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1 : : // Copyright (c) 2009-2010 Satoshi Nakamoto
2 : : // Copyright (c) 2009-2022 The Bitcoin Core developers
3 : : // Distributed under the MIT software license, see the accompanying
4 : : // file COPYING or http://www.opensource.org/licenses/mit-license.php.
5 : :
6 : : // NOTE: This file is intended to be customised by the end user, and includes only local node policy logic
7 : :
8 : : #include <policy/policy.h>
9 : :
10 : : #include <coins.h>
11 : : #include <consensus/amount.h>
12 : : #include <consensus/consensus.h>
13 : : #include <consensus/validation.h>
14 : : #include <policy/feerate.h>
15 : : #include <primitives/transaction.h>
16 : : #include <script/interpreter.h>
17 [ + - ]: 2 : #include <script/script.h>
18 [ + - ]: 2 : #include <script/solver.h>
19 : : #include <serialize.h>
20 : : #include <span.h>
21 : :
22 : : #include <algorithm>
23 : : #include <cstddef>
24 : : #include <vector>
25 : :
26 : 0 : CAmount GetDustThreshold(const CTxOut& txout, const CFeeRate& dustRelayFeeIn)
27 : : {
28 : : // "Dust" is defined in terms of dustRelayFee,
29 : : // which has units satoshis-per-kilobyte.
30 : : // If you'd pay more in fees than the value of the output
31 : : // to spend something, then we consider it dust.
32 : : // A typical spendable non-segwit txout is 34 bytes big, and will
33 : : // need a CTxIn of at least 148 bytes to spend:
34 : : // so dust is a spendable txout less than
35 : : // 182*dustRelayFee/1000 (in satoshis).
36 : : // 546 satoshis at the default rate of 3000 sat/kvB.
37 : : // A typical spendable segwit P2WPKH txout is 31 bytes big, and will
38 : : // need a CTxIn of at least 67 bytes to spend:
39 : : // so dust is a spendable txout less than
40 : : // 98*dustRelayFee/1000 (in satoshis).
41 : : // 294 satoshis at the default rate of 3000 sat/kvB.
42 [ # # ]: 0 : if (txout.scriptPubKey.IsUnspendable())
43 : 0 : return 0;
44 : :
45 : 0 : size_t nSize = GetSerializeSize(txout);
46 : 0 : int witnessversion = 0;
47 : 0 : std::vector<unsigned char> witnessprogram;
48 : :
49 : : // Note this computation is for spending a Segwit v0 P2WPKH output (a 33 bytes
50 : : // public key + an ECDSA signature). For Segwit v1 Taproot outputs the minimum
51 : : // satisfaction is lower (a single BIP340 signature) but this computation was
52 : : // kept to not further reduce the dust level.
53 : : // See discussion in https://github.com/bitcoin/bitcoin/pull/22779 for details.
54 [ # # # # ]: 0 : if (txout.scriptPubKey.IsWitnessProgram(witnessversion, witnessprogram)) {
55 : : // sum the sizes of the parts of a transaction input
56 : : // with 75% segwit discount applied to the script size.
57 : 0 : nSize += (32 + 4 + 1 + (107 / WITNESS_SCALE_FACTOR) + 4);
58 : 0 : } else {
59 : 0 : nSize += (32 + 4 + 1 + 107 + 4); // the 148 mentioned above
60 : : }
61 : :
62 [ # # ]: 0 : return dustRelayFeeIn.GetFee(nSize);
63 : 0 : }
64 : :
65 : 0 : bool IsDust(const CTxOut& txout, const CFeeRate& dustRelayFeeIn)
66 : : {
67 : 0 : return (txout.nValue < GetDustThreshold(txout, dustRelayFeeIn));
68 : : }
69 : :
70 : 0 : bool IsStandard(const CScript& scriptPubKey, const std::optional<unsigned>& max_datacarrier_bytes, TxoutType& whichType)
71 : : {
72 : 0 : std::vector<std::vector<unsigned char> > vSolutions;
73 [ # # ]: 0 : whichType = Solver(scriptPubKey, vSolutions);
74 : :
75 [ # # ]: 0 : if (whichType == TxoutType::NONSTANDARD) {
76 : 0 : return false;
77 [ # # ]: 0 : } else if (whichType == TxoutType::MULTISIG) {
78 : 0 : unsigned char m = vSolutions.front()[0];
79 : 0 : unsigned char n = vSolutions.back()[0];
80 : : // Support up to x-of-3 multisig txns as standard
81 [ # # # # ]: 0 : if (n < 1 || n > 3)
82 : 0 : return false;
