protocols/autonat: optionally use only global IPs (#2618)

Optionally only perform dial-backs on peers that are observed at a global ip-address.
This is relevant when multiple peers are in the same local network, in which case a peer could incorrectly assume themself to be public because a peer in the same local network was able to dial them. Thus servers should reject dial-back requests from clients with a non-global IP address, and at the same time clients should only pick connected peers as servers if they are global.
Behind a config flag (enabled by default) to also allow use-cases where AutoNAT is needed within a private network.

protocols/autonat/CHANGELOG.md

@@ -6,6 +6,11 @@
 
 - Update to `libp2p-request-response` `v0.18.0`.
 
+- Add `Config::only_global_ips` to skip peers that are observed at a private IP-address
+  (see [PR 2618]).
+
+[PR 2618]: https://github.com/libp2p/rust-libp2p/pull/2618
+
 # 0.3.0
 
 - Update to `libp2p-swarm` `v0.35.0`.

protocols/autonat/src/behaviour.rs

@@ -30,6 +30,7 @@ use futures_timer::Delay;
 use instant::Instant;
 use libp2p_core::{
     connection::{ConnectionId, ListenerId},
+    multiaddr::Protocol,
     ConnectedPoint, Endpoint, Multiaddr, PeerId,
 };
 use libp2p_request_response::{
@@ -77,6 +78,11 @@ pub struct Config {
     pub throttle_clients_peer_max: usize,
     /// Period for throttling clients requests.
     pub throttle_clients_period: Duration,
+    /// As a server reject probes for clients that are observed at a non-global ip address.
+    /// Correspondingly as a client only pick peers as server that are not observed at a
+    /// private ip address. Note that this does not apply for servers that are added via
+    /// [`Behaviour::add_server`].
+    pub only_global_ips: bool,
 }
 
 impl Default for Config {
@@ -93,6 +99,7 @@ impl Default for Config {
             throttle_clients_global_max: 30,
             throttle_clients_peer_max: 3,
             throttle_clients_period: Duration::from_secs(1),
+            only_global_ips: true,
         }
     }
 }
@@ -188,7 +195,8 @@ pub struct Behaviour {
     ongoing_outbound: HashMap<RequestId, ProbeId>,
 
     // Connected peers with the observed address of each connection.
-    // If the endpoint of a connection is relayed, the observed address is `None`.
+    // If the endpoint of a connection is relayed or not global (in case of Config::only_global_ips),
+    // the observed address is `None`.
     connected: HashMap<PeerId, HashMap<ConnectionId, Option<Multiaddr>>>,
 
     // Used servers in recent outbound probes that are throttled through Config::throttle_server_period.
@@ -313,12 +321,14 @@ impl NetworkBehaviour for Behaviour {
             other_established,
         );
         let connections = self.connected.entry(*peer).or_default();
-        let addr = if endpoint.is_relayed() {
-            None
-        } else {
-            Some(endpoint.get_remote_address().clone())
-        };
-        connections.insert(*conn, addr);
+        let addr = endpoint.get_remote_address();
+        let observed_addr =
+            if !endpoint.is_relayed() && (!self.config.only_global_ips || addr.is_global_ip()) {
+                Some(addr.clone())
+            } else {
+                None
+            };
+        connections.insert(*conn, observed_addr);
 
         match endpoint {
             ConnectedPoint::Dialer {
@@ -386,12 +396,14 @@ impl NetworkBehaviour for Behaviour {
             return;
         }
         let connections = self.connected.get_mut(peer).expect("Peer is connected.");
-        let addr = if new.is_relayed() {
-            None
-        } else {
-            Some(new.get_remote_address().clone())
-        };
-        connections.insert(*conn, addr);
+        let addr = new.get_remote_address();
+        let observed_addr =
+            if !new.is_relayed() && (!self.config.only_global_ips || addr.is_global_ip()) {
+                Some(addr.clone())
+            } else {
+                None
+            };
+        connections.insert(*conn, observed_addr);
     }
 
