Migrate to PacketHeader API for PacketBuffer.

Formerly, when a packet is constructed or parsed, all headers are set by the
client code. This almost always involved prepending to pk.Header buffer or
trimming pk.Data portion. This is known to prone to bugs, due to the complexity
and number of the invariants assumed across netstack to maintain.

In the new PacketHeader API, client will call Push()/Consume() method to
construct/parse an outgoing/incoming packet. All invariants, such as slicing
and trimming, are maintained by the API itself.

NewPacketBuffer() is introduced to create new PacketBuffer. Zero value is no
longer valid.

PacketBuffer now assumes the packet is a concatenation of following portions:
* LinkHeader
* NetworkHeader
* TransportHeader
* Data
Any of them could be empty, or zero-length.

PiperOrigin-RevId: 326507688

1 files changed, 18 insertions, 29 deletions

diff --git a/pkg/tcpip/network/ipv6/ipv6.go b/pkg/tcpip/network/ipv6/ipv6.go
index d7d7fc611..0ade655b2 100644
--- a/pkg/tcpip/network/ipv6/ipv6.go
+++ b/pkg/tcpip/network/ipv6/ipv6.go
@@ -99,9 +99,9 @@ func (e *endpoint) GSOMaxSize() uint32 {
 	return 0
 }
 
-func (e *endpoint) addIPHeader(r *stack.Route, hdr *buffer.Prependable, payloadSize int, params stack.NetworkHeaderParams) header.IPv6 {
-	length := uint16(hdr.UsedLength() + payloadSize)
-	ip := header.IPv6(hdr.Prepend(header.IPv6MinimumSize))
+func (e *endpoint) addIPHeader(r *stack.Route, pkt *stack.PacketBuffer, params stack.NetworkHeaderParams) {
+	length := uint16(pkt.Size())
+	ip := header.IPv6(pkt.NetworkHeader().Push(header.IPv6MinimumSize))
 	ip.Encode(&header.IPv6Fields{
 		PayloadLength: length,
 		NextHeader:    uint8(params.Protocol),
@@ -110,26 +110,20 @@ func (e *endpoint) addIPHeader(r *stack.Route, hdr *buffer.Prependable, payloadS
 		SrcAddr:       r.LocalAddress,
 		DstAddr:       r.RemoteAddress,
 	})
-	return ip
+	pkt.NetworkProtocolNumber = header.IPv6ProtocolNumber
 }
 
 // WritePacket writes a packet to the given destination address and protocol.
 func (e *endpoint) WritePacket(r *stack.Route, gso *stack.GSO, params stack.NetworkHeaderParams, pkt *stack.PacketBuffer) *tcpip.Error {
-	ip := e.addIPHeader(r, &pkt.Header, pkt.Data.Size(), params)
-	pkt.NetworkHeader = buffer.View(ip)
-	pkt.NetworkProtocolNumber = header.IPv6ProtocolNumber
+	e.addIPHeader(r, pkt, params)
 
 	if r.Loop&stack.PacketLoop != 0 {
-		// The inbound path expects the network header to still be in
-		// the PacketBuffer's Data field.
-		views := make([]buffer.View, 1, 1+len(pkt.Data.Views()))
-		views[0] = pkt.Header.View()
-		views = append(views, pkt.Data.Views()...)
 		loopedR := r.MakeLoopedRoute()
 
