Merge bitcoin/bitcoin#19426: refactor: Change * to & in MutableTransactionSignatureCreator

fac6cfc50f65c610f2df9af3ec2efff5eade6661 refactor: Change * to & in MutableTransactionSignatureCreator (MarcoFalke)

Pull request description:

  The `MutableTransactionSignatureCreator` constructor takes in a pointer to a mutable transaction. This is problematic for several reasons:

  * It would be undefined behaviour to pass in a nullptr because for signature creation, the memory of the mutable transaction is accessed
  * No caller currently passes in a nullptr, so passing a reference as a pointer is confusing

  Fix all issues by replacing `*` with `&` in `MutableTransactionSignatureCreator`

ACKs for top commit:
  theStack:
    Code-review ACK fac6cfc50f65c610f2df9af3ec2efff5eade6661
  jonatack:
    ACK fac6cfc50f65c610f2df9af3ec2efff5eade6661

Tree-SHA512: d84296b030bd4fa2709e5adbfe43a5f8377d218957d844af69a819893252af671df7f00004f5ba601a0bd70f3c1c2e58c4f00e75684da663f28432bb5c89fb86

10 files changed, 28 insertions, 26 deletions

diff --git a/src/bitcoin-tx.cpp b/src/bitcoin-tx.cpp
index cdc5960c12..580cc5839a 100644
--- a/src/bitcoin-tx.cpp
+++ b/src/bitcoin-tx.cpp
@@ -667,7 +667,7 @@ static void MutateTxSign(CMutableTransaction& tx, const std::string& flagStr)
         SignatureData sigdata = DataFromTransaction(mergedTx, i, coin.out);
         // Only sign SIGHASH_SINGLE if there's a corresponding output:
         if (!fHashSingle || (i < mergedTx.vout.size()))
-            ProduceSignature(keystore, MutableTransactionSignatureCreator(&mergedTx, i, amount, nHashType), prevPubKey, sigdata);
+            ProduceSignature(keystore, MutableTransactionSignatureCreator(mergedTx, i, amount, nHashType), prevPubKey, sigdata);
 
         if (amount == MAX_MONEY && !sigdata.scriptWitness.IsNull()) {
             throw std::runtime_error(strprintf("Missing amount for CTxOut with scriptPubKey=%s", HexStr(prevPubKey)));
diff --git a/src/psbt.cpp b/src/psbt.cpp
index 6465e353be..c1c8a385cc 100644
--- a/src/psbt.cpp
+++ b/src/psbt.cpp
@@ -234,7 +234,7 @@ void UpdatePSBTOutput(const SigningProvider& provider, PartiallySignedTransactio
     // Construct a would-be spend of this output, to update sigdata with.
     // Note that ProduceSignature is used to fill in metadata (not actual signatures),
     // so provider does not need to provide any private keys (it can be a HidingSigningProvider).
-    MutableTransactionSignatureCreator creator(&tx, /*input_idx=*/0, out.nValue, SIGHASH_ALL);
+    MutableTransactionSignatureCreator creator(tx, /*input_idx=*/0, out.nValue, SIGHASH_ALL);
     ProduceSignature(provider, creator, out.scriptPubKey, sigdata);
 
     // Put redeem_script, witness_script, key paths, into PSBTOutput.
@@ -301,7 +301,7 @@ bool SignPSBTInput(const SigningProvider& provider, PartiallySignedTransaction&
     if (txdata == nullptr) {
         sig_complete = ProduceSignature(provider, DUMMY_SIGNATURE_CREATOR, utxo.scriptPubKey, sigdata);
     } else {
-        MutableTransactionSignatureCreator creator(&tx, index, utxo.nValue, txdata, sighash);
+        MutableTransactionSignatureCreator creator(tx, index, utxo.nValue, txdata, sighash);
         sig_complete = ProduceSignature(provider, creator, utxo.scriptPubKey, sigdata);
     }
     // Verify that a witness signature was produced in case one was required.
diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index ce8f16540f..e8713fbd2e 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -567,7 +567,7 @@ static RPCHelpMan combinerawtransaction()
                 sigdata.MergeSignatureData(DataFromTransaction(txv, i, coin.out));
             }
         }
-        ProduceSignature(DUMMY_SIGNING_PROVIDER, MutableTransactionSignatureCreator(&mergedTx, i, coin.out.nValue, 1), coin.out.scriptPubKey, sigdata);
+        ProduceSignature(DUMMY_SIGNING_PROVIDER, MutableTransactionSignatureCreator(mergedTx, i, coin.out.nValue, 1), coin.out.scriptPubKey, sigdata);
 
