Merge bitcoin/bitcoin#27071: Handle CJDNS from LookupSubNet()

0e6f6ebc064c5fb425fc3699efe760ec6cd4b6af net: remove unused CConnman::FindNode(const CSubNet&) (Vasil Dimov)
9482cb780fe04c1f1d9050edd1b8e549e52c86ce netbase: possibly change the result of LookupSubNet() to CJDNS (Vasil Dimov)
53afa68026ffa1313ae4aba3664de7791d23b1c8 net: move MaybeFlipIPv6toCJDNS() from net to netbase (Vasil Dimov)
6e308651c441cbf8763c67cc099c538c333c2872 net: move IsReachable() code to netbase and encapsulate it (Vasil Dimov)
c42ded3d9bda8b273780a4a81490bbf1b9e9c261 fuzz: ConsumeNetAddr(): avoid IPv6 addresses that look like CJDNS (Vasil Dimov)
64d6f77907afd461d9b14ee10ab32335f4454734 net: put CJDNS prefix byte in a constant (Vasil Dimov)

Pull request description:

  `LookupSubNet()` would treat addresses that start with `fc` as IPv6 even if `-cjdnsreachable` is set. This creates the following problems where it is called:

  * `NetWhitelistPermissions::TryParse()`: otherwise `-whitelist=` fails to white list CJDNS addresses: when a CJDNS peer connects to us, it will be matched against IPv6 `fc...` subnet and the match will never succeed.

  * `BanMapFromJson()`: CJDNS bans are stored as just IPv6 addresses in `banlist.json`. Upon reading from disk they have to be converted back to CJDNS, otherwise, after restart, a ban entry like (`fc00::1`, IPv6) would not match a peer (`fc00::1`, CJDNS).

  * `RPCConsole::unbanSelectedNode()`: in the GUI the ban entries go through `CSubNet::ToString()` and back via `LookupSubNet()`. Then it must match whatever is stored in `BanMan`, otherwise it is impossible to unban via the GUI.

  These were uncovered by https://github.com/bitcoin/bitcoin/pull/26859.

  Thus, flip the result of `LookupSubNet()` to CJDNS if the network base address starts with `fc` and `-cjdnsreachable` is set. Since subnetting/masking does not make sense for CJDNS (the address is "random" bytes, like Tor and I2P, there is no hierarchy) treat `fc.../mask` as an invalid `CSubNet`.

  To achieve that, `MaybeFlipIPv6toCJDNS()` has to be moved from `net` to `netbase` and thus also `IsReachable()`. In the process of moving `IsReachable()`, `SetReachable()` and `vfLimited[]` encapsulate those in a class.

ACKs for top commit:
  jonatack:
    Code review ACK 0e6f6ebc064c5fb425fc3699efe760ec6cd4b6af
  achow101:
    ACK 0e6f6ebc064c5fb425fc3699efe760ec6cd4b6af
  mzumsande:
    re-ACK 0e6f6ebc064c5fb425fc3699efe760ec6cd4b6af

Tree-SHA512: 4767a60dc882916de4c8b110ce8de208ff3f58daaa0b560e6547d72e604d07c4157e72cf98b237228310fc05c0a3922f446674492e2ba02e990a272d288bd566

13 files changed, 168 insertions, 139 deletions

diff --git a/src/httpserver.cpp b/src/httpserver.cpp
index add6494f06..647e36adb3 100644
--- a/src/httpserver.cpp
+++ b/src/httpserver.cpp
@@ -682,7 +682,7 @@ CService HTTPRequest::GetPeer() const
         evhttp_connection_get_peer(con, (char**)&address, &port);
 #endif // HAVE_EVHTTP_CONNECTION_GET_PEER_CONST_CHAR
 
