Merge bitcoin/bitcoin#20234: net: don't bind on 0.0.0.0 if binds are restricted to Tor

2feec3ce3130961f98ceb030951d0e46d3b9096c net: don't bind on 0.0.0.0 if binds are restricted to Tor (Vasil Dimov)

Pull request description:

  The semantic of `-bind` is to restrict the binding only to some address.
  If not specified, then the user does not care and we bind to `0.0.0.0`.
  If specified then we should honor the restriction and bind only to the
  specified address.

  Before this change, if no `-bind` is given then we would bind to
  `0.0.0.0:8333` and to `127.0.0.1:8334` (incoming Tor) which is ok -
  the user does not care to restrict the binding.

  However, if only `-bind=addr:port=onion` is given (without ordinary
  `-bind=`) then we would bind to `addr:port` _and_ to `0.0.0.0:8333` in
  addition.

  Change the above to not do the additional bind: if only
  `-bind=addr:port=onion` is given (without ordinary `-bind=`) then bind
  to `addr:port` (only) and consider incoming connections to that as Tor
  and do not advertise it. I.e. a Tor-only node.

ACKs for top commit:
  laanwj:
    Code review ACK 2feec3ce3130961f98ceb030951d0e46d3b9096c
  jonatack:
    utACK 2feec3ce3130961f98ceb030951d0e46d3b9096c per `git diff a004833 2feec3c`
  hebasto:
    ACK 2feec3ce3130961f98ceb030951d0e46d3b9096c, tested on Linux Mint 20.1 (x86_64):

Tree-SHA512: a04483af601706da928958b92dc560f9cfcc78ab0bb9d74414636eed1c6f29ed538ce1fb5a17d41ed82c9c9a45ca94899d0966e7ef93da809c9bcdcdb1d1f040

3 files changed, 33 insertions, 29 deletions

diff --git a/src/init.cpp b/src/init.cpp
index ae96f510bc..c7565a841c 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -1717,18 +1717,6 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
         return InitError(ResolveErrMsg("bind", bind_arg));
     }
 
-    if (connOptions.onion_binds.empty()) {
-        connOptions.onion_binds.push_back(DefaultOnionServiceTarget());
-    }
-
-    if (args.GetBoolArg("-listenonion", DEFAULT_LISTEN_ONION)) {
-        const auto bind_addr = connOptions.onion_binds.front();
-        if (connOptions.onion_binds.size() > 1) {
-            InitWarning(strprintf(_("More than one onion bind address is provided. Using %s for the automatically created Tor onion service."), bind_addr.ToStringIPPort()));
-        }
-        StartTorControl(bind_addr);
-    }
-
     for (const std::string& strBind : args.GetArgs("-whitebind")) {
         NetWhitebindPermissions whitebind;
         bilingual_str error;
@@ -1736,6 +1724,27 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
         connOptions.vWhiteBinds.push_back(whitebind);
     }
 
+    // If the user did not specify -bind= or -whitebind= then we bind
+    // on any address - 0.0.0.0 (IPv4) and :: (IPv6).
+    connOptions.bind_on_any = args.GetArgs("-bind").empty() && args.GetArgs("-whitebind").empty();
+
+    CService onion_service_target;
+    if (!connOptions.onion_binds.empty()) {
+        onion_service_target = connOptions.onion_binds.front();
+    } else {
+        onion_service_target = DefaultOnionServiceTarget();
+        connOptions.onion_binds.push_back(onion_service_target);
+    }
+
+    if (args.GetBoolArg("-listenonion", DEFAULT_LISTEN_ONION)) {
+        if (connOptions.onion_binds.size() > 1) {
+            InitWarning(strprintf(_("More than one onion bind address is provided. Using %s "
+                                    "for the automatically created Tor onion service."),
+                                  onion_service_target.ToStringIPPort()));
+        }
+        StartTorControl(onion_service_target);
+    }
+
     for (const auto& net : args.GetArgs("-whitelist")) {
         NetWhitelistPermissions subnet;
         bilingual_str error;
diff --git a/src/net.cpp b/src/net.cpp
index 60059249ed..dd667793d8 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -2465,30 +2465,25 @@ bool CConnman::Bind(const CService &addr, unsigned int flags, NetPermissionFlags
     return true;
 }
 
