net: assert block hash in ProcessGetBlockData and ProcessMessage

The non-recent-block code path in `ProcessGetBlockData` already has `inv.hash` available (equaling `pindex->GetBlockHash()`).
Pass it to `ReadBlock()` and assert that the on-disk header matches the requested hash.

The `GETBLOCKTXN` message handler in `ProcessMessage` receives `req.blockhash` from the peer (equaling `pindex->GetBlockHash()`).
Pass this hash to `ReadBlock()` for verification and assert that the index lookup matches.

Co-authored-by: TheCharlatan <seb.kung@gmail.com>
Co-authored-by: Hodlinator <172445034+hodlinator@users.noreply.github.com>

src/net_processing.cpp

@@ -2298,7 +2298,7 @@ void PeerManagerImpl::ProcessGetBlockData(CNode& pfrom, Peer& peer, const CInv&
     }
 
     std::shared_ptr<const CBlock> pblock;
-    if (a_recent_block && a_recent_block->GetHash() == pindex->GetBlockHash()) {
+    if (a_recent_block && a_recent_block->GetHash() == inv.hash) {
         pblock = a_recent_block;
     } else if (inv.IsMsgWitnessBlk()) {
         // Fast-path: in this case it is possible to serve the block directly from disk,
@@ -2318,7 +2318,7 @@ void PeerManagerImpl::ProcessGetBlockData(CNode& pfrom, Peer& peer, const CInv&
     } else {
         // Send block from disk
         std::shared_ptr<CBlock> pblockRead = std::make_shared<CBlock>();
-        if (!m_chainman.m_blockman.ReadBlock(*pblockRead, block_pos)) {
+        if (!m_chainman.m_blockman.ReadBlock(*pblockRead, block_pos, inv.hash)) {
             if (WITH_LOCK(m_chainman.GetMutex(), return m_chainman.m_blockman.IsBlockPruned(*pindex))) {
                 LogDebug(BCLog::NET, "Block was pruned before it could be read, %s\n", pfrom.DisconnectMsg(fLogIPs));
             } else {
@@ -2364,7 +2364,7 @@ void PeerManagerImpl::ProcessGetBlockData(CNode& pfrom, Peer& peer, const CInv&
             // and we don't feel like constructing the object for them, so
             // instead we respond with the full, non-compact block.
             if (can_direct_fetch && pindex->nHeight >= tip->nHeight - MAX_CMPCTBLOCK_DEPTH) {
-                if (a_recent_compact_block && a_recent_compact_block->header.GetHash() == pindex->GetBlockHash()) {
+                if (a_recent_compact_block && a_recent_compact_block->header.GetHash() == inv.hash) {
                     MakeAndPushMessage(pfrom, NetMsgType::CMPCTBLOCK, *a_recent_compact_block);
                 } else {
                     CBlockHeaderAndShortTxIDs cmpctblock{*pblock, m_rng.rand64()};
@@ -4173,7 +4173,7 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
 
         if (!block_pos.IsNull()) {
             CBlock block;
-            const bool ret{m_chainman.m_blockman.ReadBlock(block, block_pos)};
+            const bool ret{m_chainman.m_blockman.ReadBlock(block, block_pos, req.blockhash)};
             // If height is above MAX_BLOCKTXN_DEPTH then this block cannot get
             // pruned after we release cs_main above, so this read should never fail.
             assert(ret);