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wgengine: flush DNS cache after major link change.
Windows has a public dns.Flush used in router_windows.go. However that won't work for platforms like Linux, where we need a different flush mechanism for resolved versus other implementations. We're instead adding a FlushCaches method to the dns Manager, which can be made to work on all platforms as needed. Fixes https://github.com/tailscale/tailscale/issues/2132 Signed-off-by: Denton Gentry <dgentry@tailscale.com>
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12
net/dns/flush_default.go
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12
net/dns/flush_default.go
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@ -0,0 +1,12 @@
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// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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//go:build !windows
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// +build !windows
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package dns
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func flushCaches() error {
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return nil
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}
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@ -9,11 +9,20 @@
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"os/exec"
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"os/exec"
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)
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)
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// Flush clears the local resolver cache.
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func flushCaches() error {
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func Flush() error {
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out, err := exec.Command("ipconfig", "/flushdns").CombinedOutput()
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out, err := exec.Command("ipconfig", "/flushdns").CombinedOutput()
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if err != nil {
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if err != nil {
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return fmt.Errorf("%v (output: %s)", err, out)
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return fmt.Errorf("%v (output: %s)", err, out)
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}
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}
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return nil
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return nil
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}
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}
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// Flush clears the local resolver cache.
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//
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// Only Windows has a public dns.Flush, needed in router_windows.go. Other
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// platforms like Linux need a different flush implementation depending on
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// the DNS manager. There is a FlushCaches method on the manager which
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// can be used on all platforms.
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func Flush() error {
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return flushCaches()
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}
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@ -212,6 +212,10 @@ func (m *Manager) Down() error {
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return nil
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return nil
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}
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}
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func (m *Manager) FlushCaches() error {
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return flushCaches()
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}
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// Cleanup restores the system DNS configuration to its original state
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// Cleanup restores the system DNS configuration to its original state
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// in case the Tailscale daemon terminated without closing the router.
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// in case the Tailscale daemon terminated without closing the router.
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// No other state needs to be instantiated before this runs.
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// No other state needs to be instantiated before this runs.
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@ -1160,6 +1160,11 @@ func (e *userspaceEngine) linkChange(changed bool, cur *interfaces.State) {
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health.SetAnyInterfaceUp(up)
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health.SetAnyInterfaceUp(up)
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e.magicConn.SetNetworkUp(up)
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e.magicConn.SetNetworkUp(up)
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if !up || changed {
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if err := e.dns.FlushCaches(); err != nil {
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e.logf("wgengine: dns flush failed after major link change: %v", err)
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}
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}
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// Hacky workaround for Linux DNS issue 2458: on
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// Hacky workaround for Linux DNS issue 2458: on
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// suspend/resume or whenever NetworkManager is started, it
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// suspend/resume or whenever NetworkManager is started, it
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