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

3 files changed, 11 insertions, 8 deletions

diff --git a/pkg/tcpip/stack/packet_buffer.go b/pkg/tcpip/stack/packet_buffer.go
index 646979d1e..9527416cf 100644
--- a/pkg/tcpip/stack/packet_buffer.go
+++ b/pkg/tcpip/stack/packet_buffer.go
@@ -364,9 +364,10 @@ func (d PacketData) PullUp(size int) (buffer.View, bool) {
 	return d.pk.data.PullUp(size)
 }
 
-// TrimFront removes count from the beginning of d. It panics if count >
-// d.Size().
-func (d PacketData) TrimFront(count int) {
+// DeleteFront removes count from the beginning of d. It panics if count >
+// d.Size(). All backing storage references after the front of the d are
+// invalidated.
+func (d PacketData) DeleteFront(count int) {
 	d.pk.data.TrimFront(count)
 }
 
diff --git a/pkg/tcpip/stack/packet_buffer_test.go b/pkg/tcpip/stack/packet_buffer_test.go
index 6728370c3..a794065d1 100644
--- a/pkg/tcpip/stack/packet_buffer_test.go
+++ b/pkg/tcpip/stack/packet_buffer_test.go
@@ -397,11 +397,11 @@ func TestPacketBufferData(t *testing.T) {
 				}
 			})
 
-			// TrimFront
+			// DeleteFront
 			for _, n := range []int{1, len(tc.data)} {
-				t.Run(fmt.Sprintf("TrimFront%d", n), func(t *testing.T) {
+				t.Run(fmt.Sprintf("DeleteFront%d", n), func(t *testing.T) {
 					pkt := tc.makePkt(t)
-					pkt.Data().TrimFront(n)
+					pkt.Data().DeleteFront(n)
 
 					checkData(t, pkt, []byte(tc.data)[n:])
 				})
diff --git a/pkg/tcpip/stack/stack_test.go b/pkg/tcpip/stack/stack_test.go
index 8ead3b8df..4fe9df999 100644
--- a/pkg/tcpip/stack/stack_test.go
+++ b/pkg/tcpip/stack/stack_test.go
@@ -138,11 +138,13 @@ func (f *fakeNetworkEndpoint) HandlePacket(pkt *stack.PacketBuffer) {
 
 	// Handle control packets.
 	if netHdr[protocolNumberOffset] == uint8(fakeControlProtocol) {
-		nb, ok := pkt.Data().PullUp(fakeNetHeaderLen)
+		hdr, ok := pkt.Data().PullUp(fakeNetHeaderLen)
 		if !ok {
 			return
 		}
-		pkt.Data().TrimFront(fakeNetHeaderLen)
+		// DeleteFront invalidates slices. Make a copy before trimming.
+		nb := append([]byte(nil), hdr...)
+		pkt.Data().DeleteFront(fakeNetHeaderLen)
 		f.dispatcher.DeliverTransportError(
 			tcpip.Address(nb[srcAddrOffset:srcAddrOffset+1]),
 			tcpip.Address(nb[dstAddrOffset:dstAddrOffset+1]),