netstack: Rename pkt.Data().TrimFront() to DeleteFront(), and ...

... it may now invalidate backing slice references

This is currently safe because TrimFront() in VectorisedView only shrinks the
view. This may not hold under the a different buffer implementation.
Reordering method calls order to allow this.

PiperOrigin-RevId: 371167610

1 files changed, 10 insertions, 6 deletions

diff --git a/pkg/tcpip/network/ipv4/icmp.go b/pkg/tcpip/network/ipv4/icmp.go
index f663fdc0b..3f2093f00 100644
--- a/pkg/tcpip/network/ipv4/icmp.go
+++ b/pkg/tcpip/network/ipv4/icmp.go
@@ -163,10 +163,12 @@ func (e *endpoint) handleControl(errInfo stack.TransportError, pkt *stack.Packet
 		return
 	}
 
-	// Skip the ip header, then deliver the error.
-	pkt.Data().TrimFront(hlen)
+	// Keep needed information before trimming header.
 	p := hdr.TransportProtocol()
-	e.dispatcher.DeliverTransportError(srcAddr, hdr.DestinationAddress(), ProtocolNumber, p, errInfo, pkt)
+	dstAddr := hdr.DestinationAddress()
+	// Skip the ip header, then deliver the error.
+	pkt.Data().DeleteFront(hlen)
+	e.dispatcher.DeliverTransportError(srcAddr, dstAddr, ProtocolNumber, p, errInfo, pkt)
 }
 
 func (e *endpoint) handleICMP(pkt *stack.PacketBuffer) {
@@ -336,14 +338,16 @@ func (e *endpoint) handleICMP(pkt *stack.PacketBuffer) {
 	case header.ICMPv4DstUnreachable:
 		received.dstUnreachable.Increment()
 
-		pkt.Data().TrimFront(header.ICMPv4MinimumSize)
-		switch h.Code() {
+		mtu := h.MTU()
+		code := h.Code()
+		pkt.Data().DeleteFront(header.ICMPv4MinimumSize)
+		switch code {
 		case header.ICMPv4HostUnreachable:
 			e.handleControl(&icmpv4DestinationHostUnreachableSockError{}, pkt)
 		case header.ICMPv4PortUnreachable:
 			e.handleControl(&icmpv4DestinationPortUnreachableSockError{}, pkt)
 		case header.ICMPv4FragmentationNeeded:
-			networkMTU, err := calculateNetworkMTU(uint32(h.MTU()), header.IPv4MinimumSize)
+			networkMTU, err := calculateNetworkMTU(uint32(mtu), header.IPv4MinimumSize)
 			if err != nil {
 				networkMTU = 0
 			}