Remove Apple services workarounds for unaffected macOS versions

CHANGELOG.md

@@ -50,6 +50,8 @@ Line wrap the file at 100 chars.                                              Th
 
 #### macOS
 - Fix packets being duplicated on LAN when split tunneling is enabled.
+- Fix DNS issues caused by forcibly using a local DNS resolver in all states.
+  Note that this fix is not present on macOS versions between 14.6 and 15.1.
 
 ### Security
 - Disable unix signal handler in release builds. The code was not signal safe and could potentially

talpid-core/src/dns/macos.rs

@@ -78,6 +78,7 @@ impl State {
         }
     }
 
+    /// Construct [`DnsSettings`] from the arguments and apply the desired addresses to all network services.
     fn apply_new_config(
         &mut self,
         store: &SCDynamicStore,
@@ -375,8 +376,9 @@ impl InterfaceSettings {
 unsafe impl Send for InterfaceSettings {}
 
 pub struct DnsMonitor {
+    /// The backing "System Configuration framework" store, which allow us to access and detect
+    /// changes to the device's network configuration.
     store: SCDynamicStore,
-
     /// The current DNS injection state. If this is `None` it means we are not injecting any DNS.
     /// When it's `Some(state)` we are actively making sure `state.dns_settings` is configured
     /// on all network interfaces.
@@ -403,6 +405,10 @@ impl super::DnsMonitorT for DnsMonitor {
         })
     }
 
+    /// Update the system config to use the DNS `config`.
+    ///
+    /// Note that the `interface` parameter does nothing on macOS. Since we can't configure DNS
+    /// on the tunnel interface, we have to configure all interfaces.
     fn set(&mut self, interface: &str, config: ResolvedDnsConfig) -> Result<()> {
         let port = config.port;
         let servers: Vec<_> = config.addresses().collect();

talpid-core/src/firewall/macos.rs

@@ -1,17 +1,20 @@
-use super::{FirewallArguments, FirewallPolicy};
+use std::env;
+use std::io;
+use std::net::{IpAddr, Ipv4Addr};
+use std::ptr;
+use std::sync::LazyLock;
+
 use ipnetwork::IpNetwork;
 use libc::{c_int, sysctlbyname};
-use pfctl::{DropAction, FilterRuleAction, Ip, Uid};
-use std::{
-    env, io,
-    net::{IpAddr, Ipv4Addr},
-    ptr,
-};
+use pfctl::{DropAction, FilterRuleAction, Ip, RedirectRule, Uid};
 use subslice::SubsliceExt;
 use talpid_types::net::{
-    self, AllowedEndpoint, AllowedTunnelTraffic, ALLOWED_LAN_MULTICAST_NETS, ALLOWED_LAN_NETS,
+    AllowedEndpoint, AllowedTunnelTraffic, TransportProtocol, ALLOWED_LAN_MULTICAST_NETS,
+    ALLOWED_LAN_NETS,
 };
 
+use super::{FirewallArguments, FirewallPolicy};
+
 pub use pfctl::Error;
 
 type Result<T> = std::result::Result<T, Error>;
@@ -20,6 +23,27 @@ type Result<T> = std::result::Result<T, Error>;
 /// replaced by allowing the anchor name to be configured from the public API of this crate.
 const ANCHOR_NAME: &str = "mullvad";
 
+/// If NAT firewall rules should be applied to force Apple services through the tunnel.
+///
+/// macOS versions 14.6 <= x < 15.1 were affected by a bug where Apple services tried to bypass the
+/// tunnel by going out on the physical interface instead. To mitigate this and force all traffic
+/// to go through the tunnel we added NAT filtering rules to redirect traffic all deviating traffic
+/// to the tunnel.
+///
+/// This is not something that we deem is necessary otherwise, and as such we disable NAT filtering
+/// on macOS versions that are unaffected by this naughty bug, but keep it were it is necessary for
+/// Apple services to function properly together with a VPN.
+pub static NAT_WORKAROUND: LazyLock<bool> = LazyLock::new(|| {
+    use talpid_platform_metadata::MacosVersion;
+    let version = MacosVersion::new().expect("Could not detect macOS version");
+    let v = |s| MacosVersion::from_raw_version(s).unwrap();
+    let apply_workaround = v("14.6") <= version && version < v("15.1");
+    if apply_workaround {
+        log::debug!("Using NAT redirect workaround");
+    };
+    apply_workaround
+});
+
 pub struct Firewall {
     pf: pfctl::PfCtl,
     pf_was_enabled: Option<bool>,
@@ -33,7 +57,7 @@ impl Firewall {
 
