Fix data race accessing referencedNetworkEndpoint.kind

Wrapping "kind" into atomic access functions.

Fixes #789

PiperOrigin-RevId: 266485501

pkg/tcpip/stack/nic.go

@@ -139,7 +139,7 @@ func (n *NIC) getMainNICAddress(protocol tcpip.NetworkProtocolNumber) (tcpip.Add
 	if list, ok := n.primary[protocol]; ok {
 		for e := list.Front(); e != nil; e = e.Next() {
 			ref := e.(*referencedNetworkEndpoint)
-			if ref.kind == permanent && ref.tryIncRef() {
+			if ref.getKind() == permanent && ref.tryIncRef() {
 				r = ref
 				break
 			}
@@ -205,7 +205,7 @@ func (n *NIC) getRefOrCreateTemp(protocol tcpip.NetworkProtocolNumber, address t
 
 	if ref, ok := n.endpoints[id]; ok {
 		// An endpoint with this id exists, check if it can be used and return it.
-		switch ref.kind {
+		switch ref.getKind() {
 		case permanentExpired:
 			if !spoofingOrPromiscuous {
 				n.mu.RUnlock()
@@ -276,14 +276,14 @@ func (n *NIC) getRefOrCreateTemp(protocol tcpip.NetworkProtocolNumber, address t
 func (n *NIC) addPermanentAddressLocked(protocolAddress tcpip.ProtocolAddress, peb PrimaryEndpointBehavior) (*referencedNetworkEndpoint, *tcpip.Error) {
 	id := NetworkEndpointID{protocolAddress.AddressWithPrefix.Address}
 	if ref, ok := n.endpoints[id]; ok {
-		switch ref.kind {
+		switch ref.getKind() {
 		case permanent:
 			// The NIC already have a permanent endpoint with that address.
 			return nil, tcpip.ErrDuplicateAddress
 		case permanentExpired, temporary:
 			// Promote the endpoint to become permanent.
 			if ref.tryIncRef() {
-				ref.kind = permanent
+				ref.setKind(permanent)
 				return ref, nil
 			}
 			// tryIncRef failing means the endpoint is scheduled to be removed once
@@ -366,7 +366,7 @@ func (n *NIC) Addresses() []tcpip.ProtocolAddress {
 	for nid, ref := range n.endpoints {
 		// Don't include expired or tempory endpoints to avoid confusion and
 		// prevent the caller from using those.
-		switch ref.kind {
+		switch ref.getKind() {
 		case permanentExpired, temporary:
 			continue
 		}
@@ -444,7 +444,7 @@ func (n *NIC) removeEndpointLocked(r *referencedNetworkEndpoint) {
 		return
 	}
 
-	if r.kind == permanent {
+	if r.getKind() == permanent {
 		panic("Reference count dropped to zero before being removed")
 	}
 
@@ -465,11 +465,11 @@ func (n *NIC) removeEndpoint(r *referencedNetworkEndpoint) {
 
 func (n *NIC) removePermanentAddressLocked(addr tcpip.Address) *tcpip.Error {
 	r := n.endpoints[NetworkEndpointID{addr}]
-	if r == nil || r.kind != permanent {
+	if r == nil || r.getKind() != permanent {
 		return tcpip.ErrBadLocalAddress
 	}
 
-	r.kind = permanentExpired
+	r.setKind(permanentExpired)
 	r.decRefLocked()
 
 	return nil
@@ -720,7 +720,7 @@ func (n *NIC) ID() tcpip.NICID {
 	return n.id
 }
 
-type networkEndpointKind int
+type networkEndpointKind int32
 
 const (
 	// A permanent endpoint is created by adding a permanent address (vs. a
@@ -759,21 +759,30 @@ type referencedNetworkEndpoint struct {
 	// triggers the automatic removal of the endpoint from the NIC.
 	refs int32
 
+	// networkEndpointKind must only be accessed using {get,set}Kind().
 	kind networkEndpointKind
 }
 
+func (r *referencedNetworkEndpoint) getKind() networkEndpointKind {
+	return networkEndpointKind(atomic.LoadInt32((*int32)(&r.kind)))
+}
+
+func (r *referencedNetworkEndpoint) setKind(kind networkEndpointKind) {
+	atomic.StoreInt32((*int32)(&r.kind), int32(kind))
+}
+
 // isValidForOutgoing returns true if the endpoint can be used to send out a
 // packet. It requires the endpoint to not be marked expired (i.e., its address
 // has been removed), or the NIC to be in spoofing mode.
 func (r *referencedNetworkEndpoint) isValidForOutgoing() bool {
-	return r.kind != permanentExpired || r.nic.spoofing
+	return r.getKind() != permanentExpired || r.nic.spoofing
 }
 
 // isValidForIncoming returns true if the endpoint can accept an incoming
 // packet. It requires the endpoint to not be marked expired (i.e., its address
 // has been removed), or the NIC to be in promiscuous mode.
 func (r *referencedNetworkEndpoint) isValidForIncoming() bool {
-	return r.kind != permanentExpired || r.nic.promiscuous
+	return r.getKind() != permanentExpired || r.nic.promiscuous
 }
 
 // decRef decrements the ref count and cleans up the endpoint once it reaches