     fn inject_new_listen_addr(&mut self, id: ListenerId, addr: &Multiaddr) {
@@ -512,3 +524,119 @@ trait HandleInnerEvent {
         event: RequestResponseEvent<DialRequest, DialResponse>,
     ) -> (VecDeque<Event>, Option<Action>);
 }
+
+trait GlobalIp {
+    fn is_global_ip(&self) -> bool;
+}
+
+impl GlobalIp for Multiaddr {
+    fn is_global_ip(&self) -> bool {
+        match self.iter().next() {
+            Some(Protocol::Ip4(a)) => a.is_global_ip(),
+            Some(Protocol::Ip6(a)) => a.is_global_ip(),
+            _ => false,
+        }
+    }
+}
+
+impl GlobalIp for std::net::Ipv4Addr {
+    // NOTE: The below logic is copied from `std::net::Ipv4Addr::is_global`, which is at the time of
+    // writing behind the unstable `ip` feature.
+    // See https://github.com/rust-lang/rust/issues/27709 for more info.
+    fn is_global_ip(&self) -> bool {
+        // Check if this address is 192.0.0.9 or 192.0.0.10. These addresses are the only two
+        // globally routable addresses in the 192.0.0.0/24 range.
+        if u32::from_be_bytes(self.octets()) == 0xc0000009
+            || u32::from_be_bytes(self.octets()) == 0xc000000a
+        {
+            return true;
+        }
+
+        // Copied from the unstable method `std::net::Ipv4Addr::is_shared`.
+        fn is_shared(addr: &std::net::Ipv4Addr) -> bool {
+            addr.octets()[0] == 100 && (addr.octets()[1] & 0b1100_0000 == 0b0100_0000)
+        }
+
+        // Copied from the unstable method `std::net::Ipv4Addr::is_reserved`.
+        //
+        // **Warning**: As IANA assigns new addresses, this logic will be
+        // updated. This may result in non-reserved addresses being
+        // treated as reserved in code that relies on an outdated version
+        // of this method.
+        fn is_reserved(addr: &std::net::Ipv4Addr) -> bool {
+            addr.octets()[0] & 240 == 240 && !addr.is_broadcast()
+        }
+
+        // Copied from the unstable method `std::net::Ipv4Addr::is_benchmarking`.
+        fn is_benchmarking(addr: &std::net::Ipv4Addr) -> bool {
+            addr.octets()[0] == 198 && (addr.octets()[1] & 0xfe) == 18
+        }
+
+        !self.is_private()
+            && !self.is_loopback()
+            && !self.is_link_local()
+            && !self.is_broadcast()
+            && !self.is_documentation()
+            && !is_shared(self)
+            // addresses reserved for future protocols (`192.0.0.0/24`)
+            && !(self.octets()[0] == 192 && self.octets()[1] == 0 && self.octets()[2] == 0)
+            && !is_reserved(self)
+            && !is_benchmarking(self)
+            // Make sure the address is not in 0.0.0.0/8
+            && self.octets()[0] != 0
+    }
+}
+
+impl GlobalIp for std::net::Ipv6Addr {
+    // NOTE: The below logic is copied from `std::net::Ipv6Addr::is_global`, which is at the time of
+    // writing behind the unstable `ip` feature.
+    // See https://github.com/rust-lang/rust/issues/27709 for more info.
+    //
+    // Note that contrary to `Ipv4Addr::is_global_ip` this currently checks for global scope
+    // rather than global reachability.
+    fn is_global_ip(&self) -> bool {
+        // Copied from the unstable method `std::net::Ipv6Addr::is_unicast`.
+        fn is_unicast(addr: &std::net::Ipv6Addr) -> bool {
+            !addr.is_multicast()
+        }
+        // Copied from the unstable method `std::net::Ipv6Addr::is_unicast_link_local`.
+        fn is_unicast_link_local(addr: &std::net::Ipv6Addr) -> bool {
+            (addr.segments()[0] & 0xffc0) == 0xfe80
+        }
+        // Copied from the unstable method `std::net::Ipv6Addr::is_unique_local`.
+        fn is_unique_local(addr: &std::net::Ipv6Addr) -> bool {
+            (addr.segments()[0] & 0xfe00) == 0xfc00
+        }
+        // Copied from the unstable method `std::net::Ipv6Addr::is_documentation`.
+        fn is_documentation(addr: &std::net::Ipv6Addr) -> bool {
+            (addr.segments()[0] == 0x2001) && (addr.segments()[1] == 0xdb8)
+        }
+
+        // Copied from the unstable method `std::net::Ipv6Addr::is_unicast_global`.
+        fn is_unicast_global(addr: &std::net::Ipv6Addr) -> bool {
+            is_unicast(addr)
+                && !addr.is_loopback()
+                && !is_unicast_link_local(addr)
+                && !is_unique_local(addr)
+                && !addr.is_unspecified()
+                && !is_documentation(addr)
+        }
+
+        // Variation of unstable method [`std::net::Ipv6Addr::multicast_scope`] that instead of the
+        // `Ipv6MulticastScope` just returns if the scope is global or not.
+        // Equivalent to `Ipv6Addr::multicast_scope(..).map(|scope| matches!(scope, Ipv6MulticastScope::Global))`.
+        fn is_multicast_scope_global(addr: &std::net::Ipv6Addr) -> Option<bool> {
+            match addr.segments()[0] & 0x000f {
+                14 => Some(true),         // Global multicast scope.
+                1..=5 | 8 => Some(false), // Local multicast scope.
+                _ => None,                // Unknown multicast scope.
+            }
+        }
+
+        match is_multicast_scope_global(self) {
+            Some(true) => true,
+            None => is_unicast_global(self),
+            _ => false,
+        }
+    }
+}

