wgenging/logger: add log control knob

updates tailscale/corp#18625

control/controlknobs/controlknobs.go

@@ -72,6 +72,9 @@ type Knobs struct {
 	// ProbeUDPLifetime is whether the node should probe UDP path lifetime on
 	// the tail end of an active direct connection in magicsock.
 	ProbeUDPLifetime atomic.Bool
+
+	// NetworkFlowLoggingDstEnable is whether network flow logging on destinations for exit nodes is enabled.
+	NetworkFlowLoggingDstEnable atomic.Bool
 }
 
 // UpdateFromNodeAttributes updates k (if non-nil) based on the provided self
@@ -96,6 +99,7 @@ func (k *Knobs) UpdateFromNodeAttributes(capMap tailcfg.NodeCapMap) {
 		forceNfTables                 = has(tailcfg.NodeAttrLinuxMustUseNfTables)
 		seamlessKeyRenewal            = has(tailcfg.NodeAttrSeamlessKeyRenewal)
 		probeUDPLifetime              = has(tailcfg.NodeAttrProbeUDPLifetime)
+		networkFlowLoggingDstEnable   = has(tailcfg.NodeAttrNetworkFlowLoggingDst)
 	)
 
 	if has(tailcfg.NodeAttrOneCGNATEnable) {
@@ -118,6 +122,7 @@ func (k *Knobs) UpdateFromNodeAttributes(capMap tailcfg.NodeCapMap) {
 	k.LinuxForceNfTables.Store(forceNfTables)
 	k.SeamlessKeyRenewal.Store(seamlessKeyRenewal)
 	k.ProbeUDPLifetime.Store(probeUDPLifetime)
+	k.NetworkFlowLoggingDstEnable.Store(networkFlowLoggingDstEnable)
 }
 
 // AsDebugJSON returns k as something that can be marshalled with json.Marshal
@@ -141,5 +146,6 @@ func (k *Knobs) AsDebugJSON() map[string]any {
 		"LinuxForceNfTables":            k.LinuxForceNfTables.Load(),
 		"SeamlessKeyRenewal":            k.SeamlessKeyRenewal.Load(),
 		"ProbeUDPLifetime":              k.ProbeUDPLifetime.Load(),
+		"NewtorkFlowLoggingDstEnable":   k.NetworkFlowLoggingDstEnable.Load(),
 	}
 }

tailcfg/tailcfg.go

@@ -2230,6 +2230,9 @@ const (
 
 	// NodeAttrDisableWebClient disables using the web client.
 	NodeAttrDisableWebClient NodeCapability = "disable-web-client"
+
+	// NodeAttrNewtorkFLowLogging enables logging destination addresses for exit nodes.
+	NodeAttrNetworkFlowLoggingDst NodeCapability = "network-flow-logging-dst"
 )
 
 // SetDNSRequest is a request to add a DNS record.

wgengine/netlog/logger.go

@@ -56,6 +56,8 @@ type Logger struct {
 
 	addrs    map[netip.Addr]bool
 	prefixes map[netip.Prefix]bool
+
+	enableLogDst bool
 }
 
 // Running reports whether the logger is running.
@@ -92,7 +94,8 @@ var testClient *http.Client
 // The IP protocol and source port are always zero.
 // The sock is used to populated the PhysicalTraffic field in Message.
 // The netMon parameter is optional; if non-nil it's used to do faster interface lookups.
-func (nl *Logger) Startup(nodeID tailcfg.StableNodeID, nodeLogID, domainLogID logid.PrivateID, tun, sock Device, netMon *netmon.Monitor) error {
+// enableLogDst is a control knob boolean.
+func (nl *Logger) Startup(nodeID tailcfg.StableNodeID, nodeLogID, domainLogID logid.PrivateID, tun, sock Device, netMon *netmon.Monitor, enableLogDst bool) error {
 	nl.mu.Lock()
 	defer nl.mu.Unlock()
 	if nl.logger != nil {
@@ -130,7 +133,7 @@ func (nl *Logger) Startup(nodeID tailcfg.StableNodeID, nodeLogID, domainLogID lo
 		addrs := nl.addrs
 		prefixes := nl.prefixes
 		nl.mu.Unlock()
-		recordStatistics(nl.logger, nodeID, start, end, virtual, physical, addrs, prefixes)
+		recordStatistics(nl.logger, nodeID, start, end, virtual, physical, addrs, prefixes, nl.enableLogDst)
 	})
 
 	// Register the connection tracker into the TUN device.
@@ -147,10 +150,12 @@ func (nl *Logger) Startup(nodeID tailcfg.StableNodeID, nodeLogID, domainLogID lo
 	nl.sock = sock
 	nl.sock.SetStatistics(nl.stats)
 
+	nl.enableLogDst = enableLogDst
+
 	return nil
 }
 
-func recordStatistics(logger *logtail.Logger, nodeID tailcfg.StableNodeID, start, end time.Time, connstats, sockStats map[netlogtype.Connection]netlogtype.Counts, addrs map[netip.Addr]bool, prefixes map[netip.Prefix]bool) {
+func recordStatistics(logger *logtail.Logger, nodeID tailcfg.StableNodeID, start, end time.Time, connstats, sockStats map[netlogtype.Connection]netlogtype.Counts, addrs map[netip.Addr]bool, prefixes map[netip.Prefix]bool, enableLogDst bool) {
 	m := netlogtype.Message{NodeID: nodeID, Start: start.UTC(), End: end.UTC()}
 
 	classifyAddr := func(a netip.Addr) (isTailscale, withinRoute bool) {
@@ -179,7 +184,7 @@ func recordStatistics(logger *logtail.Logger, nodeID tailcfg.StableNodeID, start
 			m.SubnetTraffic = append(m.SubnetTraffic, netlogtype.ConnectionCounts{Connection: conn, Counts: cnts})
 		default:
 			const anonymize = true
-			if anonymize {
+			if anonymize && !enableLogDst {
 				// Only preserve the address if it is a Tailscale IP address.
 				srcOrig, dstOrig := conn.Src, conn.Dst
 				conn = netlogtype.Connection{} // scrub everything by default

wgengine/userspace.go

@@ -932,8 +932,9 @@ func (e *userspaceEngine) Reconfig(cfg *wgcfg.Config, routerCfg *router.Config,
 	if netLogRunning && !e.networkLogger.Running() {
 		nid := cfg.NetworkLogging.NodeID
 		tid := cfg.NetworkLogging.DomainID
+		enableLogDst := e.controlKnobs.NetworkFlowLoggingDstEnable.Load()
 		e.logf("wgengine: Reconfig: starting up network logger (node:%s tailnet:%s)", nid.Public(), tid.Public())
-		if err := e.networkLogger.Startup(cfg.NodeID, nid, tid, e.tundev, e.magicConn, e.netMon); err != nil {
+		if err := e.networkLogger.Startup(cfg.NodeID, nid, tid, e.tundev, e.magicConn, e.netMon, enableLogDst); err != nil {
 			e.logf("wgengine: Reconfig: error starting up network logger: %v", err)
 		}
 		e.networkLogger.ReconfigRoutes(routerCfg)