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Merge bitcoin/bitcoin#27997: Descriptors: rule out unspendable miniscript descriptors

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c7db88af71b3204171f33399aa4f33b40a4f7cd9 descriptor: assert we never parse a sane miniscript with no pubkey (Antoine Poinsot)
a49402a9ec7431c286139b76f8759719a99a8551 qa: make sure we don't let unspendable Miniscript descriptors be imported (Antoine Poinsot)
639e3b6c9759a7a582c5c86fdbfa5ea99cb7bb16 descriptor: refuse to parse unspendable miniscript descriptors (Antoine Poinsot)
e3280eae1b53006d74d11f3cf9d7a9dc7ff2c39e miniscript: make GetStackSize() and GetOps() return optionals (Antoine Poinsot)

Pull request description:

  `IsSane()` in Miniscript does not ensure a Script is actually spendable. This is an issue as we would accept any sane Miniscript when parsing a descriptor. Fix this by explicitly checking a Miniscript descriptor is both sane and spendable when parsing it.

  This bug was exposed due to a check added in #22838 (https://github.com/bitcoin/bitcoin/pull/22838#discussion_r1226859880) that triggered a fuzz crash (https://github.com/bitcoin/bitcoin/pull/22838#issuecomment-1612510057).

ACKs for top commit:
  sipa:
    utACK c7db88af71b3204171f33399aa4f33b40a4f7cd9
  achow101:
    ACK c7db88af71b3204171f33399aa4f33b40a4f7cd9

Tree-SHA512: e79bc9f7842e98a4e8f358f05811fca51b15b4b80a171c0d2b17cf4bb1f578a18e4397bc2ece9817d392e0de0196ee6a054b7318441fd3566dd22e1f03eb64a5
This commit is contained in:
Andrew Chow 2023-07-17 19:08:56 -04:00
commit bc88f3ab90
No known key found for this signature in database
GPG Key ID: 17565732E08E5E41
5 changed files with 48 additions and 14 deletions
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10
src/script/descriptor.cpp
View File

@ -15,6 +15,7 @@
#include <common/args.h>
#include <span.h>
#include <util/bip32.h>
#include <util/check.h>
#include <util/spanparsing.h>
#include <util/strencodings.h>
#include <util/vector.h>
@ -1553,14 +1554,14 @@ std::unique_ptr<DescriptorImpl> ParseScript(uint32_t& key_exp_index, Span<const
error = std::move(parser.m_key_parsing_error);
return nullptr;
}
if (!node->IsSane()) {
if (!node->IsSane() || node->IsNotSatisfiable()) {
// Try to find the first insane sub for better error reporting.
auto insane_node = node.get();
if (const auto sub = node->FindInsaneSub()) insane_node = sub;
if (const auto str = insane_node->ToString(parser)) error = *str;
if (!insane_node->IsValid()) {
error += " is invalid";
} else {
} else if (!node->IsSane()) {
error += " is not sane";
if (!insane_node->IsNonMalleable()) {
error += ": malleable witnesses exist";
@ -1573,9 +1574,14 @@ std::unique_ptr<DescriptorImpl> ParseScript(uint32_t& key_exp_index, Span<const
} else if (!insane_node->ValidSatisfactions()) {
error += ": needs witnesses that may exceed resource limits";
}
} else {
error += " is not satisfiable";
}
return nullptr;
}
// A signature check is required for a miniscript to be sane. Therefore no sane miniscript
// may have an empty list of public keys.
CHECK_NONFATAL(!parser.m_keys.empty());
return std::make_unique<MiniscriptDescriptor>(std::move(parser.m_keys), std::move(node));
}
}

23
src/script/miniscript.h
View File

@ -1134,20 +1134,35 @@ public:
size_t ScriptSize() const { return scriptlen; }
//! Return the maximum number of ops needed to satisfy this script non-malleably.
uint32_t GetOps() const { return ops.count + ops.sat.value; }
std::optional<uint32_t> GetOps() const {
if (!ops.sat.valid) return {};
return ops.count + ops.sat.value;
}
//! Return the number of ops in the script (not counting the dynamic ones that depend on execution).
uint32_t GetStaticOps() const { return ops.count; }
//! Check the ops limit of this script against the consensus limit.
bool CheckOpsLimit() const { return GetOps() <= MAX_OPS_PER_SCRIPT; }
bool CheckOpsLimit() const {
if (const auto ops = GetOps()) return *ops <= MAX_OPS_PER_SCRIPT;
return true;
}
/** Return the maximum number of stack elements needed to satisfy this script non-malleably, including
* the script push. */
uint32_t GetStackSize() const { return ss.sat.value + 1; }
std::optional<uint32_t> GetStackSize() const {
if (!ss.sat.valid) return {};
return ss.sat.value + 1;
}
//! Check the maximum stack size for this script against the policy limit.
bool CheckStackSize() const { return GetStackSize() - 1 <= MAX_STANDARD_P2WSH_STACK_ITEMS; }
bool CheckStackSize() const {
if (const auto ss = GetStackSize()) return *ss - 1 <= MAX_STANDARD_P2WSH_STACK_ITEMS;
return true;
}
//! Whether no satisfaction exists for this node.
bool IsNotSatisfiable() const { return !GetStackSize(); }
//! Return the expression type.
Type GetType() const { return typ; }

