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[p2p] only attempt 1p1c when both txns provided by the same peer

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Now that we track all announcers of an orphan, it's not helpful to
consider an orphan provided by a peer that didn't send us this parent.
It can only hurt our chances of finding the right orphan when there are
multiple candidates.

Adapt the 2 tests in p2p_opportunistic_1p1c.py that looked at 1p1c
packages from different peers. Instead of checking that the right peer
is punished, we now check that the package is not submitted. We can't
use the functional test to see that the package was not considered
because the behavior is indistinguishable (except for the logs).
This commit is contained in:
glozow
2024-08-20 11:39:18 +01:00
parent f7658d9b14
commit 86d7135e36
6 changed files with 14 additions and 101 deletions
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34
src/node/txdownloadman_impl.cpp
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@@ -300,9 +300,11 @@ std::optional<PackageToValidate> TxDownloadManagerImpl::Find1P1CPackage(const CT
Assume(RecentRejectsReconsiderableFilter().contains(parent_wtxid.ToUint256()));
// Prefer children from this peer. This helps prevent censorship attempts in which an attacker
// Only consider children from this peer. This helps prevent censorship attempts in which an attacker
// sends lots of fake children for the parent, and we (unluckily) keep selecting the fake
// children instead of the real one provided by the honest peer.
// children instead of the real one provided by the honest peer. Since we track all announcers
// of an orphan, this does not exclude parent + orphan pairs that we happened to request from
// different peers.
const auto cpfp_candidates_same_peer{m_orphanage.GetChildrenFromSamePeer(ptx, nodeid)};
// These children should be sorted from newest to oldest. In the (probably uncommon) case
@@ -315,34 +317,6 @@ std::optional<PackageToValidate> TxDownloadManagerImpl::Find1P1CPackage(const CT
return PackageToValidate{ptx, child, nodeid, nodeid};
}
}
// If no suitable candidate from the same peer is found, also try children that were provided by
// a different peer. This is useful because sometimes multiple peers announce both transactions
// to us, and we happen to download them from different peers (we wouldn't have known that these
// 2 transactions are related). We still want to find 1p1c packages then.
//
// If we start tracking all announcers of orphans, we can restrict this logic to parent + child
// pairs in which both were provided by the same peer, i.e. delete this step.
const auto cpfp_candidates_different_peer{m_orphanage.GetChildrenFromDifferentPeer(ptx, nodeid)};
// Find the first 1p1c that hasn't already been rejected. We randomize the order to not
// create a bias that attackers can use to delay package acceptance.
//
// Create a random permutation of the indices.
std::vector<size_t> tx_indices(cpfp_candidates_different_peer.size());
std::iota(tx_indices.begin(), tx_indices.end(), 0);
std::shuffle(tx_indices.begin(), tx_indices.end(), m_opts.m_rng);
for (const auto index : tx_indices) {
// If we already tried a package and failed for any reason, the combined hash was
// cached in m_lazy_recent_rejects_reconsiderable.
const auto [child_tx, child_sender] = cpfp_candidates_different_peer.at(index);
Package maybe_cpfp_package{ptx, child_tx};
if (!RecentRejectsReconsiderableFilter().contains(GetPackageHash(maybe_cpfp_package)) &&
!RecentRejectsFilter().contains(child_tx->GetHash().ToUint256())) {
return PackageToValidate{ptx, child_tx, nodeid, child_sender};
}
}
return std::nullopt;
}