health: track whether magicsock receive functions are running

Signed-off-by: Josh Bleecher Snyder <josharian@gmail.com>

health/health.go

@@ -36,6 +36,11 @@
 	ipnState                string
 	ipnWantRunning          bool
 	anyInterfaceUp          = true // until told otherwise
+
+	receiveIPv4Running bool
+	receiveIPv6Started bool
+	receiveIPv6Running bool
+	receiveDERPRunning bool
 )
 
 // Subsystem is the name of a subsystem whose health can be monitored.
@@ -213,6 +218,18 @@ func SetAnyInterfaceUp(up bool) {
 	selfCheckLocked()
 }
 
+func SetReceiveIPv4Running(running bool) { setHealthBool(&receiveIPv4Running, running) }
+func SetReceiveIPv6Started(running bool) { setHealthBool(&receiveIPv6Started, running) }
+func SetReceiveIPv6Running(running bool) { setHealthBool(&receiveIPv6Running, running) }
+func SetReceiveDERPRunning(running bool) { setHealthBool(&receiveDERPRunning, running) }
+
+func setHealthBool(dst *bool, b bool) {
+	mu.Lock()
+	defer mu.Unlock()
+	*dst = b
+	selfCheckLocked()
+}
+
 func timerSelfCheck() {
 	mu.Lock()
 	defer mu.Unlock()
@@ -263,6 +280,15 @@ func overallErrorLocked() error {
 	_ = lastMapRequestHeard
 
 	var errs []error
+	if !receiveIPv4Running {
+		errs = append(errs, errors.New("receiveIPv4 not running"))
+	}
+	if !receiveDERPRunning {
+		errs = append(errs, errors.New("receiveDERP not running"))
+	}
+	if receiveIPv6Started && !receiveIPv6Running {
+		errs = append(errs, errors.New("receiveIPv6 not running"))
+	}
 	for sys, err := range sysErr {
 		if err == nil || sys == SysOverall {
 			continue

wgengine/magicsock/magicsock.go

@@ -1581,6 +1581,9 @@ func (c *Conn) noteRecvActivityFromEndpoint(e conn.Endpoint) {
 
 // receiveIPv6 receives a UDP IPv6 packet. It is called by wireguard-go.
 func (c *Conn) receiveIPv6(b []byte) (int, conn.Endpoint, error) {
+	health.SetReceiveIPv6Started(true)
+	health.SetReceiveIPv6Running(true)
+	defer health.SetReceiveIPv6Running(false)
 	for {
 		n, ipp, err := c.pconn6.ReadFromNetaddr(b)
 		if err != nil {
@@ -1594,6 +1597,8 @@ func (c *Conn) receiveIPv6(b []byte) (int, conn.Endpoint, error) {
 
 // receiveIPv4 receives a UDP IPv4 packet. It is called by wireguard-go.
 func (c *Conn) receiveIPv4(b []byte) (n int, ep conn.Endpoint, err error) {
+	health.SetReceiveIPv4Running(true)
+	defer health.SetReceiveIPv4Running(false)
 	for {
 		n, ipp, err := c.pconn4.ReadFromNetaddr(b)
 		if err != nil {
@@ -1646,6 +1651,8 @@ func (c *Conn) receiveIP(b []byte, ipp netaddr.IPPort, cache *ippEndpointCache)
 // If the packet was a disco message or the peer endpoint wasn't
 // found, the returned error is errLoopAgain.
 func (c *connBind) receiveDERP(b []byte) (n int, ep conn.Endpoint, err error) {
+	health.SetReceiveDERPRunning(true)
+	defer health.SetReceiveDERPRunning(false)
 	for dm := range c.derpRecvCh {
 		if c.Closed() {
 			break
@@ -2436,6 +2443,7 @@ func (c *connBind) Close() error {
 	// Unblock all outstanding receives.
 	c.pconn4.Close()
 	if c.pconn6 != nil {
+		health.SetReceiveIPv6Started(false)
 		c.pconn6.Close()
 	}
 	// Send an empty read result to unblock receiveDERP,