-        peer = LookupNumeric(address, port);
+        peer = MaybeFlipIPv6toCJDNS(LookupNumeric(address, port));
     }
     return peer;
 }
diff --git a/src/init.cpp b/src/init.cpp
index 22100dfbf9..42331d37e8 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -1314,30 +1314,24 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     }
 
     if (args.IsArgSet("-onlynet")) {
-        std::set<enum Network> nets;
+        g_reachable_nets.RemoveAll();
         for (const std::string& snet : args.GetArgs("-onlynet")) {
             enum Network net = ParseNetwork(snet);
             if (net == NET_UNROUTABLE)
                 return InitError(strprintf(_("Unknown network specified in -onlynet: '%s'"), snet));
-            nets.insert(net);
-        }
-        for (int n = 0; n < NET_MAX; n++) {
-            enum Network net = (enum Network)n;
-            assert(IsReachable(net));
-            if (!nets.count(net))
-                SetReachable(net, false);
+            g_reachable_nets.Add(net);
         }
     }
 
     if (!args.IsArgSet("-cjdnsreachable")) {
-        if (args.IsArgSet("-onlynet") && IsReachable(NET_CJDNS)) {
+        if (args.IsArgSet("-onlynet") && g_reachable_nets.Contains(NET_CJDNS)) {
             return InitError(
                 _("Outbound connections restricted to CJDNS (-onlynet=cjdns) but "
                   "-cjdnsreachable is not provided"));
         }
-        SetReachable(NET_CJDNS, false);
+        g_reachable_nets.Remove(NET_CJDNS);
     }
-    // Now IsReachable(NET_CJDNS) is true if:
+    // Now g_reachable_nets.Contains(NET_CJDNS) is true if:
     // 1. -cjdnsreachable is given and
     // 2.1. -onlynet is not given or
     // 2.2. -onlynet=cjdns is given
@@ -1345,7 +1339,7 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     // Requesting DNS seeds entails connecting to IPv4/IPv6, which -onlynet options may prohibit:
     // If -dnsseed=1 is explicitly specified, abort. If it's left unspecified by the user, we skip
     // the DNS seeds by adjusting -dnsseed in InitParameterInteraction.
-    if (args.GetBoolArg("-dnsseed") == true && !IsReachable(NET_IPV4) && !IsReachable(NET_IPV6)) {
+    if (args.GetBoolArg("-dnsseed") == true && !g_reachable_nets.Contains(NET_IPV4) && !g_reachable_nets.Contains(NET_IPV6)) {
         return InitError(strprintf(_("Incompatible options: -dnsseed=1 was explicitly specified, but -onlynet forbids connections to IPv4/IPv6")));
     };
 
@@ -1375,7 +1369,7 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
         onion_proxy = addrProxy;
     }
 
-    const bool onlynet_used_with_onion{args.IsArgSet("-onlynet") && IsReachable(NET_ONION)};
+    const bool onlynet_used_with_onion{args.IsArgSet("-onlynet") && g_reachable_nets.Contains(NET_ONION)};
 
     // -onion can be used to set only a proxy for .onion, or override normal proxy for .onion addresses
     // -noonion (or -onion=0) disables connecting to .onion entirely
@@ -1410,7 +1404,7 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
                   "reaching the Tor network is not provided: none of -proxy, -onion or "
                   "-listenonion is given"));
         }
-        SetReachable(NET_ONION, false);
+        g_reachable_nets.Remove(NET_ONION);
     }
 
     for (const std::string& strAddr : args.GetArgs("-externalip")) {
@@ -1885,12 +1879,12 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
         }
         SetProxy(NET_I2P, Proxy{addr.value()});
     } else {
-        if (args.IsArgSet("-onlynet") && IsReachable(NET_I2P)) {
+        if (args.IsArgSet("-onlynet") && g_reachable_nets.Contains(NET_I2P)) {
             return InitError(
                 _("Outbound connections restricted to i2p (-onlynet=i2p) but "
                   "-i2psam is not provided"));
         }
-        SetReachable(NET_I2P, false);
+        g_reachable_nets.Remove(NET_I2P);
     }
 
     connOptions.m_i2p_accept_incoming = args.GetBoolArg("-i2pacceptincoming", DEFAULT_I2P_ACCEPT_INCOMING);
diff --git a/src/net.cpp b/src/net.cpp
index 994abd986d..fecb4205ff 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -115,7 +115,6 @@ bool fDiscover = true;
 bool fListen = true;
 GlobalMutex g_maplocalhost_mutex;
 std::map<CNetAddr, LocalServiceInfo> mapLocalHost GUARDED_BY(g_maplocalhost_mutex);
-static bool vfLimited[NET_MAX] GUARDED_BY(g_maplocalhost_mutex) = {};
 std::string strSubVersion;
 
