Reduce MAX_PEER_TX_ANNOUNCEMENTS for non-PF_RELAY peers

Maintaining up to 100000 INVs per peer is excessive, as that is far more
than fits in a typical mempool.

Also disable the "overload" penalty for PF_RELAY peers.

1 files changed, 9 insertions, 5 deletions

diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 163c9c1f72..ee50bc1805 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -75,8 +75,11 @@ static const unsigned int MAX_INV_SZ = 50000;
 /** Maximum number of in-flight transaction requests from a peer. It is not a hard limit, but the threshold at which
  *  point the OVERLOADED_PEER_TX_DELAY kicks in. */
 static constexpr int32_t MAX_PEER_TX_REQUEST_IN_FLIGHT = 100;
-/** Maximum number of announced transactions from a peer */
-static constexpr int32_t MAX_PEER_TX_ANNOUNCEMENTS = 2 * MAX_INV_SZ;
+/** Maximum number of transactions to consider for requesting, per peer. It provides a reasonable DoS limit to
+ *  per-peer memory usage spent on announcements, while covering peers continuously sending INVs at the maximum
+ *  rate (by our own policy, see INVENTORY_BROADCAST_PER_SECOND) for several minutes, while not receiving
+ *  the actual transaction (from any peer) in response to requests for them. */
+static constexpr int32_t MAX_PEER_TX_ANNOUNCEMENTS = 5000;
 /** How long to delay requesting transactions via txids, if we have wtxid-relaying peers */
 static constexpr auto TXID_RELAY_DELAY = std::chrono::seconds{2};
 /** How long to delay requesting transactions from non-preferred peers */
@@ -754,7 +757,7 @@ void PeerManager::AddTxAnnouncement(const CNode& node, const GenTxid& gtxid, std
 {
     AssertLockHeld(::cs_main); // For m_txrequest
     NodeId nodeid = node.GetId();
-    if (m_txrequest.Count(nodeid) >= MAX_PEER_TX_ANNOUNCEMENTS) {
+    if (!node.HasPermission(PF_RELAY) && m_txrequest.Count(nodeid) >= MAX_PEER_TX_ANNOUNCEMENTS) {
         // Too many queued announcements from this peer
         return;
     }
@@ -766,12 +769,13 @@ void PeerManager::AddTxAnnouncement(const CNode& node, const GenTxid& gtxid, std
     //   - NONPREF_PEER_TX_DELAY for announcements from non-preferred connections
     //   - TXID_RELAY_DELAY for announcements from txid peers while wtxid peers are available
     //   - OVERLOADED_PEER_TX_DELAY for announcements from peers which have at least
-    //     MAX_PEER_TX_REQUEST_IN_FLIGHT requests in flight.
+    //     MAX_PEER_TX_REQUEST_IN_FLIGHT requests in flight (and don't have PF_RELAY).
     auto delay = std::chrono::microseconds{0};
     const bool preferred = state->fPreferredDownload;
     if (!preferred) delay += NONPREF_PEER_TX_DELAY;
     if (!state->m_wtxid_relay && g_wtxid_relay_peers > 0) delay += TXID_RELAY_DELAY;
-    const bool overloaded = m_txrequest.CountInFlight(nodeid) >= MAX_PEER_TX_REQUEST_IN_FLIGHT;
+    const bool overloaded = !node.HasPermission(PF_RELAY) &&
+        m_txrequest.CountInFlight(nodeid) >= MAX_PEER_TX_REQUEST_IN_FLIGHT;
     if (overloaded) delay += OVERLOADED_PEER_TX_DELAY;
     m_txrequest.ReceivedInv(nodeid, gtxid, preferred, current_time + delay);
 }