIndex** ppindex, bool min_pow_checked)
 {
     AssertLockHeld(cs_main);
+
     // Check for duplicate
     uint256 hash = block.GetHash();
     BlockMap::iterator miSelf{m_blockman.m_block_index.find(hash)};
@@ -3668,6 +3669,10 @@ bool ChainstateManager::AcceptBlockHeader(const CBlockHeader& block, BlockValida
             }
         }
     }
+    if (!min_pow_checked) {
+        LogPrint(BCLog::VALIDATION, "%s: not adding new block header %s, missing anti-dos proof-of-work validation\n", __func__, hash.ToString());
+        return state.Invalid(BlockValidationResult::BLOCK_HEADER_LOW_WORK, "too-little-chainwork");
+    }
     CBlockIndex* pindex{m_blockman.AddToBlockIndex(block, m_best_header)};
 
     if (ppindex)
@@ -3677,14 +3682,14 @@ bool ChainstateManager::AcceptBlockHeader(const CBlockHeader& block, BlockValida
 }
 
 // Exposed wrapper for AcceptBlockHeader
-bool ChainstateManager::ProcessNewBlockHeaders(const std::vector<CBlockHeader>& headers, BlockValidationState& state, const CBlockIndex** ppindex)
+bool ChainstateManager::ProcessNewBlockHeaders(const std::vector<CBlockHeader>& headers, bool min_pow_checked, BlockValidationState& state, const CBlockIndex** ppindex)
 {
     AssertLockNotHeld(cs_main);
     {
         LOCK(cs_main);
         for (const CBlockHeader& header : headers) {
             CBlockIndex *pindex = nullptr; // Use a temp pindex instead of ppindex to avoid a const_cast
-            bool accepted{AcceptBlockHeader(header, state, &pindex)};
+            bool accepted{AcceptBlockHeader(header, state, &pindex, min_pow_checked)};
             ActiveChainstate().CheckBlockIndex();
 
             if (!accepted) {
@@ -3707,7 +3712,7 @@ bool ChainstateManager::ProcessNewBlockHeaders(const std::vector<CBlockHeader>&
 }
 
 /** Store block on disk. If dbp is non-nullptr, the file is known to already reside on disk */
-bool CChainState::AcceptBlock(const std::shared_ptr<const CBlock>& pblock, BlockValidationState& state, CBlockIndex** ppindex, bool fRequested, const FlatFilePos* dbp, bool* fNewBlock)
+bool CChainState::AcceptBlock(const std::shared_ptr<const CBlock>& pblock, BlockValidationState& state, CBlockIndex** ppindex, bool fRequested, const FlatFilePos* dbp, bool* fNewBlock, bool min_pow_checked)
 {
     const CBlock& block = *pblock;
 
@@ -3717,7 +3722,7 @@ bool CChainState::AcceptBlock(const std::shared_ptr<const CBlock>& pblock, Block
     CBlockIndex *pindexDummy = nullptr;
     CBlockIndex *&pindex = ppindex ? *ppindex : pindexDummy;
 
-    bool accepted_header{m_chainman.AcceptBlockHeader(block, state, &pindex)};
+    bool accepted_header{m_chainman.AcceptBlockHeader(block, state, &pindex, min_pow_checked)};
     CheckBlockIndex();
 
     if (!accepted_header)
@@ -3790,7 +3795,7 @@ bool CChainState::AcceptBlock(const std::shared_ptr<const CBlock>& pblock, Block
     return true;
 }
 
-bool ChainstateManager::ProcessNewBlock(const std::shared_ptr<const CBlock>& block, bool force_processing, bool* new_block)
+bool ChainstateManager::ProcessNewBlock(const std::shared_ptr<const CBlock>& block, bool force_processing, bool min_pow_checked, bool* new_block)
 {
     AssertLockNotHeld(cs_main);
 