 size_t CSerializedNetMsg::GetMemoryUsage() const noexcept
@@ -232,7 +231,7 @@ static int GetnScore(const CService& addr)
 {
     CService addrLocal = pnode->GetAddrLocal();
     return fDiscover && pnode->addr.IsRoutable() && addrLocal.IsRoutable() &&
-           IsReachable(addrLocal.GetNetwork());
+           g_reachable_nets.Contains(addrLocal);
 }
 
 std::optional<CService> GetLocalAddrForPeer(CNode& node)
@@ -270,22 +269,6 @@ std::optional<CService> GetLocalAddrForPeer(CNode& node)
     return std::nullopt;
 }
 
-/**
- * If an IPv6 address belongs to the address range used by the CJDNS network and
- * the CJDNS network is reachable (-cjdnsreachable config is set), then change
- * the type from NET_IPV6 to NET_CJDNS.
- * @param[in] service Address to potentially convert.
- * @return a copy of `service` either unmodified or changed to CJDNS.
- */
-CService MaybeFlipIPv6toCJDNS(const CService& service)
-{
-    CService ret{service};
-    if (ret.IsIPv6() && ret.HasCJDNSPrefix() && IsReachable(NET_CJDNS)) {
-        ret.m_net = NET_CJDNS;
-    }
-    return ret;
-}
-
 // learn a new local address
 bool AddLocal(const CService& addr_, int nScore)
 {
@@ -297,7 +280,7 @@ bool AddLocal(const CService& addr_, int nScore)
     if (!fDiscover && nScore < LOCAL_MANUAL)
         return false;
 
-    if (!IsReachable(addr))
+    if (!g_reachable_nets.Contains(addr))
         return false;
 
     LogPrintf("AddLocal(%s,%i)\n", addr.ToStringAddrPort(), nScore);
@@ -327,25 +310,6 @@ void RemoveLocal(const CService& addr)
     mapLocalHost.erase(addr);
 }
 
-void SetReachable(enum Network net, bool reachable)
-{
-    if (net == NET_UNROUTABLE || net == NET_INTERNAL)
-        return;
-    LOCK(g_maplocalhost_mutex);
-    vfLimited[net] = !reachable;
-}
-
-bool IsReachable(enum Network net)
-{
-    LOCK(g_maplocalhost_mutex);
-    return !vfLimited[net];
-}
-
-bool IsReachable(const CNetAddr &addr)
-{
-    return IsReachable(addr.GetNetwork());
-}
-
 /** vote for a local address */
 bool SeenLocal(const CService& addr)
 {
@@ -375,17 +339,6 @@ CNode* CConnman::FindNode(const CNetAddr& ip)
     return nullptr;
 }
 
-CNode* CConnman::FindNode(const CSubNet& subNet)
-{
-    LOCK(m_nodes_mutex);
-    for (CNode* pnode : m_nodes) {
-        if (subNet.Match(static_cast<CNetAddr>(pnode->addr))) {
-            return pnode;
-        }
-    }
-    return nullptr;
-}
-
 CNode* CConnman::FindNode(const std::string& addrName)
 {
     LOCK(m_nodes_mutex);
@@ -2433,7 +2386,7 @@ std::unordered_set<Network> CConnman::GetReachableEmptyNetworks() const
     for (int n = 0; n < NET_MAX; n++) {
         enum Network net = (enum Network)n;
         if (net == NET_UNROUTABLE || net == NET_INTERNAL) continue;
-        if (IsReachable(net) && addrman.Size(net, std::nullopt) == 0) {
+        if (g_reachable_nets.Contains(net) && addrman.Size(net, std::nullopt) == 0) {
             networks.insert(net);
         }
     }
@@ -2453,7 +2406,7 @@ bool CConnman::MaybePickPreferredNetwork(std::optional<Network>& network)
 
