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// Copyright (c) 2020-2021 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include <chain.h>
#include <chainparams.h>
#include <consensus/params.h>
#include <primitives/block.h>
#include <util/system.h>
#include <versionbits.h>
#include <test/fuzz/FuzzedDataProvider.h>
#include <test/fuzz/fuzz.h>
#include <test/fuzz/util.h>
#include <cstdint>
#include <limits>
#include <memory>
#include <vector>
namespace {
class TestConditionChecker : public AbstractThresholdConditionChecker
{
private:
mutable ThresholdConditionCache m_cache;
const Consensus::Params dummy_params{};
public:
const int64_t m_begin;
const int64_t m_end;
const int m_period;
const int m_threshold;
const int m_min_activation_height;
const int m_bit;
TestConditionChecker(int64_t begin, int64_t end, int period, int threshold, int min_activation_height, int bit)
: m_begin{begin}, m_end{end}, m_period{period}, m_threshold{threshold}, m_min_activation_height{min_activation_height}, m_bit{bit}
{
assert(m_period > 0);
assert(0 <= m_threshold && m_threshold <= m_period);
assert(0 <= m_bit && m_bit < 32 && m_bit < VERSIONBITS_NUM_BITS);
assert(0 <= m_min_activation_height);
}
bool Condition(const CBlockIndex* pindex, const Consensus::Params& params) const override { return Condition(pindex->nVersion); }
int64_t BeginTime(const Consensus::Params& params) const override { return m_begin; }
int64_t EndTime(const Consensus::Params& params) const override { return m_end; }
int Period(const Consensus::Params& params) const override { return m_period; }
int Threshold(const Consensus::Params& params) const override { return m_threshold; }
int MinActivationHeight(const Consensus::Params& params) const override { return m_min_activation_height; }
ThresholdState GetStateFor(const CBlockIndex* pindexPrev) const { return AbstractThresholdConditionChecker::GetStateFor(pindexPrev, dummy_params, m_cache); }
int GetStateSinceHeightFor(const CBlockIndex* pindexPrev) const { return AbstractThresholdConditionChecker::GetStateSinceHeightFor(pindexPrev, dummy_params, m_cache); }
BIP9Stats GetStateStatisticsFor(const CBlockIndex* pindex) const { return AbstractThresholdConditionChecker::GetStateStatisticsFor(pindex, dummy_params); }
bool Condition(int32_t version) const
{
uint32_t mask = ((uint32_t)1) << m_bit;
return (((version & VERSIONBITS_TOP_MASK) == VERSIONBITS_TOP_BITS) && (version & mask) != 0);
}
bool Condition(const CBlockIndex* pindex) const { return Condition(pindex->nVersion); }
};
/** Track blocks mined for test */
class Blocks
{
private:
std::vector<std::unique_ptr<CBlockIndex>> m_blocks;
const uint32_t m_start_time;
const uint32_t m_interval;
const int32_t m_signal;
const int32_t m_no_signal;
public:
Blocks(uint32_t start_time, uint32_t interval, int32_t signal, int32_t no_signal)
: m_start_time{start_time}, m_interval{interval}, m_signal{signal}, m_no_signal{no_signal} {}
size_t size() const { return m_blocks.size(); }
CBlockIndex* tip() const
{
return m_blocks.empty() ? nullptr : m_blocks.back().get();
}
CBlockIndex* mine_block(bool signal)
{
CBlockHeader header;
header.nVersion = signal ? m_signal : m_no_signal;
header.nTime = m_start_time + m_blocks.size() * m_interval;
header.nBits = 0x1d00ffff;
auto current_block = std::make_unique<CBlockIndex>(header);
current_block->pprev = tip();
current_block->nHeight = m_blocks.size();
current_block->BuildSkip();
return m_blocks.emplace_back(std::move(current_block)).get();
}
};
std::unique_ptr<const CChainParams> g_params;
void initialize()
{
// this is actually comparatively slow, so only do it once
g_params = CreateChainParams(ArgsManager{}, CBaseChainParams::MAIN);
assert(g_params != nullptr);
}
constexpr uint32_t MAX_START_TIME = 4102444800; // 2100-01-01
FUZZ_TARGET_INIT(versionbits, initialize)
{
const CChainParams& params = *g_params;
const int64_t interval = params.GetConsensus().nPowTargetSpacing;
assert(interval > 1); // need to be able to halve it
assert(interval < std::numeric_limits<int32_t>::max());
FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
// making period/max_periods larger slows these tests down significantly
const int period = 32;
const size_t max_periods = 16;
const size_t max_blocks = 2 * period * max_periods;
const int threshold = fuzzed_data_provider.ConsumeIntegralInRange(1, period);
assert(0 < threshold && threshold <= period); // must be able to both pass and fail threshold!
