Merge #21330: Deal with missing data in signature hashes more consistently

725d7ae Use PrecomputedTransactionData in signet check (Pieter Wuille)
497718b Treat amount<0 also as missing data for P2WPKH/P2WSH (Pieter Wuille)
3820090 Make all SignatureChecker explicit about missing data (Pieter Wuille)
b77b0cc Add MissingDataBehavior and make TransactionSignatureChecker handle it (Pieter Wuille)

Pull request description:

  Currently we have 2 levels of potentially-missing data in the transaction signature hashes:
  * P2WPKH/P2WSH hashes need the spent amount
  * P2TR hashes need all spent outputs (amount + scriptPubKey)

  Missing amounts are treated as -1 (thus leading to unexpected signature failures), while missing outputs in P2TR validation cause assertion failure. This is hard to extend for signing support, and also quite ugly in general.

  In this PR, an explicit configuration option to {Mutable,}TransactionSignatureChecker is added (MissingDataBehavior enum class) to either select ASSERT_FAIL or FAIL. Validation code passes ASSERT_FAIL (as at validation time all data should always be passed, and anything else is a serious bug in the code), while signing code uses FAIL.

  The existence of the ASSERT_FAIL option is really just an abundance of caution. Always using FAIL should be just fine, but if there were for some reason a code path in consensus code was introduced that misses certain data, I think we prefer as assertion failure over silently introducing a consensus change.

  Potentially useful follow-ups (not for this PR, in my preference):
  * Having an explicit script validation error code for missing data.
  * Having a MissingDataBehavior::SUCCEED option as well, for use in script/sign.cpp DataFromTransaction (if a signature is present in a witness, and we don't have enough data to fully validate it, we should probably treat it as valid and not touch it).

ACKs for top commit:
  sanket1729:
    reACK 725d7ae
  Sjors:
    ACK 725d7ae
  achow101:
    re-ACK 725d7ae
  benthecarman:
    ACK 725d7ae
  fjahr:
    Code review ACK 725d7ae

Tree-SHA512: d67dc51bae9ca7ef6eb9acccefd682529f397830f77d74cd305500a081ef55aede0e9fa380648c3a8dd4857aa7eeb1ab54fe808979d79db0784ac94ceb31b657

Author: fanquake

src/bench/verify_script.cpp

@@ -56,7 +56,7 @@ static void VerifyScriptBench(benchmark::Bench& bench)
             txCredit.vout[0].scriptPubKey,
             &txSpend.vin[0].scriptWitness,
             flags,
-            MutableTransactionSignatureChecker(&txSpend, 0, txCredit.vout[0].nValue),
+            MutableTransactionSignatureChecker(&txSpend, 0, txCredit.vout[0].nValue, MissingDataBehavior::ASSERT_FAIL),
             &err);
         assert(err == SCRIPT_ERR_OK);
         assert(success);

src/script/bitcoinconsensus.cpp

@@ -92,7 +92,7 @@ static int verify_script(const unsigned char *scriptPubKey, unsigned int scriptP
         set_error(err, bitcoinconsensus_ERR_OK);
 
         PrecomputedTransactionData txdata(tx);
-        return VerifyScript(tx.vin[nIn].scriptSig, CScript(scriptPubKey, scriptPubKey + scriptPubKeyLen), &tx.vin[nIn].scriptWitness, flags, TransactionSignatureChecker(&tx, nIn, amount, txdata), nullptr);
+        return VerifyScript(tx.vin[nIn].scriptSig, CScript(scriptPubKey, scriptPubKey + scriptPubKeyLen), &tx.vin[nIn].scriptWitness, flags, TransactionSignatureChecker(&tx, nIn, amount, txdata, MissingDataBehavior::FAIL), nullptr);
     } catch (const std::exception&) {
         return set_error(err, bitcoinconsensus_ERR_TX_DESERIALIZE); // Error deserializing
     }

src/script/interpreter.cpp

@@ -1488,8 +1488,20 @@ static const CHashWriter HASHER_TAPLEAF = TaggedHash("TapLeaf");
 static const CHashWriter HASHER_TAPBRANCH = TaggedHash("TapBranch");
 static const CHashWriter HASHER_TAPTWEAK = TaggedHash("TapTweak");
 