     LOCK(m_nodes_mutex);
     for (const auto net : nets) {
-        if (IsReachable(net) && m_network_conn_counts[net] == 0 && addrman.Size(net) != 0) {
+        if (g_reachable_nets.Contains(net) && m_network_conn_counts[net] == 0 && addrman.Size(net) != 0) {
             network = net;
             return true;
         }
@@ -2683,7 +2636,7 @@ void CConnman::ThreadOpenConnections(const std::vector<std::string> connect)
             if (anchor && !m_anchors.empty()) {
                 const CAddress addr = m_anchors.back();
                 m_anchors.pop_back();
-                if (!addr.IsValid() || IsLocal(addr) || !IsReachable(addr) ||
+                if (!addr.IsValid() || IsLocal(addr) || !g_reachable_nets.Contains(addr) ||
                     !HasAllDesirableServiceFlags(addr.nServices) ||
                     outbound_ipv46_peer_netgroups.count(m_netgroupman.GetGroup(addr))) continue;
                 addrConnect = addr;
@@ -2738,8 +2691,9 @@ void CConnman::ThreadOpenConnections(const std::vector<std::string> connect)
                 break;
             }
 
-            if (!IsReachable(addr))
+            if (!g_reachable_nets.Contains(addr)) {
                 continue;
+            }
 
             // only consider very recently tried nodes after 30 failed attempts
             if (current_time - addr_last_try < 10min && nTries < 30) {
diff --git a/src/net.h b/src/net.h
index e8e31f72e4..ddee34168a 100644
--- a/src/net.h
+++ b/src/net.h
@@ -160,24 +160,12 @@ enum
 /** Returns a local address that we should advertise to this peer. */
 std::optional<CService> GetLocalAddrForPeer(CNode& node);
 
-/**
- * Mark a network as reachable or unreachable (no automatic connects to it)
- * @note Networks are reachable by default
- */
-void SetReachable(enum Network net, bool reachable);
-/** @returns true if the network is reachable, false otherwise */
-bool IsReachable(enum Network net);
-/** @returns true if the address is in a reachable network, false otherwise */
-bool IsReachable(const CNetAddr& addr);
-
 bool AddLocal(const CService& addr, int nScore = LOCAL_NONE);
 bool AddLocal(const CNetAddr& addr, int nScore = LOCAL_NONE);
 void RemoveLocal(const CService& addr);
 bool SeenLocal(const CService& addr);
 bool IsLocal(const CService& addr);
 CService GetLocalAddress(const CNode& peer);
-CService MaybeFlipIPv6toCJDNS(const CService& service);
-
 
 extern bool fDiscover;
 extern bool fListen;
@@ -1341,7 +1329,6 @@ private:
     uint64_t CalculateKeyedNetGroup(const CAddress& ad) const;
 
     CNode* FindNode(const CNetAddr& ip);
-    CNode* FindNode(const CSubNet& subNet);
     CNode* FindNode(const std::string& addrName);
     CNode* FindNode(const CService& addr);
 
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index f07769272c..3bfb606037 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -3830,14 +3830,15 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
                 continue;
             }
             ++num_proc;
-            bool fReachable = IsReachable(addr);
+            const bool reachable{g_reachable_nets.Contains(addr)};
             if (addr.nTime > current_a_time - 10min && !peer->m_getaddr_sent && vAddr.size() <= 10 && addr.IsRoutable()) {
                 // Relay to a limited number of other nodes
-                RelayAddress(pfrom.GetId(), addr, fReachable);
+                RelayAddress(pfrom.GetId(), addr, reachable);
             }
             // Do not store addresses outside our network
-            if (fReachable)
+            if (reachable) {
                 vAddrOk.push_back(addr);
+            }
         }
         peer->m_addr_processed += num_proc;
         peer->m_addr_rate_limited += num_rate_limit;
diff --git a/src/netaddress.h b/src/netaddress.h
index ad09f16799..08dd77c0ff 100644
--- a/src/netaddress.h
+++ b/src/netaddress.h
@@ -81,6 +81,10 @@ static const std::array<uint8_t, 6> INTERNAL_IN_IPV6_PREFIX{
     0xFD, 0x6B, 0x88, 0xC0, 0x87, 0x24 // 0xFD + sha256("bitcoin")[0:5].
 };
 
+/// All CJDNS addresses start with 0xFC. See
+/// https://github.com/cjdelisle/cjdns/blob/master/doc/Whitepaper.md#pulling-it-all-together
+static constexpr uint8_t CJDNS_PREFIX{0xFC};
+
 /// Size of IPv4 address (in bytes).
 static constexpr size_t ADDR_IPV4_SIZE = 4;
 
