move sessionfirewall into the tuntap. this needs testing. the name is also slightly wrong, since a crypto session can still be set up, packets are just accepted/rejected at the tun/tap level instead

src/tuntap/iface.go

@@ -93,6 +93,9 @@ func (tun *TunAdapter) write() {
 			continue // bad local address/subnet
 		}
 		info := tun.store.update(ed25519.PublicKey(from.(iwt.Addr)))
+		if info == nil {
+			continue // Blocked by the gatekeeper
+		}
 		if srcAddr != info.address && srcSubnet != info.subnet {
 			continue // bad remote address/subnet
 		}

src/tuntap/keystore.go

@@ -115,6 +115,18 @@ func (k *keyStore) update(key ed25519.PublicKey) *keyInfo {
 		info.address = *address.AddrForKey(ed25519.PublicKey(info.key[:]))
 		info.subnet = *address.SubnetForKey(ed25519.PublicKey(info.key[:]))
 		info.mtu = MTU(^uint16(0)) // TODO
+		var isOutgoing bool
+		if k.addrBuffer[info.address] != nil {
+			isOutgoing = true
+		}
+		if k.subnetBuffer[info.subnet] != nil {
+			isOutgoing = true
+		}
+		if !k.tun.gatekeeper(key, isOutgoing) {
+			// Blocked by the gatekeeper, so don't create an entry for this
+			k.mutex.Unlock()
+			return nil
+		}
 		k.keyToInfo[info.key] = info
 		k.addrToInfo[info.address] = info
 		k.subnetToInfo[info.subnet] = info

src/tuntap/tun.go

@@ -44,7 +44,14 @@ type TunAdapter struct {
 	iface       tun.Device
 	phony.Inbox // Currently only used for _handlePacket from the reader, TODO: all the stuff that currently needs a mutex below
 	//mutex        sync.RWMutex // Protects the below
-	isOpen bool
+	isOpen     bool
+	gatekeeper func(pubkey ed25519.PublicKey, initiator bool) bool
+}
+
+func (tun *TunAdapter) SetSessionGatekeeper(gatekeeper func(pubkey ed25519.PublicKey, initiator bool) bool) {
+	phony.Block(tun, func() {
+		tun.gatekeeper = gatekeeper
+	})
 }
 
 // Gets the maximum supported MTU for the platform based on the defaults in