+static bool HandleMissingData(MissingDataBehavior mdb)
+{
+    switch (mdb) {
+    case MissingDataBehavior::ASSERT_FAIL:
+        assert(!"Missing data");
+        break;
+    case MissingDataBehavior::FAIL:
+        return false;
+    }
+    assert(!"Unknown MissingDataBehavior value");
+}
+
 template<typename T>
-bool SignatureHashSchnorr(uint256& hash_out, const ScriptExecutionData& execdata, const T& tx_to, uint32_t in_pos, uint8_t hash_type, SigVersion sigversion, const PrecomputedTransactionData& cache)
+bool SignatureHashSchnorr(uint256& hash_out, const ScriptExecutionData& execdata, const T& tx_to, uint32_t in_pos, uint8_t hash_type, SigVersion sigversion, const PrecomputedTransactionData& cache, MissingDataBehavior mdb)
 {
     uint8_t ext_flag, key_version;
     switch (sigversion) {
@@ -1509,7 +1521,9 @@ bool SignatureHashSchnorr(uint256& hash_out, const ScriptExecutionData& execdata
         assert(false);
     }
     assert(in_pos < tx_to.vin.size());
-    assert(cache.m_bip341_taproot_ready && cache.m_spent_outputs_ready);
+    if (!(cache.m_bip341_taproot_ready && cache.m_spent_outputs_ready)) {
+        return HandleMissingData(mdb);
+    }
 
     CHashWriter ss = HASHER_TAPSIGHASH;
 
@@ -1667,6 +1681,9 @@ bool GenericTransactionSignatureChecker<T>::CheckECDSASignature(const std::vecto
     int nHashType = vchSig.back();
     vchSig.pop_back();
 
+    // Witness sighashes need the amount.
+    if (sigversion == SigVersion::WITNESS_V0 && amount < 0) return HandleMissingData(m_mdb);
+
     uint256 sighash = SignatureHash(scriptCode, *txTo, nIn, nHashType, amount, sigversion, this->txdata);
 
     if (!VerifyECDSASignature(vchSig, pubkey, sighash))
@@ -1696,7 +1713,7 @@ bool GenericTransactionSignatureChecker<T>::CheckSchnorrSignature(Span<const uns
     }
     uint256 sighash;
     assert(this->txdata);
-    if (!SignatureHashSchnorr(sighash, execdata, *txTo, nIn, hashtype, sigversion, *this->txdata)) {
+    if (!SignatureHashSchnorr(sighash, execdata, *txTo, nIn, hashtype, sigversion, *this->txdata, m_mdb)) {
         return set_error(serror, SCRIPT_ERR_SCHNORR_SIG_HASHTYPE);
     }
     if (!VerifySchnorrSignature(sig, pubkey, sighash)) return set_error(serror, SCRIPT_ERR_SCHNORR_SIG);

src/script/interpreter.h

@@ -247,11 +247,21 @@ class BaseSignatureChecker
     virtual ~BaseSignatureChecker() {}
 };
 
+/** Enum to specify what *TransactionSignatureChecker's behavior should be
+ *  when dealing with missing transaction data.
+ */
+enum class MissingDataBehavior
+{
+    ASSERT_FAIL,  //!< Abort execution through assertion failure (for consensus code)
+    FAIL,         //!< Just act as if the signature was invalid
+};
+
 template <class T>
 class GenericTransactionSignatureChecker : public BaseSignatureChecker
 {
 private:
     const T* txTo;
+    const MissingDataBehavior m_mdb;
     unsigned int nIn;
     const CAmount amount;
     const PrecomputedTransactionData* txdata;
@@ -261,8 +271,8 @@ class GenericTransactionSignatureChecker : public BaseSignatureChecker
     virtual bool VerifySchnorrSignature(Span<const unsigned char> sig, const XOnlyPubKey& pubkey, const uint256& sighash) const;
 