@@ -174,7 +178,7 @@ public:
     [[nodiscard]] bool IsTor() const { return m_net == NET_ONION; }
     [[nodiscard]] bool IsI2P() const { return m_net == NET_I2P; }
     [[nodiscard]] bool IsCJDNS() const { return m_net == NET_CJDNS; }
-    [[nodiscard]] bool HasCJDNSPrefix() const { return m_addr[0] == 0xfc; }
+    [[nodiscard]] bool HasCJDNSPrefix() const { return m_addr[0] == CJDNS_PREFIX; }
     bool IsLocal() const;
     bool IsRoutable() const;
     bool IsInternal() const;
diff --git a/src/netbase.cpp b/src/netbase.cpp
index ca1a80d72f..5e1e121bfe 100644
--- a/src/netbase.cpp
+++ b/src/netbase.cpp
@@ -32,6 +32,8 @@ bool fNameLookup = DEFAULT_NAME_LOOKUP;
 std::chrono::milliseconds g_socks5_recv_timeout = 20s;
 static std::atomic<bool> interruptSocks5Recv(false);
 
+ReachableNets g_reachable_nets;
+
 std::vector<CNetAddr> WrappedGetAddrInfo(const std::string& name, bool allow_lookup)
 {
     addrinfo ai_hint{};
@@ -651,9 +653,10 @@ bool LookupSubNet(const std::string& subnet_str, CSubNet& subnet_out)
 
     const size_t slash_pos{subnet_str.find_last_of('/')};
     const std::string str_addr{subnet_str.substr(0, slash_pos)};
-    const std::optional<CNetAddr> addr{LookupHost(str_addr, /*fAllowLookup=*/false)};
+    std::optional<CNetAddr> addr{LookupHost(str_addr, /*fAllowLookup=*/false)};
 
     if (addr.has_value()) {
+        addr = static_cast<CNetAddr>(MaybeFlipIPv6toCJDNS(CService{addr.value(), /*port=*/0}));
         if (slash_pos != subnet_str.npos) {
             const std::string netmask_str{subnet_str.substr(slash_pos + 1)};
             uint8_t netmask;
@@ -772,3 +775,12 @@ bool IsBadPort(uint16_t port)
     }
     return false;
 }
+
+CService MaybeFlipIPv6toCJDNS(const CService& service)
+{
+    CService ret{service};
+    if (ret.IsIPv6() && ret.HasCJDNSPrefix() && g_reachable_nets.Contains(NET_CJDNS)) {
+        ret.m_net = NET_CJDNS;
+    }
+    return ret;
+}
diff --git a/src/netbase.h b/src/netbase.h
index 1da4f5c51d..8b7da4109f 100644
--- a/src/netbase.h
+++ b/src/netbase.h
@@ -19,6 +19,7 @@
 #include <stdint.h>
 #include <string>
 #include <type_traits>
+#include <unordered_set>
 #include <vector>
 
 extern int nConnectTimeout;
@@ -65,6 +66,61 @@ struct ProxyCredentials
 };
 
 /**
+ * List of reachable networks. Everything is reachable by default.
+ */
+class ReachableNets {
+public:
+    void Add(Network net) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
+    {
+        AssertLockNotHeld(m_mutex);
+        LOCK(m_mutex);
+        m_reachable.insert(net);
+    }
+
+    void Remove(Network net) EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
+    {
+        AssertLockNotHeld(m_mutex);
+        LOCK(m_mutex);
+        m_reachable.erase(net);
+    }
+
+    void RemoveAll() EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
+    {
+        AssertLockNotHeld(m_mutex);
+        LOCK(m_mutex);
+        m_reachable.clear();
+    }
+
+    [[nodiscard]] bool Contains(Network net) const EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
+    {
+        AssertLockNotHeld(m_mutex);
+        LOCK(m_mutex);
+        return m_reachable.count(net) > 0;
+    }
+
+    [[nodiscard]] bool Contains(const CNetAddr& addr) const EXCLUSIVE_LOCKS_REQUIRED(!m_mutex)
+    {
+        AssertLockNotHeld(m_mutex);
+        return Contains(addr.GetNetwork());
+    }
+
+private:
+    mutable Mutex m_mutex;
+
+    std::unordered_set<Network> m_reachable GUARDED_BY(m_mutex){
+        NET_UNROUTABLE,
+        NET_IPV4,
+        NET_IPV6,
+        NET_ONION,
+        NET_I2P,
+        NET_CJDNS,
+        NET_INTERNAL
+    };
+};
+
+extern ReachableNets g_reachable_nets;
+
+/**
  * Wrapper for getaddrinfo(3). Do not use directly: call Lookup/LookupHost/LookupNumeric/LookupSubNet.
  */
 std::vector<CNetAddr> WrappedGetAddrInfo(const std::string& name, bool allow_lookup);
@@ -251,4 +307,13 @@ bool Socks5(const std::string& strDest, uint16_t port, const ProxyCredentials* a
  */
 bool IsBadPort(uint16_t port);
 