// too many blocks at 10min each might cause uint32_t time to overflow if
// block_start_time is at the end of the range above
assert(std::numeric_limits<uint32_t>::max() - MAX_START_TIME > interval * max_blocks);
const int64_t block_start_time = fuzzed_data_provider.ConsumeIntegralInRange<uint32_t>(params.GenesisBlock().nTime, MAX_START_TIME);
// what values for version will we use to signal / not signal?
const int32_t ver_signal = fuzzed_data_provider.ConsumeIntegral<int32_t>();
const int32_t ver_nosignal = fuzzed_data_provider.ConsumeIntegral<int32_t>();
// select deployment parameters: bit, start time, timeout
const int bit = fuzzed_data_provider.ConsumeIntegralInRange<int>(0, VERSIONBITS_NUM_BITS - 1);
bool always_active_test = false;
bool never_active_test = false;
int64_t start_time;
int64_t timeout;
if (fuzzed_data_provider.ConsumeBool()) {
// pick the timestamp to switch based on a block
// note states will change *after* these blocks because mediantime lags
int start_block = fuzzed_data_provider.ConsumeIntegralInRange<int>(0, period * (max_periods - 3));
int end_block = fuzzed_data_provider.ConsumeIntegralInRange<int>(0, period * (max_periods - 3));
start_time = block_start_time + start_block * interval;
timeout = block_start_time + end_block * interval;
// allow for times to not exactly match a block
if (fuzzed_data_provider.ConsumeBool()) start_time += interval / 2;
if (fuzzed_data_provider.ConsumeBool()) timeout += interval / 2;
} else {
if (fuzzed_data_provider.ConsumeBool()) {
start_time = Consensus::BIP9Deployment::ALWAYS_ACTIVE;
always_active_test = true;
} else {
start_time = Consensus::BIP9Deployment::NEVER_ACTIVE;
never_active_test = true;
}
timeout = fuzzed_data_provider.ConsumeBool() ? Consensus::BIP9Deployment::NO_TIMEOUT : fuzzed_data_provider.ConsumeIntegral<int64_t>();
}
int min_activation = fuzzed_data_provider.ConsumeIntegralInRange<int>(0, period * max_periods);
TestConditionChecker checker(start_time, timeout, period, threshold, min_activation, bit);
// Early exit if the versions don't signal sensibly for the deployment
if (!checker.Condition(ver_signal)) return;
if (checker.Condition(ver_nosignal)) return;
if (ver_nosignal < 0) return;
// TOP_BITS should ensure version will be positive and meet min
// version requirement
assert(ver_signal > 0);
assert(ver_signal >= VERSIONBITS_LAST_OLD_BLOCK_VERSION);
// Now that we have chosen time and versions, setup to mine blocks
Blocks blocks(block_start_time, interval, ver_signal, ver_nosignal);
/* Strategy:
* * we will mine a final period worth of blocks, with
* randomised signalling according to a mask
* * but before we mine those blocks, we will mine some
* randomised number of prior periods; with either all
* or no blocks in the period signalling
*
* We establish the mask first, then consume "bools" until
* we run out of fuzz data to work out how many prior periods
* there are and which ones will signal.