         UpdateInput(txin, sigdata);
     }
diff --git a/src/script/sign.cpp b/src/script/sign.cpp
index d77515f16c..7328e8d1ad 100644
--- a/src/script/sign.cpp
+++ b/src/script/sign.cpp
@@ -18,16 +18,16 @@
 
 typedef std::vector<unsigned char> valtype;
 
-MutableTransactionSignatureCreator::MutableTransactionSignatureCreator(const CMutableTransaction* tx, unsigned int input_idx, const CAmount& amount, int hash_type)
-    : txTo{tx}, nIn{input_idx}, nHashType{hash_type}, amount{amount}, checker{txTo, nIn, amount, MissingDataBehavior::FAIL},
+MutableTransactionSignatureCreator::MutableTransactionSignatureCreator(const CMutableTransaction& tx, unsigned int input_idx, const CAmount& amount, int hash_type)
+    : m_txto{tx}, nIn{input_idx}, nHashType{hash_type}, amount{amount}, checker{&m_txto, nIn, amount, MissingDataBehavior::FAIL},
       m_txdata(nullptr)
 {
 }
 
-MutableTransactionSignatureCreator::MutableTransactionSignatureCreator(const CMutableTransaction* tx, unsigned int input_idx, const CAmount& amount, const PrecomputedTransactionData* txdata, int hash_type)
-    : txTo{tx}, nIn{input_idx}, nHashType{hash_type}, amount{amount},
-      checker{txdata ? MutableTransactionSignatureChecker{txTo, nIn, amount, *txdata, MissingDataBehavior::FAIL} :
-                       MutableTransactionSignatureChecker{txTo, nIn, amount, MissingDataBehavior::FAIL}},
+MutableTransactionSignatureCreator::MutableTransactionSignatureCreator(const CMutableTransaction& tx, unsigned int input_idx, const CAmount& amount, const PrecomputedTransactionData* txdata, int hash_type)
+    : m_txto{tx}, nIn{input_idx}, nHashType{hash_type}, amount{amount},
+      checker{txdata ? MutableTransactionSignatureChecker{&m_txto, nIn, amount, *txdata, MissingDataBehavior::FAIL} :
+                       MutableTransactionSignatureChecker{&m_txto, nIn, amount, MissingDataBehavior::FAIL}},
       m_txdata(txdata)
 {
 }
@@ -50,7 +50,7 @@ bool MutableTransactionSignatureCreator::CreateSig(const SigningProvider& provid
     // BASE/WITNESS_V0 signatures don't support explicit SIGHASH_DEFAULT, use SIGHASH_ALL instead.
     const int hashtype = nHashType == SIGHASH_DEFAULT ? SIGHASH_ALL : nHashType;
 
-    uint256 hash = SignatureHash(scriptCode, *txTo, nIn, hashtype, amount, sigversion, m_txdata);
+    uint256 hash = SignatureHash(scriptCode, m_txto, nIn, hashtype, amount, sigversion, m_txdata);
     if (!key.Sign(hash, vchSig))
         return false;
     vchSig.push_back((unsigned char)hashtype);
@@ -80,7 +80,7 @@ bool MutableTransactionSignatureCreator::CreateSchnorrSig(const SigningProvider&
         execdata.m_tapleaf_hash = *leaf_hash;
     }
     uint256 hash;
-    if (!SignatureHashSchnorr(hash, execdata, *txTo, nIn, nHashType, sigversion, *m_txdata, MissingDataBehavior::FAIL)) return false;
+    if (!SignatureHashSchnorr(hash, execdata, m_txto, nIn, nHashType, sigversion, *m_txdata, MissingDataBehavior::FAIL)) return false;
     sig.resize(64);
     // Use uint256{} as aux_rnd for now.
     if (!key.SignSchnorr(hash, sig, merkle_root, {})) return false;
@@ -540,7 +540,7 @@ bool SignSignature(const SigningProvider &provider, const CScript& fromPubKey, C
 {
     assert(nIn < txTo.vin.size());
 
-    MutableTransactionSignatureCreator creator(&txTo, nIn, amount, nHashType);
+    MutableTransactionSignatureCreator creator(txTo, nIn, amount, nHashType);
 
     SignatureData sigdata;
     bool ret = ProduceSignature(provider, creator, fromPubKey, sigdata);
@@ -679,7 +679,7 @@ bool SignTransaction(CMutableTransaction& mtx, const SigningProvider* keystore,
         SignatureData sigdata = DataFromTransaction(mtx, i, coin->second.out);
         // Only sign SIGHASH_SINGLE if there's a corresponding output:
         if (!fHashSingle || (i < mtx.vout.size())) {
-            ProduceSignature(*keystore, MutableTransactionSignatureCreator(&mtx, i, amount, &txdata, nHashType), prevPubKey, sigdata);
+            ProduceSignature(*keystore, MutableTransactionSignatureCreator(mtx, i, amount, &txdata, nHashType), prevPubKey, sigdata);
         }
 
