p2p: Don't participate in addr relay with feeler connections
What the developer wrote
Authored by Daniela Brozzoni
p2p: Don't participate in addr relay with feeler connections
Feeler connections are short-lived connections made to check that a node
is alive, useful for test-before-evict from addrman, and for moving
addresses from the new to the tried table.
We currently send a GETADDR message to feelers, but then disconnect
before being able to receive a response. This wastes some bandwidth, so
we can avoid sending the GETADDR altogether.
Not sending the initial GETADDR will effectively disable addr relay:
we initialize addr relay for the peer when we send GETADDR, and the peer
initializes addr relay to us when they receive it. So the
peer will not relay any announcement to us, and we will not relay any
to them either. This is ok, since the use of feelers is to test if there
is a bitcoin node behind an address, not exchange addresses with them.
What changed, and why it matters
This change is a small network-efficiency cleanup, not a security fix. Bitcoin Core's 'feeler' connections are brief probes used to check whether another node is online. Previously, the software would ask feeler peers for addresses (sending a GETADDR message) even though it disconnects almost immediately and never reads the reply. The patch stops that unnecessary request, saving a little bandwidth. It does not fix a vulnerability and does not change how attackers could interact with the network.
No security action required. Treat as a normal network-cleanup patch; review for correctness if backporting, but it is not a vulnerability fix.
Security signals we found
No security-relevant signal: change is described by the project as a bandwidth optimization
No memory safety, cryptographic, consensus, or authorization change
No bug class such as DoS, eclipse-attack vector, or information leak is introduced or fixed
Evidence from the diff
The commit modifies PeerManagerImpl::SetupAddressRelay in src/net_processing.cpp to return false for feeler connections (node.IsFeelerConn()), and updates the version-message handling comment to include feelers alongside inbound and block-relay-only peers as cases where GETADDR is not sent. Because GETADDR is what initializes addr relay on both sides, feelers will no longer participate in address relay in either direction. A functional test is updated to assert that no GETADDR is sent to a feeler peer.
Changed components
src/net_processing.cpp: PeerManagerImpl::SetupAddressRelaysrc/net_processing.cpp: version-message GETADDR decision logictest/functional/p2p_addr_relay.pyInspect captured patch +12 / −2
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 28d7d2c1..12fc5066 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -3748,7 +3748,7 @@ void PeerManagerImpl::ProcessMessage(Peer& peer, CNode& pfrom, const std::string
// Attempt to initialize address relay for outbound peers and use result
// to decide whether to send GETADDR, so that we don't send it to
- // inbound or outbound block-relay-only peers.
+ // inbound, feelers, or outbound block-relay-only peers.
bool send_getaddr{false};
if (!pfrom.IsInboundConn()) {
send_getaddr = SetupAddressRelay(pfrom, peer);
@@ -5612,6 +5612,11 @@ bool PeerManagerImpl::SetupAddressRelay(const CNode& node, Peer& peer)
// information of addr traffic to infer the link.
if (node.IsBlockOnlyConn()) return false;
+ // We don't participate in addr relay with feeler connections because
+ // they are disconnected shortly after the handshake completes,
+ // before the node will receive the addr response.
+ if (node.IsFeelerConn()) return false;
+
if (!peer.m_addr_relay_enabled.exchange(true)) {
// During version message processing (non-block-relay-only outbound peers)
// or on first addr-related message we have received (inbound peers), initialize
diff --git a/test/functional/p2p_addr_relay.py b/test/functional/p2p_addr_relay.py
index 65b21c0d..1464e23c 100755
--- a/test/functional/p2p_addr_relay.py
+++ b/test/functional/p2p_addr_relay.py
@@ -280,12 +280,17 @@ class AddrTest(BitcoinTestFramework):
tip_header = from_hex(CBlockHeader(), self.nodes[0].getblockheader(self.nodes[0].getbestblockhash(), False))
full_outbound_peer.send_and_ping(msg_headers([tip_header]))
- self.log.info('Check that we do not send a getaddr message to a block-relay-only or inbound peer')
+ self.log.info('Check that we do not send a getaddr message to a block-relay-only, feeler or inbound peer')
block_relay_peer = self.nodes[0].add_outbound_p2p_connection(AddrReceiver(), p2p_idx=1, connection_type="block-relay-only")
block_relay_peer.sync_with_ping()
assert_equal(block_relay_peer.getaddr_received(), False)
block_relay_peer.send_and_ping(msg_headers([tip_header]))
+ feeler_peer = self.nodes[0].add_outbound_p2p_connection(AddrReceiver(), p2p_idx=2, connection_type="feeler")
+ # bitcoind closes feeler connections as soon as it receives a version message
+ assert_equal(feeler_peer.is_connected, False)
+ assert_equal(feeler_peer.getaddr_received(), False)
+
inbound_peer = self.nodes[0].add_p2p_connection(AddrReceiver(send_getaddr=False))
inbound_peer.sync_with_ping()
assert_equal(inbound_peer.getaddr_received(), False)
Why this scored 19/100
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