From 85138d31831107601cca9f40804e88277a99caf3 Mon Sep 17 00:00:00 2001
From: Brad Fitzpatrick <bradfitz@tailscale.com>
Date: Mon, 22 Mar 2021 21:41:53 -0700
Subject: [PATCH] health: track whether any network interface is up

Fixes #1562

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
---
 health/health.go      | 12 ++++++++++++
 wgengine/userspace.go |  1 +
 2 files changed, 13 insertions(+)

diff --git a/health/health.go b/health/health.go
index 81d346d15..3da92b8a4 100644
--- a/health/health.go
+++ b/health/health.go
@@ -35,6 +35,7 @@ var (
 	lastMapRequestHeard     time.Time // time we got a 200 from control for a MapRequest
 	ipnState                string
 	ipnWantRunning          bool
+	anyInterfaceUp          = true // until told otherwise
 )
 
 // Subsystem is the name of a subsystem whose health can be monitored.
@@ -195,6 +196,14 @@ func SetIPNState(state string, wantRunning bool) {
 	selfCheckLocked()
 }
 
+// SetAnyInterfaceUp sets whether any network interface is up.
+func SetAnyInterfaceUp(up bool) {
+	mu.Lock()
+	defer mu.Unlock()
+	anyInterfaceUp = up
+	selfCheckLocked()
+}
+
 func timerSelfCheck() {
 	mu.Lock()
 	defer mu.Unlock()
@@ -213,6 +222,9 @@ func selfCheckLocked() {
 }
 
 func overallErrorLocked() error {
+	if !anyInterfaceUp {
+		return errors.New("network down")
+	}
 	if ipnState != "Running" || !ipnWantRunning {
 		return fmt.Errorf("state=%v, wantRunning=%v", ipnState, ipnWantRunning)
 	}
diff --git a/wgengine/userspace.go b/wgengine/userspace.go
index 72d25db4e..c9d966a99 100644
--- a/wgengine/userspace.go
+++ b/wgengine/userspace.go
@@ -1272,6 +1272,7 @@ func (e *userspaceEngine) linkChange(changed bool, cur *interfaces.State) {
 		e.logf("[v1] LinkChange: minor")
 	}
 
+	health.SetAnyInterfaceUp(up)
 	e.magicConn.SetNetworkUp(up)
 
 	why := "link-change-minor"