-bool CConnman::InitBinds(
-    const std::vector<CService>& binds,
-    const std::vector<NetWhitebindPermissions>& whiteBinds,
-    const std::vector<CService>& onion_binds)
+bool CConnman::InitBinds(const Options& options)
 {
     bool fBound = false;
-    for (const auto& addrBind : binds) {
+    for (const auto& addrBind : options.vBinds) {
         fBound |= Bind(addrBind, (BF_EXPLICIT | BF_REPORT_ERROR), NetPermissionFlags::None);
     }
-    for (const auto& addrBind : whiteBinds) {
+    for (const auto& addrBind : options.vWhiteBinds) {
         fBound |= Bind(addrBind.m_service, (BF_EXPLICIT | BF_REPORT_ERROR), addrBind.m_flags);
     }
-    if (binds.empty() && whiteBinds.empty()) {
+    for (const auto& addr_bind : options.onion_binds) {
+        fBound |= Bind(addr_bind, BF_EXPLICIT | BF_DONT_ADVERTISE, NetPermissionFlags::None);
+    }
+    if (options.bind_on_any) {
         struct in_addr inaddr_any;
         inaddr_any.s_addr = htonl(INADDR_ANY);
         struct in6_addr inaddr6_any = IN6ADDR_ANY_INIT;
         fBound |= Bind(CService(inaddr6_any, GetListenPort()), BF_NONE, NetPermissionFlags::None);
         fBound |= Bind(CService(inaddr_any, GetListenPort()), !fBound ? BF_REPORT_ERROR : BF_NONE, NetPermissionFlags::None);
     }
-
-    for (const auto& addr_bind : onion_binds) {
-        fBound |= Bind(addr_bind, BF_EXPLICIT | BF_DONT_ADVERTISE, NetPermissionFlags::None);
-    }
-
     return fBound;
 }
 
@@ -2496,7 +2491,7 @@ bool CConnman::Start(CScheduler& scheduler, const Options& connOptions)
 {
     Init(connOptions);
 
-    if (fListen && !InitBinds(connOptions.vBinds, connOptions.vWhiteBinds, connOptions.onion_binds)) {
+    if (fListen && !InitBinds(connOptions)) {
         if (clientInterface) {
             clientInterface->ThreadSafeMessageBox(
                 _("Failed to listen on any port. Use -listen=0 if you want this."),
diff --git a/src/net.h b/src/net.h
index 01658e8973..e1f109a2c4 100644
--- a/src/net.h
+++ b/src/net.h
@@ -768,6 +768,9 @@ public:
         std::vector<NetWhitebindPermissions> vWhiteBinds;
         std::vector<CService> vBinds;
         std::vector<CService> onion_binds;
+        /// True if the user did not specify -bind= or -whitebind= and thus
+        /// we should bind on `0.0.0.0` (IPv4) and `::` (IPv6).
+        bool bind_on_any;
         bool m_use_addrman_outgoing = true;
         std::vector<std::string> m_specified_outgoing;
         std::vector<std::string> m_added_nodes;
@@ -962,10 +965,7 @@ private:
 
     bool BindListenPort(const CService& bindAddr, bilingual_str& strError, NetPermissionFlags permissions);
     bool Bind(const CService& addr, unsigned int flags, NetPermissionFlags permissions);
-    bool InitBinds(
-        const std::vector<CService>& binds,
-        const std::vector<NetWhitebindPermissions>& whiteBinds,
-        const std::vector<CService>& onion_binds);
+    bool InitBinds(const Options& options);
 
     void ThreadOpenAddedConnections();
     void AddAddrFetch(const std::string& strDest);