fix(windows): set MTU on tunnel interface (#2990)

rust/Cargo.lock

@@ -1222,6 +1222,7 @@ dependencies = [
  "url",
  "uuid",
  "webrtc",
+ "windows 0.52.0",
  "wintun",
 ]
 
@@ -2064,6 +2065,7 @@ dependencies = [
  "tracing-android",
  "uuid",
  "webrtc",
+ "windows 0.52.0",
  "wintun",
 ]
 

rust/connlib/shared/Cargo.toml

@@ -53,3 +53,10 @@ rtnetlink = { version = "0.13", default-features = false, features = ["tokio_soc
 # Windows tunnel dependencies
 [target.'cfg(target_os = "windows")'.dependencies]
 wintun = "0.3.2"
+
+# Windows Win32 API
+[target.'cfg(windows)'.dependencies.windows]
+version = "0.52.0"
+features = [
+  "Win32_Foundation",
+]

rust/connlib/shared/src/error.rs

@@ -144,6 +144,9 @@ pub enum ConnlibError {
     #[error(transparent)]
     Uuid(#[from] uuid::Error),
     #[cfg(target_os = "windows")]
+    #[error("Windows error: {0}")]
+    WindowsError(#[from] windows::core::Error),
+    #[cfg(target_os = "windows")]
     #[error(transparent)]
     Wintun(#[from] wintun::Error),
     #[error("Token has expired")]

rust/connlib/tunnel/Cargo.toml

@@ -50,3 +50,13 @@ tracing-android = "0.2"
 [target.'cfg(target_os = "windows")'.dependencies]
 uuid = { version = "1.5.0", features = ["v4"] }
 wintun = "0.3.2"
+
+# Windows Win32 API
+[target.'cfg(windows)'.dependencies.windows]
+version = "0.52.0"
+features = [
+  "Win32_Foundation",
+  "Win32_NetworkManagement_IpHelper",
+  "Win32_NetworkManagement_Ndis",
+  "Win32_Networking_WinSock",
+]

rust/connlib/tunnel/src/device_channel/tun_windows.rs

@@ -10,6 +10,13 @@ use std::{
     task::{ready, Context, Poll},
 };
 use tokio::sync::mpsc;
+use windows::Win32::{
+    NetworkManagement::{
+        IpHelper::{GetIpInterfaceEntry, SetIpInterfaceEntry, MIB_IPINTERFACE_ROW},
+        Ndis::NET_LUID_LH,
+    },
+    Networking::WinSock::AF_INET,
+};
 
 // TODO: Double-check that all these get dropped gracefully on disconnect
 pub struct Tun {
@@ -34,6 +41,8 @@ impl Drop for Tun {
 // Hides Powershell's console on Windows
 // <https://stackoverflow.com/questions/59692146/is-it-possible-to-use-the-standard-library-to-spawn-a-process-without-showing-th#60958956>
 const CREATE_NO_WINDOW: u32 = 0x08000000;
+// Copied from tun_linux.rs
+const DEFAULT_MTU: u32 = 1280;
 
 impl Tun {
     pub fn new(config: &InterfaceConfig) -> Result<Self> {
@@ -86,6 +95,8 @@ impl Tun {
             .stdout(Stdio::null())
             .status()?;
 
+        set_iface_config(adapter.get_luid(), DEFAULT_MTU)?;
+
         // Set our DNS IP as the DNS server for our interface
         // TODO: Lots of issues with this. Windows does seem to use it, but I'm not sure why. And there's a delay before some Firefox windows pick it up. Curl might be picking it up faster because its DNS cache starts cold every time.
         Command::new("powershell")
@@ -199,3 +210,30 @@ fn start_recv_thread(
         tracing::debug!("recv_task exiting gracefully");
     })
 }
+
+/// Sets MTU on the interface
+/// TODO: Set IP and other things in here too, so the code is more organized
+fn set_iface_config(luid: wintun::NET_LUID_LH, mtu: u32) -> Result<()> {
+    // Safety: Both NET_LUID_LH unions should be the same. We're just copying out
+    // the u64 value and re-wrapping it, since wintun doesn't refer to the windows
+    // crate's version of NET_LUID_LH.
+    let luid = NET_LUID_LH {
+        Value: unsafe { luid.Value },
+    };
+
+    let mut row = MIB_IPINTERFACE_ROW {
+        Family: AF_INET,
+        InterfaceLuid: luid,
+        ..Default::default()
+    };
+
+    unsafe { GetIpInterfaceEntry(&mut row) }?;
+
+    row.NlMtu = mtu;
+    // https://stackoverflow.com/questions/54857292/setipinterfaceentry-returns-error-invalid-parameter
+    row.SitePrefixLength = 0;
+
+    // Ignore error if we can't set everything
+    unsafe { SetIpInterfaceEntry(&mut row) }?;
+    Ok(())
+}

rust/windows-client/src-tauri/Cargo.toml

@@ -49,11 +49,10 @@ wintun = "0.3.2"
 version = "0.52.0"
 features = [
   "Win32_Foundation",
+  # Needed for deep_link module
   "Win32_Security",
-  "Win32_System_LibraryLoader",
+  # Needed for deep_link module
   "Win32_System_SystemServices",
-  "Win32_UI_Shell",
-  "Win32_UI_WindowsAndMessaging",
 ]
 
 [features]