 public:
-    GenericTransactionSignatureChecker(const T* txToIn, unsigned int nInIn, const CAmount& amountIn) : txTo(txToIn), nIn(nInIn), amount(amountIn), txdata(nullptr) {}
-    GenericTransactionSignatureChecker(const T* txToIn, unsigned int nInIn, const CAmount& amountIn, const PrecomputedTransactionData& txdataIn) : txTo(txToIn), nIn(nInIn), amount(amountIn), txdata(&txdataIn) {}
+    GenericTransactionSignatureChecker(const T* txToIn, unsigned int nInIn, const CAmount& amountIn, MissingDataBehavior mdb) : txTo(txToIn), m_mdb(mdb), nIn(nInIn), amount(amountIn), txdata(nullptr) {}
+    GenericTransactionSignatureChecker(const T* txToIn, unsigned int nInIn, const CAmount& amountIn, const PrecomputedTransactionData& txdataIn, MissingDataBehavior mdb) : txTo(txToIn), m_mdb(mdb), nIn(nInIn), amount(amountIn), txdata(&txdataIn) {}
     bool CheckECDSASignature(const std::vector<unsigned char>& scriptSig, const std::vector<unsigned char>& vchPubKey, const CScript& scriptCode, SigVersion sigversion) const override;
     bool CheckSchnorrSignature(Span<const unsigned char> sig, Span<const unsigned char> pubkey, SigVersion sigversion, const ScriptExecutionData& execdata, ScriptError* serror = nullptr) const override;
     bool CheckLockTime(const CScriptNum& nLockTime) const override;

src/script/sigcache.h

@@ -27,7 +27,7 @@ class CachingTransactionSignatureChecker : public TransactionSignatureChecker
     bool store;
 
 public:
-    CachingTransactionSignatureChecker(const CTransaction* txToIn, unsigned int nInIn, const CAmount& amountIn, bool storeIn, PrecomputedTransactionData& txdataIn) : TransactionSignatureChecker(txToIn, nInIn, amountIn, txdataIn), store(storeIn) {}
+    CachingTransactionSignatureChecker(const CTransaction* txToIn, unsigned int nInIn, const CAmount& amountIn, bool storeIn, PrecomputedTransactionData& txdataIn) : TransactionSignatureChecker(txToIn, nInIn, amountIn, txdataIn, MissingDataBehavior::ASSERT_FAIL), store(storeIn) {}
 
     bool VerifyECDSASignature(const std::vector<unsigned char>& vchSig, const CPubKey& vchPubKey, const uint256& sighash) const override;
     bool VerifySchnorrSignature(Span<const unsigned char> sig, const XOnlyPubKey& pubkey, const uint256& sighash) const override;

src/script/sign.cpp

@@ -14,7 +14,7 @@
 
 typedef std::vector<unsigned char> valtype;
 
-MutableTransactionSignatureCreator::MutableTransactionSignatureCreator(const CMutableTransaction* txToIn, unsigned int nInIn, const CAmount& amountIn, int nHashTypeIn) : txTo(txToIn), nIn(nInIn), nHashType(nHashTypeIn), amount(amountIn), checker(txTo, nIn, amountIn) {}
+MutableTransactionSignatureCreator::MutableTransactionSignatureCreator(const CMutableTransaction* txToIn, unsigned int nInIn, const CAmount& amountIn, int nHashTypeIn) : txTo(txToIn), nIn(nInIn), nHashType(nHashTypeIn), amount(amountIn), checker(txTo, nIn, amountIn, MissingDataBehavior::FAIL) {}
 
 bool MutableTransactionSignatureCreator::CreateSig(const SigningProvider& provider, std::vector<unsigned char>& vchSig, const CKeyID& address, const CScript& scriptCode, SigVersion sigversion) const
 {
@@ -26,6 +26,9 @@ bool MutableTransactionSignatureCreator::CreateSig(const SigningProvider& provid
     if (sigversion == SigVersion::WITNESS_V0 && !key.IsCompressed())
         return false;
 