83 [ # # # # ]: 0 : if (m < 1 || m > n)
84 : 0 : return false;
85 [ # # ]: 0 : } else if (whichType == TxoutType::NULL_DATA) {
86 [ # # # # : 0 : if (!max_datacarrier_bytes || scriptPubKey.size() > *max_datacarrier_bytes) {
# # # # ]
87 : 0 : return false;
88 : : }
89 : 0 : }
90 : :
91 : 0 : return true;
92 : 0 : }
93 : :
94 : 0 : bool IsStandardTx(const CTransaction& tx, const std::optional<unsigned>& max_datacarrier_bytes, bool permit_bare_multisig, const CFeeRate& dust_relay_fee, std::string& reason)
95 : : {
96 [ # # # # ]: 0 : if (tx.nVersion > TX_MAX_STANDARD_VERSION || tx.nVersion < 1) {
97 : 0 : reason = "version";
98 : 0 : return false;
99 : : }
100 : :
101 : : // Extremely large transactions with lots of inputs can cost the network
102 : : // almost as much to process as they cost the sender in fees, because
103 : : // computing signature hashes is O(ninputs*txsize). Limiting transactions
104 : : // to MAX_STANDARD_TX_WEIGHT mitigates CPU exhaustion attacks.
105 : 0 : unsigned int sz = GetTransactionWeight(tx);
106 [ # # ]: 0 : if (sz > MAX_STANDARD_TX_WEIGHT) {
107 : 0 : reason = "tx-size";
108 : 0 : return false;
109 : : }
110 : :
111 [ # # ]: 0 : for (const CTxIn& txin : tx.vin)
112 : : {
113 : : // Biggest 'standard' txin involving only keys is a 15-of-15 P2SH
114 : : // multisig with compressed keys (remember the 520 byte limit on
115 : : // redeemScript size). That works out to a (15*(33+1))+3=513 byte
116 : : // redeemScript, 513+1+15*(73+1)+3=1627 bytes of scriptSig, which
117 : : // we round off to 1650(MAX_STANDARD_SCRIPTSIG_SIZE) bytes for
118 : : // some minor future-proofing. That's also enough to spend a
119 : : // 20-of-20 CHECKMULTISIG scriptPubKey, though such a scriptPubKey
120 : : // is not considered standard.
121 [ # # ]: 0 : if (txin.scriptSig.size() > MAX_STANDARD_SCRIPTSIG_SIZE) {
122 : 0 : reason = "scriptsig-size";
123 : 0 : return false;
124 : : }
125 [ # # ]: 0 : if (!txin.scriptSig.IsPushOnly()) {
126 : 0 : reason = "scriptsig-not-pushonly";
127 : 0 : return false;
128 : : }
129 : : }
130 : :
131 : 0 : unsigned int nDataOut = 0;
132 : : TxoutType whichType;
133 [ # # ]: 0 : for (const CTxOut& txout : tx.vout) {
134 [ # # ]: 0 : if (!::IsStandard(txout.scriptPubKey, max_datacarrier_bytes, whichType)) {
135 : 0 : reason = "scriptpubkey";
136 : 0 : return false;
137 : : }
138 : :
139 [ # # ]: 0 : if (whichType == TxoutType::NULL_DATA)
140 : 0 : nDataOut++;
141 [ # # # # ]: 0 : else if ((whichType == TxoutType::MULTISIG) && (!permit_bare_multisig)) {
142 : 0 : reason = "bare-multisig";
143 : 0 : return false;
144 [ # # ]: 0 : } else if (IsDust(txout, dust_relay_fee)) {
145 : 0 : reason = "dust";
146 : 0 : return false;
147 : : }
148 : : }
149 : :
150 : : // only one OP_RETURN txout is permitted
151 [ # # ]: 0 : if (nDataOut > 1) {
152 : 0 : reason = "multi-op-return";
153 : 0 : return false;
154 : : }
155 : :
156 : 0 : return true;
157 : 0 : }
158 : :
159 : : /**
160 : : * Check transaction inputs to mitigate two
161 : : * potential denial-of-service attacks:
162 : : *
163 : : * 1. scriptSigs with extra data stuffed into them,
164 : : * not consumed by scriptPubKey (or P2SH script)
165 : : * 2. P2SH scripts with a crazy number of expensive
166 : : * CHECKSIG/CHECKMULTISIG operations
167 : : *
168 : : * Why bother? To avoid denial-of-service attacks; an attacker
169 : : * can submit a standard HASH... OP_EQUAL transaction,
170 : : * which will get accepted into blocks. The redemption
171 : : * script can be anything; an attacker could use a very
172 : : * expensive-to-check-upon-redemption script like:
173 : : * DUP CHECKSIG DROP ... repeated 100 times... OP_1
174 : : *
175 : : * Note that only the non-witness portion of the transaction is checked here.
