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Merge bitcoin/bitcoin#24225: wallet: Add sanity checks to DiscourageFeeSniping

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fa8e76bb90 wallet: Add sanity checks to AntiFeeSnipe (MarcoFalke)

Pull request description:

  I added those sanity checks as part of implementing BIP 326, but I think they make sense on their own. The checks require the transaction to be passed in to `DiscourageFeeSniping`. Also, replace `(int)locktime` cast with the equivalent `int(locktime)` cast.

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Tree-SHA512: 6fe37c85f074851ef09cae8addcb836257089290fecec515c129c3180e9ccb64740aaac76043af10ce7c213e5001568ca6b4b62ae9631f0994ed676b07118074
This commit is contained in:
Andrew Chow 2022-03-14 10:27:08 +00:00
commit 25d045a9ec
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1 changed files with 25 additions and 12 deletions
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37
src/wallet/spend.cpp
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@ -582,12 +582,13 @@ static bool IsCurrentForAntiFeeSniping(interfaces::Chain& chain, const uint256&
}
/**
* Return a height-based locktime for new transactions (uses the height of the
* Set a height-based locktime for new transactions (uses the height of the
* current chain tip unless we are not synced with the current chain
*/
static uint32_t GetLocktimeForNewTransaction(interfaces::Chain& chain, const uint256& block_hash, int block_height)
static void DiscourageFeeSniping(CMutableTransaction& tx, interfaces::Chain& chain, const uint256& block_hash, int block_height)
{
uint32_t locktime;
// All inputs must be added by now
assert(!tx.vin.empty());
// Discourage fee sniping.
//
// For a large miner the value of the transactions in the best block and
@ -609,22 +610,34 @@ static uint32_t GetLocktimeForNewTransaction(interfaces::Chain& chain, const uin
// now we ensure code won't be written that makes assumptions about
// nLockTime that preclude a fix later.
if (IsCurrentForAntiFeeSniping(chain, block_hash)) {
locktime = block_height;
tx.nLockTime = block_height;
// Secondly occasionally randomly pick a nLockTime even further back, so
// that transactions that are delayed after signing for whatever reason,
// e.g. high-latency mix networks and some CoinJoin implementations, have
// better privacy.
if (GetRandInt(10) == 0)
locktime = std::max(0, (int)locktime - GetRandInt(100));
if (GetRandInt(10) == 0) {
tx.nLockTime = std::max(0, int(tx.nLockTime) - GetRandInt(100));
}
} else {
// If our chain is lagging behind, we can't discourage fee sniping nor help
// the privacy of high-latency transactions. To avoid leaking a potentially
// unique "nLockTime fingerprint", set nLockTime to a constant.
locktime = 0;
tx.nLockTime = 0;
}
// Sanity check all values
assert(tx.nLockTime < LOCKTIME_THRESHOLD); // Type must be block height
assert(tx.nLockTime <= uint64_t(block_height));
for (const auto& in : tx.vin) {
// Can not be FINAL for locktime to work
assert(in.nSequence != CTxIn::SEQUENCE_FINAL);
// May be MAX NONFINAL to disable both BIP68 and BIP125
if (in.nSequence == CTxIn::MAX_SEQUENCE_NONFINAL) continue;
// May be MAX BIP125 to disable BIP68 and enable BIP125
if (in.nSequence == MAX_BIP125_RBF_SEQUENCE) continue;
// The wallet does not support any other sequence-use right now.
assert(false);
}
assert(locktime < LOCKTIME_THRESHOLD);
return locktime;
}
static bool CreateTransactionInternal(
@ -641,7 +654,6 @@ static bool CreateTransactionInternal(
AssertLockHeld(wallet.cs_wallet);
CMutableTransaction txNew; // The resulting transaction that we make
txNew.nLockTime = GetLocktimeForNewTransaction(wallet.chain(), wallet.GetLastBlockHash(), wallet.GetLastBlockHeight());
CoinSelectionParams coin_selection_params; // Parameters for coin selection, init with dummy
coin_selection_params.m_avoid_partial_spends = coin_control.m_avoid_partial_spends;
@ -787,8 +799,8 @@ static bool CreateTransactionInternal(
// Shuffle selected coins and fill in final vin
std::vector<CInputCoin> selected_coins = result->GetShuffledInputVector();
// Note how the sequence number is set to non-maxint so that
// the nLockTime set above actually works.
// The sequence number is set to non-maxint so that DiscourageFeeSniping
// works.
//
// BIP125 defines opt-in RBF as any nSequence < maxint-1, so
// we use the highest possible value in that range (maxint-2)
@ -799,6 +811,7 @@ static bool CreateTransactionInternal(
for (const auto& coin : selected_coins) {
txNew.vin.push_back(CTxIn(coin.outpoint, CScript(), nSequence));
}
DiscourageFeeSniping(txNew, wallet.chain(), wallet.GetLastBlockHash(), wallet.GetLastBlockHeight());
// Calculate the transaction fee
TxSize tx_sizes = CalculateMaximumSignedTxSize(CTransaction(txNew), &wallet, &coin_control);