Block ancient dust spam

src/main.cpp

@@ -642,7 +642,7 @@ CTxIndex::GetContainingBlock (const CDiskTxPos& pos)
 
     // Read block header
     CBlock block;
-    if (!block.ReadFromDisk(pos.nFile, pos.nBlockPos, false))
+    if (!block.ReadFromDisk (pos.nFile, pos.nBlockPos, false))
         return NULL;
 
     // Find the block in the index
@@ -1164,6 +1164,15 @@ CTransaction::ConnectInputs (DatabaseSet& dbset,
             assert (vin[i].fHasPrevInfo);
             assert (txPrev);
 
+            /* Calculate the previous output's height.  Note that the value
+               here should be ensured to be accurate, since IsUnspendable
+               below depends on it for block validation!  Thus we do not
+               use the cache introduced for priority calculation.  */
+            int prevHeight = txindex.GetHeight ();
+            if (prevHeight == -1)
+              prevHeight = pindexBlock->nHeight;
+            assert (prevHeight >= 0);
+
             if (prevout.n >= txPrev->vout.size ())
               return error ("ConnectInputs: %s prevout.n out of range"
                             " %d %d prev tx %s\n%s",
@@ -1180,6 +1189,15 @@ CTransaction::ConnectInputs (DatabaseSet& dbset,
               return error ("ConnectInputs: %s VerifySignature failed",
                             GetHash ().ToString ().substr (0, 10).c_str ());
 
+            /* Check for unspendable outputs.  This is redundant for some
+               of the checks done in IsUnspendable, but it also takes care
+               of blocking dust spam.  If not validating blocks (i. e., miner
+               or mempool), we are strict and block dust even before
+               the hardfork point.  */
+            if (IsUnspendable (txPrev->vout[prevout.n], prevHeight,
+                               pindexBlock->nHeight, !fBlock))
+              return error ("ConnectInputs: previous txo is unspendable");
+
             // If prev is coinbase, check that it's matured
             if (txPrev->IsCoinBase ())
                 for (CBlockIndex* pindex = pindexBlock; pindex && pindexBlock->nHeight - pindex->nHeight < COINBASE_MATURITY; pindex = pindex->pprev)

src/main.h

@@ -110,6 +110,7 @@ extern CHooks* hooks;
 class CReserveKey;
 class CTxDB;
 class CTxIndex;
+class CTxOut;
 
 void RegisterWallet(CWallet* pwalletIn);
 void UnregisterWallet(CWallet* pwalletIn);
@@ -141,6 +142,14 @@ std::string GetWarnings(std::string strFor);
 /** Retrieve a transaction (from memory pool, or from disk, if possible) */
 bool GetTransaction(const uint256 &hash, CTransaction &txOut, uint256 &hashBlock /*, bool fAllowSlow = false*/  );
 
+/* Check if a transaction is unspendable.  Either because it is provably
+   prunable, or because it is explicitly blocked due to some rule.  nHeight
+   is the height at which (or later) it will be spent, and nPrevHeight
+   is the one where it is included in the block chain.  The strict parameter
+   can be turned on for mempool validation (as opposed to blocks) to
+   reject transactions from the mempool even before a hardfork.  */
+bool IsUnspendable (const CTxOut& txo, int nPrevHeight,
+                    int nHeight, bool strict);
 
 
 
@@ -942,6 +951,10 @@ class CTxIndex
     static int GetHeight (const CDiskTxPos& pos);
     static int GetDepthInMainChain (const CDiskTxPos& pos);
 
+    inline int GetHeight () const
+    {
+      return GetHeight (pos);
+    }
     inline int GetDepthInMainChain () const
     {
       return GetDepthInMainChain (pos);

src/namecoin.cpp

@@ -28,6 +28,9 @@ template<typename T> void ConvertTo(Value& value, bool fAllowNull=false);
 static const int BUG_WORKAROUND_BLOCK_START = 139750;   // Bug was not exploited before block 139872, so skip checking earlier blocks
 static const int BUG_WORKAROUND_BLOCK = 150000;         // Point of hard fork
 
+/* Softfork point where the dustspam block was introduced.  */
+static const int FORK_HEIGHT_DUSTSPAM = 300000;
+
 map<vector<unsigned char>, uint256> mapMyNames;
 map<vector<unsigned char>, set<uint256> > mapNamePending;
 
@@ -1933,6 +1936,44 @@ int64 GetNameNetFee(const CTransaction& tx)
     return nFee;
 }
 
+bool
+IsUnspendable (const CTxOut& txo, int nPrevHeight, int nHeight, bool strict)
+{
+  assert (nPrevHeight <= nHeight);
+
+  /* An OP_RETURN script as per network fee payments is always
+     unspendable.  Check this.  */
+  const CScript& script = txo.scriptPubKey;
+  if (script.size () == 1 && script[0] == OP_RETURN)
+    return true;
+
+  /* Block dust spam outputs, so that they can be removed from the UTXO
+     set.  We block all 1-Swartz outputs created between blocks 39k and 41k.
+     Blocking takes effect at the softfork height.  */
+  if (txo.nValue == 1 && nPrevHeight >= 39000 && nPrevHeight <= 41000
+      && (strict || nHeight >= FORK_HEIGHT_DUSTSPAM))
+    return true;
+
+  /* A name_update or name_firstupdate is unspendable if expired.  */
+  if (nHeight >= nPrevHeight + GetExpirationDepth (nHeight))
+    {
+      int op;
+      std::vector<vchType> vvch;
+      if (DecodeNameScript (script, op, vvch))
+        switch (op)
+          {
+          case OP_NAME_FIRSTUPDATE:
+          case OP_NAME_UPDATE:
+            return true;
+
+          default:
+            break;
+          }
+    }
+
+  return false;
+}
+
 bool GetValueOfNameTx(const CTransaction& tx, vector<unsigned char>& value)
 {
     vector<vector<unsigned char> > vvch;