176 : : */
177 : 0 : bool AreInputsStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)
178 : : {
179 [ # # ]: 0 : if (tx.IsCoinBase()) {
180 : 0 : return true; // Coinbases don't use vin normally
181 : : }
182 : :
183 [ # # ]: 0 : for (unsigned int i = 0; i < tx.vin.size(); i++) {
184 : 0 : const CTxOut& prev = mapInputs.AccessCoin(tx.vin[i].prevout).out;
185 : :
186 : 0 : std::vector<std::vector<unsigned char> > vSolutions;
187 [ # # ]: 0 : TxoutType whichType = Solver(prev.scriptPubKey, vSolutions);
188 [ # # # # ]: 0 : if (whichType == TxoutType::NONSTANDARD || whichType == TxoutType::WITNESS_UNKNOWN) {
189 : : // WITNESS_UNKNOWN failures are typically also caught with a policy
190 : : // flag in the script interpreter, but it can be helpful to catch
191 : : // this type of NONSTANDARD transaction earlier in transaction
192 : : // validation.
193 : 0 : return false;
194 [ # # ]: 0 : } else if (whichType == TxoutType::SCRIPTHASH) {
195 : 0 : std::vector<std::vector<unsigned char> > stack;
196 : : // convert the scriptSig into a stack, so we can inspect the redeemScript
197 [ # # # # ]: 0 : if (!EvalScript(stack, tx.vin[i].scriptSig, SCRIPT_VERIFY_NONE, BaseSignatureChecker(), SigVersion::BASE))
198 : 0 : return false;
199 [ # # ]: 0 : if (stack.empty())
200 : 0 : return false;
201 [ # # ]: 0 : CScript subscript(stack.back().begin(), stack.back().end());
202 [ # # # # ]: 0 : if (subscript.GetSigOpCount(true) > MAX_P2SH_SIGOPS) {
203 : 0 : return false;
204 : : }
205 [ # # ]: 0 : }
206 [ # # # ]: 0 : }
207 : :
208 : 0 : return true;
209 : 0 : }
210 : :
211 : 0 : bool IsWitnessStandard(const CTransaction& tx, const CCoinsViewCache& mapInputs)
212 : : {
213 [ # # ]: 0 : if (tx.IsCoinBase())
214 : 0 : return true; // Coinbases are skipped
215 : :
216 [ # # ]: 0 : for (unsigned int i = 0; i < tx.vin.size(); i++)
217 : : {
218 : : // We don't care if witness for this input is empty, since it must not be bloated.
219 : : // If the script is invalid without witness, it would be caught sooner or later during validation.
220 [ # # ]: 0 : if (tx.vin[i].scriptWitness.IsNull())
221 : 0 : continue;
222 : :
223 : 0 : const CTxOut &prev = mapInputs.AccessCoin(tx.vin[i].prevout).out;
224 : :
225 : : // get the scriptPubKey corresponding to this input:
226 : 0 : CScript prevScript = prev.scriptPubKey;
227 : :
228 : 0 : bool p2sh = false;
229 [ # # # # ]: 0 : if (prevScript.IsPayToScriptHash()) {
230 : 0 : std::vector <std::vector<unsigned char> > stack;
231 : : // If the scriptPubKey is P2SH, we try to extract the redeemScript casually by converting the scriptSig
232 : : // into a stack. We do not check IsPushOnly nor compare the hash as these will be done later anyway.
233 : : // If the check fails at this stage, we know that this txid must be a bad one.
