From a551add5d8a5bf631cd9859c761e579fdb33ec82 Mon Sep 17 00:00:00 2001
From: Kevin Krakauer <krakauer@google.com>
Date: Mon, 13 Apr 2020 17:37:21 -0700
Subject: Remove View.First() and View.RemoveFirst()

These methods let users eaily break the VectorisedView abstraction, and
allowed netstack to slip into pseudo-enforcement of the "all headers are
in the first View" invariant. Removing them and replacing with PullUp(n)
breaks this reliance and will make it easier to add iptables support and
rework network buffer management.

The new View.PullUp(n) method is low cost in the common case, when when
all the headers fit in the first View.
---
 pkg/tcpip/stack/iptables_targets.go | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

(limited to 'pkg/tcpip/stack/iptables_targets.go')

diff --git a/pkg/tcpip/stack/iptables_targets.go b/pkg/tcpip/stack/iptables_targets.go
index 7b4543caf..8be61f4b1 100644
--- a/pkg/tcpip/stack/iptables_targets.go
+++ b/pkg/tcpip/stack/iptables_targets.go
@@ -96,9 +96,12 @@ func (rt RedirectTarget) Action(pkt PacketBuffer) (RuleVerdict, int) {
 	newPkt := pkt.Clone()
 
 	// Set network header.
-	headerView := newPkt.Data.First()
+	headerView, ok := newPkt.Data.PullUp(header.IPv4MinimumSize)
+	if !ok {
+		return RuleDrop, 0
+	}
 	netHeader := header.IPv4(headerView)
-	newPkt.NetworkHeader = headerView[:header.IPv4MinimumSize]
+	newPkt.NetworkHeader = headerView
 
 	hlen := int(netHeader.HeaderLength())
 	tlen := int(netHeader.TotalLength())
@@ -117,10 +120,14 @@ func (rt RedirectTarget) Action(pkt PacketBuffer) (RuleVerdict, int) {
 		if newPkt.TransportHeader != nil {
 			udpHeader = header.UDP(newPkt.TransportHeader)
 		} else {
-			if len(pkt.Data.First()) < header.UDPMinimumSize {
+			if pkt.Data.Size() < header.UDPMinimumSize {
+				return RuleDrop, 0
+			}
+			hdr, ok := newPkt.Data.PullUp(header.UDPMinimumSize)
+			if !ok {
 				return RuleDrop, 0
 			}
-			udpHeader = header.UDP(newPkt.Data.First())
+			udpHeader = header.UDP(hdr)
 		}
 		udpHeader.SetDestinationPort(rt.MinPort)
 	case header.TCPProtocolNumber:
@@ -128,10 +135,14 @@ func (rt RedirectTarget) Action(pkt PacketBuffer) (RuleVerdict, int) {
 		if newPkt.TransportHeader != nil {
 			tcpHeader = header.TCP(newPkt.TransportHeader)
 		} else {
-			if len(pkt.Data.First()) < header.TCPMinimumSize {
+			if pkt.Data.Size() < header.TCPMinimumSize {
 				return RuleDrop, 0
 			}
-			tcpHeader = header.TCP(newPkt.TransportHeader)
+			hdr, ok := newPkt.Data.PullUp(header.TCPMinimumSize)
+			if !ok {
+				return RuleDrop, 0
+			}
+			tcpHeader = header.TCP(hdr)
 		}
 		// TODO(gvisor.dev/issue/170): Need to recompute checksum
 		// and implement nat connection tracking to support TCP.
-- 
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