     pub fn new() -> Result<Self> {
         // Allows controlling whether firewall rules should log to pflog0. Useful for debugging the
-        // rules.
+        // rules. The firewall rules can be inspected by running `tcpdump -netttti pflog0`.
         let firewall_debugging = env::var("TALPID_FIREWALL_DEBUG");
         let rule_logging = match firewall_debugging.as_ref().map(String::as_str) {
             Ok("pass") => RuleLogging::Pass,
@@ -189,7 +213,9 @@ impl Firewall {
         anchor_change.set_scrub_rules(Self::get_scrub_rules()?);
         anchor_change.set_filter_rules(new_filter_rules);
         anchor_change.set_redirect_rules(self.get_dns_redirect_rules(policy)?);
-        anchor_change.set_nat_rules(self.get_nat_rules(policy)?);
+        if *NAT_WORKAROUND {
+            anchor_change.set_nat_rules(self.get_nat_rules(policy)?);
+        }
         self.pf.set_rules(ANCHOR_NAME, anchor_change)?;
 
         Ok(())
@@ -208,24 +234,44 @@ impl Firewall {
         &mut self,
         policy: &FirewallPolicy,
     ) -> Result<Vec<pfctl::RedirectRule>> {
-        let redirect_rules = match policy {
-            FirewallPolicy::Connected { dns_config, .. } if dns_config.is_loopback() => vec![],
-            FirewallPolicy::Blocked {
-                dns_redirect_port, ..
-            }
-            | FirewallPolicy::Connecting {
-                dns_redirect_port, ..
+        /// Redirect DNS requests to `port`. Technically this redirects UDP on port 53 to `port`.
+        ///
+        /// For this to work as expected, please make sure a DNS resolver is running on `port`.
+        fn redirect_dns_to(port: u16) -> Result<Vec<RedirectRule>> {
+            let redirect_dns = pfctl::RedirectRuleBuilder::default()
+                .action(pfctl::RedirectRuleAction::Redirect)
+                .interface("lo0")
+                .proto(pfctl::Proto::Udp)
+                .to(pfctl::Port::from(53))
+                .redirect_to(pfctl::Port::from(port))
+                .build()?;
+            Ok(vec![redirect_dns])
+        }
+
+        let redirect_rules = if *crate::resolver::LOCAL_DNS_RESOLVER {
+            match policy {
+                FirewallPolicy::Connected { dns_config, .. } if dns_config.is_loopback() => {
+                    vec![]
+                }
+                FirewallPolicy::Blocked {
+                    dns_redirect_port, ..
+                }
+                | FirewallPolicy::Connecting {
+                    dns_redirect_port, ..
+                }
+                | FirewallPolicy::Connected {
+                    dns_redirect_port, ..
+                } => redirect_dns_to(*dns_redirect_port)?,
             }
-            | FirewallPolicy::Connected {
-                dns_redirect_port, ..
-            } => {
-                vec![pfctl::RedirectRuleBuilder::default()
-                    .action(pfctl::RedirectRuleAction::Redirect)
-                    .interface("lo0")
-                    .proto(pfctl::Proto::Udp)
-                    .to(pfctl::Port::from(53))
-                    .redirect_to(pfctl::Port::from(*dns_redirect_port))
-                    .build()?]
+        } else {
+            // Only apply redirect rules in the blocked state if we should *not* use our local DNS
+            // resolver, since it will be running in the blocked state to work with Apple's captive
+            // portal check.
+            match policy {
+                FirewallPolicy::Blocked {
+                    dns_redirect_port, ..
+                } => redirect_dns_to(*dns_redirect_port)?,
+                FirewallPolicy::Connecting { .. } | FirewallPolicy::Connected { .. } => vec![],
             }
         };
         Ok(redirect_rules)
@@ -402,7 +448,9 @@ impl Firewall {
                         &mut self.get_split_tunnel_rules(&tunnel.interface, redirect_interface)?,
                     );
                 } else {
-                    rules.push(self.route_everything_to(&tunnel.interface)?);
+                    if *NAT_WORKAROUND {
+                        rules.push(self.route_everything_to(&tunnel.interface)?);
+                    }
                     rules.extend(self.get_allow_tunnel_rules(
                         tunnel.interface.as_str(),
                         &AllowedTunnelTraffic::All,
@@ -530,10 +578,7 @@ impl Firewall {
         Ok(rules)
     }
 
