Hold lock while accessing Stack.nics

Fix some occurrences of Stack.nics being read without holding the Stack.mu lock.
This can result (and has resulted) in crashes at runtime due to concurrent map
read and write operations.

Fixes #8134.

PiperOrigin-RevId: 485750713

pkg/tcpip/stack/forwarding_test.go

@@ -385,7 +385,9 @@ func fwdTestNetFactory(t *testing.T, proto *fwdTestNetworkProtocol) (*faketime.M
 		t.Fatalf("AddProtocolAddress(%d, %+v, {}): %s", 2, protocolAddr2, err)
 	}
 
+	s.mu.RLock()
 	nic, ok := s.nics[2]
+	s.mu.RUnlock()
 	if !ok {
 		t.Fatal("NIC 2 does not exist")
 	}

pkg/tcpip/stack/stack.go

@@ -90,13 +90,15 @@ type Stack struct {
 	// +checklocks:routeMu
 	routeTable []tcpip.Route
 
-	mu                       sync.RWMutex
+	mu sync.RWMutex
+	// +checklocks:mu
 	nics                     map[tcpip.NICID]*nic
 	defaultForwardingEnabled map[tcpip.NetworkProtocolNumber]struct{}
 
 	// cleanupEndpointsMu protects cleanupEndpoints.
 	cleanupEndpointsMu sync.Mutex
-	cleanupEndpoints   map[TransportEndpoint]struct{}
+	// +checklocks:cleanupEndpointsMu
+	cleanupEndpoints map[TransportEndpoint]struct{}
 
 	*ports.PortManager
 
@@ -920,7 +922,7 @@ func (s *Stack) RemoveNIC(id tcpip.NICID) tcpip.Error {
 
 // removeNICLocked removes NIC and all related routes from the network stack.
 //
-// s.mu must be locked.
+// +checklocks:s.mu
 func (s *Stack) removeNICLocked(id tcpip.NICID) tcpip.Error {
 	nic, ok := s.nics[id]
 	if !ok {
@@ -1150,6 +1152,9 @@ func (s *Stack) getAddressEP(nic *nic, localAddr, remoteAddr tcpip.Address, netP
 //
 // Returns nil if validation fails.
 func (s *Stack) NewRouteForMulticast(nicID tcpip.NICID, remoteAddr tcpip.Address, netProto tcpip.NetworkProtocolNumber) *Route {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
 	nic, ok := s.nics[nicID]
 	if !ok || !nic.Enabled() {
 		return nil
@@ -1164,7 +1169,7 @@ func (s *Stack) NewRouteForMulticast(nicID tcpip.NICID, remoteAddr tcpip.Address
 // findLocalRouteFromNICRLocked is like findLocalRouteRLocked but finds a route
 // from the specified NIC.
 //
-// Precondition: s.mu must be read locked.
+// +checklocksread:s.mu
 func (s *Stack) findLocalRouteFromNICRLocked(localAddressNIC *nic, localAddr, remoteAddr tcpip.Address, netProto tcpip.NetworkProtocolNumber) *Route {
 	localAddressEndpoint := localAddressNIC.getAddressOrCreateTempInner(netProto, localAddr, false /* createTemp */, NeverPrimaryEndpoint)
 	if localAddressEndpoint == nil {
@@ -1217,7 +1222,7 @@ func (s *Stack) findLocalRouteFromNICRLocked(localAddressNIC *nic, localAddr, re
 // A local route is a route to some remote address which the stack owns. That
 // is, a local route is a route where packets never have to leave the stack.
 //
-// Precondition: s.mu must be read locked.
+// +checklocksread:s.mu
 func (s *Stack) findLocalRouteRLocked(localAddressNICID tcpip.NICID, localAddr, remoteAddr tcpip.Address, netProto tcpip.NetworkProtocolNumber) *Route {
 	if len(localAddr) == 0 {
 		localAddr = remoteAddr
@@ -1425,7 +1430,10 @@ func (s *Stack) CheckNetworkProtocol(protocol tcpip.NetworkProtocolNumber) bool
 // CheckDuplicateAddress performs duplicate address detection for the address on
 // the specified interface.
 func (s *Stack) CheckDuplicateAddress(nicID tcpip.NICID, protocol tcpip.NetworkProtocolNumber, addr tcpip.Address, h DADCompletionHandler) (DADCheckAddressDisposition, tcpip.Error) {
+	s.mu.RLock()
 	nic, ok := s.nics[nicID]
+	s.mu.RUnlock()
+
 	if !ok {
 		return 0, &tcpip.ErrUnknownNICID{}
 	}
@@ -1795,6 +1803,7 @@ func (s *Stack) UnregisterPacketEndpoint(nicID tcpip.NICID, netProto tcpip.Netwo
 	s.unregisterPacketEndpointLocked(nicID, netProto, ep)
 }
 
+// +checklocks:s.mu
 func (s *Stack) unregisterPacketEndpointLocked(nicID tcpip.NICID, netProto tcpip.NetworkProtocolNumber, ep PacketEndpoint) {
 	// If no NIC is specified, unregister on all devices.
 	if nicID == 0 {