refactor(probe/ebpf): make ebpf setup safer

It was possible for `t.ebpfTracker` to change underneath this code
while running on a background goroutine, so change it to take
`ebpfTracker` as a parameter.

While we're here, rename the functions to better match what they do.

probe/endpoint/connection_tracker.go

@@ -34,7 +34,7 @@ func newConnectionTracker(conf ReporterConfig) connectionTracker {
 		et, err := newEbpfTracker()
 		if err == nil {
 			ct.ebpfTracker = et
-			go ct.getInitialState()
+			go feedEBPFInitialState(conf, et)
 			return ct
 		}
 		log.Warnf("Error setting up the eBPF tracker, falling back to proc scanning: %v", err)
@@ -86,7 +86,7 @@ func (t *connectionTracker) ReportConnections(rpt *report.Report) {
 			log.Warnf("ebpf tracker died, restarting it")
 			err := t.ebpfTracker.restart()
 			if err == nil {
-				t.getInitialState()
+				feedEBPFInitialState(t.conf, t.ebpfTracker)
 				t.performEbpfTrack(rpt, hostNodeID)
 				return
 			}
@@ -108,13 +108,13 @@ func (t *connectionTracker) ReportConnections(rpt *report.Report) {
 	}
 }
 
-func (t *connectionTracker) existingFlows() map[string]fourTuple {
+func existingFlowsFromConntrack(conf ReporterConfig) map[string]fourTuple {
 	seenTuples := map[string]fourTuple{}
-	if !t.conf.UseConntrack {
+	if !conf.UseConntrack {
 		// log.Warnf("Not using conntrack: disabled")
-	} else if err := IsConntrackSupported(t.conf.ProcRoot); err != nil {
+	} else if err := IsConntrackSupported(conf.ProcRoot); err != nil {
 		log.Warnf("Not using conntrack: not supported by the kernel: %s", err)
-	} else if existingFlows, err := conntrack.ConnectionsSize(t.conf.BufferSize); err != nil {
+	} else if existingFlows, err := conntrack.ConnectionsSize(conf.BufferSize); err != nil {
 		log.Errorf("conntrack existingConnections error: %v", err)
 	} else {
 		for _, f := range existingFlows {
@@ -147,18 +147,20 @@ func (t *connectionTracker) performWalkProc(rpt *report.Report, hostNodeID strin
 	return nil
 }
 
-// getInitialState runs conntrack and proc parsing synchronously only
+// getEBPFInitialState runs conntrack and proc parsing synchronously only
 // once to initialize ebpfTracker
-func (t *connectionTracker) getInitialState() {
+// This is run on a background goroutine during initial setup, so does
+// not take *connectionTracker which could change under it
+func feedEBPFInitialState(conf ReporterConfig, ebpfTracker *EbpfTracker) {
 	var processCache *process.CachingWalker
-	walker := process.NewWalker(t.conf.ProcRoot, true)
+	walker := process.NewWalker(conf.ProcRoot, true)
 	processCache = process.NewCachingWalker(walker)
 	processCache.Tick()
 
-	scanner := procspy.NewSyncConnectionScanner(processCache, t.conf.SpyProcs)
+	scanner := procspy.NewSyncConnectionScanner(processCache, conf.SpyProcs)
 
 	// Consult conntrack to get the initial state
-	seenTuples := t.existingFlows()
+	seenTuples := existingFlowsFromConntrack(conf)
 
 	conns, err := scanner.Connections()
 	if err != nil {
@@ -173,7 +175,7 @@ func (t *connectionTracker) getInitialState() {
 		}
 	})
 
-	t.ebpfTracker.feedInitialConnections(conns, seenTuples, processesWaitingInAccept, report.MakeHostNodeID(t.conf.HostID))
+	ebpfTracker.feedInitialConnections(conns, seenTuples, processesWaitingInAccept, report.MakeHostNodeID(conf.HostID))
 }
 
 func (t *connectionTracker) performEbpfTrack(rpt *report.Report, hostNodeID string) error {