Merge pull request #15 from neilalexander/packettoobig

Implement Path MTU Discovery using session MTU

src/yggdrasil/icmpv6.go

@@ -8,6 +8,7 @@ import "net"
 import "golang.org/x/net/ipv6"
 import "golang.org/x/net/icmp"
 import "encoding/binary"
+import "errors"
 
 type macAddress [6]byte
 
@@ -129,14 +130,12 @@ func (i *icmpv6) parse_packet_tun(datain []byte) ([]byte, error) {
 			response, err := i.handle_ndp(datain[ipv6.HeaderLen:])
 			if err == nil {
 				// Create our ICMPv6 response
-				responsePacket, err := i.create_icmpv6_tun(ipv6Header.Src, ipv6.ICMPTypeNeighborAdvertisement, 0, response)
+				responsePacket, err := i.create_icmpv6_tun(ipv6Header.Src, ipv6.ICMPTypeNeighborAdvertisement, 0,
+					&icmp.DefaultMessageBody{Data: response})
 				if err != nil {
 					return nil, err
 				}
 
-				// Fix the checksum because I don't even know why, net/icmp is stupid
-				responsePacket[17] ^= 0x4
-
 				// Send it back
 				return responsePacket, nil
 			} else {
@@ -145,10 +144,10 @@ func (i *icmpv6) parse_packet_tun(datain []byte) ([]byte, error) {
 		}
 	}
 
-	return nil, nil
+	return nil, errors.New("ICMPv6 type not matched")
 }
 
-func (i *icmpv6) create_icmpv6_tap(dstmac macAddress, dst net.IP, mtype ipv6.ICMPType, mcode int, mbody []byte) ([]byte, error) {
+func (i *icmpv6) create_icmpv6_tap(dstmac macAddress, dst net.IP, mtype ipv6.ICMPType, mcode int, mbody icmp.MessageBody) ([]byte, error) {
 	// Pass through to create_icmpv6_tun
 	ipv6packet, err := i.create_icmpv6_tun(dst, mtype, mcode, mbody)
 	if err != nil {
@@ -156,7 +155,7 @@ func (i *icmpv6) create_icmpv6_tap(dstmac macAddress, dst net.IP, mtype ipv6.ICM
 	}
 
 	// Create the response buffer
-	dataout := make([]byte, ETHER+ipv6.HeaderLen+len(mbody))
+	dataout := make([]byte, ETHER+len(ipv6packet))
 
 	// Populate the response ethernet headers
 	copy(dataout[:6], dstmac[:6])
@@ -168,36 +167,36 @@ func (i *icmpv6) create_icmpv6_tap(dstmac macAddress, dst net.IP, mtype ipv6.ICM
 	return dataout, nil
 }
 
-func (i *icmpv6) create_icmpv6_tun(dst net.IP, mtype ipv6.ICMPType, mcode int, mbody []byte) ([]byte, error) {
+func (i *icmpv6) create_icmpv6_tun(dst net.IP, mtype ipv6.ICMPType, mcode int, mbody icmp.MessageBody) ([]byte, error) {
+	// Create the ICMPv6 message
+	icmpMessage := icmp.Message{
+		Type: mtype,
+		Code: mcode,
+		Body: mbody,
+	}
+
+	// Convert the ICMPv6 message into []byte
+	icmpMessageBuf, err := icmpMessage.Marshal(icmp.IPv6PseudoHeader(i.mylladdr, dst))
+	if err != nil {
+		return nil, err
+	}
+
 	// Create the IPv6 header
 	ipv6Header := ipv6.Header{
 		Version:    ipv6.Version,
 		NextHeader: 58,
-		PayloadLen: len(mbody),
+		PayloadLen: len(icmpMessageBuf),
 		HopLimit:   255,
 		Src:        i.mylladdr,
 		Dst:        dst,
 	}
 
-	// Create the ICMPv6 message
-	icmpMessage := icmp.Message{
-		Type: mtype,
-		Code: mcode,
-		Body: &icmp.DefaultMessageBody{Data: mbody},
-	}
-
 	// Convert the IPv6 header into []byte
 	ipv6HeaderBuf, err := ipv6Header_Marshal(&ipv6Header)
 	if err != nil {
 		return nil, err
 	}
 
-	// Convert the ICMPv6 message into []byte
-	icmpMessageBuf, err := icmpMessage.Marshal(icmp.IPv6PseudoHeader(ipv6Header.Dst, ipv6Header.Src))
-	if err != nil {
-		return nil, err
-	}
-
 	// Construct the packet
 	responsePacket := make([]byte, ipv6.HeaderLen+ipv6Header.PayloadLen)
 	copy(responsePacket[:ipv6.HeaderLen], ipv6HeaderBuf)
@@ -210,11 +209,11 @@ func (i *icmpv6) create_icmpv6_tun(dst net.IP, mtype ipv6.ICMPType, mcode int, m
 func (i *icmpv6) handle_ndp(in []byte) ([]byte, error) {
 	// Ignore NDP requests for anything outside of fd00::/8
 	if in[8] != 0xFD {
-		return nil, nil
+		return nil, errors.New("Not an NDP for fd00::/8")
 	}
 
 	// Create our NDP message body response
-	body := make([]byte, 32)
+	body := make([]byte, 28)
 	binary.BigEndian.PutUint32(body[:4], uint32(0x20000000))
 	copy(body[4:20], in[8:24]) // Target address
 	body[20] = uint8(2)

src/yggdrasil/router.go

@@ -23,6 +23,8 @@ package yggdrasil
 //  The router then runs some sanity checks before passing it to the tun
 
 import "time"
+import "golang.org/x/net/icmp"
+import "golang.org/x/net/ipv6"
 
 //import "fmt"
 //import "net"
@@ -145,9 +147,28 @@ func (r *router) sendPacket(bs []byte) {
 		fallthrough
 	//default: go func() { sinfo.send<-bs }()
 	default:
+		// Generate an ICMPv6 Packet Too Big for packets larger than session MTU
 		if len(bs) > int(sinfo.getMTU()) {
-			// TODO: Send ICMPv6 Packet Too Big back to the TUN/TAP adapter
-			sinfo.core.log.Printf("Packet length %d exceeds session MTU %d", len(bs), sinfo.getMTU())
+			// Get the size of the oversized payload, up to a max of 900 bytes
+			window := 900
+			if int(sinfo.getMTU()) < window {
+				window = int(sinfo.getMTU())
+			}
+
+			// Create the Packet Too Big response
+			ptb := &icmp.PacketTooBig{
+				MTU:  int(sinfo.getMTU()),
+				Data: bs[:window],
+			}
+
+			// Create the ICMPv6 response from it
+			icmpv6Buf, err := r.core.tun.icmpv6.create_icmpv6_tun(bs[8:24], ipv6.ICMPTypePacketTooBig, 0, ptb)
+			if err == nil {
+				r.recv <- icmpv6Buf
+			}
+
+			// Don't continue - drop the packet
+			return
 		}
 		select {
 		case sinfo.send <- bs:

src/yggdrasil/session.go

@@ -279,7 +279,7 @@ func (ss *sessions) handlePing(ping *sessionPing) {
 		// send
 		var bs []byte
 		bs, sinfo.packet = sinfo.packet, nil
-		go func() { sinfo.send <- bs }()
+		ss.core.router.sendPacket(bs)
 	}
 }