*/
// establish the mask
const uint32_t signalling_mask = fuzzed_data_provider.ConsumeIntegral<uint32_t>();
// mine prior periods
while (fuzzed_data_provider.remaining_bytes() > 0) { // early exit; no need for LIMITED_WHILE
// all blocks in these periods either do or don't signal
bool signal = fuzzed_data_provider.ConsumeBool();
for (int b = 0; b < period; ++b) {
blocks.mine_block(signal);
}
// don't risk exceeding max_blocks or times may wrap around
if (blocks.size() + 2 * period > max_blocks) break;
}
// NOTE: fuzzed_data_provider may be fully consumed at this point and should not be used further
// now we mine the final period and check that everything looks sane
// count the number of signalling blocks
int blocks_sig = 0;
// get the info for the first block of the period
CBlockIndex* prev = blocks.tip();
const int exp_since = checker.GetStateSinceHeightFor(prev);
const ThresholdState exp_state = checker.GetStateFor(prev);
// get statistics from end of previous period, then reset
BIP9Stats last_stats;
last_stats.period = period;
last_stats.threshold = threshold;
last_stats.count = last_stats.elapsed = 0;
last_stats.possible = (period >= threshold);
int prev_next_height = (prev == nullptr ? 0 : prev->nHeight + 1);
assert(exp_since <= prev_next_height);
// mine (period-1) blocks and check state
for (int b = 1; b < period; ++b) {
const bool signal = (signalling_mask >> (b % 32)) & 1;
if (signal) ++blocks_sig;
CBlockIndex* current_block = blocks.mine_block(signal);
// verify that signalling attempt was interpreted correctly
assert(checker.Condition(current_block) == signal);
// state and since don't change within the period
const ThresholdState state = checker.GetStateFor(current_block);
const int since = checker.GetStateSinceHeightFor(current_block);
assert(state == exp_state);
assert(since == exp_since);
// check that after mining this block stats change as expected
const BIP9Stats stats = checker.GetStateStatisticsFor(current_block);
assert(stats.period == period);
assert(stats.threshold == threshold);
assert(stats.elapsed == b);
assert(stats.count == last_stats.count + (signal ? 1 : 0));
assert(stats.possible == (stats.count + period >= stats.elapsed + threshold));
last_stats = stats;
}
if (exp_state == ThresholdState::STARTED) {
// double check that stats.possible is sane
if (blocks_sig >= threshold - 1) assert(last_stats.possible);
}
// mine the final block
bool signal = (signalling_mask >> (period % 32)) & 1;
if (signal) ++blocks_sig;
CBlockIndex* current_block = blocks.mine_block(signal);
assert(checker.Condition(current_block) == signal);
const BIP9Stats stats = checker.GetStateStatisticsFor(current_block);
assert(stats.period == period);
assert(stats.threshold == threshold);
assert(stats.elapsed == period);
assert(stats.count == blocks_sig);
assert(stats.possible == (stats.count + period >= stats.elapsed + threshold));
// More interesting is whether the state changed.
const ThresholdState state = checker.GetStateFor(current_block);
const int since = checker.GetStateSinceHeightFor(current_block);
// since is straightforward:
assert(since % period == 0);
assert(0 <= since && since <= current_block->nHeight + 1);
if (state == exp_state) {
assert(since == exp_since);
} else {
assert(since == current_block->nHeight + 1);
}
// state is where everything interesting is
switch (state) {
case ThresholdState::DEFINED:
assert(since == 0);
assert(exp_state == ThresholdState::DEFINED);
assert(current_block->GetMedianTimePast() < checker.m_begin);
break;
case ThresholdState::STARTED:
assert(current_block->GetMedianTimePast() >= checker.m_begin);
if (exp_state == ThresholdState::STARTED) {
assert(blocks_sig < threshold);
assert(current_block->GetMedianTimePast() < checker.m_end);
} else {
assert(exp_state == ThresholdState::DEFINED);
}
break;
case ThresholdState::LOCKED_IN:
if (exp_state == ThresholdState::LOCKED_IN) {
assert(current_block->nHeight + 1 < min_activation);
} else {
assert(exp_state == ThresholdState::STARTED);
assert(blocks_sig >= threshold);
}
break;
case ThresholdState::ACTIVE:
assert(always_active_test || min_activation <= current_block->nHeight + 1);
assert(exp_state == ThresholdState::ACTIVE || exp_state == ThresholdState::LOCKED_IN);
break;
case ThresholdState::FAILED:
assert(never_active_test || current_block->GetMedianTimePast() >= checker.m_end);
if (exp_state == ThresholdState::STARTED) {
assert(blocks_sig < threshold);
} else {
assert(exp_state == ThresholdState::FAILED);
}
break;
default:
assert(false);
}
if (blocks.size() >= period * max_periods) {
// we chose the timeout (and block times) so that by the time we have this many blocks it's all over
assert(state == ThresholdState::ACTIVE || state == ThresholdState::FAILED);
}
if (always_active_test) {
// "always active" has additional restrictions
assert(state == ThresholdState::ACTIVE);
assert(exp_state == ThresholdState::ACTIVE);
assert(since == 0);
} else if (never_active_test) {
// "never active" does too
assert(state == ThresholdState::FAILED);
assert(exp_state == ThresholdState::FAILED);
assert(since == 0);
} else {
// for signalled deployments, the initial state is always DEFINED
assert(since > 0 || state == ThresholdState::DEFINED);
assert(exp_since > 0 || exp_state == ThresholdState::DEFINED);
}
}
} // namespace
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