Merge bitcoin/bitcoin#23542: net: open p2p connections to nodes that listen on non-default ports

36ee76d1afbb278500fc8aa01606ec933b52c17d net: remove unused CNetAddr::GetHash() (Vasil Dimov)
d0abce9a50dd4f507e3a30348eabffb7552471d5 net: include the port when deciding a relay destination (Vasil Dimov)
2e38a0e6865187d1f0d0f016d3df7cce414a7c4f net: add CServiceHash constructor so the caller can provide the salts (Vasil Dimov)
97208634b96f2d9a55f2ead7b0ef407da729d7bd net: open p2p connections to nodes that listen on non-default ports (Vasil Dimov)

Pull request description:

  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:
  https://github.com/bitcoin/bitcoin/pull/23306

ACKs for top commit:
  laanwj:
    Concept and light code review ACK 36ee76d1afbb278500fc8aa01606ec933b52c17d
  prayank23:
    ACK https://github.com/bitcoin/bitcoin/pull/23542/commits/36ee76d1afbb278500fc8aa01606ec933b52c17d
  stickies-v:
    tACK 36ee76d1a
  jonatack:
    ACK 36ee76d1afbb278500fc8aa01606ec933b52c17d
  glozow:
    utACK 36ee76d1afbb278500fc8aa01606ec933b52c17d

Tree-SHA512: 7f45ab7567c51c19fc50fabbaf84f0cc8883a8eef84272b76435c014c31d89144271d70dd387212cc1114213165d76b4d20a5ddb8dbc958fe7e74e6ddbd56d11

