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fa1303d632
Updates tailscale/corp#18960 iOS uses Apple's NetworkMonitor to track the default interface and there's no reason we shouldn't also use this on macOS, for the same reasons noted in the comments for why this change was made on iOS. This eliminates the need to load and parse the routing table when querying the defaultRouter() in almost all cases. A slight modification here (on both platforms) to fallback to the default BSD logic in the unhappy-path rather than making assumptions that may not hold. If netmon is eventually parsing AF_ROUTE and able to give a consistently correct answer for the default interface index, we can fall back to that and eliminate the Swift dependency. Signed-off-by: Jonathan Nobels <jonathan@tailscale.com>
99 lines
3.0 KiB
Go
99 lines
3.0 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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//go:build darwin || ios
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package netmon
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import (
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"log"
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"net"
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"tailscale.com/syncs"
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)
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var (
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lastKnownDefaultRouteIfName syncs.AtomicValue[string]
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)
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// UpdateLastKnownDefaultRouteInterface is called by ipn-go-bridge in the iOS app when
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// our NWPathMonitor instance detects a network path transition.
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func UpdateLastKnownDefaultRouteInterface(ifName string) {
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if ifName == "" {
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return
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}
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if old := lastKnownDefaultRouteIfName.Swap(ifName); old != ifName {
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log.Printf("defaultroute_darwin: update from Swift, ifName = %s (was %s)", ifName, old)
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}
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}
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func defaultRoute() (d DefaultRouteDetails, err error) {
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// We cannot rely on the delegated interface data on darwin. The NetworkExtension framework
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// seems to set the delegate interface only once, upon the *creation* of the VPN tunnel.
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// If a network transition (e.g. from Wi-Fi to Cellular) happens while the tunnel is
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// connected, it will be ignored and we will still try to set Wi-Fi as the default route
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// because the delegated interface is not updated by the NetworkExtension framework.
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//
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// We work around this on the Swift side with a NWPathMonitor instance that observes
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// the interface name of the first currently satisfied network path. Our Swift code will
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// call into `UpdateLastKnownDefaultRouteInterface`, so we can rely on that when it is set.
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//
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// If for any reason the Swift machinery didn't work and we don't get any updates, we will
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// fallback to the BSD logic.
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// Start by getting all available interfaces.
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interfaces, err := netInterfaces()
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if err != nil {
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log.Printf("defaultroute_darwin: could not get interfaces: %v", err)
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return d, ErrNoGatewayIndexFound
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}
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getInterfaceByName := func(name string) *Interface {
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for _, ifc := range interfaces {
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if ifc.Name != name {
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continue
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}
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if !ifc.IsUp() {
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log.Printf("defaultroute_darwin: %s is down", name)
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return nil
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}
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addrs, _ := ifc.Addrs()
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if len(addrs) == 0 {
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log.Printf("defaultroute_darwin: %s has no addresses", name)
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return nil
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}
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return &ifc
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}
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return nil
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}
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// Did Swift set lastKnownDefaultRouteInterface? If so, we should use it and don't bother
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// with anything else. However, for sanity, do check whether Swift gave us with an interface
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// that exists, is up, and has an address.
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if swiftIfName := lastKnownDefaultRouteIfName.Load(); swiftIfName != "" {
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ifc := getInterfaceByName(swiftIfName)
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if ifc != nil {
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d.InterfaceName = ifc.Name
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d.InterfaceIndex = ifc.Index
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log.Printf("defaultroute_darwin: using lastKnownDefaultRouteInterface %s %v", d.InterfaceName, d.InterfaceIndex)
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return d, nil
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}
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}
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// Fallback to the BSD logic
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idx, err := DefaultRouteInterfaceIndex()
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if err != nil {
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return d, err
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}
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iface, err := net.InterfaceByIndex(idx)
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if err != nil {
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return d, err
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}
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d.InterfaceName = iface.Name
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d.InterfaceIndex = idx
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log.Printf("defaultroute_darwin: using table dervied default if %s %v", d.InterfaceName, d.InterfaceIndex)
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return d, nil
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}
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