Add standard limits for P2WSH with tests

4 files changed, 181 insertions, 2 deletions

diff --git a/qa/rpc-tests/p2p-segwit.py b/qa/rpc-tests/p2p-segwit.py
index c2ea20bb84..16d1e86802 100755
--- a/qa/rpc-tests/p2p-segwit.py
+++ b/qa/rpc-tests/p2p-segwit.py
@@ -1706,6 +1706,116 @@ class SegWitTest(BitcoinTestFramework):
         assert(block_version & (1 << VB_WITNESS_BIT) != 0)
         self.nodes[0].setmocktime(0) # undo mocktime
 
+    def test_non_standard_witness(self):
+        print("\tTesting detection of non-standard P2WSH witness")
+        pad = chr(1).encode('latin-1')
+
+        # Create scripts for tests
+        scripts = []
+        scripts.append(CScript([OP_DROP] * 100))
+        scripts.append(CScript([OP_DROP] * 99))
+        scripts.append(CScript([pad * 59] * 59 + [OP_DROP] * 60))
+        scripts.append(CScript([pad * 59] * 59 + [OP_DROP] * 61))
+
+        p2wsh_scripts = []
+
+        assert(len(self.utxo))
+        tx = CTransaction()
+        tx.vin.append(CTxIn(COutPoint(self.utxo[0].sha256, self.utxo[0].n), b""))
+
+        # For each script, generate a pair of P2WSH and P2SH-P2WSH output.
+        outputvalue = (self.utxo[0].nValue - 1000) // (len(scripts) * 2)
+        for i in scripts:
+            p2wsh = CScript([OP_0, sha256(i)])
+            p2sh = hash160(p2wsh)
+            p2wsh_scripts.append(p2wsh)
+            tx.vout.append(CTxOut(outputvalue, p2wsh))
+            tx.vout.append(CTxOut(outputvalue, CScript([OP_HASH160, p2sh, OP_EQUAL])))
+        tx.rehash()
+        txid = tx.sha256
+        self.test_node.test_transaction_acceptance(tx, with_witness=False, accepted=True)
+
+        self.nodes[0].generate(1)
+        sync_blocks(self.nodes)
+
+        # Creating transactions for tests
+        p2wsh_txs = []
+        p2sh_txs = []
+        for i in range(len(scripts)):
+            p2wsh_tx = CTransaction()
+            p2wsh_tx.vin.append(CTxIn(COutPoint(txid,i*2)))
+            p2wsh_tx.vout.append(CTxOut(outputvalue - 5000, CScript([OP_0, hash160(hex_str_to_bytes(""))])))
+            p2wsh_tx.wit.vtxinwit.append(CTxInWitness())
+            p2wsh_tx.rehash()
+            p2wsh_txs.append(p2wsh_tx)
+            p2sh_tx = CTransaction()
+            p2sh_tx.vin.append(CTxIn(COutPoint(txid,i*2+1), CScript([p2wsh_scripts[i]])))
+            p2sh_tx.vout.append(CTxOut(outputvalue - 5000, CScript([OP_0, hash160(hex_str_to_bytes(""))])))
+            p2sh_tx.wit.vtxinwit.append(CTxInWitness())
+            p2sh_tx.rehash()
+            p2sh_txs.append(p2sh_tx)
+
+        # Testing native P2WSH
+        # Witness stack size, excluding witnessScript, over 100 is non-standard
+        p2wsh_txs[0].wit.vtxinwit[0].scriptWitness.stack = [pad] * 101 + [scripts[0]]
+        self.std_node.test_transaction_acceptance(p2wsh_txs[0], True, False, b'bad-witness-nonstandard')
+        # Non-standard nodes should accept
+        self.test_node.test_transaction_acceptance(p2wsh_txs[0], True, True)
+
+        # Stack element size over 80 bytes is non-standard
+        p2wsh_txs[1].wit.vtxinwit[0].scriptWitness.stack = [pad * 81] * 100 + [scripts[1]]
+        # It can't be used to blind a node to the transaction
+        self.std_node.announce_tx_and_wait_for_getdata(p2wsh_txs[1])
+        self.std_node.test_transaction_acceptance(p2wsh_txs[1], True, False, b'bad-witness-nonstandard')
+        self.std_node.announce_tx_and_wait_for_getdata(p2wsh_txs[1])
+        self.std_node.test_transaction_acceptance(p2wsh_txs[1], True, False, b'bad-witness-nonstandard')
+        # Non-standard nodes should accept
+        self.test_node.test_transaction_acceptance(p2wsh_txs[1], True, True)
+        # Standard nodes should accept if element size is not over 80 bytes
+        p2wsh_txs[1].wit.vtxinwit[0].scriptWitness.stack = [pad * 80] * 100 + [scripts[1]]
+        self.std_node.announce_tx_and_wait_for_getdata(p2wsh_txs[1])
+        self.std_node.test_transaction_acceptance(p2wsh_txs[1], True, True)
+
+        # witnessScript size at 3600 bytes is standard
