Use the stack clock in iptables reaper

Updates #5939.

PiperOrigin-RevId: 418707213

pkg/tcpip/stack/iptables.go

@@ -180,7 +180,6 @@ func DefaultTables(clock tcpip.Clock, rand *rand.Rand) *IPTables {
 			clock: clock,
 			rand:  rand,
 		},
-		reaperDone: make(chan struct{}, 1),
 	}
 }
 
@@ -545,7 +544,7 @@ func (it *IPTables) check(table Table, hook Hook, pkt *PacketBuffer, r *Route, a
 // beforeSave is invoked by stateify.
 func (it *IPTables) beforeSave() {
 	// Ensure the reaper exits cleanly.
-	it.reaperDone <- struct{}{}
+	it.reaper.Stop()
 	// Prevent others from modifying the connection table.
 	it.connections.mu.Lock()
 }
@@ -555,21 +554,13 @@ func (it *IPTables) afterLoad() {
 	it.startReaper(reaperDelay)
 }
 
-// startReaper starts a goroutine that wakes up periodically to reap timed out
-// connections.
+// startReaper periodically reaps timed out connections.
 func (it *IPTables) startReaper(interval time.Duration) {
-	go func() { // S/R-SAFE: reaperDone is signalled when iptables is saved.
-		bucket := 0
-		for {
-			select {
-			case <-it.reaperDone:
-				return
-				// TODO(gvisor.dev/issue/5939): do not use the ambient clock.
-			case <-time.After(interval):
-				bucket, interval = it.connections.reapUnused(bucket, interval)
-			}
-		}
-	}()
+	bucket := 0
+	it.reaper = it.connections.clock.AfterFunc(interval, func() {
+		bucket, interval = it.connections.reapUnused(bucket, interval)
+		it.reaper.Reset(interval)
+	})
 }
 
 // Preconditions:

pkg/tcpip/stack/iptables_test.go

@@ -121,7 +121,9 @@ func TestNATedConnectionReap(t *testing.T) {
 
 	// Stop the reaper if it is running so we can reap manually as it is started
 	// on the first change to IPTables.
-	iptables.reaperDone <- struct{}{}
+	if !iptables.reaper.Stop() {
+		t.Fatal("failed to stop reaper")
+	}
 
 	pkt := v6PacketBuffer()
 
@@ -224,7 +226,7 @@ func TestNATedConnectionReap(t *testing.T) {
 		bkt.mu.RLock()
 		defer bkt.mu.RUnlock()
 		for tuple := bkt.tuples.Front(); tuple != nil; tuple = tuple.Next() {
-			if tuple.id() == originalTID {
+			if tuple.id() == tid {
 				t.Errorf("unexpectedly found tuple with ID = %#v; reply = %t", tid, reply)
 			}
 		}

pkg/tcpip/stack/iptables_types.go

@@ -83,8 +83,7 @@ const (
 type IPTables struct {
 	connections ConnTrack
 
-	// reaperDone can be signaled to stop the reaper goroutine.
-	reaperDone chan struct{}
+	reaper tcpip.Timer
 
 	mu sync.RWMutex
 	// v4Tables and v6tables map tableIDs to tables. They hold builtin