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-rw-r--r--src/script/interpreter.cpp118
1 files changed, 92 insertions, 26 deletions
diff --git a/src/script/interpreter.cpp b/src/script/interpreter.cpp
index d0865d2793..5bf418472a 100644
--- a/src/script/interpreter.cpp
+++ b/src/script/interpreter.cpp
@@ -278,6 +278,70 @@ int FindAndDelete(CScript& script, const CScript& b)
return nFound;
}
+namespace {
+/** A data type to abstract out the condition stack during script execution.
+ *
+ * Conceptually it acts like a vector of booleans, one for each level of nested
+ * IF/THEN/ELSE, indicating whether we're in the active or inactive branch of
+ * each.
+ *
+ * The elements on the stack cannot be observed individually; we only need to
+ * expose whether the stack is empty and whether or not any false values are
+ * present at all. To implement OP_ELSE, a toggle_top modifier is added, which
+ * flips the last value without returning it.
+ *
+ * This uses an optimized implementation that does not materialize the
+ * actual stack. Instead, it just stores the size of the would-be stack,
+ * and the position of the first false value in it.
+ */
+class ConditionStack {
+private:
+ //! A constant for m_first_false_pos to indicate there are no falses.
+ static constexpr uint32_t NO_FALSE = std::numeric_limits<uint32_t>::max();
+
+ //! The size of the implied stack.
+ uint32_t m_stack_size = 0;
+ //! The position of the first false value on the implied stack, or NO_FALSE if all true.
+ uint32_t m_first_false_pos = NO_FALSE;
+
+public:
+ bool empty() { return m_stack_size == 0; }
+ bool all_true() { return m_first_false_pos == NO_FALSE; }
+ void push_back(bool f)
+ {
+ if (m_first_false_pos == NO_FALSE && !f) {
+ // The stack consists of all true values, and a false is added.
+ // The first false value will appear at the current size.
+ m_first_false_pos = m_stack_size;
+ }
+ ++m_stack_size;
+ }
+ void pop_back()
+ {
+ assert(m_stack_size > 0);
+ --m_stack_size;
+ if (m_first_false_pos == m_stack_size) {
+ // When popping off the first false value, everything becomes true.
+ m_first_false_pos = NO_FALSE;
+ }
+ }
+ void toggle_top()
+ {
+ assert(m_stack_size > 0);
+ if (m_first_false_pos == NO_FALSE) {
+ // The current stack is all true values; the first false will be the top.
+ m_first_false_pos = m_stack_size - 1;
+ } else if (m_first_false_pos == m_stack_size - 1) {
+ // The top is the first false value; toggling it will make everything true.
+ m_first_false_pos = NO_FALSE;
+ } else {
+ // There is a false value, but not on top. No action is needed as toggling
+ // anything but the first false value is unobservable.
+ }
+ }
+};
+}
+
bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript& script, unsigned int flags, const BaseSignatureChecker& checker, SigVersion sigversion, ScriptError* serror)
{
static const CScriptNum bnZero(0);
@@ -293,7 +357,7 @@ bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript&
CScript::const_iterator pbegincodehash = script.begin();
opcodetype opcode;
valtype vchPushValue;
- std::vector<bool> vfExec;
+ ConditionStack vfExec;
std::vector<valtype> altstack;
set_error(serror, SCRIPT_ERR_UNKNOWN_ERROR);
if (script.size() > MAX_SCRIPT_SIZE)
@@ -305,7 +369,7 @@ bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript&
{
while (pc < pend)
{
- bool fExec = !count(vfExec.begin(), vfExec.end(), false);
+ bool fExec = vfExec.all_true();
//
// Read instruction
@@ -494,7 +558,7 @@ bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript&
{
if (vfExec.empty())
return set_error(serror, SCRIPT_ERR_UNBALANCED_CONDITIONAL);
- vfExec.back() = !vfExec.back();
+ vfExec.toggle_top();
}
break;
@@ -1414,9 +1478,26 @@ bool GenericTransactionSignatureChecker<T>::CheckSequence(const CScriptNum& nSeq
template class GenericTransactionSignatureChecker<CTransaction>;
template class GenericTransactionSignatureChecker<CMutableTransaction>;
+static bool ExecuteWitnessScript(std::vector<valtype>::const_iterator begin, std::vector<valtype>::const_iterator end, const CScript& scriptPubKey, unsigned int flags, SigVersion sigversion, const BaseSignatureChecker& checker, ScriptError* serror)
+{
+ std::vector<valtype> stack{begin, end};
+
+ // Disallow stack item size > MAX_SCRIPT_ELEMENT_SIZE in witness stack
+ for (const valtype& elem : stack) {
+ if (elem.size() > MAX_SCRIPT_ELEMENT_SIZE) return set_error(serror, SCRIPT_ERR_PUSH_SIZE);
+ }
+
+ // Run the script interpreter.