234 [ # # # # ]: 0 : if (!EvalScript(stack, tx.vin[i].scriptSig, SCRIPT_VERIFY_NONE, BaseSignatureChecker(), SigVersion::BASE))
235 : 0 : return false;
236 [ # # ]: 0 : if (stack.empty())
237 : 0 : return false;
238 [ # # ]: 0 : prevScript = CScript(stack.back().begin(), stack.back().end());
239 : 0 : p2sh = true;
240 [ # # ]: 0 : }
241 : :
242 : 0 : int witnessversion = 0;
243 : 0 : std::vector<unsigned char> witnessprogram;
244 : :
245 : : // Non-witness program must not be associated with any witness
246 [ # # # # ]: 0 : if (!prevScript.IsWitnessProgram(witnessversion, witnessprogram))
247 : 0 : return false;
248 : :
249 : : // Check P2WSH standard limits
250 [ # # # # ]: 0 : if (witnessversion == 0 && witnessprogram.size() == WITNESS_V0_SCRIPTHASH_SIZE) {
251 [ # # ]: 0 : if (tx.vin[i].scriptWitness.stack.back().size() > MAX_STANDARD_P2WSH_SCRIPT_SIZE)
252 : 0 : return false;
253 : 0 : size_t sizeWitnessStack = tx.vin[i].scriptWitness.stack.size() - 1;
254 [ # # ]: 0 : if (sizeWitnessStack > MAX_STANDARD_P2WSH_STACK_ITEMS)
255 : 0 : return false;
256 [ # # ]: 0 : for (unsigned int j = 0; j < sizeWitnessStack; j++) {
257 [ # # ]: 0 : if (tx.vin[i].scriptWitness.stack[j].size() > MAX_STANDARD_P2WSH_STACK_ITEM_SIZE)
258 : 0 : return false;
259 : 0 : }
260 : 0 : }
261 : :
262 : : // Check policy limits for Taproot spends:
263 : : // - MAX_STANDARD_TAPSCRIPT_STACK_ITEM_SIZE limit for stack item size
264 : : // - No annexes
265 [ # # # # : 0 : if (witnessversion == 1 && witnessprogram.size() == WITNESS_V1_TAPROOT_SIZE && !p2sh) {
# # ]
266 : : // Taproot spend (non-P2SH-wrapped, version 1, witness program size 32; see BIP 341)
267 [ # # ]: 0 : Span stack{tx.vin[i].scriptWitness.stack};
268 [ # # # # : 0 : if (stack.size() >= 2 && !stack.back().empty() && stack.back()[0] == ANNEX_TAG) {
# # ]
269 : : // Annexes are nonstandard as long as no semantics are defined for them.
270 : 0 : return false;
271 : : }
272 [ # # ]: 0 : if (stack.size() >= 2) {
273 : : // Script path spend (2 or more stack elements after removing optional annex)
274 [ # # ]: 0 : const auto& control_block = SpanPopBack(stack);
275 [ # # ]: 0 : SpanPopBack(stack); // Ignore script
276 [ # # ]: 0 : if (control_block.empty()) return false; // Empty control block is invalid
277 [ # # ]: 0 : if ((control_block[0] & TAPROOT_LEAF_MASK) == TAPROOT_LEAF_TAPSCRIPT) {
278 : : // Leaf version 0xc0 (aka Tapscript, see BIP 342)
279 [ # # ]: 0 : for (const auto& item : stack) {
280 [ # # ]: 0 : if (item.size() > MAX_STANDARD_TAPSCRIPT_STACK_ITEM_SIZE) return false;
281 : : }
282 : 0 : }
283 [ # # ]: 0 : } else if (stack.size() == 1) {
284 : : // Key path spend (1 stack element after removing optional annex)
285 : : // (no policy rules apply)
286 : 0 : } else {
287 : : // 0 stack elements; this is already invalid by consensus rules
288 : 0 : return false;
289 : : }
290 : 0 : }
291 [ # # # ]: 0 : }
292 : 0 : return true;
293 : 0 : }
294 : :
295 : 0 : int64_t GetVirtualTransactionSize(int64_t nWeight, int64_t nSigOpCost, unsigned int bytes_per_sigop)
296 : : {
297 : 0 : return (std::max(nWeight, nSigOpCost * bytes_per_sigop) + WITNESS_SCALE_FACTOR - 1) / WITNESS_SCALE_FACTOR;
298 : : }
299 : :
300 : 0 : int64_t GetVirtualTransactionSize(const CTransaction& tx, int64_t nSigOpCost, unsigned int bytes_per_sigop)
301 : : {
302 : 0 : return GetVirtualTransactionSize(GetTransactionWeight(tx), nSigOpCost, bytes_per_sigop);
303 : : }
304 : :
305 : 0 : int64_t GetVirtualTransactionInputSize(const CTxIn& txin, int64_t nSigOpCost, unsigned int bytes_per_sigop)
306 : : {
307 : 0 : return GetVirtualTransactionSize(GetTransactionInputWeight(txin), nSigOpCost, bytes_per_sigop);
308 : : }
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