protocols/autonat/src/behaviour/as_client.rs

@@ -262,7 +262,12 @@ impl<'a> AsClient<'a> {
         let mut servers: Vec<&PeerId> = self.servers.iter().collect();
 
         if self.config.use_connected {
-            servers.extend(self.connected.iter().map(|(id, _)| id));
+            servers.extend(self.connected.iter().filter_map(|(id, addrs)| {
+                // Filter servers for which no qualified address is known.
+                // This is the case if the connection is relayed or the address is
+                // not global (in case of Config::only_global_ips).
+                addrs.values().any(|a| a.is_some()).then(|| id)
+            }));
         }
 
         servers.retain(|s| !self.throttled_servers.iter().any(|(id, _)| s == &id));

protocols/autonat/src/behaviour/as_server.rs

@@ -295,16 +295,16 @@ impl<'a> AsServer<'a> {
             .values()
             .find_map(|a| a.as_ref())
             .ok_or_else(|| {
-                let status_text = "no dial-request over relayed connections".to_string();
-                (status_text, ResponseError::DialError)
+                let status_text = "refusing to dial peer with blocked observed address".to_string();
+                (status_text, ResponseError::DialRefused)
             })?;
 
         let mut addrs = Self::filter_valid_addrs(sender, request.addresses, observed_addr);
         addrs.truncate(self.config.max_peer_addresses);
 
         if addrs.is_empty() {
             let status_text = "no dialable addresses".to_string();
-            return Err((status_text, ResponseError::DialError));
+            return Err((status_text, ResponseError::DialRefused));
         }
 
         Ok(addrs)
@@ -316,10 +316,6 @@ impl<'a> AsServer<'a> {
         demanded: Vec<Multiaddr>,
         observed_remote_at: &Multiaddr,
     ) -> Vec<Multiaddr> {
-        // Skip if the observed address is a relay address.
-        if observed_remote_at.iter().any(|p| p == Protocol::P2pCircuit) {
-            return Vec::new();
-        }
         let observed_ip = match observed_remote_at
             .into_iter()
             .find(|p| matches!(p, Protocol::Ip4(_) | Protocol::Ip6(_)))
@@ -417,23 +413,4 @@ mod test {
             .with(Protocol::P2p(peer_id.into()));
         assert_eq!(filtered, vec![expected_1, expected_2]);
     }
-
-    #[test]
-    fn skip_relayed_addr() {
-        let peer_id = PeerId::random();
-        let observed_ip = random_ip();
-        // Observed address is relayed.
-        let observed_addr = Multiaddr::empty()
-            .with(observed_ip.clone())
-            .with(random_port())
-            .with(Protocol::P2p(PeerId::random().into()))
-            .with(Protocol::P2pCircuit)
-            .with(Protocol::P2p(peer_id.into()));
-        let demanded = Multiaddr::empty()
-            .with(random_ip())
-            .with(random_port())
-            .with(Protocol::P2p(peer_id.into()));
-        let filtered = AsServer::filter_valid_addrs(peer_id, vec![demanded], &observed_addr);
-        assert!(filtered.is_empty());
-    }
 }