net: open p2p connections to nodes that listen on non-default ports

By default, for mainnet, the p2p listening port is 8333. Bitcoin Core has a strong preference for only connecting to nodes that listen on that port. Remove that preference because connections over clearnet that involve port 8333 make it easy to detect, analyze, block or divert Bitcoin p2p traffic before the connection is even established (at TCP SYN time). For further justification see the OP of: bitcoin#23306
vasild · Nov 18, 2021 · 38a7cf9 · 38a7cf9
1 parent fe03f7a
commit 38a7cf9
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Showing 4 changed files with 123 additions and 6 deletions.
diff --git a/src/net.cpp b/src/net.cpp
@@ -2084,12 +2084,8 @@ void CConnman::ThreadOpenConnections(const std::vector<std::string> connect)
                 continue;
             }
 
-            // Do not allow non-default ports, unless after 50 invalid
-            // addresses selected already. This is to prevent malicious peers
-            // from advertising themselves as a service on another host and
-            // port, causing a DoS attack as nodes around the network attempt
-            // to connect to it fruitlessly.
-            if (addr.GetPort() != Params().GetDefaultPort(addr.GetNetwork()) && nTries < 50) {
+            // Do not connect to bad ports, unless 50 invalid addresses have been selected already.
+            if (IsBadPort(addr.GetPort()) && nTries < 50) {
                 continue;
             }
 

diff --git a/src/netbase.cpp b/src/netbase.cpp
@@ -755,3 +755,91 @@ void InterruptSocks5(bool interrupt)
 {
     interruptSocks5Recv = interrupt;
 }
+
+bool IsBadPort(uint16_t port)
+{
+    switch (port) {
+    case 1:     // tcpmux
+    case 7:     // echo
+    case 9:     // discard
+    case 11:    // systat
+    case 13:    // daytime
+    case 15:    // netstat
+    case 17:    // qotd
+    case 19:    // chargen
+    case 20:    // ftp data
+    case 21:    // ftp access
+    case 22:    // ssh
+    case 23:    // telnet
+    case 25:    // smtp
+    case 37:    // time
+    case 42:    // name
+    case 43:    // nicname
+    case 53:    // domain
+    case 69:    // tftp
+    case 77:    // priv-rjs
+    case 79:    // finger
+    case 87:    // ttylink
+    case 95:    // supdup
+    case 101:   // hostriame
+    case 102:   // iso-tsap
+    case 103:   // gppitnp
+    case 104:   // acr-nema
+    case 109:   // pop2
+    case 110:   // pop3
+    case 111:   // sunrpc
+    case 113:   // auth
+    case 115:   // sftp
+    case 117:   // uucp-path
+    case 119:   // nntp
+    case 123:   // NTP
+    case 135:   // loc-srv /epmap
+    case 137:   // netbios
+    case 139:   // netbios
+    case 143:   // imap2
+    case 161:   // snmp
+    case 179:   // BGP
+    case 389:   // ldap
+    case 427:   // SLP (Also used by Apple Filing Protocol)
+    case 465:   // smtp+ssl
+    case 512:   // print / exec
+    case 513:   // login
+    case 514:   // shell
+    case 515:   // printer
+    case 526:   // tempo
+    case 530:   // courier
+    case 531:   // chat
+    case 532:   // netnews
+    case 540:   // uucp
+    case 548:   // AFP (Apple Filing Protocol)
+    case 554:   // rtsp
+    case 556:   // remotefs
+    case 563:   // nntp+ssl
+    case 587:   // smtp (rfc6409)
+    case 601:   // syslog-conn (rfc3195)
+    case 636:   // ldap+ssl
+    case 989:   // ftps-data
+    case 990:   // ftps
+    case 993:   // ldap+ssl
+    case 995:   // pop3+ssl
+    case 1719:  // h323gatestat
+    case 1720:  // h323hostcall
+    case 1723:  // pptp
+    case 2049:  // nfs
+    case 3659:  // apple-sasl / PasswordServer
+    case 4045:  // lockd
+    case 5060:  // sip
+    case 5061:  // sips
+    case 6000:  // X11
+    case 6566:  // sane-port
+    case 6665:  // Alternate IRC [Apple addition]
+    case 6666:  // Alternate IRC [Apple addition]
+    case 6667:  // Standard IRC [Apple addition]
+    case 6668:  // Alternate IRC [Apple addition]
+    case 6669:  // Alternate IRC [Apple addition]
+    case 6697:  // IRC + TLS
+    case 10080: // Amanda
+        return true;
+    }
+    return false;
+}
diff --git a/src/netbase.h b/src/netbase.h
@@ -246,4 +246,17 @@ void InterruptSocks5(bool interrupt);
  */
 bool Socks5(const std::string& strDest, uint16_t port, const ProxyCredentials* auth, const Sock& socket);
 
+/**
+ * Determine if a port is "bad" from the perspective of attempting to connect
+ * to a node on that port.
+ * See
+ * https://fetch.spec.whatwg.org/#port-blocking
+ * https://chromium.googlesource.com/chromium/src.git/+/refs/heads/main/net/base/port_util.cc
+ * https://hg.mozilla.org/mozilla-central/file/tip/netwerk/base/nsIOService.cpp
+ * https://github.com/bitcoin/bitcoin/pull/23306#issuecomment-947516736
+ * @param[in] port Port to check.
+ * @return true if the port is bad
+ */
+bool IsBadPort(uint16_t port);
+
 #endif // BITCOIN_NETBASE_H
diff --git a/src/test/netbase_tests.cpp b/src/test/netbase_tests.cpp
@@ -576,4 +576,24 @@ BOOST_AUTO_TEST_CASE(caddress_unserialize_v2)
     BOOST_CHECK(fixture_addresses == addresses_unserialized);
 }
 
+BOOST_AUTO_TEST_CASE(isbadport)
+{
+    BOOST_CHECK(IsBadPort(1));
+    BOOST_CHECK(IsBadPort(22));
+    BOOST_CHECK(IsBadPort(6000));
+
+    BOOST_CHECK(!IsBadPort(80));
+    BOOST_CHECK(!IsBadPort(443));
+    BOOST_CHECK(!IsBadPort(8333));
+
+    // Check all ports, there must be 80 bad ports in total.
+    size_t total_bad_ports{0};
+    for (uint16_t port = std::numeric_limits<uint16_t>::max(); port > 0; --port) {
+        if (IsBadPort(port)) {
+            ++total_bad_ports;
+        }
+    }
+    BOOST_CHECK_EQUAL(total_bad_ports, 80);
+}
+
 BOOST_AUTO_TEST_SUITE_END()