Merge bitcoin/bitcoin#30394: net: fix race condition in self-connect detection

16bd283b3a Reapply "test: p2p: check that connecting to ourself leads to disconnect" (Sebastian Falbesoner)
0dbcd4c148 net: prevent sending messages in `NetEventsInterface::InitializeNode` (Sebastian Falbesoner)
66673f1c13 net: fix race condition in self-connect detection (Sebastian Falbesoner)

Pull request description:

  This PR fixes a recently discovered race condition in the self-connect detection (see #30362 and #30368).

  Initiating an outbound network connection currently involves the following steps after the socket connection is established (see [`CConnman::OpenNetworkConnection`](bd5d1688b4/src/net.cpp (L2923-L2930)) method):
  1. set up node state
  2. queue VERSION message (both steps 1 and 2 happen in [`InitializeNode`](bd5d1688b4/src/net_processing.cpp (L1662-L1683)))
  3. add new node to vector `m_nodes`

  If we connect to ourself, it can happen that the sent VERSION message (step 2) is received and processed locally *before* the node object is added to the connection manager's `m_nodes` vector (step 3). In this case, the self-connect remains undiscovered, as the detection doesn't find the outbound peer in `m_nodes` yet (see `CConnman::CheckIncomingNonce`).

  Fix this by swapping the order of 2. and 3., by taking the `PushNodeVersion` call out of `InitializeNode` and doing that in the `SendMessages` method instead, which is only called for `CNode` instances in `m_nodes`.

  The temporarily reverted test introduced in #30362 is readded. Fixes #30368.

  Thanks go to vasild, mzumsande and dergoegge for suggestions on how to fix this (see https://github.com/bitcoin/bitcoin/issues/30368#issuecomment-2200625017 ff. and https://github.com/bitcoin/bitcoin/pull/30394#discussion_r1668290789).

ACKs for top commit:
  naiyoma:
    tested ACK [16bd283b3a),  built and tested locally,  test passes successfully.
  mzumsande:
    ACK 16bd283b3a
  tdb3:
    ACK 16bd283b3a
  glozow:
    ACK 16bd283b3a
  dergoegge:
    ACK 16bd283b3a

Tree-SHA512: 5b8aced6cda8deb38d4cd3fe4980b8af505d37ffa0925afaa734c5d81efe9d490dc48a42e1d0d45dd2961c0e1172a3d5b6582ae9a2d642f2592a17fbdc184445

src/net.h

@@ -991,8 +991,8 @@ public:
     /** Mutex for anything that is only accessed via the msg processing thread */
     static Mutex g_msgproc_mutex;
 
-    /** Initialize a peer (setup state, queue any initial messages) */
-    virtual void InitializeNode(CNode& node, ServiceFlags our_services) = 0;
+    /** Initialize a peer (setup state) */
+    virtual void InitializeNode(const CNode& node, ServiceFlags our_services) = 0;
 
     /** Handle removal of a peer (clear state) */
     virtual void FinalizeNode(const CNode& node) = 0;

src/net_processing.cpp

@@ -243,6 +243,9 @@ struct Peer {
      * Most peers use headers-first syncing, which doesn't use this mechanism */
     uint256 m_continuation_block GUARDED_BY(m_block_inv_mutex) {};
 
+    /** Set to true once initial VERSION message was sent (only relevant for outbound peers). */
+    bool m_outbound_version_message_sent GUARDED_BY(NetEventsInterface::g_msgproc_mutex){false};
+
     /** This peer's reported block height when we connected */
     std::atomic<int> m_starting_height{-1};
 
@@ -498,7 +501,7 @@ public:
         EXCLUSIVE_LOCKS_REQUIRED(!m_most_recent_block_mutex);
 
     /** Implement NetEventsInterface */
-    void InitializeNode(CNode& node, ServiceFlags our_services) override EXCLUSIVE_LOCKS_REQUIRED(!m_peer_mutex);
+    void InitializeNode(const CNode& node, ServiceFlags our_services) override EXCLUSIVE_LOCKS_REQUIRED(!m_peer_mutex);
     void FinalizeNode(const CNode& node) override EXCLUSIVE_LOCKS_REQUIRED(!m_peer_mutex, !m_headers_presync_mutex);
     bool HasAllDesirableServiceFlags(ServiceFlags services) const override;
     bool ProcessMessages(CNode* pfrom, std::atomic<bool>& interrupt) override
@@ -1659,7 +1662,7 @@ void PeerManagerImpl::UpdateLastBlockAnnounceTime(NodeId node, int64_t time_in_s
     if (state) state->m_last_block_announcement = time_in_seconds;
 }
 