+/**
+ * If an IPv6 address belongs to the address range used by the CJDNS network and
+ * the CJDNS network is reachable (-cjdnsreachable config is set), then change
+ * the type from NET_IPV6 to NET_CJDNS.
+ * @param[in] service Address to potentially convert.
+ * @return a copy of `service` either unmodified or changed to CJDNS.
+ */
+CService MaybeFlipIPv6toCJDNS(const CService& service);
+
 #endif // BITCOIN_NETBASE_H
diff --git a/src/netgroup.cpp b/src/netgroup.cpp
index 2d4d231f2b..a03927b152 100644
--- a/src/netgroup.cpp
+++ b/src/netgroup.cpp
@@ -52,8 +52,8 @@ std::vector<unsigned char> NetGroupManager::GetGroup(const CNetAddr& address) co
     } else if (address.IsCJDNS()) {
         // Treat in the same way as Tor and I2P because the address in all of
         // them is "random" bytes (derived from a public key). However in CJDNS
-        // the first byte is a constant 0xfc, so the random bytes come after it.
-        // Thus skip the constant 8 bits at the start.
+        // the first byte is a constant (see CJDNS_PREFIX), so the random bytes
+        // come after it. Thus skip the constant 8 bits at the start.
         nBits = 12;
     } else if (address.IsHeNet()) {
         // for he.net, use /36 groups
diff --git a/src/rpc/net.cpp b/src/rpc/net.cpp
index 5a68bf9e1f..63788c3a03 100644
--- a/src/rpc/net.cpp
+++ b/src/rpc/net.cpp
@@ -585,8 +585,8 @@ static UniValue GetNetworksInfo()
         UniValue obj(UniValue::VOBJ);
         GetProxy(network, proxy);
         obj.pushKV("name", GetNetworkName(network));
-        obj.pushKV("limited", !IsReachable(network));
-        obj.pushKV("reachable", IsReachable(network));
+        obj.pushKV("limited", !g_reachable_nets.Contains(network));
+        obj.pushKV("reachable", g_reachable_nets.Contains(network));
         obj.pushKV("proxy", proxy.IsValid() ? proxy.proxy.ToStringAddrPort() : std::string());
         obj.pushKV("proxy_randomize_credentials", proxy.randomize_credentials);
         networks.push_back(obj);
@@ -730,7 +730,7 @@ static RPCHelpMan setban()
     if (!isSubnet) {
         const std::optional<CNetAddr> addr{LookupHost(request.params[0].get_str(), false)};
         if (addr.has_value()) {
-            netAddr = addr.value();
+            netAddr = static_cast<CNetAddr>(MaybeFlipIPv6toCJDNS(CService{addr.value(), /*port=*/0}));
         }
     }
     else
diff --git a/src/test/fuzz/util/net.cpp b/src/test/fuzz/util/net.cpp
index d23e997719..5a286c05d2 100644
--- a/src/test/fuzz/util/net.cpp
+++ b/src/test/fuzz/util/net.cpp
@@ -36,7 +36,11 @@ CNetAddr ConsumeNetAddr(FuzzedDataProvider& fuzzed_data_provider) noexcept
     } else if (network == Network::NET_IPV6) {
         if (fuzzed_data_provider.remaining_bytes() >= 16) {
             in6_addr v6_addr = {};
-            memcpy(v6_addr.s6_addr, fuzzed_data_provider.ConsumeBytes<uint8_t>(16).data(), 16);
+            auto addr_bytes = fuzzed_data_provider.ConsumeBytes<uint8_t>(16);
+            if (addr_bytes[0] == CJDNS_PREFIX) { // Avoid generating IPv6 addresses that look like CJDNS.
+                addr_bytes[0] = 0x55; // Just an arbitrary number, anything != CJDNS_PREFIX would do.
+            }
+            memcpy(v6_addr.s6_addr, addr_bytes.data(), 16);
             net_addr = CNetAddr{v6_addr, fuzzed_data_provider.ConsumeIntegral<uint32_t>()};
         }
     } else if (network == Network::NET_INTERNAL) {
diff --git a/src/test/net_tests.cpp b/src/test/net_tests.cpp
index 796716d6cb..7c98c382e4 100644
--- a/src/test/net_tests.cpp
+++ b/src/test/net_tests.cpp
@@ -718,47 +718,55 @@ BOOST_AUTO_TEST_CASE(get_local_addr_for_peer_port)
 