@@ -3811,7 +3816,7 @@ bool ChainstateManager::ProcessNewBlock(const std::shared_ptr<const CBlock>& blo
         bool ret = CheckBlock(*block, state, GetConsensus());
         if (ret) {
             // Store to disk
-            ret = ActiveChainstate().AcceptBlock(block, state, &pindex, force_processing, nullptr, new_block);
+            ret = ActiveChainstate().AcceptBlock(block, state, &pindex, force_processing, nullptr, new_block, min_pow_checked);
         }
         if (!ret) {
             GetMainSignals().BlockChecked(*block, state);
@@ -4348,7 +4353,7 @@ void CChainState::LoadExternalBlockFile(
                     const CBlockIndex* pindex = m_blockman.LookupBlockIndex(hash);
                     if (!pindex || (pindex->nStatus & BLOCK_HAVE_DATA) == 0) {
                       BlockValidationState state;
-                      if (AcceptBlock(pblock, state, nullptr, true, dbp, nullptr)) {
+                      if (AcceptBlock(pblock, state, nullptr, true, dbp, nullptr, true)) {
                           nLoaded++;
                       }
                       if (state.IsError()) {
@@ -4386,7 +4391,7 @@ void CChainState::LoadExternalBlockFile(
                                     head.ToString());
                             LOCK(cs_main);
                             BlockValidationState dummy;
-                            if (AcceptBlock(pblockrecursive, dummy, nullptr, true, &it->second, nullptr)) {
+                            if (AcceptBlock(pblockrecursive, dummy, nullptr, true, &it->second, nullptr, true)) {
                                 nLoaded++;
                                 queue.push_back(pblockrecursive->GetHash());
                             }
diff --git a/src/validation.h b/src/validation.h
index 64217e6a11..e5af65cde8 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -656,7 +656,7 @@ public:
         EXCLUSIVE_LOCKS_REQUIRED(!m_chainstate_mutex)
         LOCKS_EXCLUDED(::cs_main);
 
-    bool AcceptBlock(const std::shared_ptr<const CBlock>& pblock, BlockValidationState& state, CBlockIndex** ppindex, bool fRequested, const FlatFilePos* dbp, bool* fNewBlock) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+    bool AcceptBlock(const std::shared_ptr<const CBlock>& pblock, BlockValidationState& state, CBlockIndex** ppindex, bool fRequested, const FlatFilePos* dbp, bool* fNewBlock, bool min_pow_checked) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
     // Block (dis)connection on a given view:
     DisconnectResult DisconnectBlock(const CBlock& block, const CBlockIndex* pindex, CCoinsViewCache& view)
@@ -857,11 +857,15 @@ private:
     /**
      * If a block header hasn't already been seen, call CheckBlockHeader on it, ensure
      * that it doesn't descend from an invalid block, and then add it to m_block_index.
+     * Caller must set min_pow_checked=true in order to add a new header to the
+     * block index (permanent memory storage), indicating that the header is
+     * known to be part of a sufficiently high-work chain (anti-dos check).
      */
     bool AcceptBlockHeader(
         const CBlockHeader& block,
         BlockValidationState& state,
-        CBlockIndex** ppindex) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
+        CBlockIndex** ppindex,
+        bool min_pow_checked) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
     friend CChainState;
 
 public:
@@ -997,10 +1001,15 @@ public:
      *
      * @param[in]   block The block we want to process.
      * @param[in]   force_processing Process this block even if unrequested; used for non-network block sources.
+     * @param[in]   min_pow_checked  True if proof-of-work anti-DoS checks have
+     *                               been done by caller for headers chain
+     *                               (note: only affects headers acceptance; if
+     *                               block header is already present in block
+     *                               index then this parameter has no effect)
      * @param[out]  new_block A boolean which is set to indicate if the block was first received via this call
      * @returns     If the block was processed, independently of block validity
      */
-    bool ProcessNewBlock(const std::shared_ptr<const CBlock>& block, bool force_processing, bool* new_block) LOCKS_EXCLUDED(cs_main);
+    bool ProcessNewBlock(const std::shared_ptr<const CBlock>& block, bool force_processing, bool min_pow_checked, bool* new_block) LOCKS_EXCLUDED(cs_main);
 
     /**
      * Process incoming block headers.
@@ -1009,10 +1018,11 @@ public:
      * validationinterface callback.
      *
      * @param[in]  block The block headers themselves
+     * @param[in]  min_pow_checked  True if proof-of-work anti-DoS checks have been done by caller for headers chain
      * @param[out] state This may be set to an Error state if any error occurred processing them
      * @param[out] ppindex If set, the pointer will be set to point to the last new block index object for the given headers
      */
-    bool ProcessNewBlockHeaders(const std::vector<CBlockHeader>& block, BlockValidationState& state, const CBlockIndex** ppindex = nullptr) LOCKS_EXCLUDED(cs_main);
+    bool ProcessNewBlockHeaders(const std::vector<CBlockHeader>& block, bool min_pow_checked, BlockValidationState& state, const CBlockIndex** ppindex = nullptr) LOCKS_EXCLUDED(cs_main);
 
     /**
      * Try to add a transaction to the memory pool.