Merge #20187: Addrman: test-before-evict bugfix and improvements for block-relay-only peers

16d9bfc4172b4f6ce24a3cd1a1cfa3933cd26751 Avoid test-before-evict evictions of current peers (Suhas Daftuar)
e8b215a086d91a8774210bb6ce8d1560aaaf0789 Refactor test for existing peer connection into own function (Suhas Daftuar)
4fe338ab3ed73b3ffb20eedf95500c56ec2920e1 Call CAddrMan::Good() on block-relay-only peer addresses (Suhas Daftuar)
daf55531260833d597ee599e2d289ea1be0b1d9c Avoid calling CAddrMan::Connected() on block-relay-only peer addresses (Suhas Daftuar)

Pull request description:

  This PR does two things:

  * Block-relay-only interaction with addrman.
    * Calling `CAddrMan::Connected()` on an address that was a block-relay-only peer causes the time we report in `addr` messages containing that peer to be updated; particularly now that we use anchor connections with a our block-relay-only peers, this risks leaking information about those peers.  So, stop this.
    * Avoiding calling `CAddrMan::Good()` on block-relay-only peer addresses causes the addrman logic around maintaining the new and tried table to be less good, and in particular makes it so that block-relay-only peer addresses are more likely to be evicted from the addrman (for no good reason I can think of).  So, mark those addresses as good when we connect.

  * Fix test-before-evict bug. There's a bug where if we get a collision in the tried table with an existing address that is one of our current peers, and the connection is long-lived enough, then `SelectTriedCollisions()` might return that existing peer address to us as a test-before-evict connection candidate. However, our logic for new outbound connections would later prevent us from actually making a connection; the result would be that when we get a collision with a long-lived current peer, that peer's address is likely to get evicted from the tried table.  Fix this by checking to see if a test-before-evict candidate is a peer we're currently connected to, and if so, mark it as `Good()`.

ACKs for top commit:
  sipa:
    utACK 16d9bfc4172b4f6ce24a3cd1a1cfa3933cd26751
  amitiuttarwar:
    code review ACK 16d9bfc417
  mzumsande:
    Code-Review ACK 16d9bfc4172b4f6ce24a3cd1a1cfa3933cd26751.
  jnewbery:
    utACK 16d9bfc4172b4f6ce24a3cd1a1cfa3933cd26751
  ariard:
    Code Review ACK 16d9bfc.
  jonatack:
    Tested ACK 16d9bfc4172b4f6ce24a3cd1a1cfa3933cd26751

Tree-SHA512: 188ccb814e436937cbb91d29d73c316ce83f4b9c22f1cda56747f0949a093e10161ae724e87e4a2d85ac40f85f5f6b4e87e97d350a1ac44f80c57783f4423324

1 files changed, 22 insertions, 12 deletions

diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 464e3de80a..9dafda43c8 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -837,7 +837,8 @@ void PeerManager::ReattemptInitialBroadcast(CScheduler& scheduler) const
     scheduler.scheduleFromNow([&] { ReattemptInitialBroadcast(scheduler); }, delta);
 }
 
-void PeerManager::FinalizeNode(NodeId nodeid, bool& fUpdateConnectionTime) {
+void PeerManager::FinalizeNode(const CNode& node, bool& fUpdateConnectionTime) {
+    NodeId nodeid = node.GetId();
     fUpdateConnectionTime = false;
     LOCK(cs_main);
     int misbehavior{0};
@@ -854,7 +855,8 @@ void PeerManager::FinalizeNode(NodeId nodeid, bool& fUpdateConnectionTime) {
     if (state->fSyncStarted)
         nSyncStarted--;
 
-    if (misbehavior == 0 && state->fCurrentlyConnected) {
+    if (misbehavior == 0 && state->fCurrentlyConnected && !node.IsBlockOnlyConn()) {
+        // Note: we avoid changing visible addrman state for block-relay-only peers
         fUpdateConnectionTime = true;
     }
 
@@ -2405,14 +2407,8 @@ void PeerManager::ProcessMessage(CNode& pfrom, const std::string& msg_type, CDat
             // empty and no one will know who we are, so these mechanisms are
             // important to help us connect to the network.
             //
-            // We also update the addrman to record connection success for
-            // these peers (which include OUTBOUND_FULL_RELAY and FEELER
-            // connections) so that addrman will have an up-to-date notion of
-            // which peers are online and available.
-            //
-            // We skip these operations for BLOCK_RELAY peers to avoid
-            // potentially leaking information about our BLOCK_RELAY
-            // connections via the addrman or address relay.
+            // We skip this for BLOCK_RELAY peers to avoid potentially leaking
+            // information about our BLOCK_RELAY connections via address relay.
             if (fListen && !::ChainstateActive().IsInitialBlockDownload())
             {
                 CAddress addr = GetLocalAddress(&pfrom.addr, pfrom.GetLocalServices());
@@ -2431,9 +2427,23 @@ void PeerManager::ProcessMessage(CNode& pfrom, const std::string& msg_type, CDat
             // Get recent addresses
             m_connman.PushMessage(&pfrom, CNetMsgMaker(greatest_common_version).Make(NetMsgType::GETADDR));
             pfrom.fGetAddr = true;
+        }
 
-            // Moves address from New to Tried table in Addrman, resolves
-            // tried-table collisions, etc.
+        if (!pfrom.IsInboundConn()) {
+            // For non-inbound connections, we update the addrman to record
+            // connection success so that addrman will have an up-to-date
+            // notion of which peers are online and available.
+            //
+            // While we strive to not leak information about block-relay-only
+            // connections via the addrman, not moving an address to the tried
+            // table is also potentially detrimental because new-table entries
+            // are subject to eviction in the event of addrman collisions.  We
+            // mitigate the information-leak by never calling
+            // CAddrMan::Connected() on block-relay-only peers; see
+            // FinalizeNode().
+            //
+            // This moves an address from New to Tried table in Addrman,
+            // resolves tried-table collisions, etc.
             m_connman.MarkAddressGood(pfrom.addr);
         }