-void PeerManagerImpl::InitializeNode(CNode& node, ServiceFlags our_services)
+void PeerManagerImpl::InitializeNode(const CNode& node, ServiceFlags our_services)
 {
     NodeId nodeid = node.GetId();
     {
@@ -1677,9 +1680,6 @@ void PeerManagerImpl::InitializeNode(CNode& node, ServiceFlags our_services)
         LOCK(m_peer_mutex);
         m_peer_map.emplace_hint(m_peer_map.end(), nodeid, peer);
     }
-    if (!node.IsInboundConn()) {
-        PushNodeVersion(node, *peer);
-    }
 }
 
 void PeerManagerImpl::ReattemptInitialBroadcast(CScheduler& scheduler)
@@ -5326,6 +5326,10 @@ bool PeerManagerImpl::ProcessMessages(CNode* pfrom, std::atomic<bool>& interrupt
     PeerRef peer = GetPeerRef(pfrom->GetId());
     if (peer == nullptr) return false;
 
+    // For outbound connections, ensure that the initial VERSION message
+    // has been sent first before processing any incoming messages
+    if (!pfrom->IsInboundConn() && !peer->m_outbound_version_message_sent) return false;
+
     {
         LOCK(peer->m_getdata_requests_mutex);
         if (!peer->m_getdata_requests.empty()) {
@@ -5817,6 +5821,12 @@ bool PeerManagerImpl::SendMessages(CNode* pto)
     // disconnect misbehaving peers even before the version handshake is complete.
     if (MaybeDiscourageAndDisconnect(*pto, *peer)) return true;
 
+    // Initiate version handshake for outbound connections
+    if (!pto->IsInboundConn() && !peer->m_outbound_version_message_sent) {
+        PushNodeVersion(*pto, *peer);
+        peer->m_outbound_version_message_sent = true;
+    }
+
     // Don't send anything until the version handshake is complete
     if (!pto->fSuccessfullyConnected || pto->fDisconnect)
         return true;

src/test/util/net.cpp

@@ -28,7 +28,8 @@ void ConnmanTestMsg::Handshake(CNode& node,
     auto& connman{*this};
 
     peerman.InitializeNode(node, local_services);
-    FlushSendBuffer(node); // Drop the version message added by InitializeNode.
+    peerman.SendMessages(&node);
+    FlushSendBuffer(node); // Drop the version message added by SendMessages.
 
     CSerializedNetMsg msg_version{
         NetMsg::Make(NetMsgType::VERSION,

test/functional/p2p_handshake.py

@@ -17,6 +17,7 @@ from test_framework.messages import (
     NODE_WITNESS,
 )
 from test_framework.p2p import P2PInterface
+from test_framework.util import p2p_port
 
 
 # Desirable service flags for outbound non-pruned and pruned peers. Note that
@@ -88,9 +89,11 @@ class P2PHandshakeTest(BitcoinTestFramework):
         with node.assert_debug_log([f"feeler connection completed"]):
             self.add_outbound_connection(node, "feeler", NODE_NONE, wait_for_disconnect=True)
 
-        # TODO: re-add test introduced in commit 5d2fb14bafe4e80c0a482d99e5ebde07c477f000
-        # ("test: p2p: check that connecting to ourself leads to disconnect") once
-        # the race condition causing issue #30368 is fixed
+        self.log.info("Check that connecting to ourself leads to immediate disconnect")
+        with node.assert_debug_log(["connected to self", "disconnecting"]):
+            node_listen_addr = f"127.0.0.1:{p2p_port(0)}"
+            node.addconnection(node_listen_addr, "outbound-full-relay", self.options.v2transport)
+            self.wait_until(lambda: len(node.getpeerinfo()) == 0)
 
 
 if __name__ == '__main__':