Refcount Unix transport queue

This allows us to release messages in the queue when all users close.

PiperOrigin-RevId: 218033550
Change-Id: I2f6e87650fced87a3977e3b74c64775c7b885c1b

pkg/sentry/socket/unix/transport/BUILD

@@ -29,6 +29,7 @@ go_library(
     visibility = ["//:sandbox"],
     deps = [
         "//pkg/ilist",
+        "//pkg/refs",
         "//pkg/tcpip",
         "//pkg/tcpip/buffer",
         "//pkg/waiter",

pkg/sentry/socket/unix/transport/connectioned.go

@@ -145,10 +145,12 @@ func NewPair(stype SockType, uid UniqueIDProvider) (Endpoint, Endpoint) {
 		b.receiver = &queueReceiver{q2}
 	}
 
+	q2.IncRef()
 	a.connected = &connectedEndpoint{
 		endpoint:   b,
 		writeQueue: q2,
 	}
+	q1.IncRef()
 	b.connected = &connectedEndpoint{
 		endpoint:   a,
 		writeQueue: q1,
@@ -282,12 +284,14 @@ func (e *connectionedEndpoint) BidirectionalConnect(ce ConnectingEndpoint, retur
 		idGenerator: e.idGenerator,
 		stype:       e.stype,
 	}
+
 	readQueue := newQueue(ce.WaiterQueue(), ne.Queue, initialLimit)
-	writeQueue := newQueue(ne.Queue, ce.WaiterQueue(), initialLimit)
 	ne.connected = &connectedEndpoint{
 		endpoint:   ce,
 		writeQueue: readQueue,
 	}
+
+	writeQueue := newQueue(ne.Queue, ce.WaiterQueue(), initialLimit)
 	if e.stype == SockStream {
 		ne.receiver = &streamQueueReceiver{queueReceiver: queueReceiver{readQueue: writeQueue}}
 	} else {
@@ -297,10 +301,12 @@ func (e *connectionedEndpoint) BidirectionalConnect(ce ConnectingEndpoint, retur
 	select {
 	case e.acceptedChan <- ne:
 		// Commit state.
+		writeQueue.IncRef()
 		connected := &connectedEndpoint{
 			endpoint:   ne,
 			writeQueue: writeQueue,
 		}
+		readQueue.IncRef()
 		if e.stype == SockStream {
 			returnConnect(&streamQueueReceiver{queueReceiver: queueReceiver{readQueue: readQueue}}, connected)
 		} else {

pkg/sentry/socket/unix/transport/connectionless.go

@@ -82,9 +82,13 @@ func (e *connectionlessEndpoint) UnidirectionalConnect() (ConnectedEndpoint, *tc
 	if r == nil {
 		return nil, tcpip.ErrConnectionRefused
 	}
+	q := r.(*queueReceiver).readQueue
+	if !q.TryIncRef() {
+		return nil, tcpip.ErrConnectionRefused
+	}
 	return &connectedEndpoint{
 		endpoint:   e,
-		writeQueue: r.(*queueReceiver).readQueue,
+		writeQueue: q,
 	}, nil
 }
 

pkg/sentry/socket/unix/transport/queue.go

@@ -17,6 +17,7 @@ package transport
 import (
 	"sync"
 
+	"gvisor.googlesource.com/gvisor/pkg/refs"
 	"gvisor.googlesource.com/gvisor/pkg/tcpip"
 	"gvisor.googlesource.com/gvisor/pkg/waiter"
 )
@@ -25,6 +26,8 @@ import (
 //
 // +stateify savable
 type queue struct {
+	refs.AtomicRefCount
+
 	ReaderQueue *waiter.Queue
 	WriterQueue *waiter.Queue
 
@@ -67,6 +70,13 @@ func (q *queue) Reset() {
 	q.mu.Unlock()
 }
 
+// DecRef implements RefCounter.DecRef with destructor q.Reset.
+func (q *queue) DecRef() {
+	q.DecRefWithDestructor(q.Reset)
+	// We don't need to notify after resetting because no one cares about
+	// this queue after all references have been dropped.
+}
+
 // IsReadable determines if q is currently readable.
 func (q *queue) IsReadable() bool {
 	q.mu.Lock()

pkg/sentry/socket/unix/transport/unix.go

@@ -381,7 +381,9 @@ func (q *queueReceiver) RecvMaxQueueSize() int64 {
 }
 
 // Release implements Receiver.Release.
-func (*queueReceiver) Release() {}
+func (q *queueReceiver) Release() {
+	q.readQueue.DecRef()
+}
 
 // streamQueueReceiver implements Receiver for stream sockets.
 //
@@ -694,7 +696,9 @@ func (e *connectedEndpoint) SendMaxQueueSize() int64 {
 }
 
 // Release implements ConnectedEndpoint.Release.
-func (*connectedEndpoint) Release() {}
+func (e *connectedEndpoint) Release() {
+	e.writeQueue.DecRef()
+}
 
 // baseEndpoint is an embeddable unix endpoint base used in both the connected and connectionless
 // unix domain socket Endpoint implementations.
@@ -945,4 +949,6 @@ func (e *baseEndpoint) GetRemoteAddress() (tcpip.FullAddress, *tcpip.Error) {
 }
 
 // Release implements BoundEndpoint.Release.
-func (*baseEndpoint) Release() {}
+func (*baseEndpoint) Release() {
+	// Binding a baseEndpoint doesn't take a reference.
+}