Merge bitcoin/bitcoin#23695: p2p: Always serialize local timestamp for version msg

fa1dc9b p2p: Always serialize local timestamp for version msg (MarcoFalke)

Pull request description:

  Currently we serialize the local time when connecting to outbound connections and the "adjusted network" time when someone connects to us.

  I presume the reason is to avoid a fingerprint in case the local time is misconfigured. However, the fingerprint still exits when:
  * The local time goes out-of-sync after timedata is filled up, in which case the adjusted time is *not* adjusted. See comment in `src/timedata.cpp`. (In practise I expect no adjustment to happen after timedata is filled up by one entry more than half its size).
  * The local time is off by more than 70 minutes. See `DEFAULT_MAX_TIME_ADJUSTMENT`. While there is a warning in this case, the warning might be missed by the node operator.
  * The adjusted time is poisoned by an attacker. This is only a theoretical concern after commit e457513.

  Using the adjusted time does help in a the case where the local time is off by a constant less than 70 minutes and the node quickly connects to 5 outbound peers to retrieve the adjusted time.

  Still, I think using `GetAdjustedTime` here gives a false sense of security. It will be better for node operators to instead set the correct time.

ACKs for top commit:
  naumenkogs:
    ACK fa1dc9b
  laanwj:
    Code review ACK fa1dc9b
  w0xlt:
    crACK fa1dc9b

Tree-SHA512: 70a0f4ab3500e6ddcde291620e35273018cefd1d9e94b91ad333e360139ed18862718bb1a9854af2bf79990bf74b05d95492f77d0747c7b9bdd276c020116dcb

Author: laanwj

src/net_processing.cpp

@@ -386,7 +386,7 @@ class PeerManagerImpl final : public PeerManager
         EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
 
     /** Send a version message to a peer */
-    void PushNodeVersion(CNode& pnode, int64_t nTime);
+    void PushNodeVersion(CNode& pnode);
 
     /** Send a ping message every PING_INTERVAL or if requested via RPC. May
      *  mark the peer to be disconnected if a ping has timed out.
@@ -1090,12 +1090,13 @@ void PeerManagerImpl::FindNextBlocksToDownload(NodeId nodeid, unsigned int count
 
 } // namespace
 
-void PeerManagerImpl::PushNodeVersion(CNode& pnode, int64_t nTime)
+void PeerManagerImpl::PushNodeVersion(CNode& pnode)
 {
     // Note that pnode->GetLocalServices() is a reflection of the local
     // services we were offering when the CNode object was created for this
     // peer.
     uint64_t my_services{pnode.GetLocalServices()};
+    const int64_t nTime{count_seconds(GetTime<std::chrono::seconds>())};
     uint64_t nonce = pnode.GetLocalNonce();
     const int nNodeStartingHeight{m_best_height};
     NodeId nodeid = pnode.GetId();
@@ -1167,7 +1168,7 @@ void PeerManagerImpl::InitializeNode(CNode *pnode)
         m_peer_map.emplace_hint(m_peer_map.end(), nodeid, std::move(peer));
     }
     if (!pnode->IsInboundConn()) {
-        PushNodeVersion(*pnode, GetTime());
+        PushNodeVersion(*pnode);
     }
 }
 
@@ -2599,7 +2600,9 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
 
         // Inbound peers send us their version message when they connect.
         // We send our version message in response.
-        if (pfrom.IsInboundConn()) PushNodeVersion(pfrom, GetAdjustedTime());
+        if (pfrom.IsInboundConn()) {
+            PushNodeVersion(pfrom);
+        }
 
         // Change version
         const int greatest_common_version = std::min(nVersion, PROTOCOL_VERSION);