+        p2wsh_txs[2].wit.vtxinwit[0].scriptWitness.stack = [pad, pad, scripts[2]]
+        self.test_node.test_transaction_acceptance(p2wsh_txs[2], True, True)
+        self.std_node.test_transaction_acceptance(p2wsh_txs[2], True, True)
+
+        # witnessScript size at 3601 bytes is non-standard
+        p2wsh_txs[3].wit.vtxinwit[0].scriptWitness.stack = [pad, pad, pad, scripts[3]]
+        self.std_node.test_transaction_acceptance(p2wsh_txs[3], True, False, b'bad-witness-nonstandard')
+        # Non-standard nodes should accept
+        self.test_node.test_transaction_acceptance(p2wsh_txs[3], True, True)
+
+        # Repeating the same tests with P2SH-P2WSH
+        p2sh_txs[0].wit.vtxinwit[0].scriptWitness.stack = [pad] * 101 + [scripts[0]]
+        self.std_node.test_transaction_acceptance(p2sh_txs[0], True, False, b'bad-witness-nonstandard')
+        self.test_node.test_transaction_acceptance(p2sh_txs[0], True, True)
+        p2sh_txs[1].wit.vtxinwit[0].scriptWitness.stack = [pad * 81] * 100 + [scripts[1]]
+        self.std_node.announce_tx_and_wait_for_getdata(p2sh_txs[1])
+        self.std_node.test_transaction_acceptance(p2sh_txs[1], True, False, b'bad-witness-nonstandard')
+        self.std_node.announce_tx_and_wait_for_getdata(p2sh_txs[1])
+        self.std_node.test_transaction_acceptance(p2sh_txs[1], True, False, b'bad-witness-nonstandard')
+        self.test_node.test_transaction_acceptance(p2sh_txs[1], True, True)
+        p2sh_txs[1].wit.vtxinwit[0].scriptWitness.stack = [pad * 80] * 100 + [scripts[1]]
+        self.std_node.announce_tx_and_wait_for_getdata(p2sh_txs[1])
+        self.std_node.test_transaction_acceptance(p2sh_txs[1], True, True)
+        p2sh_txs[2].wit.vtxinwit[0].scriptWitness.stack = [pad, pad, scripts[2]]
+        self.test_node.test_transaction_acceptance(p2sh_txs[2], True, True)
+        self.std_node.test_transaction_acceptance(p2sh_txs[2], True, True)
+        p2sh_txs[3].wit.vtxinwit[0].scriptWitness.stack = [pad, pad, pad, scripts[3]]
+        self.std_node.test_transaction_acceptance(p2sh_txs[3], True, False, b'bad-witness-nonstandard')
+        self.test_node.test_transaction_acceptance(p2sh_txs[3], True, True)
+
+        self.nodes[0].generate(1)  # Mine and clean up the mempool of non-standard node
+        # Valid but non-standard transactions in a block should be accepted by standard node
+        sync_blocks(self.nodes)
+        assert_equal(len(self.nodes[0].getrawmempool()), 0)
+        assert_equal(len(self.nodes[1].getrawmempool()), 0)
+
+        self.utxo.pop(0)
+
+
     def run_test(self):
         # Setup the p2p connections and start up the network thread.
         self.test_node = TestNode() # sets NODE_WITNESS|NODE_NETWORK
@@ -1778,6 +1888,7 @@ class SegWitTest(BitcoinTestFramework):
         self.test_segwit_versions()
         self.test_premature_coinbase_witness_spend()
         self.test_signature_version_1()
+        self.test_non_standard_witness()
         sync_blocks(self.nodes)
         if self.test_upgrade:
             self.test_upgrade_after_activation(self.nodes[2], 2)
diff --git a/src/main.cpp b/src/main.cpp
index c92a38be98..020378b5dc 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,5 +1,5 @@
 // Copyright (c) 2009-2010 Satoshi Nakamoto
-// Copyright (c) 2009-2015 The Bitcoin Core developers
+// Copyright (c) 2009-2016 The Bitcoin Core developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -1273,6 +1273,10 @@ bool AcceptToMemoryPoolWorker(CTxMemPool& pool, CValidationState& state, const C
         if (fRequireStandard && !AreInputsStandard(tx, view))
             return state.Invalid(false, REJECT_NONSTANDARD, "bad-txns-nonstandard-inputs");
 
+        // Check for non-standard witness in P2WSH
+        if (!tx.wit.IsNull() && fRequireStandard && !IsWitnessStandard(tx, view))
+            return state.DoS(0, false, REJECT_NONSTANDARD, "bad-witness-nonstandard", true);
+
         int64_t nSigOpsCost = GetTransactionSigOpCost(tx, view, STANDARD_SCRIPT_VERIFY_FLAGS);
 