-		e.HandlePacket(&loopedR, &stack.PacketBuffer{
-			Data: buffer.NewVectorisedView(len(views[0])+pkt.Data.Size(), views),
-		})
+		e.HandlePacket(&loopedR, stack.NewPacketBuffer(stack.PacketBufferOptions{
+			// The inbound path expects an unparsed packet.
+			Data: buffer.NewVectorisedView(pkt.Size(), pkt.Views()),
+		}))
 
 		loopedR.Release()
 	}
@@ -151,9 +145,7 @@ func (e *endpoint) WritePackets(r *stack.Route, gso *stack.GSO, pkts stack.Packe
 	}
 
 	for pb := pkts.Front(); pb != nil; pb = pb.Next() {
-		ip := e.addIPHeader(r, &pb.Header, pb.Data.Size(), params)
-		pb.NetworkHeader = buffer.View(ip)
-		pb.NetworkProtocolNumber = header.IPv6ProtocolNumber
+		e.addIPHeader(r, pb, params)
 	}
 
 	n, err := e.linkEP.WritePackets(r, gso, pkts, ProtocolNumber)
@@ -171,8 +163,8 @@ func (*endpoint) WriteHeaderIncludedPacket(r *stack.Route, pkt *stack.PacketBuff
 // HandlePacket is called by the link layer when new ipv6 packets arrive for
 // this endpoint.
 func (e *endpoint) HandlePacket(r *stack.Route, pkt *stack.PacketBuffer) {
-	h := header.IPv6(pkt.NetworkHeader)
-	if !h.IsValid(pkt.Data.Size() + len(pkt.NetworkHeader) + len(pkt.TransportHeader)) {
+	h := header.IPv6(pkt.NetworkHeader().View())
+	if !h.IsValid(pkt.Data.Size() + pkt.NetworkHeader().View().Size() + pkt.TransportHeader().View().Size()) {
 		r.Stats().IP.MalformedPacketsReceived.Increment()
 		return
 	}
@@ -181,8 +173,8 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt *stack.PacketBuffer) {
 	// - Any IPv6 header bytes after the first 40 (i.e. extensions).
 	// - The transport header, if present.
 	// - Any other payload data.
-	vv := pkt.NetworkHeader[header.IPv6MinimumSize:].ToVectorisedView()
-	vv.AppendView(pkt.TransportHeader)
+	vv := pkt.NetworkHeader().View()[header.IPv6MinimumSize:].ToVectorisedView()
+	vv.AppendView(pkt.TransportHeader().View())
 	vv.Append(pkt.Data)
 	it := header.MakeIPv6PayloadIterator(header.IPv6ExtensionHeaderIdentifier(h.NextHeader()), vv)
 	hasFragmentHeader := false
@@ -410,7 +402,7 @@ func (e *endpoint) HandlePacket(r *stack.Route, pkt *stack.PacketBuffer) {
 			//
 			// For reassembled fragments, pkt.TransportHeader is unset, so this is a
 			// no-op and pkt.Data begins with the transport header.
-			extHdr.Buf.TrimFront(len(pkt.TransportHeader))
+			extHdr.Buf.TrimFront(pkt.TransportHeader().View().Size())
 			pkt.Data = extHdr.Buf
 
 			if p := tcpip.TransportProtocolNumber(extHdr.Identifier); p == header.ICMPv6ProtocolNumber {
@@ -581,17 +573,14 @@ traverseExtensions:
 		}
 	}
 
-	// Put the IPv6 header with extensions in pkt.NetworkHeader.
-	hdr, ok = pkt.Data.PullUp(header.IPv6MinimumSize + extensionsSize)
+	// Put the IPv6 header with extensions in pkt.NetworkHeader().
+	hdr, ok = pkt.NetworkHeader().Consume(header.IPv6MinimumSize + extensionsSize)
 	if !ok {
 		panic(fmt.Sprintf("pkt.Data should have at least %d bytes, but only has %d.", header.IPv6MinimumSize+extensionsSize, pkt.Data.Size()))
 	}
 	ipHdr = header.IPv6(hdr)
-
-	pkt.NetworkProtocolNumber = header.IPv6ProtocolNumber
-	pkt.NetworkHeader = hdr
-	pkt.Data.TrimFront(len(hdr))
 	pkt.Data.CapLength(int(ipHdr.PayloadLength()))
+	pkt.NetworkProtocolNumber = header.IPv6ProtocolNumber
 
 	return nextHdr, foundNext, true
 }