Make UDP traceroute work.

Adds support to generate Port Unreachable messages for UDP
datagrams received on a port for which there is no valid
endpoint.

Fixes #703

PiperOrigin-RevId: 267034418

2 files changed, 6 insertions, 29 deletions

diff --git a/pkg/tcpip/network/ipv6/icmp.go b/pkg/tcpip/network/ipv6/icmp.go
index 1689af16f..346de9ae3 100644
--- a/pkg/tcpip/network/ipv6/icmp.go
+++ b/pkg/tcpip/network/ipv6/icmp.go
@@ -15,8 +15,6 @@
 package ipv6
 
 import (
-	"encoding/binary"
-
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
@@ -82,7 +80,7 @@ func (e *endpoint) handleICMP(r *stack.Route, netHeader buffer.View, vv buffer.V
 			return
 		}
 		vv.TrimFront(header.ICMPv6PacketTooBigMinimumSize)
-		mtu := binary.BigEndian.Uint32(v[header.ICMPv6MinimumSize:])
+		mtu := h.MTU()
 		e.handleControl(stack.ControlPacketTooBig, calculateMTU(mtu), vv)
 
 	case header.ICMPv6DstUnreachable:
@@ -130,7 +128,7 @@ func (e *endpoint) handleICMP(r *stack.Route, netHeader buffer.View, vv buffer.V
 		r := r.Clone()
 		defer r.Release()
 		r.LocalAddress = targetAddr
-		pkt.SetChecksum(icmpChecksum(pkt, r.LocalAddress, r.RemoteAddress, buffer.VectorisedView{}))
+		pkt.SetChecksum(header.ICMPv6Checksum(pkt, r.LocalAddress, r.RemoteAddress, buffer.VectorisedView{}))
 
 		if err := r.WritePacket(nil /* gso */, hdr, buffer.VectorisedView{}, header.ICMPv6ProtocolNumber, r.DefaultTTL()); err != nil {
 			sent.Dropped.Increment()
@@ -162,7 +160,7 @@ func (e *endpoint) handleICMP(r *stack.Route, netHeader buffer.View, vv buffer.V
 		pkt := header.ICMPv6(hdr.Prepend(header.ICMPv6EchoMinimumSize))
 		copy(pkt, h)
 		pkt.SetType(header.ICMPv6EchoReply)
-		pkt.SetChecksum(icmpChecksum(pkt, r.LocalAddress, r.RemoteAddress, vv))
+		pkt.SetChecksum(header.ICMPv6Checksum(pkt, r.LocalAddress, r.RemoteAddress, vv))
 		if err := r.WritePacket(nil /* gso */, hdr, vv, header.ICMPv6ProtocolNumber, r.DefaultTTL()); err != nil {
 			sent.Dropped.Increment()
 			return
@@ -233,7 +231,7 @@ func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, linkEP stack.
 	pkt[icmpV6OptOffset] = ndpOptSrcLinkAddr
 	pkt[icmpV6LengthOffset] = 1
 	copy(pkt[icmpV6LengthOffset+1:], linkEP.LinkAddress())
-	pkt.SetChecksum(icmpChecksum(pkt, r.LocalAddress, r.RemoteAddress, buffer.VectorisedView{}))
+	pkt.SetChecksum(header.ICMPv6Checksum(pkt, r.LocalAddress, r.RemoteAddress, buffer.VectorisedView{}))
 
 	length := uint16(hdr.UsedLength())
 	ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
@@ -272,24 +270,3 @@ func (*protocol) ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bo
 	}
 	return "", false
 }
-
-func icmpChecksum(h header.ICMPv6, src, dst tcpip.Address, vv buffer.VectorisedView) uint16 {
-	// Calculate the IPv6 pseudo-header upper-layer checksum.
-	xsum := header.Checksum([]byte(src), 0)
-	xsum = header.Checksum([]byte(dst), xsum)
-	var upperLayerLength [4]byte
-	binary.BigEndian.PutUint32(upperLayerLength[:], uint32(len(h)+vv.Size()))
-	xsum = header.Checksum(upperLayerLength[:], xsum)
-	xsum = header.Checksum([]byte{0, 0, 0, uint8(header.ICMPv6ProtocolNumber)}, xsum)
-	for _, v := range vv.Views() {
-		xsum = header.Checksum(v, xsum)
-	}
-
-	// h[2:4] is the checksum itself, set it aside to avoid checksumming the checksum.
-	h2, h3 := h[2], h[3]
-	h[2], h[3] = 0, 0
-	xsum = ^header.Checksum(h, xsum)
-	h[2], h[3] = h2, h3
-
-	return xsum
-}
diff --git a/pkg/tcpip/network/ipv6/icmp_test.go b/pkg/tcpip/network/ipv6/icmp_test.go
index d0dc72506..227a65cf2 100644
--- a/pkg/tcpip/network/ipv6/icmp_test.go
+++ b/pkg/tcpip/network/ipv6/icmp_test.go
@@ -153,7 +153,7 @@ func TestICMPCounts(t *testing.T) {
 		hdr := buffer.NewPrependable(header.IPv6MinimumSize + typ.size)
 		pkt := header.ICMPv6(hdr.Prepend(typ.size))
 		pkt.SetType(typ.typ)
-		pkt.SetChecksum(icmpChecksum(pkt, r.LocalAddress, r.RemoteAddress, buffer.VectorisedView{}))
+		pkt.SetChecksum(header.ICMPv6Checksum(pkt, r.LocalAddress, r.RemoteAddress, buffer.VectorisedView{}))
 
 		handleIPv6Payload(hdr)
 	}
@@ -321,7 +321,7 @@ func TestLinkResolution(t *testing.T) {
 	hdr := buffer.NewPrependable(int(r.MaxHeaderLength()) + header.IPv6MinimumSize + header.ICMPv6EchoMinimumSize)
 	pkt := header.ICMPv6(hdr.Prepend(header.ICMPv6EchoMinimumSize))
 	pkt.SetType(header.ICMPv6EchoRequest)
-	pkt.SetChecksum(icmpChecksum(pkt, r.LocalAddress, r.RemoteAddress, buffer.VectorisedView{}))
+	pkt.SetChecksum(header.ICMPv6Checksum(pkt, r.LocalAddress, r.RemoteAddress, buffer.VectorisedView{}))
 	payload := tcpip.SlicePayload(hdr.View())
 
 	// We can't send our payload directly over the route because that