         CAmount nValueOut = tx.GetValueOut();
diff --git a/src/policy/policy.cpp b/src/policy/policy.cpp
index 48080abc77..ae42b2bd74 100644
--- a/src/policy/policy.cpp
+++ b/src/policy/policy.cpp
@@ -1,5 +1,5 @@
 // Copyright (c) 2009-2010 Satoshi Nakamoto
-// Copyright (c) 2009-2015 The Bitcoin developers
+// Copyright (c) 2009-2016 The Bitcoin developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -154,6 +154,58 @@ bool AreInputsStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)
     return true;
 }
 
+bool IsWitnessStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)
+{
+    if (tx.IsCoinBase())
+        return true; // Coinbases are skipped
+
+    for (unsigned int i = 0; i < tx.vin.size(); i++)
+    {
+        // We don't care if witness for this input is empty, since it must not be bloated.
+        // If the script is invalid without witness, it would be caught sooner or later during validation.
+        if (tx.wit.vtxinwit[i].IsNull())
+            continue;
+
+        const CTxOut &prev = mapInputs.GetOutputFor(tx.vin[i]);
+
+        // get the scriptPubKey corresponding to this input:
+        CScript prevScript = prev.scriptPubKey;
+
+        if (prevScript.IsPayToScriptHash()) {
+            std::vector <std::vector<unsigned char> > stack;
+            // If the scriptPubKey is P2SH, we try to extract the redeemScript casually by converting the scriptSig
+            // into a stack. We do not check IsPushOnly nor compare the hash as these will be done later anyway.
+            // If the check fails at this stage, we know that this txid must be a bad one.
+            if (!EvalScript(stack, tx.vin[i].scriptSig, SCRIPT_VERIFY_NONE, BaseSignatureChecker(), SIGVERSION_BASE))
+                return false;
+            if (stack.empty())
+                return false;
+            prevScript = CScript(stack.back().begin(), stack.back().end());
+        }
+
+        int witnessversion = 0;
+        std::vector<unsigned char> witnessprogram;
+
+        // Non-witness program must not be associated with any witness
+        if (!prevScript.IsWitnessProgram(witnessversion, witnessprogram))
+            return false;
+
+        // Check P2WSH standard limits
+        if (witnessversion == 0 && witnessprogram.size() == 32) {
+            if (tx.wit.vtxinwit[i].scriptWitness.stack.back().size() > MAX_STANDARD_P2WSH_SCRIPT_SIZE)
+                return false;
+            size_t sizeWitnessStack = tx.wit.vtxinwit[i].scriptWitness.stack.size() - 1;
+            if (sizeWitnessStack > MAX_STANDARD_P2WSH_STACK_ITEMS)
+                return false;
+            for (unsigned int j = 0; j < sizeWitnessStack; j++) {
+                if (tx.wit.vtxinwit[i].scriptWitness.stack[j].size() > MAX_STANDARD_P2WSH_STACK_ITEM_SIZE)
+                    return false;
+            }
+        }
+    }
+    return true;
+}
+
 unsigned int nBytesPerSigOp = DEFAULT_BYTES_PER_SIGOP;
 
 int64_t GetVirtualTransactionSize(int64_t nWeight, int64_t nSigOpCost)
diff --git a/src/policy/policy.h b/src/policy/policy.h
index 9d6ff1233b..fb528d7486 100644
--- a/src/policy/policy.h
+++ b/src/policy/policy.h
@@ -30,6 +30,12 @@ static const unsigned int MAX_STANDARD_TX_SIGOPS_COST = MAX_BLOCK_SIGOPS_COST/5;
 static const unsigned int DEFAULT_MAX_MEMPOOL_SIZE = 300;
 /** Default for -bytespersigop */
 static const unsigned int DEFAULT_BYTES_PER_SIGOP = 20;
+/** The maximum number of witness stack items in a standard P2WSH script */
+static const unsigned int MAX_STANDARD_P2WSH_STACK_ITEMS = 100;
+/** The maximum size of each witness stack item in a standard P2WSH script */
+static const unsigned int MAX_STANDARD_P2WSH_STACK_ITEM_SIZE = 80;
+/** The maximum size of a standard witnessScript */
+static const unsigned int MAX_STANDARD_P2WSH_SCRIPT_SIZE = 3600;
 /**
  * Standard script verification flags that standard transactions will comply
  * with. However scripts violating these flags may still be present in valid
@@ -69,6 +75,12 @@ bool IsStandardTx(const CTransaction& tx, std::string& reason, const bool witnes
      * @return True if all inputs (scriptSigs) use only standard transaction forms
      */
 bool AreInputsStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs);
+    /**
+     * Check if the transaction is over standard P2WSH resources limit:
+     * 3600bytes witnessScript size, 80bytes per witness stack element, 100 witness stack elements
+     * These limits are adequate for multi-signature up to n-of-100 using OP_CHECKSIG, OP_ADD, and OP_EQUAL,
+     */
+bool IsWitnessStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs);
 
 extern unsigned int nBytesPerSigOp;