+ if (!EvalScript(stack, scriptPubKey, flags, checker, sigversion, serror)) return false;
+
+ // Scripts inside witness implicitly require cleanstack behaviour
+ if (stack.size() != 1) return set_error(serror, SCRIPT_ERR_CLEANSTACK);
+ if (!CastToBool(stack.back())) return set_error(serror, SCRIPT_ERR_EVAL_FALSE);
+ return true;
+}
+
static bool VerifyWitnessProgram(const CScriptWitness& witness, int witversion, const std::vector<unsigned char>& program, unsigned int flags, const BaseSignatureChecker& checker, ScriptError* serror)
{
- std::vector<std::vector<unsigned char> > stack;
CScript scriptPubKey;
if (witversion == 0) {
@@ -1426,45 +1507,30 @@ static bool VerifyWitnessProgram(const CScriptWitness& witness, int witversion,
return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_WITNESS_EMPTY);
}
scriptPubKey = CScript(witness.stack.back().begin(), witness.stack.back().end());
- stack = std::vector<std::vector<unsigned char> >(witness.stack.begin(), witness.stack.end() - 1);
uint256 hashScriptPubKey;
CSHA256().Write(&scriptPubKey[0], scriptPubKey.size()).Finalize(hashScriptPubKey.begin());
if (memcmp(hashScriptPubKey.begin(), program.data(), 32)) {
return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_MISMATCH);
}
+ return ExecuteWitnessScript(witness.stack.begin(), witness.stack.end() - 1, scriptPubKey, flags, SigVersion::WITNESS_V0, checker, serror);
} else if (program.size() == WITNESS_V0_KEYHASH_SIZE) {
// Special case for pay-to-pubkeyhash; signature + pubkey in witness
if (witness.stack.size() != 2) {
return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_MISMATCH); // 2 items in witness
}
scriptPubKey << OP_DUP << OP_HASH160 << program << OP_EQUALVERIFY << OP_CHECKSIG;
- stack = witness.stack;
+ return ExecuteWitnessScript(witness.stack.begin(), witness.stack.end(), scriptPubKey, flags, SigVersion::WITNESS_V0, checker, serror);
} else {
return set_error(serror, SCRIPT_ERR_WITNESS_PROGRAM_WRONG_LENGTH);
}
- } else if (flags & SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_WITNESS_PROGRAM) {
- return set_error(serror, SCRIPT_ERR_DISCOURAGE_UPGRADABLE_WITNESS_PROGRAM);
} else {
+ if (flags & SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_WITNESS_PROGRAM) {
+ return set_error(serror, SCRIPT_ERR_DISCOURAGE_UPGRADABLE_WITNESS_PROGRAM);
+ }
// Higher version witness scripts return true for future softfork compatibility
- return set_success(serror);
- }
-
- // Disallow stack item size > MAX_SCRIPT_ELEMENT_SIZE in witness stack
- for (unsigned int i = 0; i < stack.size(); i++) {
- if (stack.at(i).size() > MAX_SCRIPT_ELEMENT_SIZE)
- return set_error(serror, SCRIPT_ERR_PUSH_SIZE);
- }
-
- if (!EvalScript(stack, scriptPubKey, flags, checker, SigVersion::WITNESS_V0, serror)) {
- return false;
+ return true;
}
-
- // Scripts inside witness implicitly require cleanstack behaviour
- if (stack.size() != 1)
- return set_error(serror, SCRIPT_ERR_CLEANSTACK);
- if (!CastToBool(stack.back()))
- return set_error(serror, SCRIPT_ERR_EVAL_FALSE);
- return true;
+ // There is intentionally no return statement here, to be able to use "control reaches end of non-void function" warnings to detect gaps in the logic above.
}
bool VerifyScript(const CScript& scriptSig, const CScript& scriptPubKey, const CScriptWitness* witness, unsigned int flags, const BaseSignatureChecker& checker, ScriptError* serror)
generated by cgit v1.2.3 (git 2.26.2) at 2024-07-19 21:45:26 +0000