11 files changed, 274 insertions, 20 deletions

diff --git a/doc/README.md b/doc/README.md
index 2800937d30..c200ac3753 100644
--- a/doc/README.md
+++ b/doc/README.md
@@ -79,6 +79,7 @@ The Bitcoin repo's [root README](/README.md) contains relevant information on th
 - [Init Scripts (systemd/upstart/openrc)](init.md)
 - [Managing Wallets](managing-wallets.md)
 - [Multisig Tutorial](multisig-tutorial.md)
+- [P2P bad ports definition and list](p2p-bad-ports.md)
 - [PSBT support](psbt.md)
 - [Reduce Memory](reduce-memory.md)
 - [Reduce Traffic](reduce-traffic.md)
diff --git a/doc/p2p-bad-ports.md b/doc/p2p-bad-ports.md
new file mode 100644
index 0000000000..0dd7d36cf4
--- /dev/null
+++ b/doc/p2p-bad-ports.md
@@ -0,0 +1,114 @@
+When Bitcoin Core automatically opens outgoing P2P connections it chooses
+a peer (address and port) from its list of potential peers. This list is
+populated with unchecked data, gossiped over the P2P network by other peers.
+
+A malicious actor may gossip an address:port where no Bitcoin node is listening,
+or one where a service is listening that is not related to the Bitcoin network.
+As a result, this service may occasionally get connection attempts from Bitcoin
+nodes.
+
+"Bad" ports are ones used by services which are usually not open to the public
+and usually require authentication. A connection attempt (by Bitcoin Core,
+trying to connect because it thinks there is a Bitcoin node on that
+address:port) to such service may be considered a malicious action by an
+ultra-paranoid administrator. An example for such a port is 22 (ssh). On the
+other hand, connection attempts to public services that usually do not require
+authentication are unlikely to be considered a malicious action,
+e.g. port 80 (http).
+
+Below is a list of "bad" ports which Bitcoin Core avoids when choosing a peer to
+connect to. If a node is listening on such a port, it will likely receive less
+incoming connections.
+
+    1:     tcpmux
+    7:     echo
+    9:     discard
+    11:    systat
+    13:    daytime
+    15:    netstat
+    17:    qotd
+    19:    chargen
+    20:    ftp data
+    21:    ftp access
+    22:    ssh
+    23:    telnet
+    25:    smtp
+    37:    time
+    42:    name
+    43:    nicname
+    53:    domain
+    69:    tftp
+    77:    priv-rjs
+    79:    finger
+    87:    ttylink
+    95:    supdup
+    101:   hostname
+    102:   iso-tsap
+    103:   gppitnp
+    104:   acr-nema
+    109:   pop2
+    110:   pop3
+    111:   sunrpc
+    113:   auth
+    115:   sftp
+    117:   uucp-path
+    119:   nntp
+    123:   NTP
+    135:   loc-srv /epmap
+    137:   netbios
+    139:   netbios
+    143:   imap2
+    161:   snmp
+    179:   BGP
+    389:   ldap
+    427:   SLP (Also used by Apple Filing Protocol)
+    465:   smtp+ssl
+    512:   print / exec
+    513:   login
+    514:   shell
+    515:   printer
+    526:   tempo
+    530:   courier
+    531:   chat
+    532:   netnews
+    540:   uucp
+    548:   AFP (Apple Filing Protocol)
+    554:   rtsp
+    556:   remotefs
+    563:   nntp+ssl
+    587:   smtp (rfc6409)
+    601:   syslog-conn (rfc3195)
+    636:   ldap+ssl
+    989:   ftps-data
+    990:   ftps
+    993:   ldap+ssl
+    995:   pop3+ssl
+    1719:  h323gatestat
+    1720:  h323hostcall
+    1723:  pptp
+    2049:  nfs
+    3659:  apple-sasl / PasswordServer
+    4045:  lockd
+    5060:  sip
+    5061:  sips
+    6000:  X11
+    6566:  sane-port
+    6665:  Alternate IRC
+    6666:  Alternate IRC
+    6667:  Standard IRC
+    6668:  Alternate IRC
+    6669:  Alternate IRC
+    6697:  IRC + TLS
+    10080: Amanda
+
+For further information see:
+
+[pull/23306](https://github.com/bitcoin/bitcoin/pull/23306#issuecomment-947516736)
+
+[pull/23542](https://github.com/bitcoin/bitcoin/pull/23542)
+
+[fetch.spec.whatwg.org](https://fetch.spec.whatwg.org/#port-blocking)
+
+[chromium.googlesource.com](https://chromium.googlesource.com/chromium/src.git/+/refs/heads/main/net/base/port_util.cc)
+
+[hg.mozilla.org](https://hg.mozilla.org/mozilla-central/file/tip/netwerk/base/nsIOService.cpp)
diff --git a/src/init.cpp b/src/init.cpp
index ce666534ae..9813a16563 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -466,6 +466,8 @@ void SetupServerArgs(ArgsManager& argsman)
     argsman.AddArg("-peerbloomfilters", strprintf("Support filtering of blocks and transaction with bloom filters (default: %u)", DEFAULT_PEERBLOOMFILTERS), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
     argsman.AddArg("-peerblockfilters", strprintf("Serve compact block filters to peers per BIP 157 (default: %u)", DEFAULT_PEERBLOCKFILTERS), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
     argsman.AddArg("-permitbaremultisig", strprintf("Relay non-P2SH multisig (default: %u)", DEFAULT_PERMIT_BAREMULTISIG), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
+    // TODO: remove the sentence "Nodes not using ... incoming connections." once the changes from
+    // https://github.com/bitcoin/bitcoin/pull/23542 have become widespread.
     argsman.AddArg("-port=<port>", strprintf("Listen for connections on <port>. Nodes not using the default ports (default: %u, testnet: %u, signet: %u, regtest: %u) are unlikely to get incoming connections. Not relevant for I2P (see doc/i2p.md).", defaultChainParams->GetDefaultPort(), testnetChainParams->GetDefaultPort(), signetChainParams->GetDefaultPort(), regtestChainParams->GetDefaultPort()), ArgsManager::ALLOW_ANY | ArgsManager::NETWORK_ONLY, OptionsCategory::CONNECTION);
     argsman.AddArg("-proxy=<ip:port>", "Connect through SOCKS5 proxy, set -noproxy to disable (default: disabled)", ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
     argsman.AddArg("-proxyrandomize", strprintf("Randomize credentials for every proxy connection. This enables Tor stream isolation (default: %u)", DEFAULT_PROXYRANDOMIZE), ArgsManager::ALLOW_ANY, OptionsCategory::CONNECTION);
@@ -1687,12 +1689,23 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     connOptions.nMaxOutboundLimit = *opt_max_upload;
     connOptions.m_peer_connect_timeout = peer_connect_timeout;
 