+    // Signing for witness scripts needs the amount.
+    if (sigversion == SigVersion::WITNESS_V0 && amount < 0) return false;
+
     uint256 hash = SignatureHash(scriptCode, *txTo, nIn, nHashType, amount, sigversion);
     if (!key.Sign(hash, vchSig))
         return false;
@@ -292,7 +295,7 @@ SignatureData DataFromTransaction(const CMutableTransaction& tx, unsigned int nI
     Stacks stack(data);
 
     // Get signatures
-    MutableTransactionSignatureChecker tx_checker(&tx, nIn, txout.nValue);
+    MutableTransactionSignatureChecker tx_checker(&tx, nIn, txout.nValue, MissingDataBehavior::FAIL);
     SignatureExtractorChecker extractor_checker(data, tx_checker);
     if (VerifyScript(data.scriptSig, txout.scriptPubKey, &data.scriptWitness, STANDARD_SCRIPT_VERIFY_FLAGS, extractor_checker)) {
         data.complete = true;
@@ -499,7 +502,7 @@ bool SignTransaction(CMutableTransaction& mtx, const SigningProvider* keystore,
         }
 
         ScriptError serror = SCRIPT_ERR_OK;
-        if (!VerifyScript(txin.scriptSig, prevPubKey, &txin.scriptWitness, STANDARD_SCRIPT_VERIFY_FLAGS, TransactionSignatureChecker(&txConst, i, amount), &serror)) {
+        if (!VerifyScript(txin.scriptSig, prevPubKey, &txin.scriptWitness, STANDARD_SCRIPT_VERIFY_FLAGS, TransactionSignatureChecker(&txConst, i, amount, MissingDataBehavior::FAIL), &serror)) {
             if (serror == SCRIPT_ERR_INVALID_STACK_OPERATION) {
                 // Unable to sign input and verification failed (possible attempt to partially sign).
                 input_errors[i] = "Unable to sign input, invalid stack size (possibly missing key)";

src/signet.cpp

@@ -139,7 +139,9 @@ bool CheckSignetBlockSolution(const CBlock& block, const Consensus::Params& cons
     const CScript& scriptSig = signet_txs->m_to_sign.vin[0].scriptSig;
     const CScriptWitness& witness = signet_txs->m_to_sign.vin[0].scriptWitness;
 
-    TransactionSignatureChecker sigcheck(&signet_txs->m_to_sign, /*nIn=*/ 0, /*amount=*/ signet_txs->m_to_spend.vout[0].nValue);
+    PrecomputedTransactionData txdata;
+    txdata.Init(signet_txs->m_to_sign, {signet_txs->m_to_spend.vout[0]});
+    TransactionSignatureChecker sigcheck(&signet_txs->m_to_sign, /*nIn=*/ 0, /*amount=*/ signet_txs->m_to_spend.vout[0].nValue, txdata, MissingDataBehavior::ASSERT_FAIL);
 
     if (!VerifyScript(scriptSig, signet_txs->m_to_spend.vout[0].scriptPubKey, &witness, BLOCK_SCRIPT_VERIFY_FLAGS, sigcheck)) {
         LogPrint(BCLog::VALIDATION, "CheckSignetBlockSolution: Errors in block (block solution invalid)\n");