-    fn get_allow_relay_rule(
-        &self,
-        relay_endpoint: &net::AllowedEndpoint,
-    ) -> Result<pfctl::FilterRule> {
+    fn get_allow_relay_rule(&self, relay_endpoint: &AllowedEndpoint) -> Result<pfctl::FilterRule> {
         let pfctl_proto = as_pfctl_proto(relay_endpoint.endpoint.protocol);
 
         let mut builder = self.create_rule_builder(FilterRuleAction::Pass);
@@ -919,8 +964,10 @@ impl Firewall {
     fn add_anchor(&mut self) -> Result<()> {
         self.pf
             .try_add_anchor(ANCHOR_NAME, pfctl::AnchorKind::Scrub)?;
-        self.pf
-            .try_add_anchor(ANCHOR_NAME, pfctl::AnchorKind::Nat)?;
+        if *NAT_WORKAROUND {
+            self.pf
+                .try_add_anchor(ANCHOR_NAME, pfctl::AnchorKind::Nat)?;
+        }
         self.pf
             .try_add_anchor(ANCHOR_NAME, pfctl::AnchorKind::Filter)?;
         self.pf
@@ -931,6 +978,9 @@ impl Firewall {
     fn remove_anchor(&mut self) -> Result<()> {
         self.pf
             .try_remove_anchor(ANCHOR_NAME, pfctl::AnchorKind::Scrub)?;
+        // Opportunistically remove Nat anchor.
+        // This won't fail because `try_remove_anchor` promises to convert
+        // `pfctl::Error::AnchorDoesNotExist` to an `Ok(())` value.
         self.pf
             .try_remove_anchor(ANCHOR_NAME, pfctl::AnchorKind::Nat)?;
         self.pf
@@ -941,10 +991,10 @@ impl Firewall {
     }
 }
 
-fn as_pfctl_proto(protocol: net::TransportProtocol) -> pfctl::Proto {
+fn as_pfctl_proto(protocol: TransportProtocol) -> pfctl::Proto {
     match protocol {
-        net::TransportProtocol::Udp => pfctl::Proto::Udp,
-        net::TransportProtocol::Tcp => pfctl::Proto::Tcp,
+        TransportProtocol::Udp => pfctl::Proto::Udp,
+        TransportProtocol::Tcp => pfctl::Proto::Tcp,
     }
 }
 

talpid-core/src/resolver.rs

@@ -43,6 +43,40 @@ use hickory_server::{
 };
 use std::sync::LazyLock;
 
+/// If a local DNS resolver should be used at all times.
+///
+/// This setting does not affect the error or blocked state. In those states, we will want to use
+/// the local DNS resoler to work around Apple's captive portals check. Exactly how this is done is
+/// documented elsewhere.
+pub static LOCAL_DNS_RESOLVER: LazyLock<bool> = LazyLock::new(|| {
+    use talpid_platform_metadata::MacosVersion;
+    let version = MacosVersion::new().expect("Could not detect macOS version");
+    let v = |s| MacosVersion::from_raw_version(s).unwrap();
+    // Apple services tried to perform DNS lookups on the physical interface on some macOS
+    // versions, so we added redirect rules to always redirect DNS to our local DNS resolver.
+    // This seems to break some apps which do not like that we redirect DNS on port 53 to our local
+    // DNS resolver running on some other, arbitrary port, and so we disable this behaviour on
+    // macOS versions that are unaffected by this naughty bug.
+    //
+    // The workaround should only be applied to the affected macOS versions because some programs
+    // set the `skip filtering` pf flag on loopback, which meant that the pf filtering would break
+    // unexpectedly. We could clear the `skip filtering` flag to force pf filtering on loopback,
+    // but apparently it is good practice to enable `skip filtering` on loopback so we decided
+    // against this. Source: https://www.openbsd.org/faq/pf/filter.html
+    //
+    // It should be noted that most programs still works fine with this workaround enabled. Notably
+    // programs that use `getaddrinfo` would behave correctly when we redirect DNS to our local
+    // resolver, while some programs always used port 53 no matter what (nslookup for example).
+    // Also, most programs don't set the `skip filtering` pf flag on loopback, but some notable
+    // ones do for some reason. Orbstack is one such example, which meant that people running
+    // containers would run into the aforementioned issue.
+    let use_local_dns_resolver = v("14.6") <= version && version < v("15.1");
+    if use_local_dns_resolver {
+        log::debug!("Using local DNS resolver");
+    }
+    use_local_dns_resolver
+});
+
 const ALLOWED_RECORD_TYPES: &[RecordType] = &[RecordType::A, RecordType::CNAME];
 const CAPTIVE_PORTAL_DOMAINS: &[&str] = &["captive.apple.com", "netcts.cdn-apple.com"];
 