+    const auto BadPortWarning = [](const char* prefix, uint16_t port) {
+        return strprintf(_("%s request to listen on port %u. This port is considered \"bad\" and "
+                           "thus it is unlikely that any Bitcoin Core peers connect to it. See "
+                           "doc/p2p-bad-ports.md for details and a full list."),
+                         prefix,
+                         port);
+    };
+
     for (const std::string& bind_arg : args.GetArgs("-bind")) {
         CService bind_addr;
         const size_t index = bind_arg.rfind('=');
         if (index == std::string::npos) {
             if (Lookup(bind_arg, bind_addr, GetListenPort(), false)) {
                 connOptions.vBinds.push_back(bind_addr);
+                if (IsBadPort(bind_addr.GetPort())) {
+                    InitWarning(BadPortWarning("-bind", bind_addr.GetPort()));
+                }
                 continue;
             }
         } else {
@@ -1719,6 +1732,15 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     // on any address - 0.0.0.0 (IPv4) and :: (IPv6).
     connOptions.bind_on_any = args.GetArgs("-bind").empty() && args.GetArgs("-whitebind").empty();
 
+    // Emit a warning if a bad port is given to -port= but only if -bind and -whitebind are not
+    // given, because if they are, then -port= is ignored.
+    if (connOptions.bind_on_any && args.IsArgSet("-port")) {
+        const uint16_t port_arg = args.GetIntArg("-port", 0);
+        if (IsBadPort(port_arg)) {
+            InitWarning(BadPortWarning("-port", port_arg));
+        }
+    }
+
     CService onion_service_target;
     if (!connOptions.onion_binds.empty()) {
         onion_service_target = connOptions.onion_binds.front();
diff --git a/src/net.cpp b/src/net.cpp
index d200da0dea..15616613d2 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -2120,12 +2120,8 @@ 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 (nTries < 50 && (addr.IsIPv4() || addr.IsIPv6()) && IsBadPort(addr.GetPort())) {
                 continue;
             }
 
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 3cebca1a77..f05b4fd8e2 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -1775,8 +1775,10 @@ void PeerManagerImpl::RelayAddress(NodeId originator,
     // Relay to a limited number of other nodes
     // Use deterministic randomness to send to the same nodes for 24 hours
     // at a time so the m_addr_knowns of the chosen nodes prevent repeats
-    const uint64_t hashAddr{addr.GetHash()};
-    const CSipHasher hasher{m_connman.GetDeterministicRandomizer(RANDOMIZER_ID_ADDRESS_RELAY).Write(hashAddr).Write((GetTime() + hashAddr) / (24 * 60 * 60))};
+    const uint64_t hash_addr{CServiceHash(0, 0)(addr)};
+    const CSipHasher hasher{m_connman.GetDeterministicRandomizer(RANDOMIZER_ID_ADDRESS_RELAY)
+                                .Write(hash_addr)
+                                .Write((GetTime() + hash_addr) / (24 * 60 * 60))};
     FastRandomContext insecure_rand;
 
     // Relay reachable addresses to 2 peers. Unreachable addresses are relayed randomly to 1 or 2 peers.
diff --git a/src/netaddress.cpp b/src/netaddress.cpp
index 4874b82eca..f7640329f8 100644
--- a/src/netaddress.cpp
+++ b/src/netaddress.cpp
@@ -833,14 +833,6 @@ std::vector<unsigned char> CNetAddr::GetAddrBytes() const
     return std::vector<unsigned char>(m_addr.begin(), m_addr.end());
 }
 