src/test/fuzz/script_assets_test_minimizer.cpp

@@ -161,7 +161,7 @@ void Test(const std::string& str)
         tx.vin[idx].scriptWitness = ScriptWitnessFromJSON(test["success"]["witness"]);
         PrecomputedTransactionData txdata;
         txdata.Init(tx, std::vector<CTxOut>(prevouts));
-        MutableTransactionSignatureChecker txcheck(&tx, idx, prevouts[idx].nValue, txdata);
+        MutableTransactionSignatureChecker txcheck(&tx, idx, prevouts[idx].nValue, txdata, MissingDataBehavior::ASSERT_FAIL);
         for (const auto flags : ALL_FLAGS) {
             // "final": true tests are valid for all flags. Others are only valid with flags that are
             // a subset of test_flags.
@@ -176,7 +176,7 @@ void Test(const std::string& str)
         tx.vin[idx].scriptWitness = ScriptWitnessFromJSON(test["failure"]["witness"]);
         PrecomputedTransactionData txdata;
         txdata.Init(tx, std::vector<CTxOut>(prevouts));
-        MutableTransactionSignatureChecker txcheck(&tx, idx, prevouts[idx].nValue, txdata);
+        MutableTransactionSignatureChecker txcheck(&tx, idx, prevouts[idx].nValue, txdata, MissingDataBehavior::ASSERT_FAIL);
         for (const auto flags : ALL_FLAGS) {
             // If a test is supposed to fail with test_flags, it should also fail with any superset thereof.
             if ((flags & test_flags) == test_flags) {

src/test/fuzz/script_flags.cpp

@@ -48,7 +48,7 @@ FUZZ_TARGET_INIT(script_flags, initialize_script_flags)
 
         for (unsigned i = 0; i < tx.vin.size(); ++i) {
             const CTxOut& prevout = txdata.m_spent_outputs.at(i);
-            const TransactionSignatureChecker checker{&tx, i, prevout.nValue, txdata};
+            const TransactionSignatureChecker checker{&tx, i, prevout.nValue, txdata, MissingDataBehavior::ASSERT_FAIL};
 
             ScriptError serror;
             const bool ret = VerifyScript(tx.vin.at(i).scriptSig, prevout.scriptPubKey, &tx.vin.at(i).scriptWitness, verify_flags, checker, &serror);

src/test/multisig_tests.cpp

@@ -77,20 +77,20 @@ BOOST_AUTO_TEST_CASE(multisig_verify)
     keys.assign(1,key[0]);
     keys.push_back(key[1]);
     s = sign_multisig(a_and_b, keys, CTransaction(txTo[0]), 0);
-    BOOST_CHECK(VerifyScript(s, a_and_b, nullptr, flags, MutableTransactionSignatureChecker(&txTo[0], 0, amount), &err));
+    BOOST_CHECK(VerifyScript(s, a_and_b, nullptr, flags, MutableTransactionSignatureChecker(&txTo[0], 0, amount, MissingDataBehavior::ASSERT_FAIL), &err));
     BOOST_CHECK_MESSAGE(err == SCRIPT_ERR_OK, ScriptErrorString(err));
 
     for (int i = 0; i < 4; i++)
     {
         keys.assign(1,key[i]);
         s = sign_multisig(a_and_b, keys, CTransaction(txTo[0]), 0);
-        BOOST_CHECK_MESSAGE(!VerifyScript(s, a_and_b, nullptr, flags, MutableTransactionSignatureChecker(&txTo[0], 0, amount), &err), strprintf("a&b 1: %d", i));
+        BOOST_CHECK_MESSAGE(!VerifyScript(s, a_and_b, nullptr, flags, MutableTransactionSignatureChecker(&txTo[0], 0, amount, MissingDataBehavior::ASSERT_FAIL), &err), strprintf("a&b 1: %d", i));
         BOOST_CHECK_MESSAGE(err == SCRIPT_ERR_INVALID_STACK_OPERATION, ScriptErrorString(err));
 
         keys.assign(1,key[1]);
         keys.push_back(key[i]);
         s = sign_multisig(a_and_b, keys, CTransaction(txTo[0]), 0);
-        BOOST_CHECK_MESSAGE(!VerifyScript(s, a_and_b, nullptr, flags, MutableTransactionSignatureChecker(&txTo[0], 0, amount), &err), strprintf("a&b 2: %d", i));
+        BOOST_CHECK_MESSAGE(!VerifyScript(s, a_and_b, nullptr, flags, MutableTransactionSignatureChecker(&txTo[0], 0, amount, MissingDataBehavior::ASSERT_FAIL), &err), strprintf("a&b 2: %d", i));
         BOOST_CHECK_MESSAGE(err == SCRIPT_ERR_EVAL_FALSE, ScriptErrorString(err));
     }
 