 BOOST_AUTO_TEST_CASE(LimitedAndReachable_Network)
 {
-    BOOST_CHECK(IsReachable(NET_IPV4));
-    BOOST_CHECK(IsReachable(NET_IPV6));
-    BOOST_CHECK(IsReachable(NET_ONION));
-    BOOST_CHECK(IsReachable(NET_I2P));
-    BOOST_CHECK(IsReachable(NET_CJDNS));
-
-    SetReachable(NET_IPV4, false);
-    SetReachable(NET_IPV6, false);
-    SetReachable(NET_ONION, false);
-    SetReachable(NET_I2P, false);
-    SetReachable(NET_CJDNS, false);
-
-    BOOST_CHECK(!IsReachable(NET_IPV4));
-    BOOST_CHECK(!IsReachable(NET_IPV6));
-    BOOST_CHECK(!IsReachable(NET_ONION));
-    BOOST_CHECK(!IsReachable(NET_I2P));
-    BOOST_CHECK(!IsReachable(NET_CJDNS));
-
-    SetReachable(NET_IPV4, true);
-    SetReachable(NET_IPV6, true);
-    SetReachable(NET_ONION, true);
-    SetReachable(NET_I2P, true);
-    SetReachable(NET_CJDNS, true);
-
-    BOOST_CHECK(IsReachable(NET_IPV4));
-    BOOST_CHECK(IsReachable(NET_IPV6));
-    BOOST_CHECK(IsReachable(NET_ONION));
-    BOOST_CHECK(IsReachable(NET_I2P));
-    BOOST_CHECK(IsReachable(NET_CJDNS));
+    BOOST_CHECK(g_reachable_nets.Contains(NET_IPV4));
+    BOOST_CHECK(g_reachable_nets.Contains(NET_IPV6));
+    BOOST_CHECK(g_reachable_nets.Contains(NET_ONION));
+    BOOST_CHECK(g_reachable_nets.Contains(NET_I2P));
+    BOOST_CHECK(g_reachable_nets.Contains(NET_CJDNS));
+
+    g_reachable_nets.Remove(NET_IPV4);
+    g_reachable_nets.Remove(NET_IPV6);
+    g_reachable_nets.Remove(NET_ONION);
+    g_reachable_nets.Remove(NET_I2P);
+    g_reachable_nets.Remove(NET_CJDNS);
+
+    BOOST_CHECK(!g_reachable_nets.Contains(NET_IPV4));
+    BOOST_CHECK(!g_reachable_nets.Contains(NET_IPV6));
+    BOOST_CHECK(!g_reachable_nets.Contains(NET_ONION));
+    BOOST_CHECK(!g_reachable_nets.Contains(NET_I2P));
+    BOOST_CHECK(!g_reachable_nets.Contains(NET_CJDNS));
+
+    g_reachable_nets.Add(NET_IPV4);
+    g_reachable_nets.Add(NET_IPV6);
+    g_reachable_nets.Add(NET_ONION);
+    g_reachable_nets.Add(NET_I2P);
+    g_reachable_nets.Add(NET_CJDNS);
+
+    BOOST_CHECK(g_reachable_nets.Contains(NET_IPV4));
+    BOOST_CHECK(g_reachable_nets.Contains(NET_IPV6));
+    BOOST_CHECK(g_reachable_nets.Contains(NET_ONION));
+    BOOST_CHECK(g_reachable_nets.Contains(NET_I2P));
+    BOOST_CHECK(g_reachable_nets.Contains(NET_CJDNS));
 }
 