@@ -238,7 +272,7 @@ impl ResolverHandle {
         self.listening_port
     }
 
-    /// Set the DNS server to forward queries to
+    /// Set the DNS server to forward queries to `dns_servers`
     pub async fn enable_forward(&self, dns_servers: Vec<IpAddr>) {
         let (response_tx, response_rx) = oneshot::channel();
         let _ = self.tx.unbounded_send(ResolverMessage::SetConfig {

talpid-core/src/tunnel_state_machine/connected_state.rs

@@ -1,30 +1,29 @@
-use super::{
-    AfterDisconnect, ConnectingState, DisconnectingState, ErrorState, EventConsequence,
-    EventResult, SharedTunnelStateValues, TunnelCommand, TunnelCommandReceiver, TunnelState,
-    TunnelStateTransition,
-};
-use crate::{
-    dns::ResolvedDnsConfig,
-    firewall::FirewallPolicy,
-    tunnel::{TunnelEvent, TunnelMetadata},
-};
-use futures::{
-    channel::{mpsc, oneshot},
-    stream::Fuse,
-    StreamExt,
-};
+use futures::channel::{mpsc, oneshot};
+use futures::stream::Fuse;
+use futures::StreamExt;
+
 #[cfg(target_os = "android")]
 use talpid_tunnel::tun_provider::Error;
-use talpid_types::{
-    net::{AllowedClients, AllowedEndpoint, TunnelParameters},
-    tunnel::{ErrorStateCause, FirewallPolicyError},
-    BoxedError, ErrorExt,
-};
-
+use talpid_types::net::{AllowedClients, AllowedEndpoint, TunnelParameters};
+use talpid_types::tunnel::{ErrorStateCause, FirewallPolicyError};
+use talpid_types::{BoxedError, ErrorExt};
+
+#[cfg(target_os = "macos")]
+use crate::dns::DnsConfig;
+use crate::dns::ResolvedDnsConfig;
+use crate::firewall::FirewallPolicy;
+#[cfg(target_os = "macos")]
+use crate::resolver::LOCAL_DNS_RESOLVER;
 #[cfg(windows)]
 use crate::tunnel::TunnelMonitor;
+use crate::tunnel::{TunnelEvent, TunnelMetadata};
 
 use super::connecting_state::TunnelCloseEvent;
+use super::{
+    AfterDisconnect, ConnectingState, DisconnectingState, ErrorState, EventConsequence,
+    EventResult, SharedTunnelStateValues, TunnelCommand, TunnelCommandReceiver, TunnelState,
+    TunnelStateTransition,
+};
 
 pub(crate) type TunnelEventsReceiver =
     Fuse<mpsc::UnboundedReceiver<(TunnelEvent, oneshot::Sender<()>)>>;
@@ -171,27 +170,31 @@ impl ConnectedState {
 
         // On macOS, configure only the local DNS resolver
         #[cfg(target_os = "macos")]
-        if !dns_config.is_loopback() {
+        // We do not want to forward DNS queries to *our* local resolver if we do not run a local
+        // DNS resolver *or* if the DNS config points to a loopback address.
+        if dns_config.is_loopback() || !*LOCAL_DNS_RESOLVER {
+            log::debug!("Not enabling local DNS resolver");
+            shared_values
+                .dns_monitor
+                .set(&self.metadata.interface, dns_config)
+                .map_err(BoxedError::new)?;
+        } else {
+            log::debug!("Enabling local DNS resolver");
+            // Tell local DNS resolver to start forwarding DNS queries to whatever `dns_config`
+            // specifies as DNS.
             shared_values.runtime.block_on(
                 shared_values
                     .filtering_resolver
                     .enable_forward(dns_config.addresses().collect()),
             );
+            // Set system DNS to our local DNS resolver
+            let system_dns = DnsConfig::default().resolve(
+                &[std::net::Ipv4Addr::LOCALHOST.into()],
+                shared_values.filtering_resolver.listening_port(),
+            );
             shared_values
                 .dns_monitor
-                .set(
-                    "lo",
-                    crate::dns::DnsConfig::default().resolve(
-                        &[std::net::Ipv4Addr::LOCALHOST.into()],
-                        shared_values.filtering_resolver.listening_port(),
-                    ),
-                )
-                .map_err(BoxedError::new)?;
-        } else {
-            log::debug!("Not enabling DNS forwarding since loopback is used");
-            shared_values
-                .dns_monitor
-                .set(&self.metadata.interface, dns_config)
+                .set("lo", system_dns)
                 .map_err(BoxedError::new)?;
         }