Ping support via IPv4 raw sockets.

Broadly, this change:
* Enables sockets to be created via `socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)`.
* Passes the network-layer (IP) header up the stack to the transport endpoint,
  which can pass it up to the socket layer. This allows a raw socket to return
  the entire IP packet to users.
* Adds functions to stack.TransportProtocol, stack.Stack, stack.transportDemuxer
  that enable incoming packets to be delivered to raw endpoints. New raw sockets
  of other protocols (not ICMP) just need to register with the stack.
* Enables ping.endpoint to return IP headers when created via SOCK_RAW.

PiperOrigin-RevId: 235993280
Change-Id: I60ed994f5ff18b2cbd79f063a7fdf15d093d845a

2 files changed, 12 insertions, 7 deletions

diff --git a/pkg/tcpip/network/ipv4/icmp.go b/pkg/tcpip/network/ipv4/icmp.go
index f82dc098f..ea8392c98 100644
--- a/pkg/tcpip/network/ipv4/icmp.go
+++ b/pkg/tcpip/network/ipv4/icmp.go
@@ -55,7 +55,7 @@ func (e *endpoint) handleControl(typ stack.ControlType, extra uint32, vv buffer.
 	e.dispatcher.DeliverTransportControlPacket(e.id.LocalAddress, h.DestinationAddress(), ProtocolNumber, p, typ, extra, vv)
 }
 
-func (e *endpoint) handleICMP(r *stack.Route, vv buffer.VectorisedView) {
+func (e *endpoint) handleICMP(r *stack.Route, netHeader buffer.View, vv buffer.VectorisedView) {
 	v := vv.First()
 	if len(v) < header.ICMPv4MinimumSize {
 		return
@@ -67,19 +67,22 @@ func (e *endpoint) handleICMP(r *stack.Route, vv buffer.VectorisedView) {
 		if len(v) < header.ICMPv4EchoMinimumSize {
 			return
 		}
-		vv.TrimFront(header.ICMPv4MinimumSize)
-		req := echoRequest{r: r.Clone(), v: vv.ToView()}
+		echoPayload := vv.ToView()
+		echoPayload.TrimFront(header.ICMPv4MinimumSize)
+		req := echoRequest{r: r.Clone(), v: echoPayload}
 		select {
 		case e.echoRequests <- req:
 		default:
 			req.r.Release()
 		}
+		// It's possible that a raw socket expects to receive this.
+		e.dispatcher.DeliverTransportPacket(r, header.ICMPv4ProtocolNumber, netHeader, vv)
 
 	case header.ICMPv4EchoReply:
 		if len(v) < header.ICMPv4EchoMinimumSize {
 			return
 		}
-		e.dispatcher.DeliverTransportPacket(r, header.ICMPv4ProtocolNumber, vv)
+		e.dispatcher.DeliverTransportPacket(r, header.ICMPv4ProtocolNumber, netHeader, vv)
 
 	case header.ICMPv4DstUnreachable:
 		if len(v) < header.ICMPv4DstUnreachableMinimumSize {
diff --git a/pkg/tcpip/network/ipv4/ipv4.go b/pkg/tcpip/network/ipv4/ipv4.go
index 0c41519df..bfc3c08fa 100644
--- a/pkg/tcpip/network/ipv4/ipv4.go
+++ b/pkg/tcpip/network/ipv4/ipv4.go
@@ -131,7 +131,8 @@ func (e *endpoint) WritePacket(r *stack.Route, hdr buffer.Prependable, payload b
 // HandlePacket is called by the link layer when new ipv4 packets arrive for
 // this endpoint.
 func (e *endpoint) HandlePacket(r *stack.Route, vv buffer.VectorisedView) {
-	h := header.IPv4(vv.First())
+	headerView := vv.First()
+	h := header.IPv4(headerView)
 	if !h.IsValid(vv.Size()) {
 		return
 	}
@@ -153,11 +154,12 @@ func (e *endpoint) HandlePacket(r *stack.Route, vv buffer.VectorisedView) {
 	}
 	p := h.TransportProtocol()
 	if p == header.ICMPv4ProtocolNumber {
-		e.handleICMP(r, vv)
+		headerView.CapLength(hlen)
+		e.handleICMP(r, headerView, vv)
 		return
 	}
 	r.Stats().IP.PacketsDelivered.Increment()
-	e.dispatcher.DeliverTransportPacket(r, p, vv)
+	e.dispatcher.DeliverTransportPacket(r, p, headerView, vv)
 }
 
 // Close cleans up resources associated with the endpoint.