 BOOST_AUTO_TEST_CASE(LimitedAndReachable_NetworkCaseUnroutableAndInternal)
 {
-    BOOST_CHECK(IsReachable(NET_UNROUTABLE));
-    BOOST_CHECK(IsReachable(NET_INTERNAL));
-
-    SetReachable(NET_UNROUTABLE, false);
-    SetReachable(NET_INTERNAL, false);
-
-    BOOST_CHECK(IsReachable(NET_UNROUTABLE)); // Ignored for both networks
-    BOOST_CHECK(IsReachable(NET_INTERNAL));
+    // Should be reachable by default.
+    BOOST_CHECK(g_reachable_nets.Contains(NET_UNROUTABLE));
+    BOOST_CHECK(g_reachable_nets.Contains(NET_INTERNAL));
+
+    g_reachable_nets.RemoveAll();
+
+    BOOST_CHECK(!g_reachable_nets.Contains(NET_UNROUTABLE));
+    BOOST_CHECK(!g_reachable_nets.Contains(NET_INTERNAL));
+
+    g_reachable_nets.Add(NET_IPV4);
+    g_reachable_nets.Add(NET_IPV6);
+    g_reachable_nets.Add(NET_ONION);
+    g_reachable_nets.Add(NET_I2P);
+    g_reachable_nets.Add(NET_CJDNS);
+    g_reachable_nets.Add(NET_UNROUTABLE);
+    g_reachable_nets.Add(NET_INTERNAL);
 }
 
 CNetAddr UtilBuildAddress(unsigned char p1, unsigned char p2, unsigned char p3, unsigned char p4)
@@ -776,13 +784,13 @@ BOOST_AUTO_TEST_CASE(LimitedAndReachable_CNetAddr)
 {
     CNetAddr addr = UtilBuildAddress(0x001, 0x001, 0x001, 0x001); // 1.1.1.1
 
-    SetReachable(NET_IPV4, true);
-    BOOST_CHECK(IsReachable(addr));
+    g_reachable_nets.Add(NET_IPV4);
+    BOOST_CHECK(g_reachable_nets.Contains(addr));
 
-    SetReachable(NET_IPV4, false);
-    BOOST_CHECK(!IsReachable(addr));
+    g_reachable_nets.Remove(NET_IPV4);
+    BOOST_CHECK(!g_reachable_nets.Contains(addr));
 
-    SetReachable(NET_IPV4, true); // have to reset this, because this is stateful.
+    g_reachable_nets.Add(NET_IPV4); // have to reset this, because this is stateful.
 }
 
 
@@ -790,7 +798,7 @@ BOOST_AUTO_TEST_CASE(LocalAddress_BasicLifecycle)
 {
     CService addr = CService(UtilBuildAddress(0x002, 0x001, 0x001, 0x001), 1000); // 2.1.1.1:1000
 
-    SetReachable(NET_IPV4, true);
+    g_reachable_nets.Add(NET_IPV4);
 
     BOOST_CHECK(!IsLocal(addr));
     BOOST_CHECK(AddLocal(addr, 1000));
@@ -915,7 +923,7 @@ BOOST_AUTO_TEST_CASE(advertise_local_address)
                                        ConnectionType::OUTBOUND_FULL_RELAY,
                                        /*inbound_onion=*/false);
     };
-    SetReachable(NET_CJDNS, true);
+    g_reachable_nets.Add(NET_CJDNS);
 
     CAddress addr_ipv4{Lookup("1.2.3.4", 8333, false).value(), NODE_NONE};
     BOOST_REQUIRE(addr_ipv4.IsValid());
diff --git a/src/torcontrol.cpp b/src/torcontrol.cpp
index 4c99aa5746..60cf31a964 100644
--- a/src/torcontrol.cpp
+++ b/src/torcontrol.cpp
@@ -409,7 +409,7 @@ void TorController::get_socks_cb(TorControlConnection& _conn, const TorControlRe
         //
         // If NET_ONION is not reachable, then none of -proxy or -onion was given.
         // Since we are here, then -torcontrol and -torpassword were given.
-        SetReachable(NET_ONION, true);
+        g_reachable_nets.Add(NET_ONION);
     }
 }