net: fix GetListenPort() to derive the proper port

`GetListenPort()` uses a simple logic: "if `-port=P` is given, then we
must be listening on `P`, otherwise we must be listening on `8333`".
This is however not true if `-bind=` has been provided with `:port` part
or if `-whitebind=` has been provided. Thus, extend `GetListenPort()` to
return the port from `-bind=` or `-whitebind=`, if any.

Fixes https://github.com/bitcoin/bitcoin/issues/20184 (cases 1. 2. 3. 5.)

1 files changed, 36 insertions, 1 deletions

diff --git a/src/net.cpp b/src/net.cpp
index d35120794b..955eec46e3 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -126,6 +126,31 @@ void CConnman::AddAddrFetch(const std::string& strDest)
 
 uint16_t GetListenPort()
 {
+    // If -bind= is provided with ":port" part, use that (first one if multiple are provided).
+    for (const std::string& bind_arg : gArgs.GetArgs("-bind")) {
+        CService bind_addr;
+        constexpr uint16_t dummy_port = 0;
+
+        if (Lookup(bind_arg, bind_addr, dummy_port, /*fAllowLookup=*/false)) {
+            if (bind_addr.GetPort() != dummy_port) {
+                return bind_addr.GetPort();
+            }
+        }
+    }
+
+    // Otherwise, if -whitebind= without NetPermissionFlags::NoBan is provided, use that
+    // (-whitebind= is required to have ":port").
+    for (const std::string& whitebind_arg : gArgs.GetArgs("-whitebind")) {
+        NetWhitebindPermissions whitebind;
+        bilingual_str error;
+        if (NetWhitebindPermissions::TryParse(whitebind_arg, whitebind, error)) {
+            if (!NetPermissions::HasFlag(whitebind.m_flags, NetPermissionFlags::NoBan)) {
+                return whitebind.m_service.GetPort();
+            }
+        }
+    }
+
+    // Otherwise, if -port= is provided, use that. Otherwise use the default port.
     return static_cast<uint16_t>(gArgs.GetIntArg("-port", Params().GetDefaultPort()));
 }
 
@@ -221,7 +246,17 @@ std::optional<CAddress> GetLocalAddrForPeer(CNode *pnode)
     if (IsPeerAddrLocalGood(pnode) && (!addrLocal.IsRoutable() ||
          rng.randbits((GetnScore(addrLocal) > LOCAL_MANUAL) ? 3 : 1) == 0))
     {
-        addrLocal.SetIP(pnode->GetAddrLocal());
+        if (pnode->IsInboundConn()) {
+            // For inbound connections, assume both the address and the port
+            // as seen from the peer.
+            addrLocal = CAddress{pnode->GetAddrLocal(), addrLocal.nServices};
+        } else {
+            // For outbound connections, assume just the address as seen from
+            // the peer and leave the port in `addrLocal` as returned by
+            // `GetLocalAddress()` above. The peer has no way to observe our
+            // listening port when we have initiated the connection.
+            addrLocal.SetIP(pnode->GetAddrLocal());
+        }
     }
     if (addrLocal.IsRoutable() || gArgs.GetBoolArg("-addrmantest", false))
     {