-uint64_t CNetAddr::GetHash() const
-{
-    uint256 hash = Hash(m_addr);
-    uint64_t nRet;
-    memcpy(&nRet, &hash, sizeof(nRet));
-    return nRet;
-}
-
 // private extensions to enum Network, only returned by GetExtNetwork,
 // and only used in GetReachabilityFrom
 static const int NET_UNKNOWN = NET_MAX + 0;
diff --git a/src/netaddress.h b/src/netaddress.h
index b06b6c65b6..6d21dcd5cd 100644
--- a/src/netaddress.h
+++ b/src/netaddress.h
@@ -194,7 +194,6 @@ public:
     enum Network GetNetwork() const;
     std::string ToString() const;
     std::string ToStringIP() const;
-    uint64_t GetHash() const;
     bool GetInAddr(struct in_addr* pipv4Addr) const;
     Network GetNetClass() const;
 
@@ -562,6 +561,14 @@ public:
 class CServiceHash
 {
 public:
+    CServiceHash()
+        : m_salt_k0{GetRand(std::numeric_limits<uint64_t>::max())},
+          m_salt_k1{GetRand(std::numeric_limits<uint64_t>::max())}
+    {
+    }
+
+    CServiceHash(uint64_t salt_k0, uint64_t salt_k1) : m_salt_k0{salt_k0}, m_salt_k1{salt_k1} {}
+
     size_t operator()(const CService& a) const noexcept
     {
         CSipHasher hasher(m_salt_k0, m_salt_k1);
@@ -572,8 +579,8 @@ public:
     }
 
 private:
-    const uint64_t m_salt_k0 = GetRand(std::numeric_limits<uint64_t>::max());
-    const uint64_t m_salt_k1 = GetRand(std::numeric_limits<uint64_t>::max());
+    const uint64_t m_salt_k0;
+    const uint64_t m_salt_k1;
 };
 
 #endif // BITCOIN_NETADDRESS_H
diff --git a/src/netbase.cpp b/src/netbase.cpp
index a36ad7d179..9a0b800565 100644
--- a/src/netbase.cpp
+++ b/src/netbase.cpp
@@ -749,3 +749,93 @@ void InterruptSocks5(bool interrupt)
 {
     interruptSocks5Recv = interrupt;
 }
+
+bool IsBadPort(uint16_t port)
+{
+    /* Don't forget to update doc/p2p-bad-ports.md if you change this list. */
+
+    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:   // hostname
+    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
+    case 6666:  // Alternate IRC
+    case 6667:  // Standard IRC
+    case 6668:  // Alternate IRC
+    case 6669:  // Alternate IRC
+    case 6697:  // IRC + TLS
+    case 10080: // Amanda
+        return true;
+    }
+    return false;
+}
diff --git a/src/netbase.h b/src/netbase.h
index b63d53086d..f9e3872c16 100644
--- a/src/netbase.h
+++ b/src/netbase.h
@@ -247,4 +247,13 @@ 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 doc/p2p-bad-ports.md
+ * @param[in] port Port to check.
+ * @returns whether the port is bad
+ */
+bool IsBadPort(uint16_t port);
+
 #endif // BITCOIN_NETBASE_H
diff --git a/src/test/fuzz/netaddress.cpp b/src/test/fuzz/netaddress.cpp
index 6cb81901cb..35e6688c61 100644
--- a/src/test/fuzz/netaddress.cpp
+++ b/src/test/fuzz/netaddress.cpp
@@ -16,7 +16,6 @@ FUZZ_TARGET(netaddress)
     FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
 
     const CNetAddr net_addr = ConsumeNetAddr(fuzzed_data_provider);
-    (void)net_addr.GetHash();
     (void)net_addr.GetNetClass();
     if (net_addr.GetNetwork() == Network::NET_IPV4) {
         assert(net_addr.IsIPv4());
@@ -84,6 +83,8 @@ FUZZ_TARGET(netaddress)
     (void)service.ToString();
     (void)service.ToStringIPPort();
     (void)service.ToStringPort();
+    (void)CServiceHash()(service);
+    (void)CServiceHash(0, 0)(service);
 
     const CNetAddr other_net_addr = ConsumeNetAddr(fuzzed_data_provider);
     (void)net_addr.GetReachabilityFrom(&other_net_addr);
diff --git a/src/test/netbase_tests.cpp b/src/test/netbase_tests.cpp
index 6410ac565a..8e6e911ec2 100644
--- 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()