Handle removed NIC in NDP timer for packet tx

NDP packets are sent periodically from NDP timers. These timers do not
hold the NIC lock when sending packets as the packet write operation
may take some time. While the lock is not held, the NIC may be removed
by some other goroutine. This change handles that scenario gracefully.

Test: stack_test.TestRemoveNICWhileHandlingRSTimer
PiperOrigin-RevId: 315524143

1 files changed, 23 insertions, 15 deletions

diff --git a/pkg/tcpip/stack/nic.go b/pkg/tcpip/stack/nic.go
index d756ae6f5..644c0d437 100644
--- a/pkg/tcpip/stack/nic.go
+++ b/pkg/tcpip/stack/nic.go
@@ -457,8 +457,20 @@ type ipv6AddrCandidate struct {
 // remoteAddr must be a valid IPv6 address.
 func (n *NIC) primaryIPv6Endpoint(remoteAddr tcpip.Address) *referencedNetworkEndpoint {
 	n.mu.RLock()
-	defer n.mu.RUnlock()
+	ref := n.primaryIPv6EndpointRLocked(remoteAddr)
+	n.mu.RUnlock()
+	return ref
+}
 
+// primaryIPv6EndpointLocked returns an IPv6 endpoint following Source Address
+// Selection (RFC 6724 section 5).
+//
+// Note, only rules 1-3 and 7 are followed.
+//
+// remoteAddr must be a valid IPv6 address.
+//
+// n.mu MUST be read locked.
+func (n *NIC) primaryIPv6EndpointRLocked(remoteAddr tcpip.Address) *referencedNetworkEndpoint {
 	primaryAddrs := n.mu.primary[header.IPv6ProtocolNumber]
 
 	if len(primaryAddrs) == 0 {
@@ -568,11 +580,6 @@ const (
 	// promiscuous indicates that the NIC's promiscuous flag should be observed
 	// when getting a NIC's referenced network endpoint.
 	promiscuous
-
-	// forceSpoofing indicates that the NIC should be assumed to be spoofing,
-	// regardless of what the NIC's spoofing flag is when getting a NIC's
-	// referenced network endpoint.
-	forceSpoofing
 )
 
 func (n *NIC) getRef(protocol tcpip.NetworkProtocolNumber, dst tcpip.Address) *referencedNetworkEndpoint {
@@ -591,8 +598,6 @@ func (n *NIC) findEndpoint(protocol tcpip.NetworkProtocolNumber, address tcpip.A
 // or spoofing. Promiscuous mode will only be checked if promiscuous is true.
 // Similarly, spoofing will only be checked if spoofing is true.
 func (n *NIC) getRefOrCreateTemp(protocol tcpip.NetworkProtocolNumber, address tcpip.Address, peb PrimaryEndpointBehavior, tempRef getRefBehaviour) *referencedNetworkEndpoint {
-	id := NetworkEndpointID{address}
-
 	n.mu.RLock()
 
 	var spoofingOrPromiscuous bool
@@ -601,11 +606,9 @@ func (n *NIC) getRefOrCreateTemp(protocol tcpip.NetworkProtocolNumber, address t
 		spoofingOrPromiscuous = n.mu.spoofing
 	case promiscuous:
 		spoofingOrPromiscuous = n.mu.promiscuous
-	case forceSpoofing:
-		spoofingOrPromiscuous = true
 	}
 
-	if ref, ok := n.mu.endpoints[id]; ok {
+	if ref, ok := n.mu.endpoints[NetworkEndpointID{address}]; ok {
 		// An endpoint with this id exists, check if it can be used and return it.
 		switch ref.getKind() {
 		case permanentExpired:
@@ -654,11 +657,18 @@ func (n *NIC) getRefOrCreateTemp(protocol tcpip.NetworkProtocolNumber, address t
 	// endpoint, create a new "temporary" endpoint. It will only exist while
 	// there's a route through it.
 	n.mu.Lock()
-	if ref, ok := n.mu.endpoints[id]; ok {
+	ref := n.getRefOrCreateTempLocked(protocol, address, peb)
+	n.mu.Unlock()
+	return ref
+}
+
+/// getRefOrCreateTempLocked returns an existing endpoint for address or creates
+/// and returns a temporary endpoint.
+func (n *NIC) getRefOrCreateTempLocked(protocol tcpip.NetworkProtocolNumber, address tcpip.Address, peb PrimaryEndpointBehavior) *referencedNetworkEndpoint {
+	if ref, ok := n.mu.endpoints[NetworkEndpointID{address}]; ok {
 		// No need to check the type as we are ok with expired endpoints at this
 		// point.
 		if ref.tryIncRef() {
-			n.mu.Unlock()
 			return ref
 		}
 		// tryIncRef failing means the endpoint is scheduled to be removed once the
@@ -670,7 +680,6 @@ func (n *NIC) getRefOrCreateTemp(protocol tcpip.NetworkProtocolNumber, address t
 	// Add a new temporary endpoint.
 	netProto, ok := n.stack.networkProtocols[protocol]
 	if !ok {
-		n.mu.Unlock()
 		return nil
 	}
 	ref, _ := n.addAddressLocked(tcpip.ProtocolAddress{
@@ -681,7 +690,6 @@ func (n *NIC) getRefOrCreateTemp(protocol tcpip.NetworkProtocolNumber, address t
 		},
 	}, peb, temporary, static, false)
 
-	n.mu.Unlock()
 	return ref
 }