         UpdateInput(txin, sigdata);
diff --git a/src/script/sign.h b/src/script/sign.h
index 7301826ba5..71203d08ec 100644
--- a/src/script/sign.h
+++ b/src/script/sign.h
@@ -6,6 +6,7 @@
 #ifndef BITCOIN_SCRIPT_SIGN_H
 #define BITCOIN_SCRIPT_SIGN_H
 
+#include <attributes.h>
 #include <coins.h>
 #include <hash.h>
 #include <pubkey.h>
@@ -34,8 +35,9 @@ public:
 };
 
 /** A signature creator for transactions. */
-class MutableTransactionSignatureCreator : public BaseSignatureCreator {
-    const CMutableTransaction* txTo;
+class MutableTransactionSignatureCreator : public BaseSignatureCreator
+{
+    const CMutableTransaction& m_txto;
     unsigned int nIn;
     int nHashType;
     CAmount amount;
@@ -43,8 +45,8 @@ class MutableTransactionSignatureCreator : public BaseSignatureCreator {
     const PrecomputedTransactionData* m_txdata;
 
 public:
-    MutableTransactionSignatureCreator(const CMutableTransaction* tx, unsigned int input_idx, const CAmount& amount, int hash_type);
-    MutableTransactionSignatureCreator(const CMutableTransaction* tx, unsigned int input_idx, const CAmount& amount, const PrecomputedTransactionData* txdata, int hash_type);
+    MutableTransactionSignatureCreator(const CMutableTransaction& tx LIFETIMEBOUND, unsigned int input_idx, const CAmount& amount, int hash_type);
+    MutableTransactionSignatureCreator(const CMutableTransaction& tx LIFETIMEBOUND, unsigned int input_idx, const CAmount& amount, const PrecomputedTransactionData* txdata, int hash_type);
     const BaseSignatureChecker& Checker() const override { return checker; }
     bool CreateSig(const SigningProvider& provider, std::vector<unsigned char>& vchSig, const CKeyID& keyid, const CScript& scriptCode, SigVersion sigversion) const override;
     bool CreateSchnorrSig(const SigningProvider& provider, std::vector<unsigned char>& sig, const XOnlyPubKey& pubkey, const uint256* leaf_hash, const uint256* merkle_root, SigVersion sigversion) const override;
diff --git a/src/test/descriptor_tests.cpp b/src/test/descriptor_tests.cpp
index 30add9c16d..63c86a896d 100644
--- a/src/test/descriptor_tests.cpp
+++ b/src/test/descriptor_tests.cpp
@@ -312,7 +312,7 @@ void DoCheck(const std::string& prv, const std::string& pub, const std::string&
                     std::vector<CTxOut> utxos(1);
                     PrecomputedTransactionData txdata;
                     txdata.Init(spend, std::move(utxos), /*force=*/true);
-                    MutableTransactionSignatureCreator creator(&spend, 0, CAmount{0}, &txdata, SIGHASH_DEFAULT);
+                    MutableTransactionSignatureCreator creator{spend, 0, CAmount{0}, &txdata, SIGHASH_DEFAULT};
                     SignatureData sigdata;
                     BOOST_CHECK_MESSAGE(ProduceSignature(Merge(keys_priv, script_provider), creator, spks[n], sigdata), prv);
                 }
diff --git a/src/test/fuzz/script_sign.cpp b/src/test/fuzz/script_sign.cpp
index 1446eafe92..3ddb30d870 100644
--- a/src/test/fuzz/script_sign.cpp
+++ b/src/test/fuzz/script_sign.cpp
@@ -113,7 +113,7 @@ FUZZ_TARGET_INIT(script_sign, initialize_script_sign)
             }
             if (n_in < script_tx_to.vin.size()) {
                 (void)SignSignature(provider, ConsumeScript(fuzzed_data_provider), script_tx_to, n_in, ConsumeMoney(fuzzed_data_provider), fuzzed_data_provider.ConsumeIntegral<int>());
-                MutableTransactionSignatureCreator signature_creator{&tx_to, n_in, ConsumeMoney(fuzzed_data_provider), fuzzed_data_provider.ConsumeIntegral<int>()};
+                MutableTransactionSignatureCreator signature_creator{tx_to, n_in, ConsumeMoney(fuzzed_data_provider), fuzzed_data_provider.ConsumeIntegral<int>()};
                 std::vector<unsigned char> vch_sig;
                 CKeyID address;
                 if (fuzzed_data_provider.ConsumeBool()) {
diff --git a/src/test/script_tests.cpp b/src/test/script_tests.cpp
index c453f22594..19e32d0c36 100644
--- a/src/test/script_tests.cpp
+++ b/src/test/script_tests.cpp
@@ -1162,7 +1162,7 @@ SignatureData CombineSignatures(const CTxOut& txout, const CMutableTransaction&
     SignatureData data;
     data.MergeSignatureData(scriptSig1);
     data.MergeSignatureData(scriptSig2);
-    ProduceSignature(DUMMY_SIGNING_PROVIDER, MutableTransactionSignatureCreator(&tx, 0, txout.nValue, SIGHASH_DEFAULT), txout.scriptPubKey, data);
+    ProduceSignature(DUMMY_SIGNING_PROVIDER, MutableTransactionSignatureCreator(tx, 0, txout.nValue, SIGHASH_DEFAULT), txout.scriptPubKey, data);
     return data;
 }
 
