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 Zero value is no
longer valid.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, 11 insertions, 12 deletions

diff --git a/pkg/tcpip/link/tun/device.go b/pkg/tcpip/link/tun/device.go
index 22b0a12bd..3b1510a33 100644
--- a/pkg/tcpip/link/tun/device.go
+++ b/pkg/tcpip/link/tun/device.go
@@ -215,12 +215,11 @@ func (d *Device) Write(data []byte) (int64, error) {
 		remote = tcpip.LinkAddress(zeroMAC[:])
 	}
 
-	pkt := &stack.PacketBuffer{
-		Data: buffer.View(data).ToVectorisedView(),
-	}
-	if ethHdr != nil {
-		pkt.LinkHeader = buffer.View(ethHdr)
-	}
+	pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
+		ReserveHeaderBytes: len(ethHdr),
+		Data:               buffer.View(data).ToVectorisedView(),
+	})
+	copy(pkt.LinkHeader().Push(len(ethHdr)), ethHdr)
 	endpoint.InjectLinkAddr(protocol, remote, pkt)
 	return dataLen, nil
 }
@@ -265,21 +264,22 @@ func (d *Device) encodePkt(info *channel.PacketInfo) (buffer.View, bool) {
 	// If the packet does not already have link layer header, and the route
 	// does not exist, we can't compute it. This is possibly a raw packet, tun
 	// device doesn't support this at the moment.
-	if info.Pkt.LinkHeader == nil && info.Route.RemoteLinkAddress == "" {
+	if info.Pkt.LinkHeader().View().IsEmpty() && info.Route.RemoteLinkAddress == "" {
 		return nil, false
 	}
 
 	// Ethernet header (TAP only).
 	if d.hasFlags(linux.IFF_TAP) {
 		// Add ethernet header if not provided.
-		if info.Pkt.LinkHeader == nil {
+		if info.Pkt.LinkHeader().View().IsEmpty() {
 			d.endpoint.AddHeader(info.Route.LocalLinkAddress, info.Route.RemoteLinkAddress, info.Proto, info.Pkt)
 		}
-		vv.AppendView(info.Pkt.LinkHeader)
+		vv.AppendView(info.Pkt.LinkHeader().View())
 	}
 
 	// Append upper headers.
-	vv.AppendView(buffer.View(info.Pkt.Header.View()[len(info.Pkt.LinkHeader):]))
+	vv.AppendView(info.Pkt.NetworkHeader().View())
+	vv.AppendView(info.Pkt.TransportHeader().View())
 	// Append data payload.
 	vv.Append(info.Pkt.Data)
 
@@ -361,8 +361,7 @@ func (e *tunEndpoint) AddHeader(local, remote tcpip.LinkAddress, protocol tcpip.
 	if !e.isTap {
 		return
 	}
-	eth := header.Ethernet(pkt.Header.Prepend(header.EthernetMinimumSize))
-	pkt.LinkHeader = buffer.View(eth)
+	eth := header.Ethernet(pkt.LinkHeader().Push(header.EthernetMinimumSize))
 	hdr := &header.EthernetFields{
 		SrcAddr: local,
 		DstAddr: remote,