Remove ARP address workaround

- Make AddressableEndpoint optional for NetworkEndpoint.
Not all NetworkEndpoints need to support addressing (e.g. ARP), so
AddressableEndpoint should only be implemented for protocols that
support addressing such as IPv4 and IPv6.

With this change, tcpip.ErrNotSupported will be returned by the stack
when attempting to modify addresses on a network endpoint that does
not support addressing.

Now that packets are fully handled at the network layer, and (with this
change) addresses are optional for network endpoints, we no longer need
the workaround for ARP where a fake ARP address was added to each NIC
that performs ARP so that packets would be delivered to the ARP layer.

PiperOrigin-RevId: 342722547

1 files changed, 11 insertions, 27 deletions

diff --git a/pkg/tcpip/link/tun/device.go b/pkg/tcpip/link/tun/device.go
index 4c14f55d3..9a76bdba7 100644
--- a/pkg/tcpip/link/tun/device.go
+++ b/pkg/tcpip/link/tun/device.go
@@ -76,29 +76,13 @@ func (d *Device) Release(ctx context.Context) {
 	}
 }
 
-// NICID returns the NIC ID of the device.
-//
-// Must only be called after the device has been attached to an endpoint.
-func (d *Device) NICID() tcpip.NICID {
-	d.mu.RLock()
-	defer d.mu.RUnlock()
-
-	if d.endpoint == nil {
-		panic("called NICID on a device that has not been attached")
-	}
-
-	return d.endpoint.nicID
-}
-
 // SetIff services TUNSETIFF ioctl(2) request.
-//
-// Returns true if a new NIC was created; false if an existing one was attached.
-func (d *Device) SetIff(s *stack.Stack, name string, flags uint16) (bool, error) {
+func (d *Device) SetIff(s *stack.Stack, name string, flags uint16) error {
 	d.mu.Lock()
 	defer d.mu.Unlock()
 
 	if d.endpoint != nil {
-		return false, syserror.EINVAL
+		return syserror.EINVAL
 	}
 
 	// Input validations.
@@ -106,7 +90,7 @@ func (d *Device) SetIff(s *stack.Stack, name string, flags uint16) (bool, error)
 	isTap := flags&linux.IFF_TAP != 0
 	supportedFlags := uint16(linux.IFF_TUN | linux.IFF_TAP | linux.IFF_NO_PI)
 	if isTap && isTun || !isTap && !isTun || flags&^supportedFlags != 0 {
-		return false, syserror.EINVAL
+		return syserror.EINVAL
 	}
 
 	prefix := "tun"
@@ -119,18 +103,18 @@ func (d *Device) SetIff(s *stack.Stack, name string, flags uint16) (bool, error)
 		linkCaps |= stack.CapabilityResolutionRequired
 	}
 
-	endpoint, created, err := attachOrCreateNIC(s, name, prefix, linkCaps)
+	endpoint, err := attachOrCreateNIC(s, name, prefix, linkCaps)
 	if err != nil {
-		return false, syserror.EINVAL
+		return syserror.EINVAL
 	}
 
 	d.endpoint = endpoint
 	d.notifyHandle = d.endpoint.AddNotify(d)
 	d.flags = flags
-	return created, nil
+	return nil
 }
 
-func attachOrCreateNIC(s *stack.Stack, name, prefix string, linkCaps stack.LinkEndpointCapabilities) (*tunEndpoint, bool, error) {
+func attachOrCreateNIC(s *stack.Stack, name, prefix string, linkCaps stack.LinkEndpointCapabilities) (*tunEndpoint, error) {
 	for {
 		// 1. Try to attach to an existing NIC.
 		if name != "" {
@@ -138,13 +122,13 @@ func attachOrCreateNIC(s *stack.Stack, name, prefix string, linkCaps stack.LinkE
 				endpoint, ok := linkEP.(*tunEndpoint)
 				if !ok {
 					// Not a NIC created by tun device.
-					return nil, false, syserror.EOPNOTSUPP
+					return nil, syserror.EOPNOTSUPP
 				}
 				if !endpoint.TryIncRef() {
 					// Race detected: NIC got deleted in between.
 					continue
 				}
-				return endpoint, false, nil
+				return endpoint, nil
 			}
 		}
 
@@ -167,12 +151,12 @@ func attachOrCreateNIC(s *stack.Stack, name, prefix string, linkCaps stack.LinkE
 		})
 		switch err {
 		case nil:
-			return endpoint, true, nil
+			return endpoint, nil
 		case tcpip.ErrDuplicateNICID:
 			// Race detected: A NIC has been created in between.
 			continue
 		default:
-			return nil, false, syserror.EINVAL
+			return nil, syserror.EINVAL
 		}
 	}
 }