@@ -101,18 +101,18 @@ BOOST_AUTO_TEST_CASE(multisig_verify)
         s = sign_multisig(a_or_b, keys, CTransaction(txTo[1]), 0);
         if (i == 0 || i == 1)
         {
-            BOOST_CHECK_MESSAGE(VerifyScript(s, a_or_b, nullptr, flags, MutableTransactionSignatureChecker(&txTo[1], 0, amount), &err), strprintf("a|b: %d", i));
+            BOOST_CHECK_MESSAGE(VerifyScript(s, a_or_b, nullptr, flags, MutableTransactionSignatureChecker(&txTo[1], 0, amount, MissingDataBehavior::ASSERT_FAIL), &err), strprintf("a|b: %d", i));
             BOOST_CHECK_MESSAGE(err == SCRIPT_ERR_OK, ScriptErrorString(err));
         }
         else
         {
-            BOOST_CHECK_MESSAGE(!VerifyScript(s, a_or_b, nullptr, flags, MutableTransactionSignatureChecker(&txTo[1], 0, amount), &err), strprintf("a|b: %d", i));
+            BOOST_CHECK_MESSAGE(!VerifyScript(s, a_or_b, nullptr, flags, MutableTransactionSignatureChecker(&txTo[1], 0, amount, MissingDataBehavior::ASSERT_FAIL), &err), strprintf("a|b: %d", i));
             BOOST_CHECK_MESSAGE(err == SCRIPT_ERR_EVAL_FALSE, ScriptErrorString(err));
         }
     }
     s.clear();
     s << OP_0 << OP_1;
-    BOOST_CHECK(!VerifyScript(s, a_or_b, nullptr, flags, MutableTransactionSignatureChecker(&txTo[1], 0, amount), &err));
+    BOOST_CHECK(!VerifyScript(s, a_or_b, nullptr, flags, MutableTransactionSignatureChecker(&txTo[1], 0, amount, MissingDataBehavior::ASSERT_FAIL), &err));
     BOOST_CHECK_MESSAGE(err == SCRIPT_ERR_SIG_DER, ScriptErrorString(err));
 
 
@@ -124,12 +124,12 @@ BOOST_AUTO_TEST_CASE(multisig_verify)
             s = sign_multisig(escrow, keys, CTransaction(txTo[2]), 0);
             if (i < j && i < 3 && j < 3)
             {
-                BOOST_CHECK_MESSAGE(VerifyScript(s, escrow, nullptr, flags, MutableTransactionSignatureChecker(&txTo[2], 0, amount), &err), strprintf("escrow 1: %d %d", i, j));
+                BOOST_CHECK_MESSAGE(VerifyScript(s, escrow, nullptr, flags, MutableTransactionSignatureChecker(&txTo[2], 0, amount, MissingDataBehavior::ASSERT_FAIL), &err), strprintf("escrow 1: %d %d", i, j));
                 BOOST_CHECK_MESSAGE(err == SCRIPT_ERR_OK, ScriptErrorString(err));
             }
             else
             {
-                BOOST_CHECK_MESSAGE(!VerifyScript(s, escrow, nullptr, flags, MutableTransactionSignatureChecker(&txTo[2], 0, amount), &err), strprintf("escrow 2: %d %d", i, j));
+                BOOST_CHECK_MESSAGE(!VerifyScript(s, escrow, nullptr, flags, MutableTransactionSignatureChecker(&txTo[2], 0, amount, MissingDataBehavior::ASSERT_FAIL), &err), strprintf("escrow 2: %d %d", i, j));
                 BOOST_CHECK_MESSAGE(err == SCRIPT_ERR_EVAL_FALSE, ScriptErrorString(err));
             }
         }