net: only assume all local addresses if listening on any

If `-bind=` is provided then we would bind only to a particular address
and should not add all the other addresses of the machine to the list of
local addresses.

Fixes bitcoin/bitcoin#20184 (case 4.)

src/init.cpp

@@ -1664,8 +1664,6 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     LogPrintf("nBestHeight = %d\n", chain_active_height);
     if (node.peerman) node.peerman->SetBestHeight(chain_active_height);
 
-    Discover();
-
     // Map ports with UPnP or NAT-PMP.
     StartMapPort(args.GetBoolArg("-upnp", DEFAULT_UPNP), gArgs.GetBoolArg("-natpmp", DEFAULT_NATPMP));
 
@@ -1758,6 +1756,12 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
         StartTorControl(onion_service_target);
     }
 
+    if (connOptions.bind_on_any) {
+        // Only add all IP addresses of the machine if we would be listening on
+        // any address - 0.0.0.0 (IPv4) and :: (IPv6).
+        Discover();
+    }
+
     for (const auto& net : args.GetArgs("-whitelist")) {
         NetWhitelistPermissions subnet;
         bilingual_str error;

src/net.h

@@ -183,7 +183,15 @@ enum class ConnectionType {
 
 /** Convert ConnectionType enum to a string value */
 std::string ConnectionTypeAsString(ConnectionType conn_type);
+
+/**
+ * Look up IP addresses from all interfaces on the machine and add them to the
+ * list of local addresses to self-advertise.
+ * The loopback interface is skipped and only the first address from each
+ * interface is used.
+ */
 void Discover();
+
 uint16_t GetListenPort();
 
 enum

test/functional/feature_bind_port_discover.py

@@ -0,0 +1,78 @@
+#!/usr/bin/env python3
+# Copyright (c) 2020-2021 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""
+Test that -discover does not add all interfaces' addresses if we listen on only some of them
+"""
+
+from test_framework.test_framework import BitcoinTestFramework, SkipTest
+from test_framework.util import assert_equal
+
+# We need to bind to a routable address for this test to exercise the relevant code
+# and also must have another routable address on another interface which must not
+# be named "lo" or "lo0".
+# To set these routable addresses on the machine, use:
+# Linux:
+# ifconfig lo:0 1.1.1.1/32 up && ifconfig lo:1 2.2.2.2/32 up  # to set up
+# ifconfig lo:0 down && ifconfig lo:1 down  # to remove it, after the test
+# FreeBSD:
+# ifconfig em0 1.1.1.1/32 alias && ifconfig wlan0 2.2.2.2/32 alias  # to set up
+# ifconfig em0 1.1.1.1 -alias && ifconfig wlan0 2.2.2.2 -alias  # to remove it, after the test
+ADDR1 = '1.1.1.1'
+ADDR2 = '2.2.2.2'
+
+BIND_PORT = 31001
+
+class BindPortDiscoverTest(BitcoinTestFramework):
+    def set_test_params(self):
+        # Avoid any -bind= on the command line. Force the framework to avoid adding -bind=127.0.0.1.
+        self.setup_clean_chain = True
+        self.bind_to_localhost_only = False
+        self.extra_args = [
+            ['-discover', f'-port={BIND_PORT}'], # bind on any
+            ['-discover', f'-bind={ADDR1}:{BIND_PORT}'],
+        ]
+        self.num_nodes = len(self.extra_args)
+
+    def add_options(self, parser):
+        parser.add_argument(
+            "--ihave1111and2222", action='store_true', dest="ihave1111and2222",
+            help=f"Run the test, assuming {ADDR1} and {ADDR2} are configured on the machine",
+            default=False)
+
+    def skip_test_if_missing_module(self):
+        if not self.options.ihave1111and2222:
+            raise SkipTest(
+                f"To run this test make sure that {ADDR1} and {ADDR2} (routable addresses) are "
+                "assigned to the interfaces on this machine and rerun with --ihave1111and2222")
+
+    def run_test(self):
+        self.log.info(
+                "Test that if -bind= is not passed then all addresses are "
+                "added to localaddresses")
+        found_addr1 = False
+        found_addr2 = False
+        for local in self.nodes[0].getnetworkinfo()['localaddresses']:
+            if local['address'] == ADDR1:
+                found_addr1 = True
+                assert_equal(local['port'], BIND_PORT)
+            if local['address'] == ADDR2:
+                found_addr2 = True
+                assert_equal(local['port'], BIND_PORT)
+        assert found_addr1
+        assert found_addr2
+
+        self.log.info(
+                "Test that if -bind= is passed then only that address is "
+                "added to localaddresses")
+        found_addr1 = False
+        for local in self.nodes[1].getnetworkinfo()['localaddresses']:
+            if local['address'] == ADDR1:
+                found_addr1 = True
+                assert_equal(local['port'], BIND_PORT)
+            assert local['address'] != ADDR2
+        assert found_addr1
+
+if __name__ == '__main__':
+    BindPortDiscoverTest().main()

test/functional/test_runner.py

@@ -292,6 +292,7 @@
     'feature_loadblock.py',
     'p2p_dos_header_tree.py',
     'p2p_add_connections.py',
+    'feature_bind_port_discover.py',
     'p2p_unrequested_blocks.py',
     'p2p_blockfilters.py',
     'p2p_message_capture.py',