@@ -1796,7 +1796,7 @@ BOOST_AUTO_TEST_CASE(bip341_keypath_test_vectors)
             // Sign and verify signature.
             FlatSigningProvider provider;
             provider.keys[key.GetPubKey().GetID()] = key;
-            MutableTransactionSignatureCreator creator(&tx, txinpos, utxos[txinpos].nValue, &txdata, hashtype);
+            MutableTransactionSignatureCreator creator(tx, txinpos, utxos[txinpos].nValue, &txdata, hashtype);
             std::vector<unsigned char> signature;
             BOOST_CHECK(creator.CreateSchnorrSig(provider, signature, pubkey, nullptr, &merkle_root, SigVersion::TAPROOT));
             BOOST_CHECK_EQUAL(HexStr(signature), input["expected"]["witness"][0].get_str());
diff --git a/src/test/transaction_tests.cpp b/src/test/transaction_tests.cpp
index df67841b66..c3a2a66027 100644
--- a/src/test/transaction_tests.cpp
+++ b/src/test/transaction_tests.cpp
@@ -559,7 +559,7 @@ SignatureData CombineSignatures(const CMutableTransaction& input1, const CMutabl
     SignatureData sigdata;
     sigdata = DataFromTransaction(input1, 0, tx->vout[0]);
     sigdata.MergeSignatureData(DataFromTransaction(input2, 0, tx->vout[0]));
-    ProduceSignature(DUMMY_SIGNING_PROVIDER, MutableTransactionSignatureCreator(&input1, 0, tx->vout[0].nValue, SIGHASH_ALL), tx->vout[0].scriptPubKey, sigdata);
+    ProduceSignature(DUMMY_SIGNING_PROVIDER, MutableTransactionSignatureCreator(input1, 0, tx->vout[0].nValue, SIGHASH_ALL), tx->vout[0].scriptPubKey, sigdata);
     return sigdata;
 }
 
diff --git a/src/test/txvalidationcache_tests.cpp b/src/test/txvalidationcache_tests.cpp
index b1e2119c64..d41b54af20 100644
--- a/src/test/txvalidationcache_tests.cpp
+++ b/src/test/txvalidationcache_tests.cpp
@@ -329,7 +329,7 @@ BOOST_FIXTURE_TEST_CASE(checkinputs_test, Dersig100Setup)
 
         // Sign
         SignatureData sigdata;
-        BOOST_CHECK(ProduceSignature(keystore, MutableTransactionSignatureCreator(&valid_with_witness_tx, 0, 11*CENT, SIGHASH_ALL), spend_tx.vout[1].scriptPubKey, sigdata));
+        BOOST_CHECK(ProduceSignature(keystore, MutableTransactionSignatureCreator(valid_with_witness_tx, 0, 11 * CENT, SIGHASH_ALL), spend_tx.vout[1].scriptPubKey, sigdata));
         UpdateInput(valid_with_witness_tx.vin[0], sigdata);
 
         // This should be valid under all script flags.
@@ -355,9 +355,9 @@ BOOST_FIXTURE_TEST_CASE(checkinputs_test, Dersig100Setup)
         tx.vout[0].scriptPubKey = p2pk_scriptPubKey;
 
         // Sign
-        for (int i=0; i<2; ++i) {
+        for (int i = 0; i < 2; ++i) {
             SignatureData sigdata;
-            BOOST_CHECK(ProduceSignature(keystore, MutableTransactionSignatureCreator(&tx, i, 11*CENT, SIGHASH_ALL), spend_tx.vout[i].scriptPubKey, sigdata));
+            BOOST_CHECK(ProduceSignature(keystore, MutableTransactionSignatureCreator(tx, i, 11 * CENT, SIGHASH_ALL), spend_tx.vout[i].scriptPubKey, sigdata));
             UpdateInput(tx.vin[i], sigdata);
         }