7
src/test/fuzz/miniscript.cpp
View File

@ -943,7 +943,8 @@ void TestNode(const NodeRef& node, FuzzedDataProvider& provider)
assert(decoded->ToScript(PARSER_CTX) == script);
assert(decoded->GetType() == node->GetType());
if (provider.ConsumeBool() && node->GetOps() < MAX_OPS_PER_SCRIPT && node->ScriptSize() < MAX_STANDARD_P2WSH_SCRIPT_SIZE) {
const auto node_ops{node->GetOps()};
if (provider.ConsumeBool() && node_ops && *node_ops < MAX_OPS_PER_SCRIPT && node->ScriptSize() < MAX_STANDARD_P2WSH_SCRIPT_SIZE) {
// Optionally pad the script with OP_NOPs to max op the ops limit of the constructed script.
// This makes the script obviously not actually miniscript-compatible anymore, but the
// signatures constructed in this test don't commit to the script anyway, so the same
@ -954,7 +955,7 @@ void TestNode(const NodeRef& node, FuzzedDataProvider& provider)
// Do not pad more than what would cause MAX_STANDARD_P2WSH_SCRIPT_SIZE to be reached, however,
// as that also invalidates scripts.
int add = std::min<int>(
MAX_OPS_PER_SCRIPT - node->GetOps(),
MAX_OPS_PER_SCRIPT - *node_ops,
MAX_STANDARD_P2WSH_SCRIPT_SIZE - node->ScriptSize());
for (int i = 0; i < add; ++i) script.push_back(OP_NOP);
}
@ -972,7 +973,7 @@ void TestNode(const NodeRef& node, FuzzedDataProvider& provider)
if (nonmal_success) {
// Non-malleable satisfactions are bounded by GetStackSize().
assert(witness_nonmal.stack.size() <= node->GetStackSize());
assert(witness_nonmal.stack.size() <= *node->GetStackSize());
// If a non-malleable satisfaction exists, the malleable one must also exist, and be identical to it.
assert(mal_success);
assert(witness_nonmal.stack == witness_mal.stack);

10
src/test/miniscript_tests.cpp
View File

@ -297,7 +297,7 @@ void TestSatisfy(const std::string& testcase, const NodeRef& node) {
if (nonmal_success) {
// Non-malleable satisfactions are bounded by GetStackSize().
BOOST_CHECK(witness_nonmal.stack.size() <= node->GetStackSize());
BOOST_CHECK(witness_nonmal.stack.size() <= *node->GetStackSize());
// If a non-malleable satisfaction exists, the malleable one must also exist, and be identical to it.
BOOST_CHECK(mal_success);
BOOST_CHECK(witness_nonmal.stack == witness_mal.stack);
@ -375,8 +375,8 @@ void Test(const std::string& ms, const std::string& hexscript, int mode, int ops
auto inferred_miniscript = miniscript::FromScript(computed_script, CONVERTER);
BOOST_CHECK_MESSAGE(inferred_miniscript, "Cannot infer miniscript from script: " + ms);
BOOST_CHECK_MESSAGE(inferred_miniscript->ToScript(CONVERTER) == computed_script, "Roundtrip failure: miniscript->script != miniscript->script->miniscript->script: " + ms);
if (opslimit != -1) BOOST_CHECK_MESSAGE((int)node->GetOps() == opslimit, "Ops limit mismatch: " << ms << " (" << node->GetOps() << " vs " << opslimit << ")");
if (stacklimit != -1) BOOST_CHECK_MESSAGE((int)node->GetStackSize() == stacklimit, "Stack limit mismatch: " << ms << " (" << node->GetStackSize() << " vs " << stacklimit << ")");
if (opslimit != -1) BOOST_CHECK_MESSAGE((int)*node->GetOps() == opslimit, "Ops limit mismatch: " << ms << " (" << *node->GetOps() << " vs " << opslimit << ")");
if (stacklimit != -1) BOOST_CHECK_MESSAGE((int)*node->GetStackSize() == stacklimit, "Stack limit mismatch: " << ms << " (" << *node->GetStackSize() << " vs " << stacklimit << ")");
TestSatisfy(ms, node);
}
}
@ -498,8 +498,8 @@ BOOST_AUTO_TEST_CASE(fixed_tests)
// For CHECKMULTISIG the OP cost is the number of keys, but the stack size is the number of sigs (+1)
const auto ms_multi = miniscript::FromString("multi(1,03d30199d74fb5a22d47b6e054e2f378cedacffcb89904a61d75d0dbd407143e65,03fff97bd5755eeea420453a14355235d382f6472f8568a18b2f057a1460297556,0279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798)", CONVERTER);
BOOST_CHECK(ms_multi);
BOOST_CHECK_EQUAL(ms_multi->GetOps(), 4); // 3 pubkeys + CMS
BOOST_CHECK_EQUAL(ms_multi->GetStackSize(), 3); // 1 sig + dummy elem + script push
BOOST_CHECK_EQUAL(*ms_multi->GetOps(), 4); // 3 pubkeys + CMS
BOOST_CHECK_EQUAL(*ms_multi->GetStackSize(), 3); // 1 sig + dummy elem + script push
// The 'd:' wrapper leaves on the stack what was DUP'ed at the beginning of its execution.
// Since it contains an OP_IF just after on the same element, we can make sure that the element
// in question must be OP_1 if OP_IF enforces that its argument must only be OP_1 or the empty

12
test/functional/wallet_miniscript.py
View File

@ -277,6 +277,18 @@ class WalletMiniscriptTest(BitcoinTestFramework):
assert not res["success"]
assert "is not sane: witnesses without signature exist" in res["error"]["message"]
# Sanity check we wouldn't let an unspendable Miniscript descriptor in
res = self.ms_wo_wallet.importdescriptors(
[
{
"desc": descsum_create("wsh(0)"),
"active": False,
"timestamp": "now",
}
]
)[0]
assert not res["success"] and "is not satisfiable" in res["error"]["message"]
# Test we can track any type of Miniscript
for ms in MINISCRIPTS:
self.watchonly_test(ms)