Fix duplicated incoming packets when split tunneling is enabled

CHANGELOG.md

@@ -41,6 +41,7 @@ Line wrap the file at 100 chars.                                              Th
 #### macOS
 - Fix Apple services not working by forcing stray connections out through the VPN tunnel. The
   "bypass" toggle has been removed.
+- Fix packets being duplicated on LAN when split tunneling is enabled.
 
 
 ## [2024.6-beta1] - 2024-09-26

talpid-core/src/firewall/macos.rs

@@ -119,6 +119,15 @@ impl Firewall {
             }
         }
 
+        if let Some(endpoint) = policy.allowed_endpoint() {
+            // Keep states to the allowed endpoint.
+            // Note that we're not taking into account allowed clients here, because it's highly
+            // impractical.
+            if endpoint.endpoint.address == remote_address {
+                return Ok(false);
+            }
+        }
+
         let Some(peer) = policy.peer_endpoint().map(|endpoint| endpoint.endpoint) else {
             // If there's no peer, there's also no tunnel. We have no states to preserve
             return Ok(true);

talpid-core/src/firewall/mod.rs

@@ -143,6 +143,20 @@ impl FirewallPolicy {
         }
     }
 
+    /// Return the allowed endpoint, if available
+    pub fn allowed_endpoint(&self) -> Option<&AllowedEndpoint> {
+        match self {
+            FirewallPolicy::Connecting {
+                allowed_endpoint, ..
+            }
+            | FirewallPolicy::Blocked {
+                allowed_endpoint: Some(allowed_endpoint),
+                ..
+            } => Some(allowed_endpoint),
+            _ => None,
+        }
+    }
+
     /// Return tunnel metadata, if available
     pub fn tunnel(&self) -> Option<&crate::tunnel::TunnelMetadata> {
         match self {

talpid-core/src/split_tunnel/macos/tun.rs

@@ -22,9 +22,10 @@ use pnet_packet::{
 use std::{
     ffi::{c_uint, CStr},
     io::{self, IoSlice, Write},
-    net::{Ipv4Addr, Ipv6Addr},
+    net::{IpAddr, Ipv4Addr, Ipv6Addr},
 };
 use talpid_routing::RouteManagerHandle;
+use talpid_types::net::{ALLOWED_LAN_MULTICAST_NETS, ALLOWED_LAN_NETS};
 use tokio::{
     io::{AsyncReadExt, AsyncWriteExt},
     sync::broadcast,
@@ -676,6 +677,10 @@ async fn handle_incoming_data_v4(
         log::trace!("Dropping packet to VPN IP on default interface");
         return;
     }
+    if is_private_ip(IpAddr::from(ip.get_source())) {
+        // Drop packets from private IPs
+        return;
+    }
 
     fix_ipv4_checksums(&mut ip, None, Some(vpn_addr));
 
@@ -698,6 +703,10 @@ async fn handle_incoming_data_v6(
         log::trace!("Dropping packet to VPN IP on default interface");
         return;
     }
+    if is_private_ip(IpAddr::from(ip.get_source())) {
+        // Drop packets from private IPs
+        return;
+    }
 
     fix_ipv6_checksums(&mut ip, None, Some(vpn_addr));
 
@@ -710,6 +719,13 @@ async fn handle_incoming_data_v6(
     }
 }
 
+fn is_private_ip(ip: IpAddr) -> bool {
+    ALLOWED_LAN_NETS
+        .iter()
+        .chain(ALLOWED_LAN_MULTICAST_NETS.iter())
+        .any(|net| net.contains(ip))
+}
+
 // Recalculate L3 and L4 checksums. Silently fail on error
 fn fix_ipv4_checksums(
     ip: &mut MutableIpv4Packet<'_>,